Auto-focus for retinal imaging system

Abstract

A system, apparatus, and method of operation for focusing a retinal image are described herein. In an embodiment, the retinal imaging system comprises an eyepiece lens assembly; a structured light assembly configured to emit structured illumination light through the eyepiece lens assembly for receipt by an eye positioned adjacent to the eyepiece lens assembly and opposite the structured light assembly; a retinal image sensor optically coupled to the eyepiece lens assembly, wherein the retinal image sensor is positioned to receive the structured illumination light from the eye and is configured obtain a retinal image of a retina of the eye. In an embodiment, the method includes emitting structured illumination light through the eyepiece lens assembly; generating a retinal image based on the structured illumination light received from the retina of the eye; and measuring an edge strength of the structured illumination light from the retinal image.

Description

AUTO-FOCUS FOR RETINAL IMAGING SYSTEMCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of and priority7to U.S. Provisional Application No. 63 / 558,713, filed on February 28, 2024. the contents of which are hereby incorporated by reference.TECHNICAL FIELD

[0002] This disclosure relates generally to retinal imaging, and, in particular but not exclusively, relates to focusing an image of a retinal imaging system.BACKGROUND INFORMATION

[0003] Retinal imaging is a part of basic eye exams for screening, field diagnosis, and progress monitoring of many retinal diseases. A high-fidelity retinal image is important for accurate screening, diagnosis, and monitoring.

[0004] Certain retinal systems and methods use auto-focus (AF) components and methods, such as in which a system automatically focusses or attempts to automatically focus optics onto a retina for measurement. Some AF is based on finding tissue features in low-contrast infrared (IR) illumination. Optic disk / blood vessel segmentation used to find location of maximum contrast can be difficult to find due to poor contrast, made even worse in out-of-focus images.BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Non-limiting and non-exhaustive embodiments of the claimed subject matter are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified. Not all instances of an element are necessarily labeled so as not to clutter the drawings where appropriate. The drawings are not necessarily7to scale, emphasis instead being placed upon illustrating the principles being described.

[0006] FIG. 1 is an image of a retina under infrared illumination.

[0007] FIG. 2 is an image of a retina illuminated with structured illumination light according to an embodiment of the present disclosure.

[0008] FIG. 3 is a schematic illustration of a retinal imaging system according to an embodiment of the present disclosure.

[0009] FIG. 4 is a schematic illustration of a retinal imaging system according to an embodiment of the present disclosure.

[0010] FIG. 5 is a schematic illustration of a retinal imaging system according to an embodiment of the present disclosure.

[0011] FIG. 6A is a table comparing a tilt angle and slit length of a light structuring element and a range of diopter power according to an embodiment of the present disclosure.

[0012] FIG. 6B is a series of images of a retina illuminated by structured light illumination generated by a tilted slit according to an embodiment of the present disclosure.

[0013] FIG. 7A is a perspective view of a light structuring element according to an embodiment of the present disclosure.

[0014] FIG. 7B is a plan view of the light structuring element of FIG. 7A according to an embodiment of the present disclosure.

[0015] FIG. 7C is a cross-sectional view of the light structuring element of FIG. 7A according to an embodiment of the present disclosure.

[0016] FIG. 7D is a side view of the light structuring element of 7A according to an embodiment of the present disclosure.

[0017] FIG. 8 is a schematic view of a retinal imaging system of the present disclosure.

[0018] FIG. 9 is a block diagram of a method according to an embodiment of the present disclosure.DETAILED DESCRIPTION

[0019] Embodiments of a system, apparatus, and method of operation for focusing a retinal image are described herein. In the following description numerous specific details are set forth to provide a thorough understanding of the embodiments. One skilled in the relevant art will recognize, however, that the techniques described herein can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring certain aspects.

[0020] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0021] As discussed further herein, the present disclosure provides systems and methods that take advantage of the low contrast of retinal tissue, such as under infrared (IR) illumination. FIG. 1 is an image of a retina under infrared illumination. As shown, the image provides generally low contrast, which can be very challenging when trying to automatically focus the image.

[0022] In certain embodiments, the retinal imaging systems and methods of the present disclosure use an edge strength of projected structured illumination (SI) patterns on the retina to autofocus the retinal imaging system optics. An example of structured illumination received by a retinal image sensor from a retina of an eye is provided in FIG. 2. As shown, the structured illumination image of FIG. 2 provides higher contrast than the unstructured illumination image of FIG. 1, and, as described further herein, is advantageous for automatically focusing the structured light image.

[0023] In an embodiment, structured illumination or structured light refers to light having a known pattern or structure, which can be projected or emitted onto a scene, such as onto a retina of an eye. An edge strength between, on the one hand, a portion of the scene illuminated by the structured illumination light and, on the other hand, a portion of the scene not illuminated by the structured illumination light can provide greater contrast than an image of the scene illuminated by unstructured light, which is advantageous in focusing optics on to the scene, such as automatically focusing optics on to the scene.

