Visual axis identification system and method

Abstract

The devices and methods described herein provide improved methods for accurately identifying and locating the visual axis of an eye and its intersection with the iris plane. In one embodiment, a visual axis identification system includes a fixation light source, a camera, and a processing system. During operation, a patient focuses their gaze on two or more fixation light spots provided by the fixation light source on its optical axis, which creates two or more corresponding images on or near the patient's retina. The patient's head is then rotated relative to the fixation light spot while the patient continuously maintains their gaze on the fixation light spots. If the centers of the images coincide in the patient's field of view, the patient's visual axis can be located by determining the position of the fixation light source's optical axis relative to the patient's eye.

Description

[Technical Field]

[0001] Embodiments of the present disclosure relate generally to ophthalmic methods and apparatus for characterizing the optical properties of the eye, and more particularly to methods and apparatus for accurately identifying the visual axis of the eye. [Background technology]

[0002] Conventional techniques for treating presbyopia typically involve determining the relative position of the visual axis of a patient's eye. Accurate determination of this axis is essential for effective placement of bifocal, multifocal, and extended depth of focus (EDOF) intraocular lenses (IOLs). Even slight misalignment of these lenses can significantly interfere with the intended benefits of their surgical implantation. Other examples of presbyopia treatments that can also benefit from visual axis determination include LASIK, presbyopia, or multifocal LASIK, and photorefractive keratectomy (PRK) surgery, to name a few.

[0003] The visual axis is a person's actual line of sight, a line connecting the fovea, a small depression in the retina, and the clearest point of view with the fixation light source. Thus, locating the visual axis and its intersection with the iris plane is essential for determining IOL placement, because even slight misalignment can significantly disrupt the function of an intraocular lens. Currently, no diagnostic device exists for accurately and precisely determining the position of the visual axis. Instead, the position of the visual axis through the iris plane is generally approximated as being midway between the pupil center and the corneal apex or the first Purkinje image, which is the reflection of the fixation light on the outer surface of the cornea. This method is often inaccurate, especially in eyes with impaired or abnormal shapes, because the visual axis may be located far from the aforementioned midpoint.

[0004] Therefore, what is needed in the art is an improved method and apparatus for identifying the visual axis of the eye. Summary of the Invention [Means for solving the problem]

[0005] The present disclosure generally relates to methods and apparatus for accurately identifying the visual axis of the eye.

[0006] In certain embodiments, a method for determining the position of a visual axis of a patient's eye is provided. The method includes directing a fixation light toward the patient's eye, the fixation light having two or more fixation light spots formed at different positions along the optical axis of the fixation light source, corresponding to two or more images formed on or near the retina of the patient's eye. One or more digital images of the iris plane of the patient's eye are captured by a first camera when the centers of the two or more images formed on or near the retina coincide in the patient's field of view while the optical center of the first camera is aligned with the optical axis of the fixation light source. A location of a visual axis point in the iris plane is then identified based on the one or more digital images, the location of the visual axis point corresponding to the X / Y position of the optical center of the first camera relative to the X / Y position of the patient's eye displayed in the one or more digital images.

[0007] So that the above-listed features of the present disclosure can be understood in detail, a more particular description of the present disclosure briefly summarized above can be had by reference to embodiments, some of which are illustrated in the accompanying drawings. It should be noted, however, that the accompanying drawings illustrate only exemplary embodiments and should not be considered as limiting the scope thereof, as other equally effective embodiments may be recognized. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 shows a cross-sectional schematic top view of the human eye. [Figure 2] FIG. 2 shows a front view of the human eye. [Figure 3] FIG. 3 shows a schematic diagram of a visual axis identification system according to certain embodiments of the present disclosure. [Figure 4A-4B] 4A-4B show schematic diagrams of an eye focusing on multiple fixation points, according to certain embodiments of the present disclosure. [Figure 5A-5B]5A-5B show schematic diagrams of an eye focusing on multiple fixation points, according to certain embodiments of the present disclosure. [Figures 6A-6B] 6A-6B show schematic diagrams of multiplexer elements within a fixation light source, according to certain embodiments of the present disclosure. [Figure 7] FIG. 7 shows a schematic diagram of an exemplary multiplexer element that may be used in combination with the visual axis identification system of FIG. 3, according to certain embodiments of the present disclosure. [Figure 8] FIG. 8 shows a schematic diagram of an exemplary multiplexer element that may be used in combination with the visual axis identification system of FIG. 3, according to certain embodiments of the present disclosure. [Figure 9] FIG. 9 shows a schematic diagram of an exemplary multiplexer element that may be used in combination with the visual axis identification system of FIG. 3, according to certain embodiments of the present disclosure. [Figure 10] FIG. 10 shows a schematic diagram of an exemplary multiplexer element that may be used in combination with the visual axis identification system of FIG. 3, according to certain embodiments of the present disclosure. [Figure 11] FIG. 11 shows a schematic diagram of an exemplary multiplexer element that may be used in combination with the visual axis identification system of FIG. 3, according to certain embodiments of the present disclosure. [Figure 12] FIG. 12 shows a schematic diagram of an exemplary multiplexer element that may be used in combination with the visual axis identification system of FIG. 3, according to certain embodiments of the present disclosure. [Figures 13A-13B] 13A-13B show schematic diagrams of exemplary multiplexer elements that may be used in combination with the visual axis identification system of FIG. 3, according to certain embodiments of the present disclosure. [Figure 14A] FIG. 14A shows a schematic diagram of the visual axis identification system of FIG. 3, according to certain embodiments of the present disclosure. [Figure 14B] FIG. 14B shows a schematic diagram of the visual axis identification system of FIG. 3, according to certain embodiments of the present disclosure. [Figures 15A-15B] 15A-15B show schematic diagrams of an eye focusing on multiple fixation spots generated by the visual axis identification system of FIGS. 3 and 14A-14B, according to certain embodiments of the present disclosure. [Figure 16] FIG. 16 shows a front-view image of the eye generated by a camera during a method of using the visual axis identification system of FIG. 3, according to certain embodiments of the present disclosure. [Figures 17A-17D] 17A-17D show representations of a patient's visual field while using the visual axis identification system of FIGS. 3 and 14A-14B and a system for generating such representations, according to certain embodiments of the present disclosure. [Figure 17E] FIG. 17E shows a representation of a patient's visual field while using the visual axis identification system of FIGS. 3 and 14A-14B and a system for generating such representations, according to certain embodiments of the present disclosure. [Figure 18] FIG. 18 shows a schematic diagram of the visual axis identification system of FIG. 3 including a second camera, in accordance with certain embodiments of the present disclosure. [Figure 19] FIG. 19 shows a block diagram of a method for using the visual axis identification system of FIGS. 3, 14A-14B, and 18, according to certain embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0009] For ease of understanding, where possible, the same reference numerals are used to indicate identical elements that are common to multiple figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.

