Ophthalmic ranging instrument

Abstract

To provide a reliable ophthalmic ranging instrument.SOLUTION: An ophthalmic apparatus arranged to determine an indication of a distance between the ophthalmic apparatus and an eye of a subject comprises: an illumination device operable to illuminate the eye; an imaging device to acquire an image of the eye; where the illumination device and the imaging device are arranged such that the image of the eye comprises a specular highlight from the illumination device having a spatial distribution in the image which varies with the distance between the ophthalmic apparatus and the eye; and a processor. The processor is arranged to: process the image to determine a value of an indicator which is indicative of a property of the spatial distribution; and use the determined value of the indicator and a mapping which maps values of the indicator to corresponding values of the distance between the ophthalmic apparatus and the eye, so as to determine the distance between the ophthalmic apparatus and the eye.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] FIELD Example aspects herein relate generally to the field of ophthalmic devices, and more particularly to ophthalmic ranging instruments and techniques for measuring the distance between an ophthalmic ranging instrument and a subject's eye. [Background technology]

[0002] Ophthalmic devices are used by clinicians to diagnose and manage various eye conditions, for example, by using various techniques to image different portions of a subject's eye and evaluate the eye's response to stimuli, and include scanning laser ophthalmoscopes (SLOs), optical coherence tomography (OCT) imaging devices, fundus cameras, visual field testing devices, microperimetry devices, and corneal topography devices (among others), or a combination of two or more such devices.

[0003] To acquire high-quality images of an eye portion of interest, ophthalmic imaging devices (e.g., SLO and OCT scanners) often require that the position of the exit pupil of the ophthalmic imaging device be within a predetermined distance range from or within the eye suitable for acquiring such images. For example, some wide-field retinal imaging devices require that their exit pupil position be aligned with the center of the eye's pupil. A stereo distance measuring device (also called a stereo distance measuring device or stereo rangefinder) is a type of ophthalmic ranging equipment often used to measure the distance to the eye using stereo ranging techniques. For example, some ophthalmic imaging devices include a so-called pupil alignment module (PAM) configured to acquire stereo images of the eye, locate respective pupil centers in the stereo images, and determine the distance between the PAM and the pupil based on the distance interval between the located pupil centers in the stereo images.

[0004] Known stereo distance measuring devices can generally accurately measure the distance from the eye as long as the eye is in focus in the acquired stereo images. However, as the stereo images become increasingly out of focus (i.e., blurry), the accuracy with which distance can be measured decreases, and distance measurements may eventually become impossible. The stereo cameras of stereo distance measuring devices often use inexpensive complementary metal-oxide semiconductor (CMOS) sensors, and fast lenses with fixed focal lengths are typically used to compensate for the sensor's relatively low sensitivity to infrared (IR) illumination, which is typically used for patient comfort, and to avoid pupil constriction. Because such lenses typically have a narrow depth of field, conventional stereo distance measuring devices tend to produce reliable distance measurements only when the eye is located within a correspondingly narrow range of distances from the device. Because the exit pupil position is typically adjusted by moving the ophthalmic imaging device toward and away from the eye, it is desirable to be able to reliably measure the distance to the eye over a wide range of eye positions along the axial direction to improve patient alignment and therefore image quality. Furthermore, known stereo distance measurement devices typically use one or more IR light sources to illuminate the eyes when acquiring stereo images. These light sources tend to produce specular highlights in the stereo images, which can obscure the edges of the pupils in the acquired images, at least at some distances. The location of the pupil centers in the acquired stereo images can consequently be more difficult to detect, making distance measurements less reliable or even impossible, even when the eyes are within the depth of field of the stereo cameras.

[0005] It would therefore be desirable to provide an ophthalmic distance measuring device that at least partially overcomes one or more of the drawbacks of known ophthalmic distance measuring devices discussed above. Summary of the Invention

[0006] According to a first example aspect of the present disclosure, there is provided an ophthalmic device configured to determine an indication of a distance between the ophthalmic device and a subject's eye. The ophthalmic device includes an illumination device operable to illuminate the eye and an imaging device operable to capture an image of the eye, the illumination device and imaging device being arranged such that the image of the eye includes specular highlights from the illumination device having a spatial distribution within the image that varies with the distance between the ophthalmic device and the eye. The ophthalmic device further includes a processor configured to process the image to determine values ​​of spatial distribution indicators indicative of a characteristic of the spatial distribution, and to determine an indication of the distance between the ophthalmic device and the eye using the determined values ​​of the spatial distribution indicators and at least one mapping that maps the values ​​of the spatial distribution indicators to corresponding values ​​indicative of the distance between the ophthalmic device and the eye.

[0007] In an example embodiment, the illumination device is operable to illuminate the eye from at least two different positions such that the specular highlight in the image comprises a first portion and a second portion spaced apart in the image, the illumination device and the imaging device are arranged such that a distance between the first portion of the specular highlight and the second portion of the specular highlight varies with a distance between the ophthalmic device and the eye, and the value of the spatial distribution indicator indicates a distance between the first portion and the second portion in the image. The illumination device may be configured to provide point illumination of the eye from the at least two different positions such that the first portion of the specular highlight is a first spot in the image and the second portion of the specular highlight is a second spot in the image.

[0008] In another example embodiment, the illumination device and imaging device are configured so that the specular highlight has a size or shape that varies with the distance between the ophthalmic device and the eye, and the processor is configured to process the image to determine a value indicative of the size or shape of the specular highlight as a value of the spatial distribution indicator.

[0009] According to a second exemplary aspect of the present specification, there is provided a system including an ophthalmic device according to the first exemplary aspect or any of the exemplary embodiments described above, and a movement mechanism operable to move the ophthalmic device toward and away from the eye such that a spatial distribution of specular highlights in the image changes with movement, wherein the processor is further configured to determine whether a distance indicated by the determined indication is within a predetermined range of values, and if the distance indicated by the determined indication is outside the predetermined range of values, generate a control signal for adjusting the distance by the movement mechanism toward the predetermined range of values.

[0010] In one example embodiment of the system of the second example aspect, the ophthalmic device is a stereo imaging device including an additional imaging device operable to acquire additional images of the eye. In this example embodiment, if the distance indicated by the determined indication is within a predetermined range of values, the processor is further configured to process the acquired images using stereo distance measurement techniques to determine a second indication of the distance between the ophthalmic device and the eye, determine whether the distance indicated by the determined second indication is outside a second predetermined range of values, and, if the distance indicated by the second indication is outside the second predetermined range of values, generate a second control signal to cause the movement mechanism to adjust the distance between the ophthalmic device and the eye toward the second predetermined range of values. The processor may further be configured to determine the second indication of the distance between the ophthalmic device and the eye by processing each of the acquired images to locate a pupil center of each of the pupils in the image, mapping the located pupil centers to a common image frame, determining a distance separation between the pupil centers in the common image frame, and determining the second indication of the distance based on the determined distance separation between the pupil centers.

[0011] The system of any of the above-described second example aspect or embodiment examples thereof may further include an ophthalmic imaging device for imaging an eye through an exit pupil position of the ophthalmic imaging device. In this case, the moving mechanism may be configured to simultaneously move the exit pupil position and the ophthalmic device toward and away from the eye, and the exit pupil position and the ophthalmic device may be positioned relative to each other such that the exit pupil position of the ophthalmic imaging device is within a range of positions for imaging the eye when a distance between the ophthalmic device and the eye is within a predetermined range of values.

