Lenses with adjustable focal length and eyewear incorporating them

Abstract

The adjustable focal length eyewear is mounted in a frame that supports lenses in front of a user's eyes and includes two overlapping lens elements, at least one of which is a variable focal length lens, with cooperating optical surfaces shaped to change focal length depending on their relative lateral positioning. One fixed lens element is fixedly mounted to the frame, while the other movable lens element is manually movable relative to the fixed lens element to change the focal length of the lens. The movable lens element is provided with guide elements that cooperate with corresponding guide elements on the fixed lens element or frame to define and constrain movement relative to the fixed lens element to a transverse path that extends intersecting the line of sight. One or more releasable fasteners are provided that releasably secure the movable lens element to the fixed lens element or frame while allowing movement of the movable lens element along the transverse path relative to the fixed lens element.

Description

[Technical Field]

[0001] The present invention relates to adjustable focal length eyeglasses comprising two optical lenses of variable focal length of the type including two lens elements, one positioned in front of the other relative to the eye of a user, at least one of the lens elements being movable laterally relative to the other to adjust the relative positioning of the lens element with respect to the other, the lens elements having cooperating optical surfaces shaped such that the focal length of the optical lens varies depending on the relative positioning of the two lens elements. The invention makes particular reference to reading eyeglasses suitable for use by persons with presbyopia, but may find wider application within the field of ophthalmic lenses. [Background technology]

[0002] The above-mentioned types of optical lenses are well known in the art. Adjustable optical lenses of this type typically have two superimposed lens elements with cooperating tertiary or higher-order surfaces, with a relative arrangement that allows them to be moved transversely relative to the optical axis of the lens to change the optical power of the lens. While the transverse direction may suitably extend in a horizontal plane relative to the user in normal use, in some examples of this type of lens, it may also extend in a sagittal plane or, at least theoretically, in any other plane that has a component extending perpendicular to the optical axis. An example of this type of adjustable lens is the Alvarez lens disclosed in U.S. Pat. No. 3,305,294, the contents of which are incorporated herein by reference. Other adjustable lenses with tertiary and higher-order surfaces are disclosed in U.S. Pat. Nos. 3,583,790, 7,338,159, 7,717,552, 5,644,374, and WO 2013 / 030603, the contents of all of which are also incorporated herein by reference.

[0003] Various methods are known in the art for mounting such adjustable optical lenses in frames for supporting the lenses in front of a user's eyes as eyeglasses. However, a difficulty inherent in such adjustable lenses is that unless the lens elements are aligned with one another in a central position, each of them protrudes beyond the other on the opposite side of the lens, resulting in a lack of aesthetic appeal, particularly since the side edges of the lens elements are visible as lines through the lens. Furthermore, a mechanism must be provided for moving at least one of the lens elements relative to the other, and this mechanism must preferably be hidden within the frame to improve the overall appearance of the eyeglasses.

[0004] WO 2006 / 083167 discloses eyeglasses for everyday use, including a frame fitted with a lens system for correcting defective vision, including at least one pair of lenses formed by a first lens and a second lens. The first and second lenses are positioned behind each other in the line of sight and are mutually adjustable to achieve a desired degree of vision correction, with the first lens coupled to a first adjusting element and the second lens coupled to a second adjusting element. The assembled first and second adjusting elements form integral components of an adjuster, designed to move along each other for lens adjustment. The first and second adjusting elements may each comprise a first and second thread. The adjuster may also comprise a mandrel circumferentially provided with third and fourth threads designed to engage with the first and second threads of the first and second adjusting elements, respectively. The adjuster can be integrated into the frame, and the stem can have an actuator that protrudes at least beyond the outside of the frame. While the eyeglasses of WO 2006 / 083167 generally work well, the adjuster should desirably be hidden within the frame, and an actuator on the stem protruding from the frame would be aesthetically unattractive. The focal length of the pair of lenses is continuously adjustable by movement of the first and second lenses between opposite extremes defined by the adjuster.

[0005] It is an object of the present invention to provide eyeglasses with adjustable focal length that are more aesthetically appealing than eyeglasses of similar types known in the art.

[0006] Another object of the present invention is to provide adjustable focal length eyeglasses that allow a user to selectively adjust the lenses between two or more discrete focal lengths.

[0007] Another object of the present invention is to provide adjustable focal length eyeglasses of the type including two lens elements, one placed in front of the other, which are easier to clean than similar types of eyeglasses known in the art. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2006 / 083167 Summary of the Invention

[0009] Thus, one aspect of the present invention provides adjustable focal length eyewear including two lenses mounted in a frame to support the lenses in front of a user's eyes and define a line of sight through each lens. At least one of the lenses is a variable focal length lens of the type including two overlapping lens elements having cooperating optical surfaces shaped such that the focal length of the variable focal length lens varies according to the relative lateral positioning of the lens elements. Suitable variable focal length lenses include Alvarez-type lenses of the type described herein, in which the thickness of each lens element between the opposing optical surfaces is defined by a cubic function such that, in overlapping, the two lens elements are equivalent to spherical lenses. The optical power varies depending on the relative positioning of the lens elements. According to the present invention, one of the lens elements is fixedly mounted in the frame, while the other lens element is manually movable relative to the fixed lens element to change the focal length of the variable focal length lens. The movable lens element is provided with a guide element that cooperates with a corresponding guide element on the fixed lens element or the frame to define and constrain the movement of the movable lens element relative to the fixed lens element in a transverse path that transverses the line of sight. The guide component is configured to allow the movable lens element to be detached from the fixed lens element at at least one position of the movable lens element. Further, one or more releasable fasteners are provided for releasably securing the movable lens element to the fixed lens element or frame while allowing the movable lens element to move relative to the fixed lens element along the transverse path. Suitably, the lens includes at least two releasable fasteners spaced apart in a direction perpendicular to the line of sight.

[0010] In some embodiments, the one or more releasable fasteners may include one or more separable mechanical fasteners. Many suitable separable mechanical fasteners are available to those skilled in the art, including, for example, types of separable mechanical fasteners that include resilient interengaging formations on the fixed and movable lens elements. The resilient formations may define a bump fit or ball-and-socket joint in which a ball engages a slot to allow relative movement of the lens elements along the transverse path. The "ball" may be spherical or aspherical. For example, the ball may be longer in one axis than the other to prevent twisting of the ball in the socket about one or more axes. This may help strengthen the neck portion behind the ball. As a separating force is applied incrementally, urging the lens elements apart in the line of sight, the resilient interengaging formations of the fixed and movable lens elements may initially resist separation of the lens elements while allowing movement of the movable lens element along the transverse path. and eventually deforms, allowing the resilient interengaging formations to separate from one another, thereby allowing the movable lens element to be removed from the fixed lens element.

[0011] In some embodiments, the mechanical fastener defines one or more discrete detent positions in the traverse path at which the lens elements are releasably held together in the direction of the traverse path, such that additional force may be required to slide the lens elements out of the detent positions and displace them along the traverse path. For example, if the mechanical fastener includes a ball-and-socket joint in which a ball is releasably held in an elongated slot as described above, additional formations such as bumps may be provided at one or more discrete positions along the slot, e.g., at one or both ends of the slot, to hold the ball and therefore the lens elements in place until additional force is applied.

[0012] Alternatively, the one or more releasable fasteners may comprise one or more magnetic fasteners. Suitably, the one or more magnetic fasteners may comprise separate magnetic components on the movable lens element and the fixed lens element or frame that cooperate with each other to define at least two selectable separate detent positions for the movable lens element relative to the fixed lens element.

[0013] The eyewear may include a pair of glasses or goggles. In some embodiments, the eyewear may include a headset, such as, for example, an augmented or virtual reality head-up display.

[0014] The lens elements are configured to provide different focal lengths at each discrete position. It will be understood by those skilled in the art that, at each relative position of the lens elements, the variable focal length lens defines an optical (z) axis, i.e., an axis that is substantially perpendicular to the lens and represents the path of light rays through the lens with no net change in direction. Advantageously, the lens elements are configured such that as the focal length of the lens decreases, the optical axis of the lens shifts inward, i.e., toward the user's nose, and conversely, as the focal length of the lens increases, the optical axis of the lens shifts outward, i.e., toward the user's temples. This corresponds to the way the eyes move when focusing from far to near, and is intended to contribute to an improved optical experience for the user from the arrangement of the movable lens elements.

[0015] A variable focal length lens can be adjusted to change the power of the lens by up to approximately +7.5 diopters, which is adequate for correcting presbyopia in most people. In some embodiments, a narrower range of change, e.g., 1, 2, 3, 4, 5, or 6 diopters, may be provided, which may allow for the manufacture of thinner lenses. In some embodiments, a variable focal length lens may have a base focal length for myopia or hyperopia correction and / or may be configured to provide some cylinder for astigmatism correction. Thus, a variable focal length lens may typically have a base power ranging from approximately -6 to +6 diopters, although in some cases, a stronger prescription may be required.

[0016] One or more magnetic fasteners are provided to stably hold the lens elements together at two or more selectable discrete positions along the traversal path. Suitably, the strength of the magnetic fasteners is sufficient to hold the lens elements securely together during use while allowing a user to manually move and remove the movable lens element relative to the fixed lens element between the two or more discrete positions to select different focal lengths of the lens, as desired. Those skilled in the art will have no difficulty selecting magnetic fasteners of appropriate strength to control the holding force and sliding friction between the lens elements.

[0017] The magnetic fastener can define at least two selectable, distinct detent positions for the movable lens element along the traversal path relative to the fixed lens element, hi some embodiments, the magnetic fastener can define three selectable, distinct detent positions for the movable lens element along the traversal path relative to the fixed lens element.

[0018] Suitably, the lens may include two or more magnetic fasteners between the movable lens element and the fixed lens element or frame. The magnetic fasteners may be spaced apart to hold the lens elements together in a stable manner in conjunction with a guide piece, for example, to resist twisting, wobbling, or other undesired movement of the lens elements relative to one another. The two or more magnetic fasteners may be spaced apart in the direction of a transverse path relative to the user, typically extending from one lateral side of the lens to the other, or they may be positioned one above the other relative to the user. In some embodiments, it may be possible to use only one magnetic fastener per lens.

[0019] The or each magnetic fastener may include a group of individual magnetic components on one of the movable lens element or the fixed lens element or frame, and at least one cooperating magnetic component on the other of the fixed lens element or frame or the movable lens element. The magnetic components on the movable lens element and the fixed lens element or frame attract each other to attach the movable lens element to the fixed lens element or frame, while allowing the movable lens element to be manually moved relative to the fixed lens element along the traversal path and manually removed from the fixed lens element or frame, as required. Suitably, the magnetic components in a group may be spaced apart along the traversal path.

[0020] The magnetic components in the group and / or the cooperating magnetic components may comprise permanent magnets. In some embodiments, all magnetic components in the group may comprise permanent magnets, and the cooperating magnetic components may comprise permanent magnets or ferromagnetic components. Alternatively, all magnetic components in the group may comprise ferromagnetic components, and the cooperating magnetic components may comprise permanent magnets. Suitably, the magnetic components are arranged to attract each other to releasably secure the two lens elements together. Suitably, both the magnetic components in the group and the cooperating magnetic components are permanent magnets.

[0021] The groups of magnetic elements serve to define discrete relative positions of the lens elements along the traversal path, with the lens elements being most strongly attached to one another at each position. Suitably, the magnetic components are arranged to hold the lens elements together between the discrete positions, but may not be strong enough to cause the lens elements to "snap" into one of the discrete positions when moved by a user. Because the lens elements are manually movable relative to one another, the differing holding strengths between the discrete positions and other points along the traversal path may provide a degree of tactile feedback to the user when the lens elements are positioned at the discrete positions, thus providing perceptible detents at each discrete position.

[0022] As described below, in some embodiments, the magnetic components may be further positioned to hold the lens elements more tightly at one or more discrete detent positions than at other discrete detent positions. For example, the lens elements may be held together more tightly at a central detent position than at end detent positions when located at the ends of their travel along the traversal path. In particular, the traversal path may have two opposing lateral ends beyond which the lens elements cannot move further in one direction. The magnetic components may be positioned at extreme lateral ends on the traversal path such that the two outer discrete detent positions coincide with the ends of the traversal path.

[0023] In some embodiments, the magnetic components may define only two distinct outer detent positions. However, in some embodiments, a third magnetic component may be positioned to define, for example, a center detent position intermediate the outer detent positions. As previously discussed, the magnetic fastener may have a higher holding force at the center detent position than at the outer detent positions, allowing the user to feel that the lens element is centered. This differential holding strength can be provided by positioning the magnetic components so that the holding strength is greater at the center position than at the outer positions. For example, three magnetic components may be positioned close enough together so that the coupling force of a magnetic element to its cooperating magnetic component is greater at the center position than at the outer positions. Alternatively, multiple magnets, magnets of different shapes, or magnets of different grades, e.g., N52, N48, N35 (higher numbers indicate higher pulling forces for magnets of the same size / shape), can be used. In some embodiments, a similar haptic effect can be achieved by non-magnetic components, such as bump fits between lens elements, leaf springs, etc.

[0024] In some embodiments, the optical surface of the lens element can be formed on the base curve in a manner known to those skilled in the art. Thus, instead of being straight, the traversal path can in some embodiments be arcuate in a plane defined by the optical axis and a horizontal (x) axis perpendicular to the optical (z) axis, extending between the temple and nasal sides of the lens, such that movement of the movable lens element along the traversal path substantially follows the base curve. Thus, the guide elements of the movable lens element and cooperating guide elements on the fixed lens element or frame can define the curved traversal path of the movable lens element. However, in some embodiments, the traversal path can be substantially straight.