[0010] The present disclosure relates generally to methods and apparatus for identifying the visual axis of an eye.

[0011] Typically, the refractive surfaces of the eye, such as the cornea and the anterior and posterior surfaces of the lens, are not centered on the same line (e.g., axis), and the lens is tilted relative to the eye's line of sight. Due to this lack of rotational symmetry, the eye does not have a true optical axis. However, the eye does have a visual axis, which is a line connecting the fixation target with the fovea. Because the center of the eye's field of vision is focused on the fovea, where the retinal cones are particularly concentrated, visual acuity is highest along the visual axis. Optical modeling has shown that multifocal LASIK treatments must be centered on the visual axis with an accuracy of approximately 50 μm to avoid visual acuity loss. Therefore, accurately and precisely identifying the eye's visual axis, such as for positioning multifocal adjustable lenses, is important for presbyopia LASIK surgery and many other refractive ophthalmic procedures.

[0012] Currently, no device exists that can accurately identify and locate the visual axis. Rather, medical practitioners, such as ophthalmic surgeons, typically approximate the location of the visual axis through the iris plane as being at the midpoint between the pupil center and the first Purkinje image. However, this approximation is often inaccurate, especially in patients with impaired or abnormally shaped eyes. The devices and methods described herein provide improved methods for accurately identifying and locating the eye's visual axis and its intersection with the iris plane. Embodiments of the present disclosure can be utilized in corrective lens alignment and other ophthalmic procedures, including refractive ophthalmic surgeries such as multifocal LASIK or multifocal PRK surgery.

[0013] In one embodiment, the visual axis identification system includes a fixation light source, a camera, and a processing system. During operation, a patient focuses their gaze on two or more fixation light spots provided by the fixation light source, which create two or more corresponding images on or near the patient's retina. The patient's head is then rotated while the patient continuously maintains their gaze on the fixation light spots (described in further detail with reference to FIG. 14B). If the centers of the images coincide in the patient's field of view, the patient's visual axis can be located by determining the position of the optical axis of the fixation light source relative to the patient's eye.

[0014] FIG. 1 shows a schematic cross-sectional top view of an exemplary human eye 100. The temporal and nasal sides of the eye 100 are shown in FIG. 1 for reference. As shown, a pupillary axis 102 passes through a pupillary center 104 of a pupil 106 and is perpendicular to a pupillary plane 108. The eye 100 further includes a visual axis 110 that intersects the pupil 106 at a visual axis point 112. The visual axis 110 connects a fixation point 114 (e.g., a fixation target) with a fovea 122, a small depression in the retina 116. Because the center of the visual field is focused at the fovea 122, the sharpest vision of the target is achieved when the target is aligned with the fixation point 114 and the fovea 122. Therefore, accurate determination of the visual axis point 112 is essential for successful ophthalmic corrective treatment. However, as previously mentioned, no ophthalmic diagnostic device currently exists that can accurately and precisely identify the visual axis point 112. Rather, conventional ophthalmic techniques involve approximating the visual axis point 112 midway between the pupil center 104 and the corneal apex 118, or the first Purkinje image, which is defined as the location of the specular reflection from the anterior surface of the cornea as viewed from the direction of the fixation light source.