[0024] In certain embodiments, an SI pattern location is fixed and does not move with gaze angle and retina shift. In this regard, it is not necessary to segment and track retina features over time in focusing a retinal image.

[0025] Accordingly, in an aspect, the present disclosure provides a retinal imaging system. In an embodiment, the retinal imaging system comprises an eyepiece lens assembly; a structured light assembly configured to emit structured illumination light through the eyepiece lens assembly for receipt by an eye positioned adjacent to theeyepiece lens assembly and opposite the structured light assembly; a retinal image sensor optically coupled to the eyepiece lens assembly, wherein the retinal image sensor is positioned to receive the structured illumination light from the eye and is configured to obtain a retinal image of a retina of the eye; and a controller operatively coupled to the retinal image sensor, the structured light assembly, and the eyepiece lens assembly. In an embodiment, the controller includes logic that, when executed, causes the retinal imaging system to perform operations. In an embodiment, the operations comprise emitting, with the structured light assembly, structured illumination light through the eyepiece lens assembly; generating, with the retinal image sensor, a retinal image based on the structured illumination light received from the retina of the eye; and measuring an edge strength of the structured illumination light from the retinal image.

[0026] Attention is now directed to FIG. 3 in which a schematic illustration of a retinal imaging system 300 according to an embodiment of the present disclosure is shown. In the illustrated embodiment, the retinal imaging system 300 is shown to include an eyepiece lens assembly 302 and a structured light assembly 304 configured to emit structured illumination light 306 through the eyepiece lens assembly 302 for receipt by an eye 308 positioned adjacent to the eyepiece lens assembly 302 and opposite the structured light assembly 304 from the structured light assembly 304.

[0027] In an embodiment, the structured light assembly 304 is configured to emit light that is not visible to an eye, such as a human eye. In an embodiment, the structured light assembly 304 is configured to emit infrared (IR) light, such as infrared light comprising wavelengths in a range of about 700 nm to about 1,100 nm. Light that is not visible to an eye 308 generally does not cause a pupil of the eye 308 to constrict and, thus, a retina 312 of the receives more structured illumination light 306 than if the pupil constricted, such as upon receipt of illumination by visible light.

[0028] In the illustrated embodiment, the retinal imaging system 300 also includes a retinal image sensor 310 optically coupled to the eyepiece lens assembly 302. In an embodiment, the retinal image sensor 310 is positioned to receive the structured illumination light 306 from the eye 308 and is configured to obtain a retinal image of a retina 312 of the eye. In this regard, the retinal image sensor 310 is positioned to image or otherwise detect structured illumination light 306 that has been reflected, scattered, or is otherwise directed from the retina 312 to the retinal image sensor 310. As discussed further herein, such structured illumination light 306 from the retina 312, suchas an edge strength of the structured illumination light 306, can be used to automatically focus a retinal image.

[0029] As shown, the retinal imaging system 300 also includes beam splitters 339 and 338 configured to split abeam of structured light illumination 306 and provide a display image from the display 344 to the eye 308. In an embodiment, the display 344 is configured to emit infrared light, such as structured infrared illumination, such as from infrared emitters or infrared backlight to generate structured illumination. In such a configuration, the display 344 configured to provide structured illumination light can replace structured illumination source 304.

[0030] The retinal imaging system 300 is also shown to includes lenses 340, such as for shaping or focusing structured illumination light 306. In an embodiment, lenses 340 are configured to focus an image of the retina 312 onto the retinal image sensor 310, as well as structured illumination from the retina 312. In an embodiment, the controller 314 adjusts the lenses 340 based on measurements, such as based on an edge strength of the structured illumination light 306 received from the retina 312.

[0031] In the illustrated embodiment, the retinal imaging system 300 is also shown to include a retinal illuminator 334 configured to illuminate the retina 312, such as with unstructured illumination light. As discussed further herein, the retinal illuminator 334 can be used to illuminate the retinal with unstructured illumination light to obtain or capture an image of the retina 312 illuminated with the unstructured illumination light. In an embodiment, the retinal illuminator 334 is configured to emit unstructured illumination light configured to illuminate all of the retina. In an embodiment, the retinal illuminator 334 is configured to emit unstructured illumination light that includes visible unstructured illumination light, such as visible unstructured illumination light comprising wavelengths between 400 nm and 700 nm.

[0032] The retinal imaging system 300 is shown to comprise a controller 314, illustrated here operatively coupled to various retinal imaging system 300 components, such as the retinal image sensor 310, the structured light assembly 304, and the eyepiece lens assembly 302. such as to choreograph their operation. In embodiments, the controller 314 includes logic that, when executed, causes the retinal imaging system 300 to perform operations, such as one or more methods of the present disclosure. The controller 314 may include software / firmware logic executing on a microcontroller 314, hardware logic (e.g., application specific integrated circuit, field programmable gate array, etc.), or a combination of software and hardware logic. Although FIG. 3 illustratescontroller 314 as a distinct functional element, the logical functions performed by controller 314 may be decentralized across a number hardware elements. The controller 314 may further include input / output (I / O ports), communication systems, or otherwise.