[0012] According to a third example aspect of the present specification, there is provided a method for determining an indication of a distance between an ophthalmic device and an eye of a subject, the method including acquiring an image of the eye using illumination that produces specular highlights in the image, the specular highlights having a spatial distribution in the image that varies with the distance between the ophthalmic device and the eye, processing the image to determine values ​​of spatial distribution indicators that characterize the spatial distribution, and determining an indication of the distance between the ophthalmic device and the eye using the determined values ​​of the spatial distribution indicators and at least one mapping that maps the values ​​of the spatial distribution indicators to corresponding values ​​indicative of the distance between the ophthalmic device and the eye.

[0013] In one example embodiment, the eye is illuminated from at least two different positions such that the specular highlight in the image includes a first portion and a second portion spaced apart in the image, a distance separation between the first portion of the specular highlight and the second portion of the specular highlight varies with the distance between the ophthalmic device and the eye, and the value of the spatial distribution indicator indicates the distance separation between the first portion and the second portion in the image. In this example embodiment, point illumination of the eye may be provided from at least two different positions such that the first portion of the specular highlight is a first spot in the image and the second portion of the specular highlight is a second spot in the image.

[0014] In another embodiment, the specular highlight has a size or shape that varies with the distance between the ophthalmic device and the eye, and the image is processed to determine a value indicative of the size or shape of the specular highlight as a value of the spatial distribution indicator.

[0015] The method of any of the above-described third example aspects or example embodiments thereof may further include determining whether the distance indicated by the determined indication is within a predetermined range of values, and generating a control signal to adjust the distance between the ophthalmic device and the eye toward the predetermined range of values ​​if the distance indicated by the determined indication is outside the predetermined range of values. The method may further include acquiring additional images of the eye such that the image and the additional images are stereo images of the eye, and may further include processing the stereo images using stereo ranging techniques to determine a second indication of the distance between the ophthalmic device and the eye if the distance indicated by the determined indication is within the predetermined range of values, and determining whether the distance indicated by the determined second indication is within a second predetermined range of values. If the distance indicated by the second indication is outside the second predetermined range of values, the method may further include generating a second control signal to adjust the distance between the ophthalmic device and the eye toward the second predetermined range of values.

[0016] A second representation of the distance between the ophthalmic device and the eye may be determined by processing each of the acquired images to locate a pupil center of each of the pupils in the image, mapping the located pupil centers to a common image frame, determining a distance separation between the pupil centers in the common image frame, and determining the second representation of the distance based on the determined distance separation between the pupil centers.

[0017] Example embodiments will now be described in detail, by way of non-limiting example only, with reference to the accompanying figures described below, in which like reference numbers appearing in different figures may indicate identical or functionally similar elements, unless otherwise indicated, and in which: [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic diagram of a system for imaging a subject's eye, including an ophthalmic device according to an example embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic diagram showing details of an ophthalmic device according to an example embodiment of the present specification. [Figure 3] FIG. 3 is a schematic diagram of an example embodiment of the ophthalmic device shown in FIG. [Figure 4A] FIG. 4A is a schematic side view of the ophthalmic device shown in FIG. 3, showing one of the cameras and two of the LEDs of the ophthalmic device. [Figure 4B] FIG. 4B is a schematic diagram of the ophthalmic device shown in FIG. 3 along the z-axis, showing two cameras and four LEDs of the device. [Figure 5A] FIG. 5A shows an example of an image acquired by an ophthalmic device of an example embodiment at a distance between the ophthalmic device and the eye, where the ophthalmic device is furthest from the eye. [Figure 5B] FIG. 5B shows example images acquired by an ophthalmic device of an example embodiment at different distances between the ophthalmic device and the eye. [Figure 5C] FIG. 5C shows example images acquired by an ophthalmic device of an example embodiment at further different distances between the ophthalmic device and the eye, with the ophthalmic device being closest to the eye. [Figure 6] FIG. 6 is a schematic diagram of programmable signal processing hardware that can be configured to perform the functions of the processor described herein. [Figure 7] FIG. 7 is a flow diagram illustrating a process by which a processor in an example embodiment processes an image of the eye to determine an indication of the distance between the ophthalmic device and the eye, and optionally generates a control signal to adjust the distance using the determined indication. [Figure 8] FIG. 8 shows a tabular representation of the mapping used in example embodiments herein to determine an indication of the distance between the ophthalmic device and the eye. [Figure 9]FIG. 9 is a flow diagram illustrating a process by which a processor in an example embodiment may determine a second indicator of the distance between the ophthalmic device and the eye using stereoscopic distance measurement techniques and generate a second control signal for adjusting the distance using the determined second indicator. DETAILED DESCRIPTION OF THE INVENTION

[0019] In view of the background provided above, the present inventors have devised a distance measurement technique that uses specular highlights (e.g., caused by reflections from the cornea of ​​the eye) to measure the distance to the eye. The distance measurement technique may be implemented by an ophthalmic device comprising an illumination device and an imaging device, the illumination device and the imaging device being positioned relative to one another such that, when the ophthalmic device is in use, an image of the eye captured by the imaging device includes specular highlights from the illumination device, the spatial distribution of the specular highlights in the image changing as the distance between the ophthalmic device and the eye changes. The ophthalmic device further comprises a processor configured to process the image to determine a value of a spatial distribution indicator indicative of a characteristic of the spatial distribution (e.g., the size or shape of the specular highlights, or, for example, the distance spacing between two separated portions thereof), and to use the determined value of the spatial distribution indicator to determine an indication (i.e., an index) of the distance between the ophthalmic device and the eye.

[0020] The distance measurement techniques described herein have the advantage of not requiring the acquisition of a second (stereo or other) image of the eye and processing of the second image to determine the distance to the eye, at least to determine a change in distance or obtain a distance estimate. As a result, hardware and processing requirements are less stringent. Furthermore, the distance measurement techniques described herein may be more reliable than previously known stereo ranging (or distance measurement) techniques when the acquired image is defocused. This is because specular highlights are typically higher contrast features than the edges of the pupil and are therefore often difficult to distinguish from the iris in defocused (blurred) images. This is particularly true when the illumination device produces specular highlights in images containing two or more spots whose distance spacing is used to quantify the distance to the eye. This is because the high contrast of the spots makes them easy to locate, and the location of the spot center is largely independent of the degree of blur in the image.

[0021] The distance measurement techniques described herein may complement the use of conventional stereoscopic distance measurement techniques, for example, by ensuring that the distance between the ophthalmic device and the eye can be achieved within a predetermined range so that any subsequently acquired stereo images are sufficiently focused for conventional stereoscopic distance measurement techniques to produce reliable results. Thus, in some example embodiments, the distance measurement techniques described herein may address (at least in part) the aforementioned image quality concerns by using a reliable first measurement of distance that is resilient to image blur before the distance is adjusted based on the first measurement so that conventional stereoscopic distance measurement techniques can be later used to fine-tune the exit pupil position (or another reference position) of the ophthalmic imaging device relative to the eye.

[0022] Furthermore, the distance measurement techniques described herein may require only a portion of the hardware of a typical conventional stereoscopic distance measurement device, such as the PAM described above, for their implementation. Thus, the aforementioned advantages can be achieved without the associated increase in hardware complexity. More specifically, the inventors have recognized that specular highlights, which tend to reduce the reliability of conventional stereoscopic distance measurement devices for the reasons explained above, may form the basis of an alternative approach to distance measurement that is not bound by the limitations of conventional stereoscopic distance measurement techniques.

[0023] Example embodiments will now be described in detail with reference to the accompanying drawings.

[0024] 1 is a schematic diagram of a system 100 for imaging an eye 110 of a (human) subject 111. The system 100 comprises an ophthalmic apparatus 120 (which may also be referred to as an ophthalmic distance measuring instrument or an ophthalmic distance measuring device) and a movement mechanism 130. The system 100 may further comprise an ophthalmic imaging device 140, as in this example of the embodiment.