[0015] 2 shows a front view of an eye 100 as seen by a clinician (e.g., an ophthalmologist) during the procedure. In FIG. 2, the visual axis point 112 is assumed to be located midway between the pupil center 104 and the corneal apex 118. However, in many cases, especially in eyes with asymmetry, irregularities, or disorders, the visual axis point 112 is not midway between the pupil center 104 and the corneal apex 118. Therefore, approximations of the location of the visual axis point 112 may be inaccurate, imprecise, and unreliable, which may lead to suboptimal presbyopia LASIK or PRK treatment.

[0016] 3 shows a simplified schematic diagram of an exemplary visual axis identification system 300 according to some embodiments. The visual axis identification system 300 is utilized to accurately and precisely determine the visual axis point 112 of the visual axis 110 of the eye 100. Generally, the visual axis identification system 300 includes a fixation light source 302, a camera 304, and a processing system 306.

[0017] The fixation light source 302 has two or more fixation light spots P along its optical axis 312 on which the patient's eye, represented by eye 100, can focus during use of the visual axis identification system 300. N (e.g., the fixation points shown in Figures 4A and 4B). N The subject focuses on the fixation spot P and attempts to visually align them by moving their head. N Alignment or superposition of the two fixation light spots P occurs when the visual axis 110 of the eye 100 and the optical axis 312 of the fixation light source 302 coincide. Thus, once aligned, the visual axis point 112 can be identified. To generate light, the fixation light source 302 can include any suitable light-emitting device, including a light-emitting diode (LED), a filament lamp, or the like. In certain embodiments, the generated light is multiplexed by a multiplexer 320 into two or more fixation light spots P N and then relayed along optical axis 312 by relay lens 322.

[0018] In a particular embodiment, the visual axis identification system 300 detects a fixation light spot P N The optical system further includes an optical relay device 310 along the optical axis 312 for relaying the optical axis 312 and / or manipulating the propagation path of the optical axis 312. For example, the optical relay device 310 may be used to align the optical axis 312 of the fixation light source 302 with the optical axis 314 of the camera 304. Examples of suitable types of optical relay devices include relay lenses, beam splitters, filters, etc. Although one optical relay device 310 is shown, the use of two or more optical relay devices 310 is contemplated.

[0019] The camera 304 may include any suitable type of digital imaging device or detector, such as an eye-tracking camera or similar optical sensor, to capture images and determine the position (e.g., X / Y translational position) of the eye 100. Generally, the camera 304 is configured to allow the patient to focus on the fixation light spot P formed by the fixation light source 302. NThe camera 304 is configured to record an image or video of the iris plane of the eye 100 while focusing on the iris. The image or video is then transmitted to a processing system 306 for analysis to determine the relative X / Y position of the eye 100 and its visual axis point 112. In certain embodiments, the camera 304 is an infrared camera. In certain embodiments, the camera 304 is configured to track movement of the eye 100, and in particular the pupil center 104, by mapping and detecting shifts (e.g., movement) in the vasculature (e.g., blood vessels) within the eye 100, such as the scleral veins. The camera 304 is communicatively coupled to the processing system 306, and in certain embodiments, forms a single device therewith. In certain other embodiments, the camera 304 and the processing system 306 may be separate devices or components of the visual axis identification system 300.

[0020] To illustrate an exemplary operation of the visual axis identification system 300, FIGS. 4A-4B and 5A-5B depict simplified schematic diagrams of the eye 100 focusing on two fixation light spots P1 and P0. FIGS. 4A and 5A schematically illustrate the image formation of the fixation light spots P1 and P0 in the eye 100, while FIGS. 4B and 5B show the corresponding images C1 and C0 formed on the retina 116. The imaging system 120 represents the image-forming components of the eye, such as the cornea, which has a typical refractive power of approximately 43 diopters, and the natural crystalline lens, which has a typical refractive power of approximately 17 diopters. As described above, the fixation light source 302 is configured to generate light and focus the light on at least two fixation light spots P1 and P0 aligned on its optical axis 312. 4A, fixation light spot P0 is imaged on retina 116, while fixation light spot P1 is imaged very close to (e.g., slightly in front of) retina 116. As a result, image C0 appears small and sharp to the patient, and image C1 appears larger and less sharp (e.g., blurrier) than image C0.

[0021] As shown in Figures 4A and 4B, when the optical axis 312 of the fixation light source 302 (shown in Figure 3) is aligned with the visual axis 110 of the patient's eye 100, the centers of images C1 and C0 coincide on the retina 116. Thus, as shown in Figure 4B, the patient visualizes a small, sharp image C0 as aligned or superimposed on the center of a large, blurry image C1. However, as shown in Figures 5A and 5B, when the optical axis 312 and the visual axis 110 are not aligned, images C1 and C0 are spatially shifted relative to each other. Thus, as shown in Figure 5B, both C1 and C0 are visible to the patient even though their centers are not aligned or coincident. Using this principle, in certain embodiments, the location of visual axis point 112 can then be identified by having the patient move or adjust their head up and down or left and right while maintaining line of sight to fixation light spots P1 and P0 until the patient visualizes centered or superimposed images C1 and C0, thereby indicating alignment of visual axis 110 with optical axis 312 of fixation light source 302. A more detailed description of patient head movements is provided below with reference to FIG. 14B.

