Programmable, high-speed, adaptive optics partially confocal multi-spot ophthalmoscope using a digital micromirror device.

A high-speed, adaptive optics partially confocal multi-spot ophthalmoscope (AO-pcMSO) using a digital micromirror device (DMD) in the illumination channel and a fast 2D CMOS camera is described. The camera is synchronized with the DMD allowing projection of multiple, simultaneous AO-corrected spots onto the human retina. Spatial filtering on each raw retinal image before reconstruction works as an array virtual pinholes. A frame acquisition rate of 250 fps is achieved by applying this parallel projection scheme. The contrast improves by 2-3 fold when compared to a standard flood illumination architecture. Partially confocal images of the human retina show cone and rod photoreceptors over a range of retinal eccentricities.

Rapid measurement of individual cone photoreceptor pointing using focus diversity.

A novel method is presented to rapidly measure the pointing direction of individual human cone photoreceptors using adaptive-optics (AO) retinal imaging. For a fixed entrance pupil position, the focal plane is rapidly modulated to image the guided light in various axial planes. For cones with different pointing directions, this focus diversity will cause a shift in their apparent position, allowing for their relative pointing to be determined. For four normal human subjects, retinal images were acquired, registered, and the positions of individual cones tracked throughout the dataset. Variation in cone tilt was 0.02 radians, agreeing with other objective measurements on the same subjects at the same retinal locations.

Quantitative Analysis of the Vasculature and Cone Photoreceptors in Subjects With Diabetes Without Diabetic Retinopathy.

PURPOSE: To characterize any differences in the vasculature and cone photoreceptor packing geometry (CPG) between subjects with diabetes without/no diabetic retinopathy (NDR) and healthy controls. METHODS: Eight NDR and five controls were enrolled. Optical coherence tomography angiography (OCTA) taken at the macula was used to measure vessel density, vessel length density, and vessel density index (VDI) in three vascular plexuses, namely, the superficial vascular plexus, intermediate capillary plexus, and deep capillary plexus (DCP). The choriocapillaris (CC) flow deficit (FD) was also measured. OCTA images were binarized and processed to extrapolate the parafovea and parafoveal quadrants and the OCTA indices mentioned above. The CC was processed with six different radii to quantify FD. Adaptive optics - scanning laser ophthalmoscopy images were acquired and processed to extract CPG indices, i.e., cone density (CD), cone-to-cone spacing (CS), linear dispersion index, heterogeneity packing index and percent of cells with six neighbors at 3.6° in the temporal retina. RESULTS: In all eyes, statistically significant differences were found (i) in parafoveal FD across the six radii (p < 0.001) and (ii) in the correlation between the parafoveal temporal quadrant (PTQ) DCP VDI and CS (r = 0.606, p = 0.048). No other significant correlations were found. For OCTA or CPG indices, no significant differences were found between the cohorts in the parafovea or parafoveal quadrants. CONCLUSIONS: CS is the most sensitive CPG index for detecting alterations in the cone mosaic. The DCP and the cone photoreceptors are significantly correlated, indicating that alterations in the DCP can affect the cones. Future work elucidating the vascular alterations and neurodegeneration present in diabetic eyes should focus on the DCP and multiple CPG indices, not solely CD. Moreover, such alterations are highly localized, hence using larger regions e.g. parafovea versus smaller areas, such as the PTQ, will potentially mask significant correlations.

High-speed, phase contrast retinal and blood flow imaging using an adaptive optics partially confocal multi-line ophthalmoscope.

High-speed, phase contrast retinal and blood flow imaging using an adaptive optics partially confocal multi-line ophthalmosocope (AO-pcMLO) is described. It allows for simultaneous confocal and phase contrast imaging with various directional multi-line illumination by using a single 2D camera and a digital micromirror device (DMD). Both vertical and horizontal line illumination directions were tested, for photoreceptor and vascular imaging. The phase contrast imaging provided improved visualization of retinal structures such as cone inner segments, vessel walls and red blood cells with images being acquired at frame rates up to 500 Hz. Blood flow velocities of small vessels (<40 µm in diameter) were measured using kymographs for capillaries and cross-correlation between subsequent images for arterioles or venules. Cardiac-related pulsatile patterns were observed with normal resting heart-beat rate, and instantaneous blood flow velocities from 0.7 to 20 mm/s were measured.