[0025] The ophthalmic imaging device 140 is configured to image the eye 110 through an exit pupil position FP of the ophthalmic imaging device 140. The ophthalmic imaging device 140 may be operable to acquire an image of the retina of the eye 110 by illuminating an area of ​​the retina through the exit pupil position Fp of the ophthalmic imaging device 140 and recording light reflected from the illuminated area and collected by the ophthalmic imaging device 140 through the exit pupil position Fp. The exit pupil position FP is located along an imaging axis 141 of the ophthalmic imaging device 140, which extends along the same direction as the z-axis in FIG. 1 . The ophthalmic imaging device 140 may be an optical coherence tomography (OCT) imaging device in the form of a swept-source OCT (SS-OCT) imaging device, as in this example embodiment. However, the ophthalmic imaging device 140 may also be another type of Fourier-domain OCT (FD-OCT) imaging device, such as a spectral-domain OCT (SD-OCT) imaging device, or a time-domain OCT (TD-OCT) imaging device. In such a case, the OCT imaging device may be operable to acquire an image of the retina of the eye 110 by illuminating an area of ​​the retina through an exit pupil position Fp and recording light reflected from the illuminated area and collected by the OCT imaging device through the exit pupil position Fp. However, the ophthalmic imaging device 110 is not limited thereto and may be other types of ophthalmic imaging devices that image the eye 110 through the exit pupil position FP of the ophthalmic imaging device 140, such as, for example, a scanning laser ophthalmoscope (SLO) or a fundus camera.

[0026] The OCT imaging device may include well-known components, such as a light beam generator, a scanning system, an interferometer, a photodetector, and OCT data processing hardware (not shown). The scanning system may be configured to perform one-dimensional and / or two-dimensional point scanning of a light beam across the retina of the eye 110 through an exit pupil position Fp of one or more lenses or curved (e.g., ellipsoidal) mirrors and collect light scattered by the retina through the exit pupil position Fp during the point scanning. Thus, the OCT imaging device can acquire A-scans at each scan position distributed across the surface of the retina by sequentially illuminating multiple scan positions with a light beam, one scan position at a time, and collecting at least a portion of the light scattered by the retina at each scan position. The OCT imaging device may be configured to acquire OCT images in the form of B-scans, for example, by performing point scanning to acquire successive A-scans along a straight line. However, the OCT imaging device may alternatively be configured to acquire B-scans by a scanning system performing a line scanning, using hardware well known to those skilled in the art. More generally, the OCT imaging device may be configured to acquire OCT images in the form of B-scans or C-scans by performing point or line scans using predetermined scan patterns (e.g., spiral scans) well known to those skilled in the art, or by using a full-field setup.

[0027] The system 100 may further comprise, as in this example of the embodiment, a patient interface 142 having a contact surface 143. The contact surface 143 is positioned to contact the head 112 of the subject 111 during imaging of the eye 110, thus fixing the position of the eye 110 along the z-axis relative to the position of the contact surface 143. The patient interface 142 may, as in this example of the embodiment, be provided in the form of a chin rest having an upwardly facing contact surface 143 on which the subject's 111 chin rests during imaging of the eye 110 by the ophthalmic imaging device 140. However, the contact surface 143 may also be provided on other types of patient interfaces, such as, for example, a mask (referred to herein as "goggles") contoured to fit around the eyes and over the bridge of the subject's 111 nose through which the subject 111 looks during imaging of the eye 110 by the ophthalmic imaging device 140, a forehead rest against which the subject's 111 forehead presses during imaging, a combination of a chin rest and forehead rest, or one or two eyecups.

[0028] The distance along the z-axis between the patient interface 142 and the ophthalmic imaging device 140 may be adjusted by moving the ophthalmic imaging device 140 along the z-axis toward or away from the patient interface 142 while the patient interface 142 remains fixed in place (i.e., immovable along the z-axis), as in this example embodiment. For example, the patient interface 142 may be fixed to a table (not shown), and the ophthalmic imaging device 140 may be mounted to the table so that it can slide toward or away from the patient interface 142 along the z-axis, as desired. However, the position of the patient interface 142 relative to the ophthalmic imaging device 140 may alternatively be adjustable by moving the patient interface 142 axially (i.e., along the z-axis) while the ophthalmic imaging device 140 remains fixed in place. For example, the ophthalmic imaging device 140 may be fixed to a table, and the patient interface 142 may be slidably mounted to the table so that it can slide relative to the ophthalmic imaging device 140. As a further alternative, the position of the patient interface 142 relative to the ophthalmic imaging device 140 may be adjustable by axially moving both the ophthalmic imaging device 140 and the patient interface 142 relative to a support table or other support structure. In all of these cases, the position of the eye 110 relative to the ophthalmic imaging device 140 may be adjusted when preparing to image the eye 110 by adjusting the distance between the patient interface 142 and the ophthalmic imaging device 140.

[0029] The movement mechanism 130 may be configured, as in this example embodiment, to simultaneously move the exit pupil position FP and the ophthalmic apparatus 120 toward or away from the eye 110, as desired, thereby changing the spatial distribution of specular highlights in the image. For example, the ophthalmic apparatus 120 may, as in this example embodiment, be attached to the ophthalmic imaging device 140, and both may be movable back and forth along the z-axis relative to the (fixed) patient interface 142 by the movement mechanism 130. Thus, when preparing to image the eye 110, the movement mechanism 130 may simultaneously move both the ophthalmic apparatus 120 and the exit pupil position FP of the ophthalmic imaging device 140 together relative to the eye 110 by moving the ophthalmic imaging device 140 axially (i.e., along the z-axis) relative to the patient interface 142.

[0030] The moving mechanism 130, as in this example of the embodiment, may comprise a linear actuator (e.g., rack and pinion) controllable by a processor (which may be the processor 126 described later in this specification) or an operator, for example, using buttons on a handset, to simultaneously move the exit pupil position FP and the ophthalmic device 120 toward or away from the eye 110, as described above. The exit pupil position FP and the ophthalmic device 120 are positioned relative to each other such that when the distance between the ophthalmic device 120 and the eye 110 is within a predetermined range of values, as described below, the exit pupil position FP of the ophthalmic imaging device 140 is within a predetermined range of positions suitable for imaging a desired portion of the eye 110 (e.g., the retina or anterior segment).

[0031] Although adjustment of the distance between the patient interface 142 and the ophthalmic imaging device 140 has been generally described above, the adjustment may instead be adjustment of the distance between the patient interface 142 and only some of the components of the ophthalmic imaging device 140. For example, the axial position of the patient interface 142 may be fixed relative to the portion of the ophthalmic imaging device 140 comprising (or consisting of) the interferometer, detector, light source, and OCT data processing hardware, and the remaining components of the ophthalmic imaging device 110 comprising (or consisting of) the scanning system may be movable relative to said portions, e.g., by the movement mechanism 130. Such an arrangement may be achieved, for example, by optically coupling the scanning system to the interferometer with optical fibers and providing a translation mechanism using, e.g., a stepper motor, to move the scanning system relative to the remaining components of the ophthalmic imaging device 140. The scanning system and ophthalmic device 120 may be arranged in a fixed spatial arrangement that is movable by a moving mechanism 130 along the z-axis so that the exit pupil position FP of the ophthalmic imaging device 140 (which may be determined by optical elements in the scanning system) and the ophthalmic device 120 can be simultaneously moved towards and away from the eye 110 to change the spatial distribution of specular highlights in the image.

[0032] In a further variation, the movement mechanism 130 is configured to adjust the axial position of the exit pupil position FP of the ophthalmic imaging device 140, for example, by moving one or more optical elements of the scanning system. In this variation, the axial position of the patient interface 142 relative to the ophthalmic imaging device 140 remains fixed, and the movement mechanism 130 is configured to simultaneously move the exit pupil position FP together with the ophthalmic apparatus 120 towards and away from the eye 110.