[0025] The guide parts of the fixed and movable lens elements may form at least two linear or curved guides that define a traversal path. Suitably, the guide parts may be spaced apart from one another in the direction of the traversal path. This may help to support rotation of the movable lens element about the optical axis relative to the fixed lens element.

[0026] In some embodiments, the guide components may be formed or attached directly to the lens elements. For example, in some embodiments, each guide may include a dowel attached to one of the lens elements and a slot formed in the other lens element. The dowel may engage an edge of the other lens element around the slot to constrain relative movement of the two lens elements with respect to the transverse path.

[0027] In some embodiments, the dowel is magnetic, and a group of two or more magnetic components may be attached to the other lens element at two or more distinct positions within the slot to cooperate with the magnetic dowel to secure the two lens elements together and define selectable, distinct detent positions. Suitably, the slot may be a blind slot having a front or rear wall formed by an area of ​​reduced thickness of the other lens element adjacent to the slot. The magnetic components of the group may fit into recesses formed in the front or rear wall. The slot has two opposing lateral ends. The group of two or more magnetic components may include two magnetic components secured to the other lens element, one at each end of the slot.

[0028] Suitably, the front or rear wall of the other lens element may form an axial seating surface that engages the end of the dowel to stabilize the movable lens element in the line of sight relative to the fixed lens element. The front or rear wall of the slot may have a seating surface within the slot. The seating surface may be treated or coated to form a low friction surface.

[0029] Alternatively, a magnetic component may be secured adjacent a dowel on one lens element, and a group of two or more magnetic components may be secured at two or more discrete locations adjacent a slot on the other lens element to cooperate with the magnetic component on one lens element to attach the two lens elements together and define selectable discrete detent positions.

[0030] Generally, the guide elements allow the lens elements to be freely separated from one another, particularly in the line of sight. However, in some embodiments, the guide elements may include retaining elements arranged to prevent removal of the movable lens element from the fixed lens element except when the movable lens element is positioned in a specific position relative to the fixed lens element, e.g., one or more discrete locations. Suitably, therefore, the dowel may be configured to engage with a cooperating rib of the other lens element extending into the slot to prevent removal of the movable lens element except in at least one position of the movable lens element relative to the fixed lens element. Thus, in some embodiments, the rib stops short of at least one lateral end of the slot, allowing the movable lens element, together with the dowel, to move to a position at that end of the slot where the dowel disengages from the rib, thereby enabling removal of the movable lens element from the fixed lens element.

[0031] In other embodiments, the rib may be notched midway between the lateral ends of the slot, thereby providing two spaced-apart rib portions. In these embodiments, the rib is configured to allow the movable lens element to move with the dowel to a position in the notch where the dowel disengages from the rib portion. For example, the rib may extend between the lateral ends of the slot, and the notch may be formed substantially midway in the rib between the lateral ends of the slot. In this embodiment, the movable lens element may be moved with the dowel to a position midway between the lateral ends of the slot to disengage the dowel from the rib, thereby allowing the movable lens element to be detached and removed from the fixed lens element.

[0032] The variable focal length lens of the present invention, in which the guide pieces and magnetic fasteners are attached directly to the lens element, can be attached to regular frames, including rimless frames, without the need for customizing the frame.

[0033] According to another aspect of the present invention, there is provided a variable focal length lens of the type comprising two lens elements having cooperating optical surfaces superimposed on one another in a line of sight through the lens, the focal length of the variable focal length lens being shaped so as to vary with the relative lateral positioning of the lens elements in a direction transverse to the line of sight. Cooperating guide elements are provided on the lens elements to define and constrain relative movement of the lens elements to a transverse path extending in the transverse direction. One or more releasable fasteners are provided to releasably secure the two lens elements together while allowing relative movement of the lens elements along the transverse path.

[0034] As noted above, the one or more releasable fasteners may include one or more separable mechanical fasteners or one or more magnetic fasteners. Suitably, the one or more magnetic fasteners may include mutually cooperating individual magnetic components on the lens elements that define at least two selectable, distinct detent positions of the lens elements relative to one another. Two or more magnetic fasteners may be provided between the lens elements, which define at least two selectable, distinct detent positions of the lens elements relative to one another along the traversal path. In some embodiments, the magnetic fasteners may define three selectable, distinct detent positions of the lens elements relative to one another along the traversal path.

[0035] The variable focal length lenses of the present invention can be mounted in a suitable frame to form a pair of eyeglasses. The frame may be rimless or may include a rim around each lens in addition to the usual temple arms and nose bridge. In some embodiments, the lenses can be mounted in the frame so that both lens elements are movable within the frame. In some embodiments, the two lens elements can be connected to move equally and in opposite directions along a transverse path. In such cases, the position of the optical axis remains substantially fixed relative to the frame, regardless of the relative placement of the lens elements.

[0036] In some embodiments, the frame may include temple arms that are attached to fixed lens elements over slots.

[0037] Alternatively, each guide may include a bearing fixed to or integrally formed with the frame and a mount fixed to the movable lens element. The bearing may define a slot, and the mount may be shaped to engage the bearing in the slot to restrict relative movement of the two lens elements to a transverse path.

[0038] In some embodiments, the frame may include an elbow interconnecting the temple arm and the fixed lens element. Conveniently, a bearing may be provided in the elbow. A mount may be attached to the movable lens element at a corresponding position.

[0039] In some embodiments, the frame may include a nose bridge interconnecting two lenses and having two opposing ends. A bearing may be provided at one end of the nose bridge. A mount may be attached to the movable lens element at a corresponding position.

[0040] Suitably, the frame may include temple bearings at the elbows and a nose bearing at the end of the nose bridge. In a complete pair of eyeglasses having two temple arms and a nose bridge, each temple arm may have an elbow including a bearing for engaging with a temple mount formed on a respective one of the lenses, and the nose bridge may have nose bearings formed at both ends for engaging with nose mounts formed on each lens.

[0041] The magnetic components can be secured to the mount, and groups of two or more magnetic components can be secured to the bearings at two or more discrete locations within the slot to cooperate with the magnetic components on the mount to attach the two lens elements together and define selectable discrete detent positions. In some embodiments, the group of magnetic components can include two magnetic components secured to the bearings, one at each end of the slot. In some embodiments, the group of magnetic components can further include a magnetic component secured to the bearing at a central detent position intermediate the ends of the slot.

[0042] Thus, according to the present invention, the magnetic fastener can define two or more use modes for the lens. In a first mode, the lens elements can be configured in a relatively low refractive power (long focal length) configuration, which may be suitable for distance vision. In a second mode, the lens elements can be configured in a relatively high refractive power (short focal length) configuration, which may be suitable for reading. If three or more distinct detent positions are defined by the magnetic fastener, there may be one or more intermediate distance modes, suitable for computer use, for example. The intermediate distance mode may be achieved when the lens elements are configured between the two extreme positions of the first and second modes.

[0043] Suitably, the bearing may include one or more retaining nibs constructed and arranged to prevent removal of the mount from the bearing except at one or more discrete detent positions. For example, the retaining nib may be positioned relative to the slot to prevent the mount from disengaging from the bearing of the lens element intermediate two end detent positions where the lens element is located at the ends of the traversal path. Alternatively, if one or more intermediate detent positions are provided, the retaining nib may be positioned to prevent removal of the mount except at one of the intermediate detent positions, for example, a central detent position if there are three discrete detent positions.

[0044] In some embodiments, the magnetic components of the bearing and mount may be oriented in the line of sight, i.e., generally parallel to the optical axis of the lens, or may be oriented perpendicular to the line of sight, e.g., substantially parallel to a vertical (y) axis that is substantially orthogonal to the optical (z) axis and horizontal (x) axis defined above.

[0045] Advantageously, the group of magnets in the slot may be mounted in an insert which is fixed to a bearing in the slot, the insert having a low friction bearing surface which engages the mount.

[0046] In another aspect of the present invention, at least a portion of one of the top or bottom edges of the movable lens element may overhang or underhang a corresponding portion of the top or bottom edge of the fixed lens element, respectively, to facilitate a user's manual movement of the movable lens element between the individual detent positions and / or removal of the movable lens element from the fixed lens element. In some embodiments, at least a portion of the bottom or top edge of the fixed lens element may overhang at least a portion of the bottom or top edge of the movable lens element. In this manner, a user can simply engage a finger and a thumb on one edge of the movable lens element and the opposite edge of the fixed lens element to apply a sliding force to the movable lens element. A similar arrangement may be provided in a variable focal length lens of the present invention in which both lens elements are movable. At least a portion of the top or bottom edge of one of the lens elements may overhang or underhang at least a portion of the corresponding edge of the other lens element. At least a portion of the other of the bottom and top edges of the other lens element may overhang or underhang at least a portion of the corresponding edge of the one lens element. Alternatively, at least a portion of each of the upper and lower edges of the movable lens element may protrude above and below the corresponding upper and lower edges of the fixed lens element, respectively, to facilitate manual movement of the movable lens element by a user between the discrete detent positions or removal of the movable lens element from the fixed lens element for cleaning, repair, etc.

[0047] In some embodiments, the frame can include a rim extending at least partially around the variable focal length lens. Each guide can include a guide pin protruding from the rim or the movable lens element toward the other of the movable lens element or the rim, and a slot formed in the movable lens element or the rim, respectively. The guide pin can engage an edge of the movable lens element or the rim when the case is around the slot to constrain relative movement of the two lens elements to a transverse path.

[0048] To mount the movable lens element on the frame and define selectable, distinct detent positions, groups of two or more magnetic components can be mounted to the rim portion or the movable lens element at two or more distinct locations, with cooperating magnetic components mounted to the movable lens element or rim portion, respectively. Suitably, the groups of two or more magnetic components and cooperating magnetic components can be mounted to the rim portion and the movable lens element proximate the top or bottom edge of the lens. The rim portion can include temples and nose sides. Advantageously, the movable lens element can be wider in the transverse direction, i.e., the x-axis direction, than the fixed lens element. Thus, the temples and nose sides of the movable lens element can be dimensioned to remain behind the gaze direction of the temples and nose sides of the rim portion, regardless of the position of the movable lens element along the transverse path.

[0049] An advantage of the present invention is that the lenses can be molded (e.g., by injection molding) or cut using standard ophthalmic edging (cutting) equipment and do not require specialized tooling or skill for assembly.

[0050] According to a further aspect of the invention, there is provided a method of manufacturing a lens element for use as a lens element in the above-described aspects of the invention. The method includes using a rebate extending partway through the thickness of the lens element as a reference for cutting one or more other features into the lens element. This manufacturing process, in which the rebate is used as a reference for cutting other features into the lens element, facilitates the manufacture of lens elements having different sizes, shapes, and optical powers. For example, by using a rebate of a fixed size and shape as a reference for the entire range of lens element sizes, thicknesses, and shapes, the process of cutting other features into the lens element can be standardized so that it does not need to be significantly modified when switching between different lens element configurations.

[0051] The method may include forming a rebate on a surface of the lens element. The rebate may be formed on the front or back of the lens element. If the lens element is manufactured by a molding process (e.g., injection molding), the rebate may be molded into the lens element. Alternatively, the rebate may be cut into the lens element. The rebate may be shaped to accept one or more portions of a frame or frame member, such as a temple arm or nose bridge. For example, the rebate may be provided on the front of the lens element, with an elbow positioned flush with the front of the lens element and shaped to accept the elbow of the temple arm. The rebate may thus provide a standardized surface for attaching portions of a frame or frame member that is independent of the size, thickness, shape, and user prescription of the lens element. Multiple rebates may be provided on the lens element. For example, a rebate may be provided on the nose side of the lens element, and a second rebate may be provided on the temple side of the lens element.

[0052] One or more other features may be cut into the rebate. The one or more other features may be configured to accommodate one or more magnetic components, such as, for example, magnetic dowel pins or permanent magnets. The one or more other features may be configured to secure the lens elements to one or more of the frame, temple arms, or nose bridge. The one or more other features may be configured to accommodate guide components that define and constrain movement of the movable lens element relative to the fixed lens element. The one or more other features may be, for example, one or more slots, ribs, ribbed portions, or holes.

[0053] The following is a description, by way of example only, of embodiments of the present invention, with reference to the accompanying drawings in which: [Brief explanation of the drawings]

[0054] The drawings will now be described.