[0033] As discussed further herein, the controller 314 is configured to perform operations to emit structured illumination light 306, generate a retinal image based on structured illumination light 306 received from a retina 312, and measure an edge strength of the structured illumination light 306 in the retinal image. In particular, the operations can include, for example, emitting, with the structured light assembly 304, structured illumination light 306 through the eyepiece lens assembly 302; generating, with the retinal image sensor 310, a retinal image based on the structured illumination light 306 received from the retina 312 of the eye; and measuring an edge strength of the structured illumination light 306 from the retinal image.

[0034] The operations can further include adjusting a focus focal length of the retinal imaging system 300 based on the edge strength of the structured illumination light 306. In an embodiment, adjusting the focus can include moving retinal image sensor 310 and the beam splitters 338 and 339 closer or farther away from the eyepiece lens assembly 302. In an embodiment adjusting the focus can also include moving the display 344, the beam splitter 339, and the structured light assembly closer or farther away from the eyepiece lens assembly 302. In an embodiment, adjusting the focus of the retinal imaging system 300 includes adjusting a focal length of lenses 340.

[0035] In an embodiment, the present disclosure provides a retinal imaging system including a structured light assembly comprising a light source configured to emit illumination light and a light structuring element configured to structure the illumination light, such as by blocking a portion of the illumination light from reaching an eyepiece lens assembly.

[0036] In this regard, attention is directed to FIG. 4 in which a schematic illustration of a retinal imaging system 400 according to an embodiment of the present disclosure is provided.

[0037] As shown, the retinal imaging system 400 is shown to include an eyepiece lens assembly 402; a structured light assembly 404 configured to emit structured illumination light 406 through the eyepiece lens assembly 402 for receipt by an eye 408 positioned adjacent to the eyepiece lens assembly 402 and opposite the structured light assembly 404; a retinal image sensor 410 optically coupled to theeyepiece lens assembly 402, wherein the retinal image sensor 410 is positioned to receive the structured illumination light 406 from the eye 408 and is configured to obtain a retinal image of a retina 412 of the eye 408. The retinal imaging system 400 is also shown to include a controller 414 configured to choreograph operation of various components operatively coupled to the controller 414, such as to perform one or more methods of the present disclosure.

[0038] As shown, the structured light assembly 404 comprises a light source 416 configured to emit structured illumination light 406 onto the eyepiece lens assembly 402 for receipt of the eye 408, particularly the retina 412 of the eye 408, positioned adjacent to the eyepiece lens assembly 402; and a light structuring element 418 shaped and positioned to preclude a portion of the illumination light from reaching the eyepiece lens assembly 402 to provide structured illumination light 406 thereon. In the illustrated embodiment, the light structuring element 418 is shown to comprise a light baffle 420, such as comprising an optically opaque material, configured to block a first portion of the illumination light. As also shown, the light baffle 420 defines an aperture 422 configured to allow a second portion of the illumination light to reach the eyepiece lens assembly 402, such as in the form of the structured light illumination light 406. The aperture 422 is shown to define a slit 424 shaped to provide the structured illumination light 406 on the eyepiece lens assembly 402 in the form of a slit of structured illumination light 406.

[0039] While a slit 424 is illustrated and described, it will be understood that apertures defining other shapes are possible and within the scope of the present disclosure, such as shapes configured to provide structured illumination light 406, whose edge strength can be measured to aid in autofocusing a retinal image. Additionally, while a structured light assembly 404 comprising a light source 416 and a light baffle 420 are shown and described, it will be understood that other structured light sources or assemblies are possible and within the scope of the present disclosure. As an example, the structured light assembly 404 can include a plurality of light sources, such as a plurality of light-emitting diodes, configured to emit structured light 406. In an embodiment, light sources of the plurality of light sources are arranged to emit structured light 406, such as in the form of a linear array configured to emit light as if passing through an aperture or slit.

[0040] As shown, the light baffle 420 is positioned conjugate to an intermediate image plane 442 using a beam splitter 438 positioned between the intermediate imageplane 442 and the eyepiece lens assembly 402. In such a configuration, structured illumination light 406 is only perfectly in focus for eyes with 0 diopter correction. However, as discussed further herein, a best focus (i.e., the closest the system 400 can focus structured light onto the retina 412) of the structured illumination light 406 can nevertheless be used when the retina 412 was focused.

[0041] In the illustrated embodiment, the retinal imaging system 400 is shown to include a diffuser 436 configured to diffuse the illumination light. As shown, the diffuser 436 is positioned between the light source 416 and the light structuring element 418. In this regard, light received by the light baffle 420 is diffuse light, such as diffuse IR light, which subsequently passes through the aperture 422 to provide diffuse structured illumination light 406 to the eyepiece lens assembly 402.