[0022] 6A and 6B show simplified schematic diagrams of a multiplexer 320 and relay lens 322 for a fixation light source 302 that forms two or more fixation light spots, according to certain embodiments of the present disclosure. As previously mentioned, the fixation light spots generated by the multiplexer 320 are viewed by the patient during operation of the visual axis identification system 300 using the relay lens 322. As further noted above, visual alignment of the fixation light spots can be used to locate the patient's visual axis point 112. While FIGS. 6A and 6B illustrate the functionality of the multiplexer 320, specific examples or types of multiplexers are described in more detail below with reference to FIGS. 7-13B.

[0023] In FIG. 6A , multiplexer 320 is a spot doubler that focuses incident light 602 onto two fixation light spots P1 and P0 on optical axis 312. In FIG. 6B , multiplexer 320 is a spot multiplexer that focuses incident light 602 onto three fixation light spots P2, P1, and P0. While only three fixation light spots are shown in FIG. 6B , it is contemplated that multiplexer 320 can generate four or more fixation light spots. In certain embodiments, increasing the number of fixation light spots improves the accuracy of visual discrimination system 300. In both illustrated examples, the fixation light spots generated by multiplexer 320 are viewed by the patient via relay lens 322, which serves at least two functional purposes: First, the relay lens 322 relays the fixation light spot to the eye 100 (e.g., like a magnifying glass), and second, the relay lens 322 compensates for the refractive error of the eye 100 so that the fixation light spot appears sharp to the patient (e.g., functions as a Badal system).

[0024] 7-13B illustrate a particular embodiment of a multiplexer 320 that may be utilized to focus the light in the fixation light source 302 onto two or more fixation light spots on its optical axis, such as optical axis 312. The fixation light spots formed by the multiplexer 320 are viewed by the patient, who attempts to align the fixation spots to assist the visual axis identification system 300 in identifying the visual axis point 112.

[0025] In the example shown in Figure 7, the multiplexer 320 is a bifocal lens 720 having two focal points F0 and F1 that focus the light 602. As described with reference to Figure 4A, the focus of the light 602 at these two focal points F0 and F1 results in two fixation light spots on the optical axis 312 that are relayed towards the patient's eye. In another example shown in Figure 8, the multiplexer 320 is a multifocal diffractive lens 820. The multifocal diffractive lens 820 includes one or more features 822 or characteristics configured to focus the light 602 at multiple focal points with different diffraction orders on the optical axis 312. As shown in Figure 8, the multifocal diffractive lens 820 has a zero-order focus F0 and higher-order focuses F1, F2, F3, F4, F5, F6, F7, F8, F9, F10, F11, F12, F13, F14, F15, F16, F17, F18, F19, F20, F21, F22, F23, F24, F25, F26, F27, F28, F29, F39, F40, F41, F42, F43, F44, F45, F46, F47, F48, F49, F50, F51, F52, F53, F54, F55, F56, F57, F58, F59, F60, F61, F62, F63, F64, F65, F66, F67, F68, F69, F69, F70, F71, F72, F73, F74, F75, F76, F77, F78, F79, F80, F81, F82, F83, F84, F -1 and F -2 The light 602 is focused at five different focal points, including focal points F0, F1, F2, and F -1 and F -2 Each of the focal points corresponds to a fixation light spot that can be observed by the patient. Although five focal points are shown, it is contemplated that the multifocal diffractive lens 820 can form fewer or more than five focal points. In certain embodiments, the multifocal diffractive lens 820 is a Fresnel-type lens. In certain other embodiments, the multifocal diffractive lens 820 is a holographic lens or a diffractive optical element formed by holographic or lithographic techniques.

[0026] FIG. 9 shows another example of a multiplexer 320 that can be utilized in the fixation light source 302. The multiplexer 320 of FIG. 9 is a lens 902 having a coating 904 on both major surfaces 906. Because the coating 904 is partially reflective and partially transparent, light 602 is both reflected and transmitted by the coating 904, forming multiple focal points. When an incident beam of light 602 is parallel to and centered on the optical axis 312, the multiple focal points formed by the lens 902 coincide with the optical axis 312. As shown, focus F0 is the focal point that results when light 602 transmits through the lens 902 without any internal reflections. However, focus F1 results from two internal reflections by the coating 904. Foci F2 and F3 result from four and six internal reflections, respectively. Foci F0, F1, F2, and F3 are formed at different locations on optical axis 312 as a result of at least one of major surfaces 906 being curved, resulting in different angles of reflection and / or reflectivity.

[0027] In certain embodiments, the coating 904 enables spectral separation of the light 602. For example, a reflectance peak (e.g., maximum reflectance) of the coating 904 may correspond to a wavelength of the light 602 that is visualized by the patient. In another example, the coating 904 may have zero reflectance at the wavelength of the light 602 that is detected by the camera 304. Thus, unwanted reflections of the light 602 toward the camera 304 may be eliminated or significantly reduced by the coating 904.