[0033] Additionally, while the system 100 described above includes a patient interface 142, this is optional and may be omitted. For example, the patient may move to a predetermined position to be maintained during imaging (e.g., sitting upright in a chair in front of the ophthalmic imaging device 140), after which the axial position of the ophthalmic imaging device 140 may be adjusted as needed. Thus, when the ophthalmic apparatus 120 and the exit pupil position Fp are at their respective fixed axial positions relative to the ophthalmic imaging device 140, the movement mechanism 130 may simultaneously move the exit pupil position Fp and the ophthalmic apparatus 120 together toward or away from the eye 110, as described above. Similarly, when the position of the exit pupil position Fp of the ophthalmic imaging device 140 along the z-axis is adjustable relative to the ophthalmic imaging device 140, the movement mechanism 130 may simultaneously move the exit pupil position Fp and the ophthalmic apparatus 120 relative to the ophthalmic imaging device 140, for example, by moving or otherwise controlling one or more optical elements in a scanning system.

[0034] The ophthalmic device 120 is configured to determine at least one indication (or measure) Id of the distance d between the ophthalmic device 120 and the eye 110 of the subject 111. The indication Id may, as in this example of embodiment, be a value of the distance in the z-axis direction between the ophthalmic device 120 and the eye 110, as shown with respect to a line 113 in the plane of the pupil of the eye 110 in FIG. 1 , perpendicular to the z-axis direction. The indication of the distance may be provided in a variety of different forms, for example, with respect to the distance between the ophthalmic device 120 and the eye 110 expressed in metric or any other length units (e.g., a multiple of a predetermined distance, e.g., 0.9D, 1.2D, etc.), or the distance between the eye 110 and a suitable reference point, calculated, for example, using the distance d.

[0035] 2 is a schematic diagram showing details of an example embodiment of an ophthalmic device 120. The ophthalmic device 120-1 of FIG.

[0036] The illumination device 122 is operable to illuminate the eye 110, preferably with infrared light, and the imaging device 124 is operable to acquire at least one image 127 of the eye 110. The image 127 may, for example, capture a portion 114 of the head 112 of the subject 111, including the entire eye 110.

[0037] The illumination device 122 and the imaging device 124 are positioned relative to one another such that an image 127 of the eye 110 acquired by the imaging device 124 includes specular highlights 128 from the illumination device 122, the specular highlights 128 having a spatial distribution within the image 127 that varies with the distance d between the ophthalmic instrument 120 and the eye 110. The specular highlights 128 may be formed by direct specular reflection of light from the illumination device 122 off the cornea of ​​the eye 110, which acts as a convex reflector, as in this example embodiment.

[0038] The change in the spatial distribution of the specular highlight 128 with distance d may be quantified by the change in one or more measurable characteristics of the spatial distribution with d. For example, the characteristic of the spatial distribution may be the distance separation between spatially separated (i.e., disconnected) portions of the specular highlight 128, as in this example embodiment and described below. However, the characteristic of the spatial distribution is not so limited and may alternatively be the size (e.g., length or area) or shape of the specular highlight 128, for example, the degree of curvature of the highlight's edge or the degree of barrel distortion of the highlight. For example, the illumination device 122 may project a line of light onto the eye 110 (e.g., using a mask with a slit) such that the specular highlight 128 takes the shape of the line segment in the image 127. In this case, the length of the linear specular highlight 128 varies with distance d and may therefore be used to obtain an indication of the distance d. Additionally or alternatively, the linear specular highlight 128 may have a curvature that varies with distance d, and therefore the degree of curvature may be quantified and used to obtain a measure of distance d.

[0039] Therefore, as described in more detail below, one or more characteristics of the spatial distribution of the specular highlights 128 in the image 127 may be selected that contain information about the distance d between the ophthalmic device 120 and the eye 110 and can therefore be used by the processor 126 to determine the representation Id of the distance d.

[0040] FIG. 3 is a schematic diagram of an example of an embodiment of the ophthalmic apparatus 120 of FIG. 2. In the ophthalmic apparatus 120-1 shown in FIG. 3, the imaging device 124 includes a first camera 124-1 and a second camera 124-2 configured to acquire stereo images 127-1 and 127-2 of the eye 110. The cameras 124-1 and 124-2 each have a CMOS sensor, but the form of the camera is not particularly limited. For example, a charge-coupled device (CCD) sensor may be used instead of the CMOS sensor. The first camera 124-1 and the second camera 124-2 may be positioned at the same position along the z-axis and have their respective optical axes parallel to the imaging axis 141 of the ophthalmic imaging device 140. However, the optical axes of the first camera 124-1 and the second camera 124-2 do not need to be parallel and may, for example, converge toward the imaging axis 141.

[0041] Furthermore, illumination device 122 comprises, in this example, four light emitting diodes (LEDs) 122-1 to 122-4, which are preferably IR LEDs but may additionally or alternatively emit light at other (e.g., visible) wavelengths. The LEDs generate respective specular highlights in each of acquired images 127-1 and 127-2, which have four spaced apart portions (in this case, spots) 128-1 to 128-4, the distance between which varies with distance d.

[0042] This form of illumination device 122 is by way of example only, and instead, fewer or more than four LEDs may be provided in a variety of different arrangements so that the eye 110 can be illuminated from two or more different positions, and it will be appreciated that the specular highlight in the acquired image will have portions spaced apart from one another, the separation of these portions varying with distance d. Furthermore, illumination device 122 may illuminate the eye 110 from two or more different positions by means other than LEDs, for example from the ends of optical fibers positioned around the imaging device 124, or from openings in a backlit mask surrounding the imaging device 124 in the xy plane.

[0043] 4A is a schematic side view of the cameras and LEDs of the ophthalmic apparatus 120-1 shown in FIG. 3, while FIG. 4B is a schematic view of the arrangement of the cameras and LEDs of the ophthalmic apparatus 120-1 along the z-axis in the xy plane. The illustrated positional relationship between the cameras 124-1 and 124-2, LEDs 122-1 to 122-4, and imaging axis 141 of the ophthalmic imaging device 140 is fixed, and the cameras 124-1 and 124-2 and LEDs 122-1 to 122-4 are arranged to move along the imaging axis integrally with the exit pupil position FP of the ophthalmic imaging device 140, as described above.

[0044] 3, 4A, and 4B, much of the hardware of a conventional stereo distance measuring device can be used, but the processor 126 is configured to process acquired images of the eye 110 using techniques described herein to measure the distance d based on specular highlights in the images. In the example embodiment of FIG. 3, the ophthalmic device 120-1 may be used to provide an indication of the distance d between the ophthalmic device 120-1 and the eye 110 using conventional stereo distance measuring techniques, as described below.

[0045] The four LEDs 122-1 to 122-4 are spaced apart from one another and are therefore positioned to provide point illumination of the eye 110 from their four different locations such that the specular highlight 128 in each of the images 127-1 and 127-2 of the eye 110 includes four spots 128-1 to 128-4 that are not connected to one another by other portions of the specular highlight 128 in the image. The LEDs 122-1 to 122-4 and the cameras 124-1 and 124-2 are also positioned such that the separation between each pair of the four spots 128-1 to 128-4 in the images 127-1 and 127-2 varies with the distance d between the ophthalmic device 120 and the eye 110. The separation between any two of the spots 128-1 to 128-4 may therefore be considered a characteristic of the spatial distribution of the specular highlight 127 that varies with the distance d, as described herein.

[0046] 5A-5C show examples of three images 500-1, 500-2, and 500-3 acquired by the first camera 124-1 at different distances da, db, and dc between the ophthalmic device 120-1 and the subject's left eye, respectively, where da>db>dc. Similar images of the left eye can be acquired by the second camera 124-2 from a different viewpoint of the second camera 124-2.