[0042] The retinal imaging system 400 is shown to further include a display 444, such as a display 444 configured to provide a fixation or alignment target to the eye 408, beam splitter 439 configured to split beam of light, such as beams of light from the display 444 for receipt by the eye 408 and beams of light from the eye 408 for receipt by the retinal image sensor 410. The retinal imaging system 400 is also shown to include lenses 440 for focusing or otherwise shaping light passing through the retinal illuminator 434 configured to illuminate the retina 412.

[0043] In an embodiment, the present disclosure provides a retinal imaging system including a slanted or tilted light structuring element that is slanted or tilted relative to an optical axis of the retinal imaging system. In this regard, attention is directed to FIG. 5 in which a retinal imaging system 500 according to an embodiment of the present disclosure is illustrated. FIG. 5 is a schematic illustration of the retinal imaging system 500.

[0044] In the illustrated embodiment, the retinal imaging system 500 is shown to include an eyepiece lens assembly 502; a structured light assembly 504 configured to emit structured illumination light 506 through the eyepiece lens assembly 502 for receipt by an eye 508 positioned adjacent to the eyepiece lens assembly 502 and opposite the structured light assembly 504; a retinal image sensor 510 optically coupled to the eyepiece lens assembly 502, wherein the retinal image sensor 510 is positioned to receive the structured illumination light 506 from the eye 508 and is configured to obtain a retinal image of a retina 512 of the eye 508; and a controller 514 operatively coupled to the retinal image sensor 510, the structured light assembly 504. and the eyepiece lens assembly 502. In an embodiment, the controller 514 includes logic that.when executed, causes the retinal imaging system 500 to perform operations, such as operations for performing one or more methods of the present disclosure. As shown, the retinal imaging system 500 further includes lenses 540 shaped to focus or otherwise structure light received by the retinal image sensor 510. The retinal imaging system 500 is shown to include a display 544 and beam splitter 539 configured to provide an image, such as a fixation target, to the eye 508 to aid in retinal alignment with the retinal imaging system 500.

[0045] As shown, the structured light assembly 504, positioned between the retinal illuminator 534 and the image plane 542, comprises a light source 516 configured to emit illumination light onto the eyepiece lens assembly 502 for receipt of the eye 508 positioned adjacent to the eyepiece lens assembly 502; and a light structuring element 518 shaped and positioned to preclude a portion of the illumination light from reaching the eyepiece lens assembly 502 to provide structured illumination thereon. As shown, the structured light assembly 504 further includes a diffuser 536 configured to diffuse light from the light source 516, where the diffuser 536 is positioned between the light source 516 and the light baffle 520. The retinal imaging system 500 is further shown to include a retinal illuminator 534 configured to illuminate the retina 512 with unstructured illumination light suitable for generally imaging the retina 512.

[0046] As shown, the beam splitter 538 is positioned in front of the IIP and uses projector lens 540 to locate an image of slit 524 at IIP. As previously discussed, an image of the structured illumination light 506 received from the retina 512 would only truly be in focus for eyes with 0 diopter correction, but a best focus could still be used or determined from an edge strength of the structured illumination light 506 received by the retinal image sensor 510 from the retina 512 when retina 512 was focused.

[0047] In the illustrated embodiment, the light structuring element 518 comprises a light baffle 520 configured to block a first portion of the illumination light, wherein the light baffle 520 defines an aperture 522 configured to allow a second portion of the illumination light to reach the eyepiece lens assembly 502. In particular, the aperture 522 defines a slit 524 shaped to provide the structured illumination light 506 on the eyepiece lens assembly 502 in the form of a slit of structured illumination light 506.

[0048] The retinal image sensor 510 and the eyepiece lens assembly 502 are shown positioned aligned with an optical axis 526 of the retinal imaging system 500. As also shown, a major axis 528 of the light baffle 520 is positioned neither parallel tonor orthogonal to the optical axis 526. Rather, in the illustrated embodiment, the major axis 528 of the light baffle 520 is oriented at an angle between orthogonal and parallel to the optical axis 526. In this regard, the light baffle 520 and the slit 524 defined therein may be described as titled relative to the optical axis 526.

[0049] By placing portions of the slit 524 at various distances from the retina 512 through tilting the slit 524, the structured illumination light 506 spans a range of diopters, as shown in FIG. 6A, which is a table comparing a tilt angle and slit 524 length of a light structuring element 518 and a range of diopter power according to an embodiment of the present disclosure.

[0050] Correspondingly, a location of narrowest “waist of focus” directly correlates to diopter power of eye. as shown in FIG. 6B. which provides a series of images of a retina 512 illuminated by structured light illumination generated by a tilted slit 524 according to an embodiment of the present disclosure. As shown, a waist of the structured illumination light 506 on the retina 512 is only truly in focus when the retina 512 is in focus, but a location of waist is fixed and can be estimated in blurry images for faster convergence.