[0028] In FIG. 10 , the exemplary multiplexer 320 is a Fabry-Perot interferometer (FPI) 1020 having two parallel and semi-transparent (e.g., partially reflective) mirrors 1004 combined with a convex focusing lens 1010. The convex focusing lens 1010 focuses a collimated beam of light 602 onto the FPI 1020, which then internally reflects and / or transmits the light to form several foci on the optical axis 312. Four foci F, F, F, and F are shown in FIG. 10 , although more or fewer are contemplated. The first focus F is the result of light 602 transmitting through the FPI 1020 without any internal reflections. However, foci F, F, and F are the result of two, four, and six reflections, respectively.

[0029] In another example, shown in FIG. 11 , the multiplexer 320 is an interferometer 1120. In particular, FIG. 11 shows a Michelson-type interferometer 1120 having two peripheral and fully reflective mirrors 1114A and 1114B and a semi-transparent (e.g., partially reflective) central mirror 1112. Each of the peripheral mirrors 1114A and 1114B is positioned at a different distance (e.g., arm length) from the central mirror 1112. As shown, the central mirror 1112 reflects a portion of the incident light 602 to the peripheral mirror 1114A and transmits another portion of the light 602 to the peripheral mirror 1114B. Upon reflection by the mirrors 1114A and 1114B, the light 602 is again reflected or transmitted through the central mirror 1112, which is positioned along the optical axis 312. The different arm lengths of the peripheral mirrors 1114A and 1114B allow the light 602 reflected from each mirror to be directed toward a focal point F. A and F B 11. In certain embodiments, interferometer 1120 is optically coupled to convex focusing lens 1110 to focus light 602 onto central mirror 1112. Furthermore, although interferometer 1120 is shown as a Michelson-type interferometer, any suitable type of interferometer can be utilized as multiplexer 320. For example, interferometer 1120 can be a Mach-Zehnder, Twyman-Green, or Gilles-Tournois interferometer in certain embodiments.

[0030] 12, 13A, and 13B show examples of a multiplexer 320 configured to generate a Bessel beam (e.g., a non-diffracting beam). A Bessel beam has a very long focal line, which can be interpreted as many multiplexed foci that overlap in depth. In operation, a patient observes a fixation light spot formed by the Bessel beam and rotates their head to align the Bessel beam with their visual axis 110, thereby making the Bessel beam appear as a single spot. Once the Bessel beam is visualized as a single spot, the patient's visual axis point 112 can be located.

[0031] 12, multiplexer 320 is an axicon 1220 having at least one conical refractive surface 1206. Conical surface 1206 has rotational symmetry about optical axis 312 and therefore refracts light 602 to form a very long focal line F on optical axis 312. L to form crossed beams (e.g., Bessel beams).

[0032] 13A and 13B show a front plan view and a side schematic view of an annular ring (e.g., annular aperture) 1320 formed in a screen 1322. When the annular ring 1320 is axially aligned with the convex focusing lens 1310, the light 602 passes through the annular ring 1320 and is focused by the convex focusing lens 1310 to form a focal line F along the optical axis 312, similar to the axicon 1220. L In still further examples, multiplexer 320 may also include a diffractive or holographic optical element configured to generate a Bessel beam.

[0033] As mentioned above, the different multiplexers shown in Figures 7-13B can be used in a visual axis identification system, such as the visual axis identification system 300 of Figure 3. Figures 14A and 14B are slightly simplified versions of the visual axis identification system 300 of Figure 3, and exemplary operation of the visual axis identification system 300 is described in more detail herein with respect to Figures 14A and 14B. As shown, fixation light spots P0-P4 are generated by a multiplexer 320 of the fixation light source 302 (which may be, for example, one of the multiplexers of Figures 7-13B) and relayed onto an optical axis 312 by a relay lens 322. The optical axis 312 is directed toward the patient's eye 100 by utilizing one or more optical relay devices 310. While the patient continuously fixates their gaze on the fixation light spots P0-P4, the patient rotates their head in a "yes" (e.g., rotation about the Y axis) and / or "no" (e.g., rotation about the X axis) movement until the fixation light spots P0-P4 appear to be centrally coincident or aligned. When alignment of the corresponding images C0-C4 (shown in FIGS. 15A and 15B) of the fixation light spots P0-P4 occurs, the optical axis 312 is aligned with the visual axis 110 of the patient's eye 100.

[0034] 14B also shows how a "no" movement of the head results in a lateral or planar shift of the eye 100. For example, if the distance D between the cornea and the vertical anatomical axis of rotation X of the head is 80 mm, then a rotation of the head by 1° about the vertical axis of rotation X (i.e., a "no" movement) will result in a lateral shift of the eye 100 of 80 mm * sin(1°) = 1.4 mm.

[0035] Concurrent with the patient's head rotation, camera 304 captures an image or video of the iris plane of eye 100 from a direction along which light generated by fixation light source 302 travels to eye 100. In certain embodiments, optical axis 314 of camera 304 is aligned with optical axis 312 of fixation light source 302 and therefore also aligned with visual axis 110 of patient's eye 100 when the patient views centrally coincident or aligned images C0-C4 of fixation spots P0-P4. Thus, at the time the patient views the coincident images C0-C4 of fixation light spots P0-P4, the optical center of camera 304 (with optical axis 314 aligned with optical axis 312 of fixation light source 302) corresponds to visual axis point 112 of eye 100. In certain embodiments, the optical center of camera 304 is marked on the captured image or video or on a display screen viewed by a user (e.g., a surgeon).