[0055] [Figure 1] FIG. 1 is a perspective view from above and left of the front of a pair of rimless eyeglasses according to a first embodiment of the present invention, including two variable focal length lenses mounted in a frame. [Figure 2] FIG. 2 is a perspective view from above and to the left of the front of the rimless eyeglasses of FIG. 1, showing the rear lens element of the variable focal length lens detached from the cooperating front lens element. [Figure 3] FIG. 3 is a perspective view from above of the rear of the rimless eyeglasses of FIGS. 1 and 2 with the rear lens elements removed. [Figure 4] FIG. 4 is an exploded perspective view from above and from the left side of the rear of the rimless eyeglasses of FIGS. 1-3. [Figure 5] FIG. 5 is a left perspective view of the upper front half of the left rear lens element of the rimless eyeglasses of FIGS. 1-4. [Figure 6] FIG. 6 is a front view of the left front lens element of the rimless eyeglasses of FIGS. 1-4, which is configured to mate with the left rear lens element of FIG. [Figure 7]FIG. 7 is an enlarged front view of the left side of a portion of the left front lens element of FIG. [Figure 8] FIG. 8 is an enlarged view from above and to the left of a portion of the rear of the rimless eyeglasses of FIGS. 1-7, showing the attachment of the left temple arm to the left front lens element and the area of ​​increased friction on the top edge of the rear lens element to facilitate manual manipulation of the lenses. [Figure 9A] FIG. 9A is a schematic rear view of one of three alternative embodiments of the front and rear lens elements of the rimless eyeglasses of FIGS. 1-8. [Figure 9B] FIG. 9B is a schematic diagram showing the rear view of another of three alternative embodiments of the front and rear lens elements of the rimless eyeglasses of FIGS. [Figure 9C] FIG. 9C is a schematic rear view of yet another of three alternative embodiments of the front and rear lens elements of the rimless eyeglasses of FIGS. 1-8. [Figure 10A] FIG. 10A is a corresponding schematic side view of an alternative embodiment of the front and rear lens elements of FIG. 9A. [Figure 10B] FIG. 10B is a corresponding schematic side view of an alternative embodiment of the front and rear lens elements of FIG. 9B. [Figure 10C] FIG. 10C is a corresponding schematic side view of an alternative embodiment of the front and rear lens elements of FIG. 9C. [Figure 11] FIG. 11 is a schematic view from behind of the front and rear lens elements of FIGS. 9A and 10A, showing an integral area of ​​increased friction on the top edge of the rear lens element to facilitate manual lateral sliding of the lens elements relative to one another. [Figure 12] FIG. 12 is a schematic view from behind of an alternative embodiment of the front and rear lens elements of FIGS. 9A and 10A , showing the addition of a small feature to the top edge of the rear lens element, including an area of ​​increased friction to facilitate manual lateral sliding of the lens elements relative to one another. [Figure 13]FIG. 13 is a perspective view from above and left of a variable focal length lens according to a second embodiment of the present invention, including front and rear lens elements arranged for relative lateral movement to adjust the focal length of the lens. [Figure 14] FIG. 14 is a cutaway perspective view from above and left of the variable focal length lens of FIG. 13, showing the guide elements and magnetic coupling elements between the front and rear lens elements. [Figure 15] FIG. 15 is an exploded perspective view from above and left of the front of the variable focal length lens of FIGS. 13 and 14, showing the magnetic dowel pin attached to the rear surface of the front lens element and the permanent magnet attached to the blind slot in the front surface of the rear lens element. [Figure 16] FIG. 16 is another exploded perspective view from above and left of the front of the variable focal length lens of FIGS. 13 and 14, with the magnetic dowel pins and permanent magnets removed for clarity. [Figure 17] 17 is a perspective view from above and left of the front of another pair of rimless eyeglasses according to a third embodiment of the invention, including two variable focal length lenses of the type having front and rear lens elements arranged for relative lateral movement to adjust the optical power of the lenses, with the rear lens element of the left lens shown removed; [Figure 18] 18 is a rear perspective view from above of a pair of rimless eyeglasses according to the third embodiment of the present invention of FIG. 17 with the rear lens element of the left lens removed. [Figure 19] FIG. 19 is a front view of the front lens element of the left variable focal length lens of the rimless eyeglasses of FIGS. [Figure 20] FIG. 20 is a front view of the rear lens element of the left variable focal length lens of the rimless eyeglasses of FIGS. [Figure 21]FIG. 21 is a perspective view from above and to the left of the front of the rear lens element of the left variable focal length lens of the rimless eyeglasses of FIGS. 18 and 19, showing two mounts fixed to opposite sides of the rear lens element, each incorporating a permanent magnet. [Figure 22] 22 is an enlarged perspective view from above and to the right of the front of the left one of the mounts on the rear lens element of FIG. 21. FIG. [Figure 23] FIG. 23 is a rear view of the left lens of the eyeglasses of FIGS. 18 and 19 with the rear lens element removed, showing the temple bearing for the rear lens element formed at the elbow of the left temple arm and the nose bearing for the rear lens element formed at the nose bridge. [Figure 24] FIG. 24 is an enlarged perspective view from below and to the right of the temple bearing shown in FIG. 23. [Figure 25] 25 is a rear perspective view of the lower part of a pair of rimless eyeglasses according to a fourth embodiment of the invention, including two variable focal length lenses of the type in which the front and rear lens elements are laterally slidable relative to one another to adjust the optical power of the lenses, with the rear lens element of the right lens shown detached from the corresponding front lens element; [Figure 26] FIG. 26 is a perspective view from above and left of the rear of the rimless eyeglasses of FIG. 25, showing the right rear lens element detached from the corresponding front lens element. [Figure 27] FIG. 27 is a rear elevational view of the right rear lens element of the rimless eyeglasses of FIGS. 25 and 26, showing the left and right mounts of the rear lens element separately for clarity. [Figure 28] FIG. 28 is a perspective view from the back of the bottom of the rimless eyeglasses of FIGS. 25 and 26, showing the right variable focal length lens exploded. [Figure 29] FIG. 29 is an enlarged perspective view from above of the rear of the temple elbow assembly with the mating bearing assembly removed for clarity, as attached to the left front lens element. [Figure 30]30 is an enlarged perspective view from above and left of the temple elbow assembly of FIG. 29 with the bearing assembly installed; FIG. [Figure 31] FIG. 31 is a perspective view from above and rear of the right side of the low friction bearing forming part of the left temple bearing assembly of FIGS. 29 and 30. [Figure 32] 32 is a rear and left perspective view of the lower portion of the low friction bearing of FIG. 31. FIG. [Figure 33] FIG. 33 is a perspective view from above and from the left side of a pair of framed eyeglasses according to a fifth embodiment of the invention, including frames and two variable focal length lenses of a type including front and rear lens elements arranged for lateral movement relative to one another to adjust the optical power of the lenses. [Figure 34] FIG. 34 is a perspective view from the back of the top of the framed eyeglasses of FIG. [Figure 35] FIG. 35 is an exploded perspective view from above and left of the rear of the framed eyeglasses of FIGS. 33 and 34, with the permanent magnet forming the magnetic coupling between the front and rear lens elements shown in the left lens but omitted from the right lens for clarity. [Figure 36] FIG. 36 is a rear elevational view of the front left portion of the eyeglass frame of FIG. 35, showing the rearwardly projecting temples and nose pins which form guide elements for engaging the rear lens elements. [Figure 37] FIG. 37 is an enlarged view of a portion of FIG. 36 showing the temples and nose pins and the intermediate socket for holding the permanent magnet. [Figure 38] FIG. 38 is a front view of the rear lens element of the left variable focal length lens of the eyeglasses of FIGS. 33-35, showing the temple and nose pins adjacent the upper and lower edges of the rear lens element and slots positioned to receive recesses for receiving permanent magnets. [Figure 39]FIG. 39 is an enlarged view of a portion of the left lens of the eyeglasses of FIGS. 33-35, showing the assembly of the front and rear lens elements with the temples and nose pins on the front lens element extending into slots in the rear lens element. DETAILED DESCRIPTION OF THE INVENTION

[0056] Example 1 A pair of rimless eyeglasses 11 according to a first embodiment of the present invention is shown in Figures 1 to 4. The eyeglasses 11 comprise two variable focal length lenses 21, 22 of the type consisting of two solid optically transparent lens elements positioned one in front of the other in the line of sight through the lenses (indicated by the z-axis in Figure 3 for each of the lenses 21, 22) and slidable relative to each other in a direction transverse to the line of sight (indicated by the x-axis in Figures 2 and 8) to vary the focal length of the lenses.

[0057] This type of variable focal length lens is well known in the art and is often referred to generically as an Alvarez lens. Alvarez lenses are disclosed in U.S. Patent No. 3,305,294, but numerous variations of this type of lens are known, for example, in U.S. Patent Nos. 3,583,790, 7,338,159, 7,717,552, 5,644,374, and International Publication WO 2013 / 030603. Generally, this type of adjustable lens includes two stacked lens elements, each having opposing front and back optical surfaces, and configured to control the thickness of each lens element between the surfaces, so that when light rays pass through both lens elements in succession, the lens converges or diverges them in a manner equivalent to a spherical lens. The thickness of each lens element varies according to a cubic function in the xy plane perpendicular to the line of sight through the lens to complement the other lens element, so that the spherical power of the lens varies with the relative lateral placement of the lens elements.

[0058] A suitable formula for defining the thickness t of each lens element between its opposing front and back surfaces is: t=A(x^3 / 3+xy^2)+Dx+E (I) where D is a constant representing the coefficient of prism removed to minimize lens thickness and may be zero; E is a constant representing the thickness of the lens element at the optical axis z of the lens; x and y represent coordinates in a Cartesian coordinate system centered on and lying in a plane perpendicular to the optical axis; A is a constant representing the rate of change of lens power with relative lens element movement in the x direction and is positive for one lens element and negative for the other. However, as noted above, many variations of this formula are known in the art, and the invention is not limited in this respect.

[0059] As one skilled in the art will appreciate, a single lens element of an Alvarez lens does not have its own optical axis, but a pair of lens elements functions like a normal spherical lens, so that the optical axis can be defined as a position relative to the center of the effective spherical lens. In equation (I) above, the "optical axis" is the origin of the equation, which can be conveniently used to define the z-axis for aligning lenses in optical programs, etc., but does not necessarily correspond to the effective optical axis of the lens.

[0060] Conveniently, one surface of each lens element is flat or formed as a regular surface of revolution, e.g., spherical, while the other surface has a tertiary surface of the type described above to control the thickness of the lens element. The tertiary surface of each lens element may, in some embodiments, suitably be formed on a spherical base curve in a manner known in the art. Thus, the lens elements may be arranged to slide relative to each other along a line or along a defined path, e.g., an arc having a z-axis component and a center on the optical axis. For example, in some embodiments, the lens elements may be arranged to slide relative to each other on an arc in a horizontal (xz) plane relative to the user.

[0061] In this embodiment, the two lenses 21, 22 are similar in terms of their structure, and therefore for convenience only the left lens 21 (as seen from the user's perspective) will be described below, but the right lens 22 is similarly a mirror image of the left lens 21 in a median plane extending in the z-direction midway between the two lenses 21, 22. Therefore, the following description of the left lens 21 applies equally to the right lens 22.

[0062] Thus, variable focal length lens 21 includes front lens element 31 and rear lens element 41. Front element 31 has a spherical or spherical-cylindrical front surface 32 and a cubic rear surface 33 of the type described above. Rear lens element 41 has a cubic front surface 42 of the type described above that complements the rear surface 33 of front lens element 31 to form an Alvarez lens, and a spherical or spherical-cylindrical rear surface 43. Surfaces 32, 33, 42, 43 of both lens elements 31, 41 can be molded or cut to shape from preformed polished pucks in a manner known in the art for optical use. In some embodiments, front surface 32 of front lens element 31 and rear surface 43 of rear lens element 41 can have the same spherical curvature and therefore do not contribute to the net optical power of lens 21. However, in some embodiments, the front surface 32, 33 of the front lens element 31 and the rear surface 43 of the rear lens element 41 can be configured relative to each other to cause convergence or divergence of light rays passing through both elements, like a spherical lens with positive or negative refractive power. Thus, the lens 21 can have a fixed prescription according to the user's requirements. In some embodiments, the front and rear surfaces 32, 33 of the front lens element 31 and the front and rear surfaces 42, 43 of the front lens element 41 can be shaped to divide the user's prescription between the front and rear lens elements 31, 41, allowing the lens elements 31, 41 to be as thin as possible. In this sense, the tertiary surface 33, 42 of each lens element 31, 41 can be formed on a spherical base curve with a different radius of curvature than the corresponding spherical surface 32, 43. In practice, one of the front lens element 31 and the rear lens element 41 can have a standard base refractive power, while the refractive power of the other lens element 41, 31 can be adjusted according to the user's prescription. This allows at least one of the lens elements 31, 41 to be manufactured in a range of SKUs, while requiring customization for each user for only the other lens element 41, 31. As noted above, the lens elements 31, 41 may also be configured to provide an amount of cylindrical correction to light passing through the lens 21. Suitably, any required degree of astigmatism is included in the other lens element 41, 31 that is customized for the user.In a further variation, one or both of the front surface 32 of the front lens element 31 or the back surface 43 of the rear lens element may be formed with a graduated addition surface to vary the base power of the lens.

[0063] As described above, lens elements 31, 41 are configured so that the net refractive power of lens 21 varies according to the relative lateral positioning of lens elements 31, 41 on a horizontal axis x extending transverse to line of sight z, as shown in FIGS. 2 and 8. Suitably, the additional refractive power provided by lens elements 31, 41 may vary from 0 to 2 diopters and may provide additional refractive power suitable for correcting presbyopia in addition to fixed base spherical and / or cylindrical powers of the type described in the previous paragraph. A problem with Alvarez-type lenses is that the lens elements can become quite thick when a wide range of refractive powers is required. Therefore, it may be desirable to limit the range of additional refractive power provided by shifting lens elements 31, 41 relative to one another to only a few diopters. However, those skilled in the art will appreciate that the present invention may equally be used with lenses having a wider range of additional refractive powers, for example, 0-5 diopters, 0-6 diopters, or 0-10 diopters, if one is willing to compromise the aesthetic appearance of the lenses 21, 22 for the thickness of the required lens elements 31, 41.

[0064] The lenses 21, 22 are mounted in a frame 12, as shown in FIGS. 1 and 4. The eyeglasses 11 of this embodiment are rimless, and the frame 12 includes a nose bridge 14 that interconnects and secures the two lenses 21, 22, and left and right temple arms 15, 16, as described in more detail below. Like the lenses 21, 22, the left and right temple arms 15, 16 are mirror images of each other in the medial plane. The left temple arm 15 is secured to the left lens 21, and the right temple arm 16 is secured to the right lens 22. The lenses 21, 22 are mounted in the frame 12 such that the horizontal axis x of the sliding of the lens elements 31, 41 is oriented substantially horizontally relative to the user in normal use, as shown in FIG. 2. In other embodiments of the present invention, the lenses 21, 22 may be mounted in a frame that includes a complete or partial rim around the lenses.