[0051] Additionally, as described elsewhere herein, an edge strength of the structured illumination light 506 received by the retinal image sensor 510 can be used to determine a focus of the retinal image. In this regard, the controller 514 can include logic that, when executed, causes the retinal imaging system 500 to perform operations comprising measuring a position along the structured illumination light 506 received from the retina 512 having a highest edge strength. The controller 514 can further include logic that, when executed, causes the retinal imaging system 500 to perform operations comprising determining an optical power of the eye 508 based on the position along the structured light from the retina 512 having the highest edge strength. As shown in FIG. 6B, the position along the structured light having the highest edge strength corresponds to an optical pow er, such as in diopters, of the eye 508.

[0052] The edge strength can also be used to adjust optics of the retinal imaging system 500 to improve focus of the retinal imaging system 500. In this regard, in an embodiment, the controller 514 further comprises logic that, when executed, causes the retinal imaging system 500 to perform operations comprising adjusting the focus of the retinal imaging system 500 so that the position along the structured illumination light 506 from the retina 512 having the highest edge strength is in a middle of the structured illumination light 506 received from the retina 512. When the position along thestructured light from the retina 512 having the highest edge strength is in the middle of the structured illumination light 516. the optics are focused or nearly focused on the retina 512.

[0053] In an embodiment, the present disclosure provides a retinal imaging system comprising a light structuring element comprising two or more apertures. In this regard, attention is directed to FIGS. 7A-7D in which a light structuring element 718 according to an embodiment of the present disclosure is illustrated. FIG. 7A is a perspective view of the light structuring element 718. FIG. 7B is a plan view of the light structuring element 718 of FIG. 7A. FIG. 7C is a cross-sectional view of the light structuring element 718 of FIG. 7A. FIG. 7D is a side view of the light structuring element 718 of 7A.

[0054] In an embodiment, the light structuring element 718 is an example of the light structuring element 416 of FIG. 4 or the light structuring element 516 of FIG. 5. In an embodiment, the light structuring element 718 is a component of structured light assembly 304 described further herein with respect to FIG. 3.

[0055] As above, a tilted slit 724 having various positions at different distances from the retina and / or eyepiece lens assembly (see FIGS. 3, 4, and 5) can span a range of diopters due to the varying distance. In the illustrated embodiment, the light baffle 720 defines a first aperture 722 and a second aperture 732 positioned closer to the eyepiece lens assembly than the first aperture 722. In this regard, the light structuring element 718 comprises two or more apertures positioned at different distances relative to an eyepiece assembly, which are configured to project patterns at different focal points. The tilted first aperture 722 and second aperture 732 are configured to span a wider range of diopters than might otherwise be possible with a single aperture. In this regard, for a given cross-section of the light baffle 720, the varying depths of the first aperture 722 and second aperture 732 can provide a wider range of distances from the retina or eyepiece lens assembly.

[0056] FIG. 8 is a schematic view of a retinal imaging system of the present disclosure. The illustrated embodiment of retinal imaging system 800 includes an eye cup 802, an illuminator 805, an image sensor 810 (also referred to as a retinal image sensor), a controller 815, a user interface 820, a display 825, alignment tracking camera(s) 830, and an optical relay system. The illustrated embodiment of the optical relay system includes lens assemblies 835, 840, 845 and a beam splitter 850. Theillustrated embodiment of illuminator 805 comprises illuminator arrays 865 and a center aperture 855. The illustrated embodiment is shown to include an eye cup 802.

[0057] The optical relay system serves to direct (e.g., pass or reflect) illumination light 880 output from illuminator 805 along an illumination path through the pupil of eye 870 to illuminate retina 875 while also directing image light 885 of retina 875 (i.e., the retinal image) along an imaging path to image sensor 810. Image light 885 is formed by the scattered reflection of illumination light 880 off of retina 875. In the illustrated embodiment, the optical relay system further includes beam splitter 850, which passes at least a portion of image light 885 to image sensor 810 while also optically coupling fixation target 891 to eyepiece lens assembly 835 and directing display light 890 output from display 825 to eye 870. Beam splitter 850 may be implemented as a polarized beam splitter, a non-polarized beam splitter (e.g., 90% transmissive and 10% reflective, 50 / 50 beam splitter, etc.), a dichroic beam splitter, or otherwise. The optical relay system includes a number of lenses, such as lenses 835, 840, and 845, to focus the various light paths as needed. For example, lens 835 may include one or more lensing elements that collectively form an eyepiece lens assembly 835 that is housed within a lens tube (not illustrated in FIG. 8). The eyepiece lens assembly 835 is displaced from the cornea of eye 870 by an eye relief 895 during operation. Lens 840 may include one or more lens elements for bringing image light 885 to a focus on image sensor 810. Lens 845 may include one or more lens elements for focusing display light 890. It should be appreciated that optical relay system may be implemented with a number and variety of optical elements (e.g., refractive lenses, reflective surfaces, diffractive surfaces, etc.) and may vary from the configuration illustrated in FIG. 8.