[0047] As shown in first image 500-1, the arrangement of the four LEDs 122-1 through 122-4 relative to first camera 124-1 results in a specular highlight including four distinct spots 510-1 through 510-4, each corresponding to a direct specular reflection of light from a respective one of LEDs 122-1 through 122-4 from the cornea of ​​the eye. In first image 500-1, captured when the distance between ophthalmic device 120-1 and eye 110 was da, there is a distance separation Sa between first spot 510-1 and second spot 510-2. In this example, the arrangement of LEDs 122-1 through 122-4 is such that the four spots 510-1 through 510-4 form a square in first image 500-1.

[0048] The second image 500-2 shown in FIG. 5B was acquired when the distance between the ophthalmic device 120-1 and the eye 110 was db, which is less than the distance da. As shown in FIG. 5B, the distance Sb between the first spot 520-1 (which is a less blurred, brighter version of the first spot 510-1 in FIG. 5A) and the second spot 520-2 (which is a less blurred, brighter version of the second spot 510-2 in FIG. 5A) has increased from Sa. The third image 500-3 shown in FIG. 5C was acquired when the distance between the ophthalmic device 120-1 and the eye 110 was dc, which is less than the distance db. In FIG. 5C, the distance Sc between the first spot 530-1 (corresponding to the first spot 520-1 in FIG. 5B) and the second spot 530-2 (corresponding to the second spot 520-2 in FIG. 5B) has increased from Sb.

[0049] Although the four LEDs 122-1 to 122-4 of the illumination device 122 provide point illumination of the eye 110 from their respective different positions such that the specular highlight 128 in the image 127 of the eye 110 comprises four spots spaced apart from one another in the image 127, the illumination device 122 may more generally be configured to illuminate the eye from at least two different positions such that the specular highlight 128 in the acquired image 127 comprises a first portion and a second portion spaced apart from one another in the image 1127. For example, the illumination device 122 may comprise a single LED that emits light through a mask with two openings through which the light from the LED illuminates the eye 110. The first and second portions in the resulting image may be spots or have any other desired shapes defined by the shapes of the corresponding openings. In this more general case, the illumination device 122 and the imaging device 124 may be arranged in a manner similar to that described in connection with Figures 5A to 5C so that the distance between the first portion of the specular highlight 128 and the second portion of the specular highlight 128 (as a measurable characteristic of the spatial distribution in this case) varies with the distance d between the ophthalmic device 120 and the eye 110.

[0050] Furthermore, the second camera 124-2 is optional and need not be provided for the purpose of measuring the distance between the ophthalmic device 120 and the eye 110. This is because the distance measurement techniques described herein require only a single camera or other imaging device to capture changes in selected characteristics of the specular distribution of the specular highlights 128 with distance between the ophthalmic device 120 and the eye 110. However, the inclusion of the second camera 124-2 and the configuration of the processor 126 to process the images 127-2 acquired by the second camera 124-2 in the same manner as the images 127-1 may enhance the reliability of the ophthalmic device 120-1 by allowing additional distance measurements to be performed using a different approach that does not rely on specular reflection, i.e., known stereoscopic ranging techniques. Furthermore, providing the second camera 124-2 in addition to the first camera 124-1 can eliminate ambiguity in changes in the captured images due to movement of the eye 110 along the z-axis and x-axis, and can also determine the position of the pupil along the x-axis.

[0051] The second camera 124-2 is configured to acquire at least one second image 127-2 of the eye 110 that includes specular highlights from the lighting device 122, although the second camera 124-2 need not be configured to capture specular highlights from the lighting device 122 and may acquire further images of the eye 110 without specular highlights such that this image and the images acquired by the first camera 124-1 are stereo images that can be processed using known stereo ranging techniques for distance measurement.

[0052] 2 , the processor 126 is configured to acquire the image 127 captured by the imaging device 124 using illumination from the illumination device 122, as described above. The processor 126 may, in this example embodiment, control the illumination device 122 and the imaging device 124 to acquire the image 127 while the illumination device 122 illuminates the eye 110, and then receive the acquired image 127. The processor 126 is further configured to process the image 127 using at least one mapping M, as described below, to determine at least one representation Id of the distance d between the ophthalmic device 120 and the eye 110.

[0053] The processor 126 may, as in this example embodiment, generate at least one control signal CS for adjusting the distance d between the ophthalmic device 120 and the eye 110. For example, if the movement mechanism 130 is controllable by the processor 126, as in this example embodiment, the control signal CS may control the movement mechanism 130 by directly controlling an actuator of the movement mechanism 130 or by instructing a controller of the movement mechanism 130. Alternatively, if the movement mechanism 130 is controllable by an operator, the control signal CS may instruct the operator (e.g., via a display of the system 100) to appropriately control the movement mechanism 130.

[0054] The processor 126 may be provided in any suitable form, for example as a processor 620 of programmable signal processing hardware 600 of the type shown schematically in FIG. 6 . Components of the programmable signal processing hardware 600 may be included within the ophthalmic device 120. The programmable signal processing hardware 600 comprises a communication interface (I / F) 610 for receiving at least one image 127 from the imaging device 124. The I / F 610 may also receive one or more mappings M and may output at least one representation Id of the distance d between the ophthalmic device 120 and the eye 110. The I / F 610 may output at least one control signal CS for adjusting the distance d between the ophthalmic device 120 and the eye 110 by the movement mechanism 130. The signal processing hardware 600 further comprises a processor 620 (e.g., a central processing unit, CPU, and / or a graphics processing unit, GPU), a working memory 630 (e.g., random access memory), and an instruction store 640 that stores a computer program 645 containing computer-readable instructions that, when executed by the processor 620, cause the processor 620 to perform various functions of the processor 126 described herein. The working memory 630 stores information used by the processor 620 during execution of the computer program 645, including the mapping M.

[0055] The instruction store 640 may comprise a ROM (e.g., in the form of an Electrically Erasable Programmable Read-Only Memory (EEPROM) or flash memory) that is pre-loaded with computer-readable instructions. Alternatively, the instruction store 640 may comprise a RAM or similar type of memory, and the computer-readable instructions for the computer program 645 may be input from a computer program product, such as a non-transitory computer-readable storage medium 650 in the form of a CD-ROM, DVD-ROM, etc., or a computer-readable signal 660 carrying the computer-readable instructions. In either case, the computer program 645, when executed by the processor 620, causes the processor 620 to perform the functions of the processor 126 described herein. In other words, the processor 126 in this example embodiment may comprise the computer processor 620 and a memory 640 that stores computer-readable instructions that, when executed by the computer processor 620, cause the computer processor 620 to perform the functions of the processor 126 described herein.

[0056] It should be noted, however, that the processor 126 may alternatively be implemented as non-programmable hardware, such as an ASIC, FPGA, or other integrated circuit dedicated to performing the functions of the processor 126 described herein, or as a combination of non-programmable and programmable hardware as described above in connection with Figure 6. Furthermore, in some example embodiments, the programmable signal processing hardware 600 may further perform at least one of the functions of OCT data processing hardware if the ophthalmic imaging device 140 is an OCT imaging device, or the functions of a controller of the movement mechanism 130 of the imaging device 124, if provided.

[0057] FIG. 7 is a flow diagram illustrating the process by which the processor 126 processes the image 127 to determine at least one representation Id of the distance d between the ophthalmic device 120 and the eye 110.

[0058] 7, the processor 126 acquires a first image 127-1 of the eye 110 using illumination that produces specular highlights 128 in the first image 127-1. The processor 126 may receive the first image 127-1 from a memory (e.g., working memory 630) that stores the first image 127-1 after it is captured by the ophthalmic imaging device 140 under the control of the processor 126 or other means. The processor 126 may acquire the image 500-1 of FIG. 5A from the first camera 124-1 as the first image 127-1, as described above.