[0065] As best shown in FIG. 6 , the front lens element 31 is generally rectangular, having upper and lower edges 34, 35, respectively, and left and right lateral or side edges, i.e., a temple side portion 36 adjacent the left temple arm 15 and a nose side portion 37 adjacent the nose bridge 14. The present invention is not limited to a particular lens shape; therefore, the lens elements 31, 32 can have any suitable lens shape, such as any of those well known in the art. Some standard ophthalmic lens shapes are more circular than others and may have less clearly defined sides than the lens 21 of the present embodiment. Nevertheless, one skilled in the art would have no difficulty adapting the lens shape to other shapes as needed.

[0066] The rear lens element 41 has a shape similar to that of the front lens element 31, as best seen in Figures 11 and 12, which have upper and lower edges 44, 45, respectively, and temple and nose edges 46, 47, respectively. The rear lens element 41 is shorter than the front lens element 31 in the x-direction between its temple and nose edges 46, 47, accommodating lateral movement of the rear lens element 41 relative to the front lens element 31 to adjust the focal length of the lens 21, as described below. The front and rear lens elements 31, 41 are mounted such that at least a portion of the top edge 44 of the rear lens element 41 protrudes slightly above at least a portion of the front top edge 34, as best seen in Figures 9A, 10A, 11 and 12, to facilitate manual movement of the rear lens element 41 relative to, and complete removal of, the rear lens element 41 from, the front lens element 31, as will be described in more detail below. Advantageously, the top edge 44 of the rear lens element 41 is formed with knurled portions 48 to increase friction, as best seen in Figure 8, which may further facilitate manual manipulation of the lens 21 by the user. Alternatively, the friction of at least a portion of the top edge 44 of the rear lens element 41 can be increased by creating one or more raised (or lowered, or both) edges or surfaces as part of the lens edging process, or in the molding tool if the lens element 41 is injection molded by laser etching, chemically etching, or CNC post-machining the desired surface. In a variation of this embodiment, instead of forming the rear lens element 41 with an integral knurled portion 48, a small, friction-increasing component 48' can be attached to the top edge 44 of the rear lens element 41, as shown in FIG. 12. This can be achieved by gluing a special agent (such as clear sandpaper), embedding small ball bearings or other agents into the top edge 44, using a coating (e.g., dipped or sprayed), or two-shot molding (overmolding) a high-friction elastomeric (e.g., TPU) material.

[0067] In a further variation of this embodiment, as shown in Figures 9B and 10B, rear lens element 41 can be positioned relative to front lens element 31 so that at least a portion of its lower edge 45 extends below at least a portion of the lower edge 35 of the front lens element. Alternatively, the height between the upper and lower edges 44, 45 of rear lens element 41 can be slightly greater than the height of front lens element 31, such that the upper and lower edges 44, 45 of rear lens element 41 extend beyond the corresponding edges 34, 35 of front lens element 31, as shown in Figures 9C and 10C. These arrangements of front and rear lens elements 31, 41 are equally applicable to other embodiments of the invention described below.

[0068] 6 and 7, the front surface 32 of the front lens element 31 is formed with rebates 58 juxtaposed on each side 36, 37 and extending partway up the front lens element 31. Within each rebate 58, the front lens element 31 is formed with slots 51, 52 and a plurality of holes 61, 62, 63, as described below.

[0069] In some embodiments, during the manufacture of the front lens element 31, the rebates 58 are first cut into the front lens element 31 and then used as datum when cutting the slots 51, 52 and holes 61, 62, 63. This allows the rebates to be used as datum to facilitate the manufacture of lens elements of various sizes and shapes. For example, by using a fixed size and shape rebate as datum across a range of lens element sizes, thicknesses, and shapes, the process of cutting the slots 51, 52 and holes 61, 62, 63 into the lens elements can be standardized and does not need to be significantly changed when switching between lens element sizes.

[0070] An elongated slot 51, 52 is formed in each rebate 58. That is, temple slot 51 is adjacent temple side 36, and nose slot 52 is adjacent nose side 37. Slots 51, 52 are of the same length, each extending completely through front lens element 31 in the transverse direction x as defined above. The slots have semicircular temple and nose ends 53, 54, as shown in FIG. 7. One of the upper or lower walls 55 of slots 51, 52 is stepped relative to temple slot 51, as best seen in FIG. 7, to define a retaining rib 56 that extends from nose end 54 along the top or bottom of slot 51, which is juxtaposed to back surface 33 of front lens element 31, stopping short of temple end 53. In this embodiment, rib 56 is formed on the lower wall 55 of the slot, but in variations, rib 56 can be formed on the opposite upper wall, which allows for a flatter and deeper lower surface. The retaining rib 56 has a front surface 56 .

[0071] The front surface 32 of the front lens element 31 is slightly recessed at 58 around each of the slots 51, 52 for securing the temple arms 15 and nose bridge 14, as described below, as shown in FIGS. 6 and 7. Within the recesses 58, the front lens element 31 is formed with two large holes 61, 62 juxtaposed at each end 53, 54 of the slot 51, and two smaller holes 63 positioned between the larger holes 61, 62. Those skilled in the art will appreciate that the size of the holes is not critical, and in some embodiments, the holes 61, 62, and 63 may be substantially the same size. The holes 61-63 extend completely through the front lens element 31. The larger holes accommodate the front permanent magnets 65, 66, respectively, as best seen in FIGS. 4 and 8. The smaller holes 63 allow the temple arms 15 and nose bridge 14 to be secured to the front lens element 31 using suitable fasteners, such as grooved, threaded, ridged, or barbed fixtures 71, as shown in FIG. 8 . The fixtures 71 are attached to the rear surface 18 of the temple arm elbows 17, which fit within rebates 58 that are flush with the front surface 32 of the front lens element 31. In this embodiment, the front lens element 31 is securely secured to the frame 12 in this manner. Advantageously, this arrangement allows for the creation of a common surface on the front surface 32 of the front lens element 31, which can vary depending on the SKU / user prescription. The temple arms 15 can then be attached to the common surface regardless of the user's prescription or the base power of the SKU. The rear surface 18 of the elbows 17 and the front surface of the rebates 58 lie on the same spherical radius, which defines an arcuate traversal path (e.g., in the x-z plane described above) with the movement of the rear lens element 41. The front lens element 31 can be attached to the nose bridge 14 by a similar arrangement relative to the nose side 37 of the front lens element 31. It will be appreciated that in a variation of this arrangement, two or more permanent magnets 65, 66 can be accommodated in the front lens element 31, for example, by a third larger hole (not shown) between the two holes 61, 62 described above.

[0072] The rear lens element 41 is coupled to the front lens element 31 by two spaced-apart cylindrical dowel pins 81, 82 that mount within and project forwardly from respective recesses 91, 92 formed in the rear lens element 41, as shown in FIG. 5 . The dowel pins 81, 82 align with slots 51, 52 in the front lens element 31, with one dowel pin 81 located near the temple side 46 of the rear lens element 41 and the other 82 located near the nose side 47. Each dowel pin 81, 82 includes a notch 83 defining an end 84 having circular front and rear faces 85 and 86. Each dowel pin 81, 82 extends into a corresponding one of the slots 51, 52 and is retained therein by the interengagement of the rear face 85 of the end 84 on the front face 56 of the retaining rib 56. Thus, slots 51, 52 and dowel pins 81, 82 act as guide elements to allow lateral movement of rear lens element 41 in a transverse direction transverse to line of sight z relative to front lens element 31 while constraining movement of rear lens element 41 relative to front lens element 31 with a small tolerance in a transverse direction x transverse to line of sight z relative to front lens element 31. Dowel pins 81, 82 are sized to fit snugly within slots 51, 52 to prevent movement of rear lens element 41 relative to front lens element 31 in a y direction orthogonal to the x axis and yaw of rear lens element 41 relative to front lens element 31 in the xy plane. The front faces 85 of the temple dowel pins 81 engage the rear faces 18 of the elbows 17 of the temple arms 15, and the front faces 85 of the nose dowel pins 82 engage the corresponding rear faces of the nose bridge 14 to prevent axial movement in the z-direction of the rear lens element 41 relative to the front lens element 31. Suitably, the elbows 17 and the rear faces of the nose bridge 14 may be provided with low friction bearings (e.g., PTFE, POM). Alternatively, plastic dowel pins 81, 82 can be used.

[0073] The dowel pins 81, 82 are spaced so that, during left-right movement of the rear lens element 41, they simultaneously engage the front lens element 31 at either the temple end 53 or the nose end 54 of each slot 51, 52. By moving the rear lens element 41 toward the temple end 53 of the slot 51, 52, the dowel pins 81, 82 can be removed from the front lens element 31 at a position where the retaining ribs 56 stop short of the ends of the slots. In a variation of this embodiment, the ribs 56 can instead extend from the temple ends 53 of the slots 51, 52 and stop short of the nose ends 54, such that the rear lens element 41 can be removed from the front lens element 31 when the rear lens element 41 is slid fully into the nose position.

[0074] In another variation of this embodiment, a first portion of rib 56 can extend from nose ends 54 of slots 51, 52, and a second portion of rib 56 can extend from temple ends 53 of slots 51, 52. Thus, first and second portions of rib 56 rest close together to define a notch therebetween of appropriate size and dimension so that rear lens element 41 can be detached from front lens element 31 when rear lens element 41 is slid to a position intermediate the nose and temple positions.

[0075] As described above, the front and rear lens elements 31, 41 are configured such that changing their relative lateral positioning changes the focal length of the lens 21. Suitably, the front and rear lens elements 31, 41 are configured such that sliding the rear lens element 41 from the temple end 53 of the slots 51, 52 to the nasal end 54 increases the optical power of the lens 21. In this manner, the lens 21 can be configured to provide two modes of use: a distance mode when the rear lens element 41 is positioned at the temple end 53 of the slots 51, 52, and a reading position with increased optical power when the rear lens element 41 is positioned at the nasal end 54 of the slots 51, 52. This is consistent with the way the eye moves when focusing from far to near, and is intended to contribute to an improved optical experience from the movable Alvarez lens configuration. When a third magnet is provided in an intermediate position as described above, the lens 21 can provide three modes of use.

[0076] As shown in FIG. 5, the rear lens element 41 is formed with two additional holes 93, 94 that extend into the rear lens element 41. While these holes are shown extending through the rear lens element 41 in the figures, in variations of this embodiment they may be blind holes to provide a more attractive finish. Each of these additional holes 93, 94 is positioned juxtaposed with a respective one of the dowel pins 81, 82 and accommodates a rear permanent magnet 88, 89. Each of the rear permanent magnets 88, 89 is positioned to cooperate with two front permanent magnets 65, 66 adjacent to each of the slots 51, 52 of the two front lens elements 31. In particular, when the rear lens element 41 is positioned at the temple position, each of the rear permanent magnets 88, 89 aligns with the front permanent magnet 65 at the temple end 53 of the corresponding slot 51, 52, and when the rear lens element 41 is positioned at the nose position, each of the rear permanent magnets 88, 89 aligns with the front permanent magnet 66 at the nose end 53 of the corresponding slot 51, 52. The front and rear permanent magnets 65, 66, 88, 89 are oriented to attract each other to hold the rear lens element 41 in a stable equilibrium at the temple and nose positions. Intermediately between the temple and nose positions, the magnets continue to hold the front and rear lens elements 31, 41 together, but the rear lens element 41 is in an unstable equilibrium state with a tendency to move to either extreme position.

[0077] Suitably, the front and rear magnets 65, 66, 88, 89 serve to hold and precisely position the front and rear lens elements 31, 41 relative to one another in each mode, while allowing the lens elements 31, 41 to be separated when the rear lens element 41 is in the temple position described above, for example for cleaning. In particular, the front and rear magnets 65, 66, 88, 89 pull the front and rear lens elements 31, 41 together so that the front faces 85 of the dowel pins 81, 82 engage the elbow 17 and the rear face 18 of the nose bridge 14, respectively, thereby controlling the movement of the rear lens element 41 along a precise arcuate transverse path. The front and rear magnets 65, 66, 88, 89 thus position the lens elements 31, 41 in discrete detent positions and provide positive feedback to the user during setup. When changing modes, the magnitude of the force can be easily overcome through the user interface resulting from the combination of the tactile interface described above, the size relationship between the front and rear lens elements 31, 41, and the magnetic coupling formed by the front and rear magnets 65, 66, 88, 89. This allows the user to accurately and easily adjust the refractive power of the lens 21.

[0078] To provide a "superior" optical experience, the relationship between the front and rear lens elements is controlled within a defined tolerance range to eliminate or minimize unwanted movement (wobble, twist, etc. in various degrees of freedom). Meanwhile, to provide a good user interface experience, it is desirable to control the friction between the mating surfaces of the front and rear lens elements 31, 41. The sliding friction depends on the holding force. The strength of the magnets can be selected to optimize the generated sliding force and actuation force.

[0079] Thus, the rimless eyeglasses 11 of the first embodiment represent a lightweight design that allows for a more traditional glazing approach compared to the other embodiments described below. The slots 51, 52 can be formed in the front lens element 31 during molding or cutting, while the recesses 91, 92 for the dowel pins 81, 82 (plastic or metal) can be formed during the cutting process of the rear lens element 41. The rear magnets 88, 89 are attached directly to the rear lens element 41 in holes 93, 94, which can be formed during the cutting process of the rear lens element 41. The front magnets 65, 66 are attached directly to the front lens element 31 in holes 61, 62, which can be formed during the lens cutting process. Forming the slots 51, 52 directly in the front lens element 31 helps minimize tolerance chains and ensure good alignment of the front and rear lens elements 31, 41. The use of separate slots 51, 52 and front magnets 65, 66 allows the slots 51, 52 to be the full thickness of the lens element 31, allowing a wider selection of magnets to fit within the thickness of the lens element 31.