[0058] In one embodiment, display light 890 output from display 825 represents a fixation target. The fixation target may be an image of a plus-sign, a bullseye, a cross, atarget, or other shape (e.g., see demonstrative fixation target images 891). The fixation target not only can aid with obtaining fine or precise alignment between eyepiece lens 835 and eye 870 by providing visual feedback to the patient, but also gives the patient a fixation target upon which to accommodate and stabilize their vision. Display 825 may be implemented with a variety of technologies including a liquid crystal display (LCD), light emitting diodes (LEDs), various illuminated shapes (e.g., an illuminated cross or concentric circles), or otherwise. Of course, the fixation targetmay be implemented in other manners than a virtual image on a display. For example, the fixation target may be a physical object (e.g., crosshairs, etc.).

[0059] As shown, the eye cup 802 defines a viewing aperture 824 about a longitudinal axis 808 generally in line with the optical relay.

[0060] In the illustrated embodiment, the system 800 is shown to further include a light source 836 configured to emit illumination light through an aperture 822 of light baffle 812 to provide structured illumination light 806. As shown, structured illumination light 806 impinges upon beam splitter 852 and is directed through eyepiece lens assembly 835 and on to the retina 875 of the eye 870. As discussed elsewhere herein, scattered structured illumination light 806 is received by the retinal image sensor 810, which generates a retinal image or other signal whose edge strength can be measured to auto-focus optics of the system 800, such as lens assemblies 835 and / or 840.

[0061] Image sensor 810 may be implemented using a variety of imaging technologies, such as complementary metal-oxide-semiconductor (CMOS) image sensors, charged-coupled device (CCD) image sensors, or otherwise. In one embodiment, image sensor 810 includes an onboard memory buffer or attached memory to store / buffer retinal images.

[0062] Alignment tracking camera(s) 830 operates to track lateral and eye relief offset alignment (or misalignment) between retinal imaging system 800 and eye 870, and in particular, between eyepiece lens assembly 835 and eye 870. Alignment tracking camera 830 may operate using a variety of different techniques to track the relative position of eye 870 to retinal imaging system 800 including pupil tracking, iris tracking, or otherwise. In the illustrated embodiment, alignment tracking camera 830 includes two cameras disposed on either side of eyepiece lens assembly 835 to enable triangulation and obtain X, Y, and Z position information about the pupil or iris. In one embodiment, alignment tracking camera 830 includes one or more infrared (IR) emitters to track eye 870 via IR light while retinal images are acquired with visible spectrum light, and in some cases, with IR light as well.

[0063] Eye position, including lateral alignment and / or eye relief offset alignment, may be measured and tracked using retinal images acquired by image sensor 810 for precise alignment tracking, or separately / additionally, by alignment tracking camera(s) 830. Alignment tracking camera(s) 830 provide coarse alignment tracking via the pupil or iris. In the illustrated embodiment, alignment trackingcamera(s) 830 are positioned externally to view eye 870 from outside of eyepiece lens assembly 835. In other embodiments, alignment tracking camera(s) 830 may be optically coupled via the optical relay components to view and track eye 870 through eyepiece lens assembly 835.

[0064] Controller 815 is coupled to image sensor 810, display 825, illuminator 805, alignment tracking camera 830, and visual guidance indicator 801 to choreograph their operation. Controller 815 may include software / firmware logic executing on a microcontroller, hardware logic (e g., application specific integrated circuit, field programmable gate array, etc.), or a combination of software and hardware logic. Although FIG. 8 illustrates controller 815 as a distinct functional element, the logical functions performed by controller 815 may be decentralized across a number hardware elements. Controller 815 may further include input / output (I / O ports), communication systems, or otherwise. Controller 815 is coupled to user interface 820 to receive user input and provide user control over retinal imaging system 800. User interface 880 may include one or more buttons, dials, feedback displays, indicator lights, etc.

[0065] During operation, controller 815 operates illuminator 805 and retinal image sensor 810 to capture one or more retinal images. Illumination light 880 is directed through the pupil of eye 870 to illuminate retina 875. The scattered reflections from retina 875 are directed back along the image path through aperture 855 to image sensor 810. When eye 870 is properly aligned within the eyebox of system 800, aperture 855 operates to block deleterious reflections and light scattering that would otherwise malign the retinal image while passing the image light itself. Prior to capturing the retinal image, controller 815 operates visual guidance indicator 801 and alignment tracking camera(s) 830 to provide real-time visual feedback to eye 870 to achieve coarse alignment, at which point the user can see the fixation target. Controller 815 further operates display 825 to output a fixation target image 891 to guide the patient's gaze into fine or precise alignment. Once fine alignment is achieved, controller 815 deems eye 870 to be within the eyebox of retinal imaging system 800, and thus acquires a retinal image with image sensor 810.