[0059] In optional process S1A of Figure 7, processor 126 acquires second image 127-2 of eye 110, as described above, such that first image 127-1 and second image 127-2 are stereo images of eye 110. This process is necessary to perform processes S6 to S8 of Figure 9, which will be described below. Processor 126 may, for example, receive second image 127-2 from a memory (e.g., working memory 630) that stores second image 127-2 (as well as first image 127-1) after second image 127-2 is captured by ophthalmic imaging device 140 under the control of processor 126 or other means.

[0060] In process S2 of Figure 7, processor 126 processes first image 127-1 to determine values ​​of spatial distribution indicators that indicate characteristics of the spatial distribution of specular highlights 128. The spatial distribution indicators may quantify the characteristics of the spatial distribution. Processor 126 may identify portions of first image 127-1 that correspond to specular reflections 128 in first image 127-1, for example, by using image segmentation techniques well known to those skilled in the art, as in this example of the present embodiment. Processor 126 may then determine the spatial distribution using the identified portions of first image 127-1.

[0061] 5A, portions 510-1 to 510-4 of a first image 500-1 in the form of spots may be identified by image segmentation. The centroids of the first spot 510-1 and the second spot 510-2 may then be calculated for the frame of the first image 500-1, and the distance between these centroids may be determined by the processor 126 as the value of the spatial distribution indicator. The determined distance indicates the distance separation Sa between the first spot 510-1 and the second spot 510-2.

[0062] Configuring illumination device 122 to provide point illumination of eye 110 so that specular highlights 128 comprise spots, i.e., round or substantially round bright regions (e.g., as shown at 128-1 through 128-4 in FIG. 3 and 510-1 through 510-4 in FIG. 5A), may provide the above-described advantage of enabling the spots and their spacing to be reliably and accurately detected regardless of the degree of focus (i.e., blur) of the acquired image. This is because these round (or rounded) specular highlights stand out from the surrounding areas in image 127-1, which are generally much less bright, and the location of the centroid of each of the highlights is largely unaffected by the degree of focus and / or size of the highlights in image 127-1.

[0063] In process S3 of Fig. 7, the processor 126 determines a first representation Id1 of the distance d between the ophthalmic device 120 and the eye 110 using the determined values ​​of the spatial distribution indicator and a mapping M that maps the values ​​of the spatial distribution indicator to corresponding values ​​indicative of the distance d between the ophthalmic device 120 and the eye 110. Fig. 8 shows a representation in the form of a table 800 of the mapping M used in this example of embodiment to determine the first representation Id1 of the distance d. The table 800 includes a first column 801 with values ​​SDv1, SDv2, ... SDvn of the spatial distribution indicator and a second column 802 with corresponding values ​​LDv1, LDv2, ... LDvn of the distance d along the z-axis between the ophthalmic device 120 and the eye 110. However, the form of the mapping M is not limited to this and may be defined, for example, by a function. The mapping M may be determined by calibration, specifically by acquiring a set of images of the eye 110 at different measurement distances from the ophthalmic device 120 and determining how the measured distance separation between a pair of specular highlight spots varies with distance.

[0064] In this manner, the processor 126 determines a first representation Id1 of the distance d using the specular reflection 128 in the first image 127-1 acquired by the first camera 124-1. This distance measurement technique can be used to quickly determine the distance d when coarsely aligning the subject 111 with the ophthalmic imaging device 140.

[0065] 7 relate to adjusting the distance d between the ophthalmic device 120 and the eye 110, which may be performed using the first image 127-1 acquired by the first camera 124-1. These processes are optional and may be omitted if the distance measurement techniques described above are used for other purposes (e.g., simply to provide information about the distance d).

[0066] In process S4 of FIG. 7, processor 126 determines whether the distance d indicated by first representation Id1 is within a first range R1 of predetermined values. The first range R1 may be, for example, a span of values ​​of distance d for which the image captured by imaging device 124 has a measured image quality, measured by image sharpness (i.e., clarity), that exceeds a predetermined threshold. Sharpness may be quantified in various ways, such as by measuring image contrast, which may be done by calculating the variance (or standard deviation) of pixel values. Alternatively, sharpness may be quantified using, for example, a calculated average gradient magnitude or the amount of high-frequency spectral content in a Fast Fourier Transform (FFT) of the image.

[0067] As an example, the range R1 of values ​​for the distance d may be set to correspond to the depth of field of the first camera 124-1, whose limits are defined using a maximum allowable circle of confusion. The maximum allowable circle of confusion may be set for the stereoscopic ranging techniques described herein so that an indication of the distance d can be determined based on the stereo images 127-1 and 127-2 with a confidence level above a predetermined confidence threshold. The range R1 of values ​​may alternatively be defined as a predetermined distance range centered on the exit pupil position of the first camera 124-1 (e.g., within 1%, 5%, or 10% of the distance to the exit pupil position). In some example embodiments, the boundaries of the first predetermined range R1 of values ​​may be set to respectively result in a minimum and maximum size of the eye 110 captured in the image 127-1.

[0068] For example, FIGS. 5A and 5B show images 500-1 and 500-2 acquired when the corresponding distance between the ophthalmic device 120-1 and the eye 110 was outside a first predetermined range of values ​​R1. Image 500-1 was acquired by the first camera 124-1 when it was too far from the eye 110 to acquire a focused image. In this case, the value of the distance d indicated by the first representation Id1 is outside the predetermined first range of values ​​R1. Image 500-2 in FIG. 5B was acquired by the first camera 124-1 when it was approximately close enough to the eye 110 for the first and second cameras 124-1 and 124-2 to acquire stereo images suitable for use in the stereoscopic ranging process described below in connection with FIG. 9. In this case, the value of the distance d indicated by the first representation Id1 is within the predetermined first range of values ​​R1. FIG. 5C shows an image 500-3 that was acquired too close to the eye 110, such that the value of the distance d indicated by the first representation Id1 is not within the predetermined first range of values ​​R1.

[0069] If the value of the distance d indicated by the first display Id1 is determined not to be within the predetermined first range of values ​​R1 in process S4, then in process S5 of FIG. 7 , the processor 126 generates a first control signal Cs1 to adjust the distance d between the ophthalmic device 120 and the eye 110 toward the predetermined first range of values ​​R1. The first control signal Cs1 may, as in this example embodiment, control the movement mechanism 130 to adjust the distance d toward the predetermined first range of values ​​R1. However, the first control signal Cs1 may alternatively instruct the operator to control the movement mechanism 130 to adjust the distance d toward the first range of values ​​R1, as described above.

[0070] In some example embodiments, the processor 126 loops back from process S5 to process S1 of FIG. 7, thus repeating processes S1-S5 by acquiring a new first image of the eye 110 in an iteration of process S1, subsequently processing the new first image in an iteration of processes S2 and S3, and repeating processes S4 and S5 based on the newly determined value of the distance before looping back to process S1 again. This iteration of processes S1-S5 continues until the value of the distance d indicated by the first representation Id1 is determined to be within the predetermined first value range R1 in the iteration of process S4. That is, the processor 126 acquires additional images of the eye 110 captured by the first camera 124-1, then processes these images to determine the respective values ​​of the first representation Id1 of the distance d, and performs the determination of process S4 for each of the images. If the value of the distance d indicated by the first representation Id1 is determined to be within the predetermined first value range R1 in the iteration of process S4, the process proceeds to S6 of FIG. 9.