[0036] Once the patient achieves alignment of the fixation light spots P0-P4, the patient holds their position to maintain that alignment while the camera 304 captures images of the eye 100 to locate the visual axis point 112 corresponding to the optical center of the camera 304. In certain embodiments, a video or series of images is captured by the camera 304 for a desired period of time while the patient maintains alignment of the fixation light spots P0-P4 in the images C0-C4. In certain embodiments, the video or series of images (including the series of images) captured by the camera 304 is analyzed by a processing system 306 (not shown in FIGS. 14A and 14B ) to determine an average X / Y position of the optical center of the camera 304 relative to the X / Y position of the eye 100, thereby averaging out any unintended eye and / or head movements by the patient when viewing the fixation light spots P0-P4. The average X / Y position of the optical center of the camera 304 corresponds to the visual axis point 112 of the eye 100. The determined average X / Y position of the optical center of the camera 304 relative to the X / Y position of the eye 100 corresponds to the average of all X / Y positions of the optical center of the camera 304 in the sequence of images or videos, as will be explained in more detail below with reference to FIG. 16.

[0037] 15A and 15B are schematic diagrams of eye 100 observing multiple fixation light spots P0-P4 generated by multiplexer 320 of FIGS. 14A and 14B. As shown in FIG. 15A, when all fixation light spots P0-P4 are aligned with visual axis 110 of patient's eye 100, they form coincident images C1-C4 on retina 116. The patient can achieve such alignment by moving their head in a "yes" or "no" motion around the X and / or Y axes while continuously maintaining focus on fixation light spots P0-P4, as described above and shown in FIG. 14B. Once aligned, the patient attempts to maintain that position so that camera 304 can capture an image or video of eye 100's position relative to the optical center of camera 304. As shown in FIG. 15B, if the fixation light spots P0-P4 (and optical axis 312) are not aligned with the visual axis 110, the fixation light spots P0-P4 will form spatially shifted images C0-C4 on the retina 116, and the patient will have to adjust their head position.

[0038] FIG. 16 shows a front-view image of the eye 100 during use of the visual axis identification system of FIGS. 3 and 14A-14B, in accordance with certain embodiments of the present disclosure. The field of view shown in FIG. 16 may be that of the camera 304, which may be displayed on a display screen for viewing by a surgeon. As shown, a trace 1610 indicates the historical position of the optical axis 312 of the fixation light source 302 on the iris plane of the eye 100, and a marker 1610 designates the center of gravity of the trace 1620. During operation, the optical center of the camera 304 is configured to coincide with the optical axis 312 of the fixation light source 302. The position of the optical center (and therefore the optical axis 312) of the camera 304 is tracked by the trace 1620 in an image or video captured while the patient is observing a centered fixation spot. The trace 1620 is then analyzed to determine the X / Y position of the marker 1610, which specifies the centroid position of the trace 1620 relative to the X / Y position of the eye 100 corresponding to the "average" visual axis point 112. In certain embodiments, the relative X / Y positioning of the marker 1610 and the eye 100 is determined by mapping and tracking the scleral veins 1602.

[0039] 17A to 17D show the fixation light spot P formed by the fixation light source 302. N 17A-17C, when the optical axis 312 and the visual axis 110 are not aligned, the patient will see a fixation light spot P that progresses in both size and sharpness. N17D ). However, when axis 312 and axis 110 are aligned, the fixation light spots spatially coincide or overlap, as shown in FIG. 17D . FIG. 17E shows a system 1700 utilized to obtain the above representation. The system includes a point-like fixation light source 1702 for generating a fixation light, a coated lens 1722 for focusing the fixation light into two or more fixation light spots, and a camera 1704 for capturing images of the fixation light spots focused by the coated lens 1722. When the optical center 1706 of camera 1704, the optical center 1724 of coated lens 1722, and the optical axis 1712 of fixation light source 1702 coincide, camera 1704 captures an image similar to that of FIG. 17D . These circumstances represent a scenario in which the patient's visual axis 110 coincides with the optical axis 312 of fixation light source 302. When the optical center 1724 of the coated lens 1722 is shifted spatially (e.g., in the X or Y direction) relative to the optical axis 1712 and / or optical center 1706 of the camera 1704, the camera 1704 captures images similar to those in Figures 17A-17C. These circumstances represent scenarios in which the patient's visual axis 110 is spatially shifted relative to the optical axis 312 of the fixation light source 302.

[0040] FIG. 18 shows a simplified schematic diagram of an alternative visual axis identification system 1800 in accordance with certain embodiments of the present disclosure. As shown, visual axis identification system 1800 is substantially similar to visual axis identification system 300, but includes an additional camera 1804, which can be operatively coupled to processing system 306 (shown in FIG. 3 ) and / or camera 304 to trigger image capture by camera 304. Camera 1804 focuses on the retina of eye 100 and thus may be a fundus-type camera. In certain embodiments, camera 1804 monitors or surveys the retina for the formation of images, such as images C0-C4 on the retina corresponding to fixation light spots generated by fixation light source 302. When images C0-C4 overlap on the retina, camera 1804 recognizes the overlap event and can trigger camera 304 (e.g., by either communicating directly with camera 304 or via processing system 306) to record or capture an image of the iris plane of eye 100. As described above, when images C0-C4 are superimposed on the retina, visual axis 110 is aligned with optical axis 312, which also coincides with the optical center of camera 304. Thus, image capture by camera 304 is automatically triggered by camera 1804 when its optical center is aligned with visual axis 110, thereby eliminating or reducing inaccuracies caused by the patient's limited cooperation skills.