[0066] FIG. 9 is a flow chart illustrating a process 900 of operating a retinal imaging system. In an embodiment, process 900 is performed on a retinal imaging system of the present disclosure, such as retinal imaging systems 300, 400, 500. and 800, described further herein with respect to FIGS. 3-5 and 8, respectively.

[0067] The order in which some or all of the process blocks appear in process 900 should not be deemed limiting. Rather, one of ordinary skill in the art having the benefit of the present disclosure will understand that some of the process blocks may be executed in a variety of orders not illustrated, or even in parallel.

[0068] In an embodiment, method 900 begins with process block 901, which includes emitting, with a structured light assembly, structured illumination light through an eyepiece lens assembly, to provide structured illumination thereon. In an embodiment, the structured illumination light comprises IR or otherwise non-visible structured illumination light, as discussed elsewhere herein.

[0069] In an embodiment, emitting structured illumination light comprises emitting illumination light through a light structuring element to provide structured illumination light.

[0070] In an embodiment, process block 901 is followed by process block 903, which includes generating, with the retinal image sensor, a retinal image based on the structured illumination light received from the retina of the eye. In an embodiment, the retinal image includes an image of structured illumination light scattered off the retina.

[0071] In an embodiment, process block 903 is followed by process block 905, which includes measuring an edge strength of the structured illumination light from the retinal image. Measuring an edge strength of the structured illumination light can include measuring a sharpness or abruptness of image brightness at a transition from a portion of the retinal image including the structured illumination and a portion of the retinal image that does not include the structured illumination light. Various methods of determining an edge strength can be used and can include, for example, search-based and zero-crossing based approaches. While certain methods of edge strength measurement are described, it will be understood that other methods are possible and within the scope of the present disclosure.

[0072] In an embodiment, process block 905 is followed by process block 907, which includes adjusting a focus of the retinal imaging system based on the edge strength of the structured illumination light. By adjusting the focus, the retinal image can be brought into greater focus, such as measured by an increased edge strength. In this regard, in an embodiment, adjusting the focus of the retinal imaging system comprises adjusting the focus to obtain a highest edge strength of the structured illumination light. In an embodiment, process block 907 is optional.

[0073] In an embodiment, process blocks 905 and / or 907 is / are followed by process block 909, which includes illuminating, with a retinal illuminator, the retina with unstructured illumination light. By generally illuminating the retina, such as with visible light, the whole of the retina may be imaged. In this regard, in an embodiment, process block 909 is followed by processing block 911, which includes obtaining a retinal image of the retina with the adjusted focus, such as when the retina is illuminated by the retinal illuminator. In an embodiment, either or both process blocks 909 and 911 are optional.

[0074] In an embodiment, process blocks 905, 907, 909, and / or 911 are followed by process block 913, which includes measuring a position along the structured illumination light from the retina having a highest edge strength. Such measurements can be used in conjunction with a tilted slit or other light baffle comprising an aperture, as described further herein with respect to FIG. 5. As discussed further herein with respect to FIG. 6B, a position along structured light received from the retina can vary, such as based upon an optical power of an eye. In this regard, process block 913 can be followed by process block 915, which includes determining an optical power of the eye based on the position along the structured light from the retina having the highest edge strength. Process block 915 can include referring to a look up table or other data structure and identifying an optical power of the eye based on the position having the highest edge strength in. for example, the look up table.

[0075] In an embodiment, process blocks 913 and / or 915 is / are followed by process block 917, which includes adjusting the focus of the retinal imaging system so that the position along the structured light from the retina having the highest edge strength is in a middle of the structured light. Based on where a position having highest edge strength is located, such as toward an end of the structured light illumination, the process can include adjusting the focal length to move the portion having the highest edge strength toward the middle of the structured illumination light, thereby bringing the retinal image into greater focus.

[0076] The processes explained above are described in terms of computer software and hardware. The techniques described may constitute machine-executable instructions embodied within a tangible or non- transitory machine (e.g., computer) readable storage medium, that when executed by a machine will cause the machine to perform the operations described. Additionally, the processes may be embodied within hardware, such as an application specific integrated circuit (“ASIC”) or otherwise.

[0077] A tangible machine-readable storage medium includes any mechanism that provides (i.e., stores) information in a non-transitory form accessible by a machine (e.g., a computer, network device, personal digital assistant, manufacturing tool, any device with a set of one or more processors, etc.). For example, a machine-readable storage medium includes recordable / non-recordable media (e.g., read only memory' (ROM), random access memory’ (RAM), magnetic disk storage media, optical storage media, flash memory devices, etc.).

[0078] The above description of illustrated embodiments of the invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific embodiments of, and examples for. the invention are described herein for illustrative purposes, various modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize.