[0071] FIG. 9 is a flow diagram illustrating further processes executed by the processor 126 when the value of the distance d indicated by the first representation Id1 is determined to be within the predetermined first range R1 in S4 of FIG. 7 . These further processes implement a stereoscopic distance measurement technique that may be performed after the distance measurement technique based on the analysis of the specular reflection 128 described above. However, these further processes are optional and may be omitted. In that case, the ophthalmic imaging device 140 may begin imaging the eye 110 in response to the processor 126 determining in process S4 of FIG. 7 that the value of the distance indicated by the determined representation Id1 is within the predetermined first range R1. In either case, the processor 126 may perform the following steps after determining that the value of the distance indicated by the determined representation Id1 is within the predetermined first range R1. In process S4, an indicator is generated indicating that no adjustment of the distance d between the ophthalmic device 120 and the eye 110 is required based on the determined first representation Id1 of the distance d.

[0072] 9, the processor 126 may process both the first image 127-1 captured by the first camera 124-1 and the second image 127-2 captured by the second camera 124-2 using any known stereoscopic ranging technique that estimates distance using concepts of parallax and triangulation to determine a second representation Id2 of the distance d between the ophthalmic device 120 and the eye 110. For example, the processor 126 may determine the second representation Id2 by processing each of the acquired images to locate the pupil centers of each of the pupils in the image, mapping the located pupil centers to a common image frame, determining a distance interval between the pupil centers in the common image frame, and determining the second representation Id2 of the distance d using the determined distance interval that is inversely proportional to the distance d.

[0073] 9, the processor 126 determines whether the distance d indicated by the second representation Id2 is within a predetermined second range of values ​​R2. The predetermined second range of values ​​R2 may be, as in this example embodiment, a range of values ​​for the distance d within which the exit pupil position FP of the ophthalmic imaging device 140 is within a predetermined portion of the eye 110 (along the z-axis) suitable for imaging the eye 110. For example, the range of values ​​for the distance d may be such that the exit pupil position FP of the ophthalmic imaging device 140 is within a predetermined axial distance (e.g., within 0.01 mm, 0.1 mm, or 1 mm) of the pupil plane of the eye 110.

[0074] In process S8 of FIG. 9 , if the determination in process S7 is that the distance d indicated by the second indication Is2 is outside the second predetermined range of values ​​R2, the processor 126 generates a second control signal Cs2 to adjust the distance d between the ophthalmic apparatus 120 and the eye 110 toward the second predetermined range of values ​​R2. The second control signal Cs2 may be used to adjust the distance d as described above with respect to the first control signal Cs1. If the second predetermined range of values ​​R2 is such that the exit pupil position FP of the ophthalmic imaging device 140 is within a predetermined portion of the eye 110, the second control signal Cs2 adjusts the distance d toward the second predetermined range of values ​​R2, and due to the configuration of the movement mechanism 130 that simultaneously moves the exit pupil position FP of the ophthalmic imaging device 140 and the ophthalmic apparatus 120 toward and away from the eye 110 (as described above), this results in a simultaneous adjustment of the exit pupil position FP toward the predetermined portion of the eye.

[0075] In some example embodiments, the processor 126 repeats processes S6 to S8 until it determines that the distance d indicated by the second representation Id2 repeatedly determined in the repetitions of process S7 is within a second predetermined value range R2, as shown in Figure 9. In this case, the processor 126 acquires additional stereo images of the eye captured by the first camera 124-1 and the second camera 124-2 in process S9 of each repetition, and then processes these newly acquired images in the repetition of process S6 to determine each second representation Id2 of the distance d between the ophthalmic device 120 and the eye 110 before making the determination in process S7 using the most recent second representation Id2 in each repetition.

[0076] If the determination in process S7 of FIG. 9 is that the distance d indicated by the determined second display Is2 is within a second predetermined value range R2, the ophthalmic imaging device 140 may, in some example embodiments, begin imaging the eye 110.

[0077] In the foregoing description, exemplary aspects have been described with reference to several exemplary embodiments. Accordingly, the present specification should be considered illustrative rather than restrictive. Similarly, the diagrams shown in the drawings that highlight the functionality and advantages of the exemplary embodiments are presented for illustrative purposes only. The architecture of the exemplary embodiments is sufficiently flexible and configurable that it may be utilized in ways other than those shown in the accompanying figures.

[0078] Some aspects of the examples presented herein, such as the functionality of processor 126, may be provided as computer programs, or software, e.g., one or more programs having instructions or sequences of instructions contained in or stored on an article of manufacture, such as a machine-accessible or machine-readable medium, instruction store, or computer-readable storage device, each of which may be non-transitory in one example embodiment. The programs or instructions on the non-transitory machine-accessible medium, machine-readable medium, instruction store, or computer-readable storage device may be used to program a computer system or other electronic device. Machine- or computer-readable medium, instruction store, and storage device may include, but is not limited to, floppy diskettes, optical disks, and magneto-optical disks, or other types of media / machine-readable medium / instruction store / storage device suitable for storing or transmitting electronic instructions. The techniques described herein are not limited to any particular software configuration; they may find applicability in any computing or processing environment. As used herein, the terms "computer-readable," "machine-accessible medium," "machine-readable medium," "instruction store," and "computer-readable storage device" are intended to include any medium that can store, encode, or transmit instructions or sequences of instructions for execution by a machine, computer, or computer processor, causing the machine / computer / computer processor to perform any one of the methods described herein. Furthermore, it is common in the art to refer to software, in one form or another (e.g., program, procedure, process, application, module, unit, logic, etc.), as taking an action or causing a result. Such expressions are merely a shorthand way of stating that execution of the software by a processing system causes the processor to perform an operation to produce a result.

[0079] Some or all of the functionality of processor 126 may also be implemented by the preparation of application specific integrated circuits, field programmable gate arrays, or by interconnecting an appropriate network of conventional component circuits.

[0080] The computer program product may be provided in the form of one or more storage media, instruction stores, or storage devices having stored thereon instructions that can be used to cause a computer or computer processor to control or execute any of the procedures of the example embodiments described herein. The storage media / instruction storage devices may include, by way of example and not limitation, optical disks, ROM, RAM, EPROM, EEPROM, DRAM, VRAM, flash memory, flash cards, magnetic cards, optical cards, nanosystems, molecular memory integrated circuits, RAID, remote data storage / archive / warehousing, and / or any other type of device suitable for storing instructions and / or data.

[0081] Some implementations, stored on any one of one or more computer-readable media, one or more instruction stores, or one or more storage devices, include software for controlling both the system's hardware and for enabling the system or microprocessor to utilize the results of the exemplary embodiments described herein to interact with a human user or other mechanism. Such software may include, but is not limited to, device drivers, operating systems, and user applications. Finally, such computer-readable media or storage devices further include software for performing exemplary aspects of the present invention, as described above.

[0082] The programming and / or software of the system includes software modules for performing the procedures described herein. In some exemplary embodiments herein, the modules include software, while in other exemplary embodiments herein, the modules include hardware or a combination of hardware and software.

[0083] While various exemplary embodiments of the present invention have been described above, it should be understood that they are presented by way of example, not limitation. Various changes in form and detail will be apparent to those skilled in the art. Therefore, the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

[0084] While this specification contains details of many specific embodiments, these should not be construed as limitations on the scope of any invention or what may be claimed, but rather as descriptions of features unique to the particular embodiments described herein. Certain features described herein in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable subcombination. Furthermore, while features may be described above as acting in particular combinations and initially claimed as such, one or more features from a claimed combination may, in some cases, be deleted from the combination, and a claimed combination may be directed to a subcombination or a variation of a subcombination.

[0085] In certain circumstances, multitasking and parallel processing may be advantageous. Furthermore, the spacing of the various components in the foregoing embodiments should not be understood to require such spacing in all embodiments, and it should be understood that the described program components and systems may generally be integrated together in a single software product or packaged into multiple software products.