[0041] 19 shows a flow diagram of a method 1900 for determining the location of the visual axis point 112 using the visual axis identification system 300 and 1800, in accordance with certain embodiments of the present disclosure. Generally, while using the visual axis identification system 300 or 1800, a patient focuses their gaze on a fixation light spot generated by a fixation light source 302 in operation 1910. The fixation light spot is focused on the optical axis 312 of the fixation light source 302 and relayed toward the patient's eye 100. In operation 1920, a camera 304, having an optical axis 314 aligned with the optical axis 312 of the fixation light source 302, is focused on the iris plane of the patient's eye 100. In certain embodiments, the optical center of the camera 304 and the corresponding optical axis 314 are marked within the field of view of the camera 304.

[0042] In operation 1930, the patient is asked to rotate their head while continuously maintaining their gaze on the fixation light spot until the center of the fixation spot is aligned with the patient's field of view. The patient can move or rotate their head in the X or Y rotational direction to align the center of the fixation light spot within their field of view. Concurrently with the patient's head movement, camera 304 captures images or video of eye 100 while tracking its X / Y position relative to the X / Y position of optical axis 314. In certain embodiments, tracking of the relative X / Y position of eye 100 is performed using traces of scleral blood vessels, such as the scleral veins described above. In certain embodiments, the patient is asked to rotate their head to align the fixation spot during a “test” or “trial” period during which camera 304 does not capture images of eye 100. For example, the patient is asked to practice such movements during a trial period of approximately 30 seconds, after which a “measurement” period begins and camera 304 can begin capturing images or video.

[0043] In certain embodiments, the center of the fixation spot is aligned in operation 1940, and the patient is asked to maintain the aligned nature or state of the fixation light spot while the camera 304 continues to capture images or video of the patient's eye 100. For example, the patient maintains the aligned state of the fixation light spot for a desired period of time, such as about 30 seconds, while the camera 304 continuously or intermittently records the X / Y position of the eye 100 and relays the images to the processing system 306. The processing system 306 then analyzes the video or series of images in operation 1950 to determine the average X / Y position of the optical axis 314 of the camera 304 relative to the X / Y position of the eye 100, thereby being able to compensate for the patient's unintentional eye and / or head movement. Thus, identifying the average X / Y position of the optical axis 314 corresponds to the approximate X / Y position of the visual axis point 112.

[0044] In certain other embodiments, the second camera 1804 monitors the retina of the patient's eye 100 in operation 1940 and automatically triggers the camera 304 to capture an image of the eye 100 once the corresponding image of the fixation light spot on the retina is aligned. The use of the second camera 1804 allows for automatic image capture of the eye 100 upon alignment of the optical axis 314 with the visual axis 110, thereby eliminating or significantly reducing any inaccuracies caused by the patient's unintentional eye and / or head movement and patients with limited coordination skills. After image capture by the camera 304, the image is analyzed by the processing system 306 in operation 1950 to determine the X / Y location of the visual axis point 112.

[0045] The above-described methods and apparatus provide a novel visual axis identification system that can be utilized to improve the effectiveness of ophthalmic procedures, such as presbyopia treatments involving the fitting of corrective lenses, refractive surgery, artificial lens implants, and multifocal corneal inlays. The described visual axis identification system can also be utilized in combination with any suitable ophthalmic diagnostic device. Examples of suitable diagnostic devices include corneal topographers, optical coherence tomographs, wavefront meters (e.g., aberrometers), image-guided biometers, surgical microscopes, and other image-based diagnostic devices. In some examples, the visual axis identification systems 300 and 1800 can be utilized in combination with the Verion™, Topolyzer™, ORA™ System, LenSx™, and LuxOR™ LX3 platforms manufactured by Alcon, Inc. of Fort Worth, Texas. In some examples, the visual axis identification systems 300 and 1800 can be utilized in combination with ophthalmic platforms provided by other manufacturers.