[0080] Example 2 13-16 illustrate a variable focal length lens 121 according to a second embodiment of the present invention. The lens 121 is suitable for use in a pair of eyeglasses to correct presbyopia and, optionally, fixed refractive errors such as myopia, hyperopia, and astigmatism. Similar to the lenses 21 and 22 used in the rimless eyeglasses of Example 1 above, the variable focal length lens 121 of this embodiment includes two solid, optically transparent lens elements, positioned one in front of the other in the line of sight through the lens (indicated by the z-axis in FIG. 15 ) and slidable relative to one another in a direction transverse to the line of sight (indicated by the x-axis in FIG. 15 ) to vary the focal length of the lens. Suitably, the lens 121 may be an Alvarez-type lens; for the sake of brevity, the details of such a lens described above with respect to Example 1 will not be repeated here. The following description focuses on aspects of the second embodiment that differ from the first embodiment.

[0081] Thus, lens 121 comprises a front lens element 131 and a rear lens element 141. The front lens element has a front surface 132 and a rear surface 133. The front surface is spherical or spherocylindrical, and the rear surface 133 is configured as a cubic surface of the type described above with respect to a spherical base curve. The rear lens element 141 has a cubic front surface 142 and a spherical or spherocylindrical rear surface 143. In addition to the variable optical power provided by the combination of the cubic surfaces 133, 142, lens 121 may include base spherical and / or cylindrical optical power. As in the first embodiment, the front and rear lens elements 131, 141 are coupled together by guide elements to allow lateral movement of the lens elements relative to one another on a linear or curved transverse path across the z-axis to change the focal length of the lens.

[0082] The front lens element 131 has a top edge 134, a bottom edge, and two opposing side edges 136, 137. When shaped for use in eyeglasses, one side edge 136 may form a temple-side edge positioned toward the temples of a user's head, while the other side edge 137 may form a nose-side edge positioned juxtaposed with the user's nose. Toward each side edge 136, 137, and generally toward the top edge 134, the front lens element 131 is formed with a series of three holes spaced apart in the x-direction. The three holes include a larger central hole 161 extending through the front lens element 131 and shaped to receive a magnetic dowel pin 181 that protrudes rearward from the back surface 133 of the front lens element 131, and two smaller holes 163 that can be used to attach the lens 121 to a frame in a manner similar to that described in the previous example. It will be appreciated that in full-frame eyeglasses, the smaller holes 163 are redundant and may be omitted. Magnetic dowel pin 181 is securely fixed in central hole 161. In some embodiments, an interference press fit may be sufficient to hold magnetic dowel pin 181 securely in place, although in some embodiments, adhesive cement may also be applied. Thus, anterior lens element 131 has two rearwardly extending magnetic dowel pins 181, one adjacent temple edge 136 and the other adjacent nose edge 137.

[0083] The rear lens element 141 has a shape similar to that of the front lens element 131, as best seen in FIGS. 13 and 14 . Thus, the rear lens element 141 has top and bottom edges 144, 145, and side edges 146, 147. As described with reference to FIGS. 9A-C, 10A-C, 11, and 12, the rear lens element 141 is narrower than the front lens element 131 between its two side edges 146, 147, and may be shaped and / or positioned relative to the front lens element 131 such that either the top edge 144 or the bottom edge 145, or both, of the rear lens element 141 protrude beyond the corresponding edge of the front lens element 131 to facilitate manual manipulation of the lens 121. As with the first embodiment, the top and / or bottom edges 144, 145 of the rear lens element may further include integral or additional regions (not shown) of increased friction to aid in the movement of the lens 121.

[0084] Each of the two magnetic dowel pins 181 has a rear end that is received in a corresponding blind slot 151 formed in the front surface 142 at a corresponding position toward the two side edges 146, 147 and the top edge 144 of the rear lens element. Each slot 151 is recessed from the front surface 142 of the rear lens element 141, and the front surface 152 defines a rear wall within the slot 151. Each magnetic dowel pin 181 has a rear surface 182 that engages with the front surface 152 of the rear wall of the respective slot 151 to form an axial bearing between the two lens elements 131, 141. Suitably, the front surface 152 and / or the rear surface 182 can be formed of a low-friction material to facilitate sliding one over the other. Each slot 151 has opposing temple and nose ends 153, 154, and a magnetic dowel pin 181 fits snugly into each slot 151 to guide relative lateral movement of the front and rear lens elements 131, 141 along a transverse path between the two ends 153, 154, while preventing unwanted movement of the lens elements 131, 141 in any other direction, including the y-axis direction extending between the upper and lower edges 134, 135, 144, 145 of the front and rear lens elements 131, 141 as shown in Figure 15. The magnetic dowel pins 181 and slots 151 are positioned and dimensioned so that two magnetic dowel pins 181 are simultaneously positioned at the temples or nose ends 153, 154.

[0085] Adjacent each of its temple and nose ends 153, 154, each of the slots 151 houses a rear permanent magnet 188 that is received in a corresponding hole 193 that extends from the front face 152 of the rear wall through the rear lens element 141. Thus, there are two magnets 188 in each slot 151. The rear permanent magnets 188 fill these holes 193, are flush with the front face 153 of the rear wall of the slots 151, and are positioned to cooperate with magnetic dowel pins 181 to couple the front and rear lens elements 131, 141 together in two distinct locations when the dowel pins 181 are positioned at the temple end 153 or nose end 154 of the respective slots 151, respectively. As before, the holding force between the magnetic dowel pin 181 and the rear magnet 188 can be strong enough to hold the front and rear lens elements 131, 141 together in any relative positioning of the two elements between the temple and nose ends 153, 154 of the slot 151. However, due to the proximity of the magnets at these end locations, the front and rear lens elements 131, 141 are held in an unstable equilibrium between the two discrete positions defined by the ends of the slot 151, which can result in the lens elements 131, 141 tending to move to their discrete positions and provide tactile feedback to the user. In this manner, the magnetic dowel pin 181 and rear magnet 188 define two modes of use for the lens 121 of this embodiment: when the lens elements are positioned at the temple end 153 of the slot 151 by the magnetic dowel pin 181, and when the lens elements are positioned at the nose end 153 of the slot 151 by the magnetic dowel pin 181. As with the first embodiment, lens elements 131, 141 may be configured such that lens 121 has greater optical power when magnetic dowel pin 181 is located at nose end 154 of slot 151. Thus, lens 121 may have a distance mode in which magnetic dowel pin 181 is located at temple end 153 of slot 151, and a reading mode in which magnetic dowel pin 181 is located at nose end 153 of slot 151. Lens 121 of this embodiment may be readily adapted to include a third magnet in an intermediate position in each slot 151 to provide a third, intermediate use mode.

[0086] In this embodiment, the magnetic coupling between the magnetic dowel pin 181 and the rear permanent magnet 188 is the only means of holding the front and rear lens elements 131, 141 together. Unlike the first embodiment, the mechanical guide element formed by the magnetic dowel pin 181 and slot 151 does not have a retaining element corresponding to the rib 56 of the first embodiment.

[0087] As with the first embodiment, the magnetic dowel pins 181 and rear magnets 188 help hold and precisely position the front and rear lens elements 131, 141 relative to each other in each of the aforementioned modes while allowing for easy separation of the lens elements 131, 141 for cleaning, repair, etc. The magnetic dowel pins 181 and rear magnets 188 position the lens elements 131, 141 in their individual positions and provide positive feedback to the user during setup. When changing modes, the magnitude of the force can be easily overcome through the user interface resulting from a combination of the tactile interface described above, the size relationship between the front and rear lens elements 131, 141, and the magnetic coupling formed by the magnetic dowel pins. This allows the user to precisely and easily adjust the optical power of the lens 121.

[0088] An advantage of the lens 121 of this embodiment is that the entire lens switching mechanism is contained within the lens 121, all formed during the lens cutting process (in the case of prescription lenses). Two slots 151 are strategically placed on the lens 121 to allow for easy switching and prevent the lens elements 131, 141 from twisting relative to each other. For rimless variations, these can be located behind the temple and nose framework. For framed variations, these are likely to be adjacent to the top edges 134, 144 of the front / rear lens element pair and the temple side edges 136, 146. This allows for the use of many pre-fabricated frames, including rimless, half-rim, and full-frame styles.

[0089] Example 3 Another pair of rimless eyeglasses 211 according to a third embodiment of the present invention is shown in Figures 17 and 18 of the accompanying drawings. Like the first embodiment of eyeglasses described in Example 1 above, the eyeglasses of this embodiment comprise two variable focal length lenses 221, 222 of a type comprising two overlapping lens elements arranged for relative movement transverse to the line of sight (z-axis in Figure 17) to vary the focal length of the lenses. Details of such lenses are provided above in relation to the first embodiment of the present invention and will not be repeated here for the sake of brevity. Broadly speaking, the eyeglasses 211 of this embodiment function similarly to those of Example 1 above, except that whereas the lenses 21, 22 of the first embodiment each provide only two modes of use, distance vision and reading, the lenses 221, 222 of this embodiment have three modes of use, including an intermediate mode, which is described in more detail below.

[0090] The lenses 221, 222 are mounted in a rimless frame that includes a nose bridge 214 and left and right temple arms 215, 216 (from the perspective of the user wearing the eyeglasses). As shown in Figures 17 and 18, the lenses 221, 222 form the left and right lenses of the eyeglasses 211, with the left lens 221 connected between the left temple arm 215 and the nose bridge 214. The right lens 222 is connected between the right temple arm 216 and the nose bridge 214. Because the left and right lenses 221, 222 are essentially mirror images of each other across the median plane, the left lens 221 will be described below, but the structure and operation of the right lens 222 is substantially the same.

[0091] The left lens 221 includes front and rear lens elements 231, 241, which are substantially the same as the front and rear lens elements 31, 41, 131, 141 of Examples 1 and 2 above. The front lens element 231 has a front surface 232 and a rear surface 233, as shown in FIG. 19. The front lens element 231 is generally rectangular and has an overall shape of a type suitable for use in a pair of eyeglasses, including a top edge 234, a bottom edge 235, a temple edge 236, and a nose edge. Many other lens shapes can be used in accordance with the present invention. Toward the top edge 234, each of the temple and nose edges 236, 237 are cut out at 238 and 239, respectively, to provide fitment for the left temple arm 215 and nose bridge 214, respectively. 23 and 24, a temple-side cutout 238 receives elbow 217 of left temple arm 215. Elbow 217 includes an integral temple bearing 271 having upper and lower surfaces 272, 273, which form a press fit within cutout 238. As best shown in FIG. 24, upper and lower surfaces 272, 273 of temple bearing 271 and the corresponding edge of front lens element 231 at cutout 238 are shaped to form a bump fit at 274 and 275 to securely fasten elbow 217 to front lens element 231. The joint between elbow 217 of temple arm 215 and front lens element 231 can be supplemented with an adhesive, if desired. Nose bridge 214 includes two similar nose bearings 276, 277, one on each end, for attaching the nose bridge in a similar manner to the front lens element 231 of the left and right lenses 221, 222, respectively. Nose bridge 214 is secured to the front lens element 231 of the left lens 221 by left nose bearing 276, which forms a press fit in cutout 239 in the front lens element 231. Nose bridge 214 is secured to the front lens element 231 of the right lens 222 by right nose bearing 277 in a similar manner.

[0092] The temple bearing 271 of the elbow 217 has a rear surface 218 formed with a generally rectangular recess 251 extending laterally between an inner temple side wall 253 and an inner nose side wall 254, as shown in Figure 24. The rectangular recess 251 also has inner lower and upper walls 255, 256 and an inner front wall 257 set forward of the rear surface 218. The temple bearing 271 is formed with three spaced recesses extending forward from the inner front wall 257, each housing a front permanent magnet 265, 266, 267 flush with the inner front wall 257. The holes and the magnets received therein are spaced substantially laterally between the temple and nose walls 253, 245 along an x-axis extending transverse to the line of sight as shown in FIG. 17, such that the group of three magnets includes a front temple magnet 265 adjacent the temple wall 253, a front nose magnet 267 adjacent the nose wall 245, and a front central magnet 266 between the front temple and nose magnets 265, 267.

[0093] The left nose bearing 276 on the nose bridge 214 is similar to the temple bearing 217, having a similar rectangular recess 252 extending between the inner temple sidewall 263 and the inner nasal sidewall 264, with inner upper and lower walls 265, 266 and a front wall 267. The front wall 267 of the nose bearing 276 on the nose bridge 214 is formed with three laterally spaced recesses, as best seen in FIG. 23. However, in this embodiment, only the central recess houses a front permanent magnet 268 that is flush with the front wall 267, while the recesses adjacent the inner temple and nasal walls 263, 264 are empty. In other embodiments, these recesses may also receive permanent magnets or may be absent. The spacing between the inner side walls 263, 264 of nose bearing 276 is equal to the spacing between the inner side walls 253, 254 of the temple bearings, and recesses 251, 252 correspond to slots 51, 52 in rear lens element 41 of the first embodiment described above in that they allow side-to-side movement of rear lens element 241 relative to front lens element 231, as described below.

[0094] The left rear lens element 241 has a front surface 242 and a back surface 243 and is formed with a shape corresponding to that of the front lens element 231, as shown in FIG. 20 , having top and bottom edges 244, 245 and temple and nose side edges 246, 247. As with the first and second embodiments described above, the rear lens element 241 has a width between its temple sides 246 and nose side 247 that is narrower than the width of the front lens element 231, as seen in FIG. 18 . Similarly, the rear lens element 241 may be positioned or shaped or sized relative to the front lens element such that one or both of its top and bottom edges 244, 245 protrude slightly beyond the corresponding edge or edges of the front lens element 231 to facilitate manipulation of the rear lens element 241 by the user, as described below. Towards its upper edge 244, the rear lens element 241 is formed with female (cut-out) dovetail grooves 249, 250 at its temple and nose edges 246, 247, respectively.