Assessing the efficacy of 2D and 3D CNN algorithms in OCT-based glaucoma detection.

Glaucoma is a progressive neurodegenerative disease characterized by the gradual degeneration of retinal ganglion cells, leading to irreversible blindness worldwide. Therefore, timely and accurate diagnosis of glaucoma is crucial, enabling early intervention and facilitating effective disease management to mitigate further vision deterioration. The advent of optical coherence tomography (OCT) has marked a transformative era in ophthalmology, offering detailed visualization of the macula and optic nerve head (ONH) regions. In recent years, both 2D and 3D convolutional neural network (CNN) algorithms have been applied to OCT image analysis. While 2D CNNs rely on post-prediction aggregation of all B-scans within OCT volumes, 3D CNNs allow for direct glaucoma prediction from the OCT data. However, in the absence of extensively pre-trained 3D models, the comparative efficacy of 2D and 3D-CNN algorithms in detecting glaucoma from volumetric OCT images remains unclear. Therefore, this study explores the efficacy of glaucoma detection through volumetric OCT images using select state-of-the-art (SOTA) 2D-CNN models, 3D adaptations of these 2D-CNN models with specific weight transfer techniques, and a custom 5-layer 3D-CNN-Encoder algorithm. The performance across two distinct datasets is evaluated, each focusing on the macula and the ONH, to provide a comprehensive understanding of the models' capabilities in identifying glaucoma. Our findings demonstrate that the 2D-CNN algorithm consistently provided robust results compared to their 3D counterparts tested in this study for glaucoma detection, achieving AUC values of 0.960 and 0.943 for the macular and ONH OCT test images, respectively. Given the scarcity of pre-trained 3D models trained on extensive datasets, this comparative analysis underscores the overall utility of 2D and 3D-CNN algorithms in advancing glaucoma diagnostic systems in ophthalmology and highlights the potential of 2D algorithms for volumetric OCT image-based glaucoma detection.

Foveal cone loss in tamoxifen maculopathy: a case report.

BACKGROUND: Tamoxifen is used in low dose concentrations (20-40 mg per day) as a therapy for breast cancer but is known to have ocular side effects. In this case report, the foveal cone integrity in a tamoxifen-treated patient who complained of a small central scotoma in the left eye while reading was examined using high resolution adaptive optics imaging. CASE PRESENTATION: Both eyes of a 54-year-old Caucasian, non-hispanic female who had been treated with tamoxifen for 1.5 years were examined using various imaging modalities including fundus photography, fundus autofluorescence, fluorescein angiography, spectral-domain optical coherence tomography, and adaptive optics scanning laser ophthalmoscopy. Clinical spectral-domain optical coherence tomography showed a very small disruption to the photoreceptor layer at the fovea in the left eye only. However, adaptive optics scanning laser ophthalmoscopy imaging revealed foveal cone loss in both eyes, but to a lesser extent in the right eye. Inner retinal changes were not observed in either eye. CONCLUSION: The area of cone loss was similar in size to a single newsprint letter when projected onto the retina, matching the patient's description of a scotoma in the left eye. Given the isolated loss of foveal cone photoreceptors with the absence of previously reported inner retinal and vascular changes, our results may indicate the earliest retinal changes associated with tamoxifen retinopathy.

High Resolution Imaging of the Outer Retina in Type 2 Acute Macular Neuroretinopathy.

PURPOSE: To investigate the outer retinal changes in a patient with type 2 acute macular neuroretinopathy (AMN). METHODS: A 35-year-old Caucasian female complaining of a unilateral blind spot was imaged using various retinal imaging modalities including clinical optical coherence tomography (OCT), OCT-angiography, fundus fluorescein angiography and adaptive optics (AO). RESULTS: Fundus examination revealed multiple paracentral reddish-brown petaloid lesions in the symptomatic left eye, while the other eye was unremarkable. Clinical OCT showed areas of hyper-reflectance at the outer plexiform layer / outer nuclear layer complex with a disrupted inner /outer segment junction, which are characteristic features of type 2 AMN. AO imaging further revealed either shortening or absence of cone outer segments within the AMN lesions attributing to the darker features observed in the enface images from fundus photography and scanning laser ophthalmoscopy. CONCLUSION: The AO findings indicate that the petaloid lesions in type 2 AMN are caused by a combination of the shortening and absence of the outer segment in individual cone photoreceptors.