[0086] Having now described several exemplary embodiments and implementations, it should be apparent that the foregoing is presented by way of example, not limitation. In particular, while many of the examples presented herein involve particular combinations of device or software elements, those elements may be combined in other ways to achieve the same purpose. Operations, elements, and features discussed only in connection with one embodiment are not intended to be excluded from a similar role in other embodiments or implementations.

Claims

1. an ophthalmic device (120) configured to determine an indication of a distance (d) between the ophthalmic device (120) and the subject's eye (110); an illumination device (122) operable to illuminate the eye (110); an imaging device (124) operable to acquire an image (127; 127-1) of said eye (110); Equipped with the illumination device (122) and the imaging device (124) are arranged such that the image (127; 127-1) of the eye (110) includes specular highlights (128) from the illumination device (122) having a spatial distribution in the image (127; 127-1) that varies with the distance (d) between the ophthalmic apparatus (120) and the eye (110); a processor (126) comprising: processing said image (127; 127-1) to determine values ​​of spatial distribution indicators characteristic of said spatial distribution; determining the indication of the distance (d) between the ophthalmic device (120) and the eye (110) using the determined values ​​of the spatial distribution indicator and at least one mapping (M) that maps the values ​​of the spatial distribution indicator to corresponding values ​​indicative of the distance (d) between the ophthalmic device (120) and the eye (110); An ophthalmic device (120) configured to:

2. the illumination device (122) is operable to illuminate the eye (110) from at least two different positions such that the specular highlight (128) in the image includes a first portion (128-1) and a second portion (128-2) that are spaced apart from one another in the image (127-1); the illumination device (122) and the imaging device (124) are positioned such that a distance between the first portion (128-1) of the specular highlight (128) and the second portion (128-2) of the specular highlight (128) varies with the distance (d) between the ophthalmic device (120) and the eye (110); The value of the spatial distribution indicator indicates a distance interval between the first portion (128-1) and the second portion (128-2) in the image (127-1). The ophthalmic device (120) of claim 1.

3. 3. The ophthalmic apparatus of claim 2, wherein the illumination devices are configured to provide point illumination of the eye from the at least two different positions such that the first portion of the specular highlight is a first spot in the image and the second portion of the specular highlight is a second spot in the image.

4. the illumination device (122) and the imaging device (124) are configured such that the specular highlight (128) has a size or shape that varies with the distance (d) between the ophthalmic device (120) and the eye (110); the processor (126) is configured to process the image (127) to determine a spatial distribution indicator value indicative of the size or shape of the specular highlight (128); The ophthalmic device (120) of claim 1.

5. An ophthalmic device (120) according to any one of claims 1 to 4; a movement mechanism (130) operable to move the ophthalmic device (120) toward and away from the eye (110), such that the spatial distribution of the specular highlights (128) in the image (127) changes with the movement; Equipped with the processor (126) is further configured to determine whether the distance indicated by the determined indication is within a predetermined range of values, and if the distance indicated by the determined indication is outside the predetermined range of values, generate a control signal (Cs) for adjusting the distance (d) by the movement mechanism (130) toward the predetermined range of values. System (100).

6. the ophthalmic apparatus (120) is a stereo imaging apparatus comprising a further imaging device (124-2) operable to acquire a further image (127-2) of the eye (110); If the distance indicated by the determined indication is within the predetermined range of values, the processor (126) processing the acquired images (127-1, 127-2) using stereo ranging techniques to determine a second indication of the distance (d) between the ophthalmic device (120) and the eye (110); determining whether the distance indicated by the determined second indication is within a second predetermined range of values, and if the distance indicated by the second indication is outside the second predetermined range of values, generating a second control signal to cause the movement mechanism to adjust the distance (d) between the ophthalmic device (120) and the eye (110) toward the second predetermined range of values. The system (100) of claim 5, further configured to:

7. 7. The system of claim 6, wherein the processor is configured to determine the second representation of the distance between the ophthalmic device and the eye by processing each image of the acquired images to locate a pupil center of each of the pupils in the images, mapping the located pupil centers to a common image frame, determining a separation between the pupil centers in the common image frame, and determining the second representation of the distance based on the determined separation between the pupil centers.

8. an ophthalmic imaging device (140) for imaging the eye (110) through an exit pupil position (FP) of the ophthalmic imaging device (140); the moving mechanism (130) is configured to simultaneously move the exit pupil position (FP) and the ophthalmic device (120) toward and away from the eye (110); the exit pupil position (FP) and the ophthalmic apparatus (120) are positioned relative to each other such that the exit pupil position (FP) of the ophthalmic imaging device (140) is within a range of positions for imaging the eye (110) when the distance between the ophthalmic apparatus (120) and the eye (110) is within the predetermined value range. The system (100) of claim 5.

9. 1. A method for determining an indication of a distance between an ophthalmic device (120) and an eye (110) of a subject, comprising: acquiring (S1) an image (127; 127-1) of the eye (110) using illumination that produces specular highlights (128) in the image, the specular highlights (128) having a spatial distribution in the image (127) that varies with the distance (d) between the ophthalmic device (120) and the eye (110); processing the image (127) to determine (S2) values ​​of spatial distribution indicators characteristic of the spatial distribution; determining (S3) the indication of the distance (d) between the ophthalmic device (120) and the eye (110) using the determined values ​​of the spatial distribution indicator and at least one mapping (M) that maps the values ​​of the spatial distribution indicator to corresponding values ​​indicative of the distance between the ophthalmic device (120) and the eye (110); The method includes:

10. the eye (110) is illuminated from at least two different positions such that the specular highlight (128) in the image (127-1) includes a first portion (128-1) and a second portion (128-2) that are spaced apart from one another in the image (127-1); a distance between the first portion (128-1) of the specular highlight (128) and the second portion (128-2) of the specular highlight (128) varies with a distance (d) between the ophthalmic device (120) and the eye (110); the value of the spatial distribution indicator indicates a distance interval between the first portion (128-1) and the second portion (128-2) in the image (127-1); 10. The method of claim 9.

11. 11. The method of claim 10, wherein point illumination of the eye (110) is provided from the at least two different positions such that the first portion (128-1) of the specular highlight (128) is a first spot in the image (127-1) and the second portion (128-2) of the specular highlight (128) is a second spot in the image (127-1).

12. the specular highlight (128) has a size or shape that varies with the distance (d) between the ophthalmic device (120) and the eye (110); the image (127) is processed to determine a value of the spatial distribution indicator that is indicative of the size or shape of the specular highlight (128); 10. The method of claim 9.

13. 13. The method of claim 9, further comprising: determining whether the distance (d) indicated by the determined indication is within a predetermined range of values; and, if the distance (d) indicated by the determined indication is outside the predetermined range of values, generating a control signal (Cs) for adjusting the distance between the ophthalmic device (120) and the eye (110) toward the predetermined range of values.

14. further comprising acquiring (S1A) a further image (127-2) of the eye (110) such that the image (127-1) and the further image (127-2) are stereo images of the eye (110); if the distance indicated by the determined indication is within the range of the predetermined value; processing the stereo images (127-1, 127-2) using stereo ranging techniques to determine a second representation of the distance between the ophthalmic device (120) and the eye (110); determining whether the distance indicated by the determined second representation is within a second predetermined range of values; a process for generating a second control signal to adjust the distance between the ophthalmic device (120) and the eye (110) toward the second predetermined range of values ​​when the distance indicated by the second indication is outside the second predetermined range of values; The method of claim 13 further comprising:

15. 15. The method of claim 14, wherein the second representation of the distance between the ophthalmic device and the eye is determined by processing each image of the acquired images to locate a pupil center of each of the pupils in the image, mapping the located pupil centers to a common image frame, determining a separation between the pupil centers in the common image frame, and determining the second representation of the distance based on the determined separation between the pupil centers.

Images