[0095] As best shown in FIG. 21 , each of the female dovetail grooves 249, 250 receives a mount 281, 282. Thus, the female dovetail groove 249 on the temple edge 246 of the rear lens element 241 seats the temple mount 281, while the female dovetail groove 250 on the nose edge 247 of the rear lens element 241 seats the nose mount 282. Each of the temple and nose mounts 281, 282 includes a male dovetail groove 283, as shown in FIG. 22 , that is molded to mate with a corresponding female dovetail groove 249, 250 to form a tight interference fit. Additional slots 260 formed in the temple and nose edges 246, 247 allow the fit to the temple and nose mounts 281, 282 to be adjusted to provide a secure press fit, which can be supplemented with adhesive cement if necessary.

[0096] Each of the temple and nose mounts 281, 282 comprises a generally rectangular block 284 disposed on a corresponding side edge 246, 247 of the rear lens element 241 and projecting forward of the front surface 242 of the rear lens element 241. The temple and nose mounts 281, 282 are received in the rectangular recesses 251, 252, respectively, to guide lateral movement of the rear lens element 241 relative to the front lens element 231 along a transverse path transverse to the line of sight defined by the rectangular recesses 251, 252 of the temple and nose bearings 217, 276. Each block 284 has a front surface 289 positioned to engage and form an axial bearing with the front wall 257, 267 of the corresponding temple or nose bearing 217, 276, and upper and lower surfaces 285, 286, which slidably engage the interior upper and lower walls 255, 256, 265, 266 of the corresponding temple or nose bearing 217, 276, respectively, to prevent wobble, twisting, or other undesired movement of the rear lens element 241 relative to the front lens element 231. The mounts 281, 282 and bearings 271, 276 thus help to constrain the relative movement of the front and rear lens elements 231, 241 to a transverse path. The distance between the temple mount 281 and the nose mount 282 is equal to the distance between the corresponding portions of the temple bearing 271 and the nose bearing 276, and each block also has a temple side surface 287 arranged to engage the inner temple side wall 253, 263 of the corresponding temple or nose bearing 217, 276 when the posterior lens element 241 is moved fully toward the temple, and a nose side surface 288 arranged to engage the inner nose side wall 254, 264 of the corresponding temple or nose bearing 217, 276 when the posterior lens element 241 is moved fully toward the nose.

[0097] As best seen in FIG. 22 , the top surface 285 of the temple mount 281 is formed with a lateral groove 291 configured to receive a retaining nib 292 formed on the interior top wall of the recess 251 of the temple bearing 271 when the rear lens element 241 is fully moved toward the temple or toward the nose, as described in the previous paragraph. The retaining nib 292 serves to retain the temple mount 281 in the recess 251 when the rear lens element 241 is disposed in either of these two positions as a means of helping to prevent accidental removal of the rear lens element 241 while in use in these positions. As shown in FIG. 24 , when the rear lens element 241 is disposed in a central position between the temple position and the nose position, there is no retaining nib. This means that the temple mount 281 can be removed from the temple bearing 271 when the rear lens element 241 is in the central position. 21, nose mount 282 is formed with a similar lateral groove 291 on its underside that is similarly arranged to receive a retaining nib 293 formed in the inner lower wall of recess 252 formed in left nose bearing 276 when rear lens element 241 is fully moved toward the temple or nose and not in the center position. Thus, rear lens element 241 can be fully removed from front lens element 231 in the center position.

[0098] Each temple and nose mount 281, 282 is fitted with a rear permanent magnet 298 that is received in a recess 299 formed in the front surface 289 of the rectangular block 284. The magnet 298 is oriented along the visual axis z and is positioned to cooperate with the magnets 265, 266, 267, 268 in the corresponding temple or nose bearing 271, 276 to form a magnetic coupling between the front and rear lens elements 231, 241. The front and rear magnets 265, 266, 267, 268 are most strongly attracted to the rear magnet 298 when the rear magnet 298 is aligned with one of the front magnets. The front and rear magnets therefore serve to define three distinct positions of the rear lens element 241 relative to the front lens element 231. the temple position when the rear magnet 298 of the temple mount 281 aligns with the temple magnet 265 of the temple bearing 271; the nose position when the rear magnet 298 of the temple mount 281 aligns with the nose magnet 267 of the temple bearing 271; and the center position when the rear magnet 298 of the temple mount 281 aligns with the center magnet 266 of the temple bearing 271. When the rear lens element 241 is positioned in the center position, the rear magnet 298 on the nose mount 282 is attracted to the rear magnet 268 in the nose bearing 276. As in the first and second embodiments above, the strength of the front and rear magnets 265, 266, 267, 268, 298 is sufficient to hold the front and rear lens elements 231, 241 together stably, while allowing them to be manually slid between the temple, center, and nose positions described above, and for the rear lens element 241 to be removed in the center position if necessary, for example for cleaning.

[0099] The strength of the magnetic coupling between the front and rear magnets 265, 266, 267, 268, 298 defines the user's tactile experience when manipulating the rear lens element 241 between the discrete positions. Because the strength of the holding force generated by the magnets is greatest when the magnets are aligned, the user can feel through the user's fingers when the rear lens element 241 is in one of the discrete positions. In this sense, the spaced magnets 265, 266, 267 in the temple bearing 271 help provide a series of three detents. In some embodiments, the center magnet 266 can be stronger than the temple and nose magnets 265, 267, allowing the user to feel when the rear lens element 241 is in the central position and helping the user select the central position without easily overrunning to the outer positions. In this embodiment, the magnets 265, 266, 267 are positioned so that the central position generates a greater holding force than the temple or nose positions. In other embodiments, this effect can be achieved by using multiple magnets, different shaped magnets, or different grades of magnets (e.g., N52, N48, N35, where higher numbers provide higher pulling forces for magnets of the same size / shape.) It is also contemplated that this can be achieved by other (non-magnetic) means, such as a bump fit between the front and rear lens elements 231, 241, leaf springs, etc.

[0100] Thus, the magnetic coupling between the front and rear lens elements 231, 241 defines three different modes of use, compared to only two modes in the first and second embodiments described above. As described in Examples 1 and 2, the front and rear lens elements 231, 241 of this embodiment can be conveniently positioned so that the optical power of the lens 221 increases from the temple position through the central position to the nasal position. The lens 221 provides, for example, a distance-vision mode in the temple position, an intermediate "office" mode (e.g., for computer use) in the central position, and a reading mode in the nasal position. Suitably, the Alvarez components of the front and rear lens elements may not generate any additional optical power beyond the base spherical or cylindrical optical power built into the lens elements in the distance mode. In the reading mode, the front and rear lens elements 231, 241 can be configured and arranged to provide an additional optical power, e.g., +2 diopters, in addition to any base optical power. In the central position, the anterior and posterior lens elements 231, 241 may be constructed and arranged to provide, for example, +1 diopter of additional refractive power. Of course, these powers are given purely by way of example, and one skilled in the art would be able to adapt this embodiment to provide different amounts of additional refractive power at different individual positions of the lens elements.

[0101] Example 4 A fourth embodiment of a pair of rimless eyeglasses 311 according to the present invention is shown in Figures 25 and 26. In some respects, the eyeglasses 311 of this embodiment are similar to the eyeglasses 211 of the previous example. The following description focuses on the differences between the two embodiments for the sake of brevity.

[0102] Similar to the eyeglasses 211 of Example 3 above, the eyeglasses 311 of this embodiment comprise two variable focal length lenses 321, 322 mounted on a frame 312 having a nose bridge 314 interconnecting the two lenses 321, 322 and left and right temple arms 315, 316 for fitting the eyeglasses 311 on the user's head. As before, terms such as "left" and "right," "front," "back," "upper," "lower," "temples," and "nose" are used from the user's perspective. Thus, the two lenses 321, 322 comprise a left lens 321 and a right lens 322. The two lenses 321, 322 are mirror images of each other across the midline bisecting the nose bridge 314; with the exception of Figures 29-32, only the right lens 322 is described. The structure and operation of the left lens 321 can be assumed to be identical. 29-32 show the left side components of the eyeglasses 311, but the corresponding right side components can be assumed to be identical, albeit mirror images about the midline.

[0103] Thus, the right lens 322 includes front and rear lens elements 331 and 341, respectively, configured to provide a variable focal length according to the relative lateral positioning of the two lens elements 331 and 341 along a linear or curved transverse path extending in the x-direction, perpendicular to the user's line of sight z, as shown in FIG. 26 . In normal use, the x-axis and z-axis are approximately horizontal when the user is sitting or standing with their head upright. Suitably, the variable focal length lenses 321 and 322 may be Alvarez-type lenses of the type described in detail above with respect to the first embodiment. While the x-direction is shown as a straight line in FIG. 26 , it will be understood that in most, if not all, embodiments of the present invention, the relative lateral movement of the lens elements 331 and 341 follows an arcuate path corresponding to the base curve of the lenses 321 and 322. Typically, the arcuate path lies in the xz plane. The lenses 321, 322 may have a fixed base spherical and / or cylindrical refractive power according to the user's prescription, with or without gradual addition, and may be adjustable to add additional spherical power according to the relative arrangement of the lens elements 331, 341 to correct presbyopia.

[0104] The front lens element 331 is generally rectangular and has upper and lower edges 334, 335 and temple and nose edges 336, 337, respectively. As previously mentioned, the present invention is not limited to the particular shape or size of the lenses 321, 322 and is applicable to a wide variety of ophthalmic lens styles known in the art, which may have peripheral edges that are more or less curved than those shown in the accompanying drawings. One skilled in the art would also be able to adapt the lenses 321, 322 of this embodiment for use in half-rim or full-frame eyeglasses. The front lens element 331 has a front surface 332, which is typically spherical, and a rear surface 333 formed with a cubic surface, as described above. The rear lens element 341 has a shape and size that matches the shape and size of the front lens element 331 and has respective upper and lower edges 344, 345 and respective temple and nose edges 346, 347. In this embodiment, rear lens element 341 is narrower between its temple and nose edges 346, 347 than the corresponding dimensions of front lens element 331 to accommodate the sliding movement of rear lens element 341 relative to front lens element 331 as described herein. At least a portion of top and / or bottom edges 344, 345 may protrude beyond the corresponding portions of edges 334, 335 of front lens element 331 and may include integral or additional areas of increased friction to assist the user in manually manipulating lens 322, as described with reference to Figures 9A-C, 10A-C, 11 and 12 in connection with the first embodiment.

[0105] Toward its upper edge 334, the front lens element 331 is formed with elongated cutouts 338, 339 on each of its temple and nose sides, respectively. Juxtaposed to the interior ends (relative to the front lens element 331) of each cutout 338, 339, the front lens element 331 also is formed with openings 361, 362 extending entirely through the front lens element 331. (The location of the openings 361, 362 can be varied to vary the thickness of the web of material between the slots.) This arrangement creates a press fit between the components during the lens edging process. As best shown in FIGS. 29 and 30, which refer to the left lens 321, the cutouts 338, 339 and openings 361, 362 are constructed and arranged to secure elbow and nose assemblies 371, 381, respectively, to the front lens element 331. The elbow assembly 371 is connected to the elbow 317 of the adjacent temple arm 315. As shown in Figures 26 and 28, which refer to the right lens 322, a nose assembly 381 is formed at the right lateral end of the nose bridge 314, and a similar nose bridge assembly 381 is provided at the opposite left lateral end of the nose bridge 314 for attachment to the front lens element 331 of the left lens 321.

[0106] Referring to FIG. 29 , elbow assembly 371 includes a first elongated, generally rectangular block 372 integrally formed with or secured to elbow portion 317 of temple arm 315. Block 372 has upper and lower walls 373, 374 extending laterally therebetween and defining an elongated recess 375. The upper and lower walls 373, 374 define a rear surface 376 of the block that is stepped forwardly intermediate 377 the temple and nose ends of block 372 to define flanges that securely engage corresponding upper and lower slots 363 formed in temple edge 336 of front lens element 331 juxtaposed to the temple end of notch 338. At its nose end, block 372 is formed with a rearwardly projecting lug 378 configured to form a press fit in opening 361. Thus, it is securely attached to the front lens element 331 by engagement of the lugs 378 in the openings 361 and the flanges on the upper and lower walls 373, 374 of the block 372 in the upper and lower slots 363. The upper and lower slots 363 can be adjusted during edging to ensure a good (tight) interface for holding the elbow and nose bridge assembly 371, 381 to the front lens element 331. In this embodiment, the block 372 is held in place by friction alone; however, in other embodiments, adhesive can be used. The back surface 376 of the block 372, between the flanges and the lugs 378, is shaped to fit adjacent the front surface 332 of the front lens element 331. The lower wall 374 of the block 372 is formed with a secondary pin 379 that projects rearward between the stepped portion 377 and the nose end, as best seen in FIG. 29 . It is positioned to engage a corresponding notch formed in the front lens element 331 adjacent the cutout 338 so as to distribute the load applied to the front lens element 331 so that the load is not all concentrated at the opening 361 and / or is less dependent on the adhesive applied. The nose bridge assembly 381 includes a cubic block 381 similar to that shown in FIG.