[0046] While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, which scope is determined by the claims that follow. The present disclosure also includes the following aspects. [Aspect 1] 1. A method for determining a location of a visual axis point of a patient's eye, comprising: directing a fixation light toward the patient's eye, the fixation light including two or more fixation light spots formed at different positions along an optical axis of a fixation light source and corresponding to two or more images formed on or near the retina of the patient's eye; capturing one or more digital images of the iris plane of the patient's eye using a first camera when centers of the two or more images formed on or near the retina coincide in the patient's field of view while the optical center of the first camera is aligned with the optical axis on which the fixation light spot is formed; identifying the location of the visual axis point in the iris plane based on the one or more digital images, the location of the visual axis point corresponding to an X / Y position of the optical center of the first camera relative to an X / Y position of the patient's eye displayed in the one or more digital images; A method comprising: [Aspect 2] The method of aspect 1, wherein the location of the visual axis point further corresponds to the X / Y position of the optical axis of the fixation light source in the iris plane when the center of the image coincides in the patient's visual field. Aspect 3 the one or more digital images include a plurality of images; and 2. The method of claim 1, wherein identifying the location of the visual axis point of the patient's eye further comprises spatially averaging an X / Y position of the optical center of the first camera relative to an X / Y position of the patient's eye displayed in a corresponding plurality of digital images. Aspect 4 4. The method of embodiment 3, wherein the plurality of images are captured over a period of about 30 seconds. Aspect 5 2. The method of claim 1, further comprising receiving an indication that the centers of the images are aligned in the patient's field of view. Aspect 6 The method of aspect 5, wherein the capture of the one or more digital images by the first camera is triggered upon receiving the indication that the centers of the images are aligned. Aspect 7 The method of aspect 6, wherein the instructions are generated by a second camera focused on the retina of the patient's eye, the second camera configured to recognize when the centers of the images are aligned. Aspect 8 2. The method of aspect 1, further comprising determining the X / Y position of the patient's eye by mapping and tracking vasculature within the sclera of the patient's eye. Aspect 9 2. The method of claim 1, wherein capturing the one or more digital images is triggered by a user upon receiving an indication from the patient that the centers of the images are aligned. Aspect 10 1. A system for determining a location of a visual axis point of a patient's eye, comprising: a fixation light source configured to generate two or more fixation light spots at different locations along an optical axis; a first camera configured to capture digital images of the iris plane of the patient's eye and to track the X / Y position of the patient's eye while the optical center of the first camera is aligned with the optical axis along which the fixation light spot is generated; a processing system configured to identify the location of the visual axis point in the iris plane based on the digital image captured by the first camera; and wherein the visual axis point of the eye corresponds to an X / Y position of the optical center of the first camera relative to the X / Y position of the patient's eye when a center of an image formed by the two or more fixation light spots coincides on or near a retina of the patient's eye in the patient's field of view. Aspect 11 the processing system configured to identify the location of the visual axis point of the patient's eye; averaging the X / Y position of the optical center of the first camera relative to the X / Y position of the patient's eye while the patient maintains their gaze on the fixation light source so that the patient observes that the centers of the images are coincident. 11. The system of claim 10, comprising the processing system configured to: Aspect 12 The system of aspect 10, wherein the first camera is configured to map and track vasculature within the sclera of the patient's eye to determine the X / Y position of the patient's eye. Aspect 13 The system of aspect 10, wherein the first camera is an infrared camera. Aspect 14 The system of aspect 10 further includes a second camera configured to monitor the retina of the patient's eye and recognize when the centers of the images formed by the two or more fixation light spots coincide thereon, and when the centers coincide, the second camera is further configured to trigger the first camera to capture a digital image of the iris plane. Aspect 15 The system of aspect 10, wherein the fixation light source further includes a multiplexer configured to generate the two or more fixation light spots from incident light, and the multiplexer is one of a bifocal lens, a multifocal diffractive lens, a coated lens, a Fabry-Perot type system, a non-diffractive Bessel beam generator, or an interferometer.

Claims

1. 1. A method for operating a system for determining a location of a visual axis point of a patient's eye, the system including the processing system, a fixation light source, and a first camera, the method comprising: directing a fixation light to the patient's eye, the fixation light including two or more fixation light spots formed at different positions along an optical axis of the fixation light source and corresponding to two or more images formed on or near a retina of the patient's eye; capturing one or more digital images of an iris plane of the patient's eye using the first camera when centers of the two or more images formed on or near the retina in the patient's visual field coincide while the optical center of the first camera is aligned with the optical axis on which the fixation light spot is formed; the processing system identifying, based on the one or more digital images, the location of the visual axis point in the iris plane, the location of the visual axis point corresponding to an X / Y position of the optical center of the first camera relative to an X / Y position of the patient's eye displayed in the one or more digital images; The method further includes the processing system determining the X / Y position of the patient's eye by mapping and tracking vasculature within the sclera of the patient's eye.

2. 2. The method of claim 1, wherein the location of the visual axis point further corresponds to an X / Y position of the optical axis of the fixation light source in the iris plane when the center of the image coincides in the patient's visual field.

3. the one or more digital images include a plurality of images; and 2. The method of claim 1, wherein identifying the location of the visual axis point of the patient's eye further comprises the system spatially averaging an X / Y position of the optical center of the first camera relative to an X / Y position of the patient's eye displayed in a corresponding plurality of digital images.

4. The method of claim 3 , wherein the plurality of images are captured over a period of about 30 seconds.

5. The method of claim 1, further comprising the first camera receiving an indication that the center of the image is aligned in the patient's field of view.

6. The method of claim 5 , wherein the capture of the one or more digital images by the first camera is triggered when the first camera receives the indication that the centers of the images are aligned.

7. 7. The method of claim 6, wherein the indication is generated by a second camera focused on the retina of the patient's eye, the second camera configured to recognize when the centers of the images are aligned.

Images