[0079] These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.

Claims

CLAIMSWhat is claimed is:

1. A retinal imaging system comprising: an eyepiece lens assembly; a structured light assembly configured to emit structured illumination light through the eyepiece lens assembly for receipt by an eye positioned adjacent to the eyepiece lens assembly and opposite the structured light assembly; a retinal image sensor optically coupled to the eyepiece lens assembly, wherein the retinal image sensor is positioned to receive the structured illumination light from the eye and is configured obtain a retinal image of a retina of the eye; and a controller operatively coupled to the retinal image sensor, the structured light assembly, and the eyepiece lens assembly, the controller including logic that, when executed, causes the retinal imaging system to perform operations comprising: emitting, with the structured light assembly, structured illumination light through the eyepiece lens assembly; generating, with the retinal image sensor, a retinal image based on the structured illumination light received from the retina of the eye; and measuring an edge strength of the structured illumination light from the retinal image.

2. The retinal imaging system of Claim 1, wherein the structured light assembly comprises: a light source configured to emit illumination light onto the eyepiece lens assembly for receipt of the eye positioned adjacent to the eyepiece lens assembly; and a light structuring element shaped and positioned to preclude a portion of the illumination light from reaching the eyepiece lens assembly to provide structured illumination thereon.

3. The retinal imaging system of Claim 2, wherein the light structuring element comprises a light baffle configured to block a first portion of the illumination light, wherein the light baffle defines an aperture configured to allow a second portion of the illumination light to reach the eyepiece lens assembly.

4. The retinal imaging system of Claim 3, wherein the aperture defines a slit shaped to provide the structured illumination light on the eyepiece lens assembly in the form of a slit of structured illumination light.

5. The retinal imaging system of Claim 3, wherein the retinal image sensor and the eyepiece lens assembly are aligned along an optical axis of the retinal imaging system, wherein a major axis of the light baffle is positioned neither parallel to nor orthogonal to the optical axis.

6. The retinal imaging system of Claim 5, wherein the controller further comprises logic that, when executed, causes the retinal imaging system to perform operations comprising: measuring a position along the structured light received from the retina having a highest edge strength.

7. The retinal imaging system of Claim 6, wherein the controller further comprises logic that, when executed, causes the retinal imaging system to perform operations comprising: determining an optical power of the eye based on the position along the structured light from the retina having the highest edge strength.

8. The retinal imaging system of Claim 6, wherein the controller further comprises logic that, when executed, causes the retinal imaging system to perform operations comprising: adjusting a focus of the retinal imaging system so that the position along the structured light from the retina having the highest edge strength is in a middle of the structured light.

9. The retinal imaging system of Claim 3, wherein the aperture is a first aperture, and wherein the light baffle defines a second aperture positioned closer to the eyepiece lens assembly than the first aperture.

10. The retinal imaging system of Claim 1, wherein the controller further comprises logic that, when executed, causes the retinal imaging system to perform operations comprising:adjusting a focus of the retinal imaging system based on the edge strength of the structured illumination light.

11. The retinal imaging system of Claim 10, wherein adjusting the focus comprises adjusting the focus to obtain a highest edge strength of the structured illumination.

12. The retinal imaging system of Claim 10, further comprising a retinal illuminator configured to illuminate the retina with unstructured illumination light, wherein the controller further comprises logic that, when executed, causes the retinal imaging system to perform operations compnsing: illuminating, with the retinal illuminator, the retina with the unstructured illumination light; and obtaining a retinal image of the retina using the adjusted focus.

13. The retinal imaging system of Claim 1, further comprising a diffuser configured to diffuse the illumination light, wherein the diffuser is positioned between the light source and the light structuring element.

14. A method of operating a retinal imaging system, the method comprising: emitting, with a structured light assembly, structured illumination light through an eyepiece lens assembly, to provide structured illumination thereon; generating, with a retinal image sensor, a retinal image based on structured illumination light received from a retina of an eye; and measuring an edge strength of the structured illumination light from the retinal image.

15. The method of Claim 14, further comprising adjusting a focus of the retinal imaging system based on the edge strength of the structured illumination light.

16. The method of Claim 15. wherein adjusting the focus comprises adjusting the focus to obtain a highest edge strength of the structured illumination light.

17. The method of Claim 16, further comprising obtaining a retinal image of the retina with the adjusted focus.

18. The method of Claim 17, further comprising illuminating, with a retinal illuminator, the retina with unstructured illumination light.

19. The method of Claim 14, wherein the method further comprises measuring a position along the structured light from the retina having a highest edge strength.

20. The method of Claim 19, further comprising determining an optical power of the eye based on the position along the structured light from the retina having the highest edge strength.

21. The method of Claim 19, further comprising adjusting the focus of the retinal imaging system so that the position along the structured light from the retina having the highest edge strength is in a middle of the structured light.

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