[0107] Referring to FIG. 30, an elongated recess 375 in block 372 houses a generally linear bearing 380, which is shown in detail in FIGS. 31 and 32. Bearing 380 is coupled to elongated recess 375 of block 372 and has a lower surface 381 configured to engage the upper surface of lower wall 374 of block 372, and an upper surface 382 with a low-friction finish. Lower surface 381 is recessed, as shown in FIG. 32, to accommodate a group of front permanent magnets 365, 366 to form a bearing assembly. In the mounted position, front magnets 365, 366 are received in recesses formed in bearing 380 and corresponding recesses 383 formed in the upper surface of lower wall 374 of block 372, as shown in FIG. 29. One of the front magnets 365 is located at the temple end of recess 375, and the other is located at the nose end of recess 375. Note that this embodiment has only two front magnets 365, 366 in each bearing assembly. However, variations of the present invention can use three front magnets, as in Example 3 above, or more than two front magnets, to define more discrete positions for rear lens element 341. Front magnets 365, 366 are vertically oriented, aligned with a y-axis that is substantially perpendicular to the x- and z-axes, as shown in FIG. 26 . In this respect, this embodiment differs from the arrangement of Example 3 above, in which magnets 265, 266, 267, 268 are generally aligned with the z-axis. This arrangement allows this embodiment to be thinner and lighter when viewed from the front, while still maintaining good guidance and retention of rear lens element 341 along a defined traverse path, as described below.

[0108] An upper surface 382 of bearing 380 is spaced below and positioned below the lower surface of the block's upper wall 373 and defines an elongated slot that functions similarly to slots 51, 52 and 151, 152 and recesses 251, 252 of the first, second and third embodiments described in Examples 1, 2 and 3 above, respectively, i.e., providing a guide for movement of rear lens element 341 relative to front lens element 331. As shown in FIG. 31 , bearing 380 further includes a substantially centrally located, upstanding retaining protrusion 384 that functions similarly to retaining nibs 292, 293 of Example 3 above.

[0109] 27 , rear lens element 341 has two apertures 349, 350 formed in its juxtaposed temple and nose-side edges 346, 347, respectively, generally toward its upper edge 344. The apertures extend through rear lens element 341 and are configured to secure temple and post-nasal mounts 391, 392, respectively. Each of temple and post-nasal mounts 391, 392 includes an integral rearwardly projecting lug 393 configured to form a tight press fit in the corresponding aperture 349, 350 to secure rear mount 391, 392 to rear lens element 341 in a manner similar to the attachment of elbow and nose assemblies 371, 381 to front lens element 331. Accordingly, in a similar manner, side edges 346, 347 of rear lens element 341 are formed with slots 394 configured to position rear mounts 391, 392 relative to adjacent side edges 346, 347. The depth of the slot 394 can be adjusted during edging of the rear lens element 341 to ensure a tight fit between the rear temple and rear nose mounts 391 , 392 for the rear lens element 341 .

[0110] Each of the temple and post-nose mounts 391, 392 includes a generally linear body portion 395 that projects forward of the front surface 342 of the posterior lens element 341 and is shaped and sized to fit snugly into an elongated slot in the corresponding elbow or nose bridge assembly 371, 381 intermediate the upper surface 382 of the bearing 380, thereby allowing the body portion 395 to slide back and forth along the elongated slot between the upper wall 373 of the block 372 and the upper surface 382 of the insert while substantially preventing wobble, twisting, or other undesired movement of the posterior lens element 341 relative to the front lens element 331. Suitably, the body portion 395 has flat upper and lower surfaces for engaging the inner surfaces of the corresponding elongated slots. The body portion 395 houses a rear magnet 396 (see FIG. 28) that is received in a recess formed in the underside of the body portion 395, the rear permanent magnet 396 being oriented generally vertically on the y-axis to cooperate with a group of similarly oriented front magnets 365, 366 in a corresponding bearing assembly.

[0111] As with the previous embodiment, the front and rear magnets 365, 366, 396 attract each other to releasably hold the front and rear lens elements 331, 341 together in a plurality of discrete positions. In this embodiment, the magnets 365, 366, 396 serve to position the rear lens element 341 in either a temple position, where it slides fully toward the temple arms 315, 316, or a nose position, where it slides fully toward the nose bridge 314. Between these positions, the magnets serve to hold the front and rear lens elements 331, 341 together, but are not so strong that the rear lens element 341 has a tendency to want to move to one of the discrete positions. The strength of the magnets is such that a user can feel this through their fingers as they manipulate the rear lens element 341 to shift laterally between positions, with the positioning defining detents at each discrete position. In this embodiment, rear mounts 391, 392 may be prevented from accidental removal from front elbow and nose bridge assemblies 371, 381 by upstanding retaining protrusions 384 on bearings 380 in the center positions of elongated slots. Rear lens element 341 may be selectively removed from front lens element 331 when it is in one of its end positions.

[0112] As in the previous embodiment, the front and rear lens elements 331, 341 are appropriately configured so that the refractive power of the lenses 321, 322 increases as they slide laterally inward relative to the front lens element toward the nose bridge 314. Thus, the lenses 321, 322 have a distance mode when the rear lens element 341 is in the temple position and a reading mode when the rear lens element 341 is in the nose position. Compared to the third embodiment described above, reducing the number of modes from three to two potentially reduces the thickness of the lenses 321, 322. This potentially reduces the weight of the product. As a result, the eyeglasses 311 of this embodiment can be thinner and less bulky than the eyeglasses 211 of Example 3. Maintaining the same weight as a conventional eyeglass set is important to ensure comfort, familiarity, and the like.

[0113] The arrangement of this embodiment also aims to thin the material across the nose and into the elbow to provide some additional give / spring, thus removing load from the glazing joint by flexing the front lens element 331 assembly. Additionally, in this embodiment, the rear mounts 391, 392 are assembled from the front surface 342 of the rear lens element 341. This can provide a benefit if it is desired to add a user prescription to the lenses 321, 322, as described in Example 1 above, which would affect the back surface 343 of the rear lens element 341. As such, this aspect is not constrained by the rest of the design of this embodiment.

[0114] Example 5 While Examples 1, 3, and 4 above all relate to rimless eyeglasses, the present invention is equally well suited for use with framed eyeglasses. Thus, Figures 33-35 show a pair of eyeglass frames 411 according to a fifth embodiment of the present invention. The eyeglasses 411 comprise two variable focal length lenses 421, 422 mounted in a frame 412. The frame comprises a frame front 413 incorporating two left and right molded rim portions 417, 418, an integral nose bridge portion 414, and left and right temple arms 415, 416, each hinged to a respective one of the rim portions 417, 418 in a conventional manner.

[0115] Each of the variable focal length lenses 421, 422 comprises two superimposed lens elements 431, 441 of a type arranged to slide relative to one another in a direction transverse to the line of sight to adjust the focal power of the lenses 421, 422. Lenses of this type include the Alvarez-type lenses described in detail in Example 1 above. The description of such lenses in Example 1 applies equally to the lenses 421, 422 of this embodiment and need not be repeated here. Thus, the lenses 421, 422 comprise front and rear lens elements 431, 441, respectively, as clearly shown in FIG. 35. The front lens element 431 is securely fixed to the respective rim portions 417, 418, while the rear lens element 441 is slidable relative to the front lens element 431 in a direction indicated by the x-axis of FIG. 35. The x-axis of FIG. 35 extends generally transversely to the line of sight indicated by the z-axis. In some embodiments, the frame 412 and front lens element 431 of the lenses 421, 422 are molded as a single piece or as three pieces (frame, left front lens element, right front lens element) and can be assembled in a conventional manner (e.g., using a conventional bevel fit). In the first through fourth embodiments above, the corresponding front and rear lens elements are formed with base curves in a manner known in the art, so that the traversal path followed by the rear lens element is, in fact, an arc in the xz plane rather than a straight line, as previously described. However, in this embodiment, the traversal path is actually a straight line.

[0116] The structure and operation of the left and right lenses 421, 422 are substantially the same, except that one is a mirror image of the other in the mid-yz plane (not shown) that bisects the frame's nose bridge 414. Therefore, only the left lens 421 will be described in detail below, but the same description applies equally to the right lens 422.

[0117] Front lens element 431 has a front surface 432 and a back surface 433. Front lens element 431 is generally rectangular with arcuate sides and corners and has a top edge 434, a bottom edge 435, a temple edge 436, and a nose edge 437 (see FIG. 35 ). As best seen in FIG. 36 , top edge 434 of front lens element 431 is attached to rim portion 417 adjacent to top portion 404 of rim portion 417, while bottom edge 435 of front lens element 431 is attached to rim portion 417 adjacent to bottom portion 405 of rim portion 417. Temple and nose edges 436, 437 of front lens element 431 are attached to rim portion 417 adjacent to corresponding temple and nose portions 406, 407 of rim portion 417, respectively. The top, bottom, and sides 404-407 of the frame 412 define a substantially planar back surface 409. The widths of the sides 406, 407 are described in more detail below.

[0118] The upper portion 404 of the rim portion 417 is formed with two guide pins 481, 482 spaced apart in the x-direction, as shown in FIGS. 36 and 37 . The guide pins 481, 482 protrude rearward from the rear surface 409 of the rim portion 417. An upper recess 491 is formed in the rear surface of the upper portion 404 midway between the two guide pins 481, 482, to accommodate an upper permanent magnet 481 oriented along the z-axis. The magnet 481 is positioned flush with the rear surface 409. The lower portion 405 of the rim portion 417 is formed with a similar lower recess 492 in a substantially central position that also accommodates a front lower permanent magnet 482, as shown in FIG. 35 .

[0119] As shown in FIG. 38 , the rear lens element 441 has front and rear surfaces 442, 443 and is shaped and sized to match the front lens element 431. The rear lens element 441 has an upper edge 444, a lower edge 445, and temple and nose edges 446, 447. Unlike the first through fourth embodiments described above, the width of the rear lens element 441 between the temple and nose edges 446, 447 is greater than the corresponding width of the front lens element 431, as will be described in more detail below. The rear lens element 441 is formed with two elongated slots 451, 452 extending therethrough and adjacent the upper edge 444, oriented along the x-axis. Each slot 451, 452 has a temple end 453 and a nose end 454 and is positioned to slidably receive a respective one of the guide pins 481, 482 on the front lens element 431, as shown in FIG. 39 . It will be appreciated that in an alternative embodiment, the guide pins may instead be formed on the rear lens element 441 , protrude forwardly, and be received in corresponding slots in the front lens element 431 .

[0120] Between the two slots 451, 452, the front surface of rear lens element 441 is formed with two spaced-apart upper recesses 461, 462, each housing a rear upper permanent magnet 464, 465, respectively. Rear upper permanent magnets 464, 465 are oriented along the z-axis for coupling with front upper magnet 481 of front lens element 431 and are flush with front surface 442 of rear lens element 441. Aligned with upper recesses 461, 462, front surface 442 of rear lens element 441 further defines two lower recesses 466, 467 juxtaposed with lower edge 445. Each of lower recesses 466, 467 houses a rear permanent magnet (not shown) oriented along the z-axis for coupling with front lower magnet 482 and is flush with front surface 442 of rear lens element 441.

[0121] By separating the permanent magnets 464, 465, 466, 467, 481, 482 from the guide elements formed by the slots 451, 452 and the guide pins 481, 482, this embodiment allows for the use of permanent magnets of a size that is not constrained by the size of the slots 451, 452.

[0122] Guide pins 481, 482 fit snugly into slots 451, 452, allowing rear lens element 441 to slide back and forth relative to front lens element 431 to change the focal length of lens 421, while preventing unwanted twisting of the front and rear lens elements 431, 441 relative to each other. Sides 406, 407 of rim portion 417 are sized so that in each position of rear lens element 441, temples and nose rims 446, 447 of rear lens element 441 are masked by frame 412 and therefore "invisible" from an onlooker's perspective, while the outer edge of the rear lens element remains visible from the side.

[0123] As in the previous embodiment, slots 451, 452 and guide pins 481, 482 form guide elements for guiding movement of rear lens element 441 relative to front lens element 431 along a transverse path to change the focal length of lens 421. Front and rear upper and lower permanent magnets 464, 465, 466, 467, 481, 482 magnetically couple front and rear lens elements 431, 441 together with sufficient holding force to fold lens elements 431, 441 together. Front and rear lens elements 431, 441 are held together more strongly when front upper and lower magnets 481, 482 are aligned with upper and lower temple rear magnets 464, 466 or upper and lower nose rear magnets 465, 467, respectively. This therefore serves to define two distinct positions of rear lens element 441 relative to front lens element 431. Suitably, the front and rear lens elements 431, 441 have greater optical power when the front and rear lens elements 441 are in the nasal position and are aligned with the upper and lower post-nasal magnets 465, 467 than when the rear lens element 441 is in the temple position and are aligned with the upper and lower temple post-magnets 464, 466. It will be appreciated that in variations of this embodiment, the upper and lower groups of magnets on the front surface 442 of the rear lens element 441 may include more than two magnets, for example, three or more magnets, to define more distinct positions.

[0124] In a variation of Example 5, guide pins 481, 482 may include notches (not shown) defining their ends, such that guide pins 481, 482 may be retained within slots 51, 52 during actuation of lens 421 between the discrete detent positions defined by magnets 464, 465, 466, 467, 481, 482 by interengagement of the end of each guide pin 481, 482 with a retaining rib (not shown) formed within each slot 51, 52, in a manner similar to that described above with respect to the first embodiment.

Claims

1. Eyewear with adjustable focal length, comprising two lenses mounted in a frame for support in front of a user's eyes to define a line of sight; at least one of the lenses is a variable focal length lens of the type comprising two superimposed lens elements having cooperating optical surfaces shaped to vary their focal length depending on their relative lateral positioning; one of the lens elements is fixedly attached to the frame as a fixed lens element, and the other of the lens elements is detachably attached to the frame or the fixed lens element and is manually movable relative to the fixed lens element as a movable lens element to change the focal length of the variable focal length lens; a guide component is provided on the movable lens element and cooperates with a corresponding guide component on the fixed lens element or the frame to define and constrain movement of the movable lens element relative to the fixed lens element to a transverse path extending transversely to the line of sight, while allowing the movable lens element to be manually attached to or detached from the frame or fixed lens element in the line of sight at at least one position of the movable lens element relative to the fixed lens element; and one or more releasable fasteners configured to releasably secure the movable lens element to the fixed lens element or frame while allowing movement of the movable lens element relative to the fixed lens element along the traversal path, the one or more releasable fasteners comprising cooperating parts on the movable lens element and the fixed lens element or the frame, the cooperating parts of each fastener configured to be manually separable from one another upon application of a pulling force on the fixed and movable lens elements in a direction parallel to the line of sight, thereby allowing the movable lens element to be removed from the fixed lens element or the frame in at least one position and subsequently recombined to reattach the movable lens element to the frame or fixed lens element.

2. The adjustable focal length eyewear of claim 1 , including at least two releasable fasteners spaced apart transverse to the line of sight on the lens.

3. 3. The adjustable focal length eyewear of claim 1, wherein the one or more releasable fasteners include one or more separable mechanical fasteners including resilient interengaging formations on the fixed and movable lens elements, which, upon application of an increasing separation force urging the lens elements apart in the line of sight, initially resist separation of the lens elements while allowing movement of the movable lens element along the transverse path, and eventually deform to separate the resilient interengaging formations from each other, thereby enabling removal of the movable lens element from the fixed lens element.

4. 4. The adjustable focal length eyewear of claim 3, wherein the one or more mechanical fasteners define one or more discrete detent positions in the traversal path at which the lens elements are releasably held together in the direction of the traversal path, such that additional force is required to release from the detent positions in order to slide the lens elements along the traversal path.

5. The one or more releasable fasteners include one or more separable magnetic fasteners including cooperating individual magnetic components on the movable lens element and the fixed lens element or the frame.

3. The eyewear with adjustable focal length according to claim 1 or 2.

6. 6. The adjustable focal length eyewear of claim 5, wherein the movable lens element and the cooperating individual magnetic components on the fixed lens element or frame define at least two selectable individual detent positions for the movable lens element relative to the fixed lens element.

7. 7. The adjustable focal length eyewear of claim 5 or 6, including two or more magnetic fasteners between the movable lens element and the fixed lens element or frame, the two or more magnetic fasteners defining at least two selectable distinct detent positions for the movable lens element along the traversal path relative to the fixed lens element.

8. 7. The adjustable focal length eyewear of claim 5 or 6, wherein the one or more magnetic fasteners define three selectable distinct detent positions for the movable lens element along the traversal path relative to the fixed lens element.

9. 9. Adjustable focal length eyewear according to any one of claims 5 to 8, wherein the or each magnetic fastener comprises a group of individual magnetic components on one of the movable lens element or the fixed lens element or frame and at least one cooperating magnetic component on the other of the fixed lens element or frame or the movable lens element, the magnetic components on the movable lens element and the fixed lens element or frame attracting each other to attach the movable lens element to the fixed lens element or frame while allowing manual movement of the movable lens element along the traversal path relative to the fixed lens element and manual removal of the movable lens element from the fixed lens element or frame, as required.

10. The adjustable focal length eyewear of claim 9 , wherein the magnetic components of the group are spaced apart along the transverse path.

11. 11. Eyewear with adjustable focal length according to claim 9 or 10, wherein the magnetic components in the group and / or the cooperating magnetic components comprise permanent magnets.

12. 12. The adjustable focal length eyewear of claim 1, wherein the guide parts on the movable lens element and the cooperating guide parts on the fixed lens element or frame form at least two straight or curved guides that define the traversal path.

13. The adjustable focal length eyewear of claim 12 , wherein the guides are spaced apart in the direction of the traversal path on the lens.

14. 14. The adjustable focal length eyewear of claim 12 or 13, wherein each guide includes a dowel on one of the lens elements and a slot in the other of the lens elements, the dowel engaging an edge of the other of the lens elements around the slot to constrain relative movement of the two lens elements to the transverse path.

15. 15. The adjustable focal length eyewear of claim 14, wherein the dowel is magnetic and a group of two or more magnetic components is secured to one of the lens elements at two or more distinct positions within the slot, cooperating with the magnetic dowel to attach the two lens elements together and define two or more selectable distinct detent positions for the movable lens element along the traversal path relative to the fixed lens element.

16. 16. The adjustable focal length eyewear of claim 15, wherein the slot has two opposing ends, and the group of two or more magnetic components includes two magnetic components fixed to other of the lens elements, one juxtaposed at each end of the slot.

17. 15. The adjustable focal length eyewear of claim 14, wherein a magnetic component is secured to one of the lens elements adjacent the dowel, and a group of two or more magnetic components is secured to the other of the lens elements at two or more discrete locations adjacent the slot, cooperating with the magnetic component on one of the lens elements to attach the two lens elements together and define two or more selectable discrete detent positions for the movable lens element along the traversal path relative to the fixed lens element.

18. 18. The adjustable focal length eyewear of any one of claims 14 to 17, wherein the dowels are configured to interengage with cooperating ribs extending into the slots to prevent disengagement of the movable lens element except in at least one position of the movable lens element relative to the fixed lens element.

19. The adjustable focal length eyewear of any one of claims 14 to 18, wherein the frame includes temple arms attached to the fixed lens elements over the slots.

20. The adjustable focal length eyewear of any one of claims 14 to 18, wherein the frame includes a nose bridge attached to a fixed lens element over the slot.

21. 14. Adjustable focal length eyewear as described in claim 12 or claim 13, wherein each guide comprises a bearing fixed to or integrally formed with the frame and a mount fixed to the movable lens element, the bearing being positioned adjacent to a slot and the mount being shaped to engage the bearing in the slot to constrain relative movement of the two lens elements to the transverse path.

22. 22. The adjustable focal length eyewear of claim 21, wherein the frame includes an elbow interconnecting a temple arm and a fixed lens element, the bearing attached to the elbow, and the mount attached to the movable lens element at a corresponding position.

23. 17. The adjustable focal length eyewear of claim 16, wherein the frame includes a nose bridge interconnecting the two lenses and having two opposing ends with a bearing on one end, and a mount attached to the movable lens element at a corresponding position.

24. 24. The adjustable focal length eyewear of any one of claims 21, 22 or 23, wherein the mount is or includes a magnetic component, and a group of two or more magnetic components is secured to the frame or fixed lens element at two or more discrete locations within or adjacent to the slot and cooperates with the magnetic components on the mount to hold the two lens elements together and define two or more selectable discrete detent positions along the traversal path.

25. 25. The adjustable focal length eyewear of claim 24, wherein the group of magnetic components includes two magnetic components secured to bearings, one at each end of the slot.

26. 26. The adjustable focal length eyewear of claim 25, wherein the group of magnetic components further includes a magnetic component fixed to the bearing at a central location intermediate the ends of the slot.

27. 27. The adjustable focal length eyewear of claim 24, claim 25 or claim 26, wherein the bearing includes one or more retaining nibs constructed and arranged to prevent removal of the mount from the bearing except at one or more discrete locations.

28. The adjustable focal length eyewear of any one of claims 24 to 27, wherein the bearing and the magnetic components on the mount are oriented in the line of sight.

29. The adjustable focal length eyewear of any one of claims 24 to 27, wherein the bearing and the magnetic components on the mount are oriented perpendicular to the line of sight.

30. Eyewear with adjustable focal length according to any one of claims 24 to 29, wherein the group of magnetic components in the slot is mounted in an insert that is fixed in the slot, the insert having a low friction bearing surface that engages with the mount.

31. 31. The adjustable focal length eyewear of any one of claims 1 to 30, wherein at least a portion of an upper or lower edge of the movable lens element protrudes above or below, respectively, a corresponding portion of an upper or lower edge of the fixed lens element to facilitate manual movement of the movable lens element by a user.

32. 31. The adjustable focal length eyewear of any one of claims 1 to 30, wherein at least a portion of each of the upper and lower edges of the movable lens element protrudes above and below the corresponding upper and lower edges of the fixed lens element, respectively, to facilitate manual movement of the movable lens element by a user.

33. 14. The adjustable focal length eyewear of claim 12 or 13, wherein the frame includes a rim portion extending at least partially around the variable focal length lens, and each guide comprises a guide pin protruding from the rim portion or the movable lens element and a slot formed in the movable lens element or the rim portion, respectively, and the guide pin engages with an edge of the movable lens element or rim portion around the slot to constrain relative movement of the two lens elements to the transverse path.

34. 34. The adjustable focal length eyewear of claim 33, wherein a group of two or more magnetic components is attached to the rim portion or the movable lens element at two or more discrete locations, and cooperating magnetic components are attached to the movable lens element or the rim portion, respectively, to attach the movable lens element to the frame and define two or more selectable discrete detent positions along the traversal path.

35. 35. The adjustable focal length eyewear of claim 34, wherein the group of two or more magnetic components and cooperating magnetic components are attached to the rim portion and the movable lens element adjacent the top or bottom edge of the lens.

36. Eyewear with adjustable focal length according to any one of claims 33 to 35, wherein the rim portion includes temples and nose sides, the movable lens element is wider than the fixed lens element in the transverse direction, and the temples and nose sides of the movable lens element are behind the temples and nose sides of the rim portion in the line of sight, regardless of the position of the movable lens element along the transverse path.

37. 1. A variable focal length lens of the type comprising two lens elements having cooperating optical surfaces superimposed on one another in a line of sight through the lens, and shaped so that the focal length of the variable focal length lens varies as a function of the relative lateral positioning of the lens elements transverse to the line of sight, wherein at least one position, cooperating guide elements are provided on both lens elements to define the relative movement of the lens elements and to constrain them to a transverse path extending in the transverse direction while allowing one lens element to be manually attached to or detached from the other lens element in a direction parallel to the line of sight, and a variable focal length lens comprising one or more releasable fasteners that releasably secure two lens elements together while allowing relative movement of the lens elements, the one or more releasable fasteners comprising cooperating parts on both lens elements, the cooperating parts of each fastener being configured to be manually separable from one another upon application of a pulling force on the lens elements in a direction parallel to the line of sight, thereby allowing the lens elements to be detached from one another in at least one position and subsequently reattached to one another.

38. 38. The variable focal length lens of claim 37, including at least two releasable fasteners spaced apart on the lens in a direction transverse to the line of sight.

39. 39. A variable focal length lens as described in claim 37 or 38, wherein the one or more releasable fasteners include one or more separable mechanical fasteners including resilient interengaging formations on the two lens elements that, when an increasing separation force is applied urging the lens elements apart in the line of sight, initially resist separation of the lens elements while allowing movement of one of the lens elements along the transverse path, and eventually deform to cause the resilient interengaging formations to separate from each other, thereby enabling removal of one lens element from the other lens element.

40. 40. The variable focal length lens of claim 39, wherein the one or more mechanical fasteners define one or more discrete detent positions within the traversal path at which the lens elements are releasably held together in the direction of the traversal path, such that additional force is required to release from the detent positions in order to slide the lens elements along the traversal path.

41. 39. A variable focal length lens according to claim 37 or 38, wherein the one or more releasable fasteners include one or more magnetic fasteners including cooperating individual magnetic components on the lens element.

42. 42. The variable focal length lens of claim 41, wherein the cooperating individual magnetic components on the lens elements define at least two selectable individual detent positions of the lens elements relative to one another.

43. 43. A variable focal length lens as described in claim 41 or 42, including two or more magnetic fasteners between the lens elements, the two or more magnetic fasteners defining at least two selectable distinct detent positions of the lens elements relative to each other along the traversal path.

44. 43. A variable focal length lens as claimed in claim 41 or claim 42, wherein the one or more magnetic fasteners define three selectable distinct detent positions of the lens elements relative to one another along the traversal path.

45. 45. A variable focal length lens as claimed in any one of claims 41 to 44, wherein the or each magnetic fastener comprises a group of individual magnetic components on one of the lens elements and at least one cooperating magnetic component on the other of the lens elements, the magnetic components on the lens elements attracting each other to hold the lens elements together while allowing manual movement of the lens elements relative to each other along the traversal path and manual removal of the lens elements from each other as required.

46. 46. ​​The variable focal length lens of claim 45, wherein the magnetic components of the group are spaced apart along the transverse path.

47. 47. A variable focal length lens according to claim 45 or 46, wherein the magnetic components in the group and / or the cooperating magnetic components comprise permanent magnets.

48. A variable focal length lens according to any one of claims 41 to 47, wherein the guide parts on the lens element cooperate to form at least two straight or curved guides that define the traversal path.

49. 49. A variable focal length lens as claimed in claim 48, wherein the guides are spaced apart in the direction of the traversal path on the lens.

50. 50. A variable focal length lens as described in claim 48 or 49, wherein each guide includes a dowel on one of the lens elements and a slot in the other of the lens elements, the dowel engaging an edge of the other of the lens elements around the slot to constrain relative movement of the two lens elements to the transverse path.

51. 51. The variable focal length lens of claim 50, wherein the dowel is magnetic and a group of two or more magnetic components is secured to one of the lens elements at two or more distinct positions within the slot, cooperating with the magnetic dowel to attach the two lens elements together and define two or more selectable distinct detent positions of the lens elements relative to one another along the transverse path.

52. 52. The variable focal length lens of claim 51, wherein the slot has two opposing ends, and the group of two or more magnetic components includes two magnetic components fixed to other of the lens elements, one at each end of the slot.

53. 52. The variable focal length lens of claim 51 , wherein a magnetic component is secured to one of the lens elements adjacent the dowel, and a group of two or more magnetic components is secured to the other of the lens elements at two or more discrete locations adjacent the slot, cooperating with the magnetic component on one of the lens elements to attach the two lens elements together and define two or more selectable discrete detent positions of the lens elements relative to one another along the traversal path.

54. 54. A variable focal length lens as claimed in any one of claims 50 to 53, wherein the dowel is configured to interengage with a cooperating rib extending into the slot to prevent detachment of one of the lens elements except for the relative position of at least one of the lens elements.

Images