Using deep learning for the automated identification of cone and rod photoreceptors from adaptive optics imaging of the human retina.

Adaptive optics imaging has enabled the enhanced in vivo retinal visualization of individual cone and rod photoreceptors. Effective analysis of such high-resolution, feature rich images requires automated, robust algorithms. This paper describes RC-UPerNet, a novel deep learning algorithm, for identifying both types of photoreceptors, and was evaluated on images from central and peripheral retina extending out to 30° from the fovea in the nasal and temporal directions. Precision, recall and Dice scores were 0.928, 0.917 and 0.922 respectively for cones, and 0.876, 0.867 and 0.870 for rods. Scores agree well with human graders and are better than previously reported AI-based approaches.

CONE PHOTORECEPTOR INTEGRITY ASSESSED WITH ADAPTIVE OPTICS IMAGING AFTER LASER POINTER-INDUCED RETINAL INJURY.

PURPOSE: To examine the three-dimensional foveal cone photoreceptor structure in a patient who had suffered laser pointer-induced retinal injury. METHODS: Patient underwent standard fundus photography and clinical spectral domain optical coherence tomography imaging. High-resolution imaging was performed using an adaptive optics-optical coherence tomography-scanning laser ophthalmoscope. RESULTS: Adaptive optics imaging revealed loss of inner and outer segments of cone photoreceptors whereas the anterior retinal layers appeared healthy. Analysis of cone topology showed an increase in Voronoi domain area and a less regular hexagonal packing structure closer to the lesion site. CONCLUSION: Exposure to laser pointer radiation, however brief, can result in damage to the retina. Here, repeated imaging nine months later showed a decrease in the size of the lesions (ranging from 3.7 to 23.9%) compared with the first time point. However, the longer-term prognosis is likely permanent scarring.

In vivo imaging of the human rod photoreceptor mosaic.

Although single cone receptors have been imaged in vivo, to our knowledge there has been no observation of rods in the living normal eye. Using an adaptive optics ophthalmoscope and post processing, evidence of a rod mosaic was observed at 5° and 10° eccentricities in the horizontal temporal retina. For four normal human subjects, small structures were observed between the larger cones and were observed repeatedly at the same locations on different days, and with varying wavelengths. Image analysis gave spacings that agree well with rod measurements from histological data.

Role of high-order aberrations in senescent changes in spatial vision.

The contributions of optical and neural factors to age-related losses in spatial vision are not fully understood. We used closed-loop adaptive optics to test the visual benefit of correcting monochromatic high-order aberrations (HOAs) on spatial vision for observers ranging in age from 18 to 81 years. Contrast sensitivity was measured monocularly using a two-alternative forced-choice (2AFC) procedure for sinusoidal gratings over 6 mm and 3 mm pupil diameters. Visual acuity was measured using a spatial 4AFC procedure. Over a 6 mm pupil, young observers showed a large benefit of AO at high spatial frequencies, whereas older observers exhibited the greatest benefit at middle spatial frequencies, plus a significantly larger increase in visual acuity. When age-related miosis is controlled, young and old observers exhibited a similar benefit of AO for spatial vision. An increase in HOAs cannot account for the complete senescent decline in spatial vision. These results may indicate a larger role of additional optical factors when the impact of HOAs is removed, but also lend support for the importance of neural factors in age-related changes in spatial vision.

Structural Integrity of Individual Cone Photoreceptors After Short-Wavelength Subthreshold Micropulse Laser Therapy for Diabetic Macular Edema.

BACKGROUND AND OBJECTIVE: Subthreshold micropulse laser (SML) treatment at 577 nm has been proposed as a safe and efficacious therapy for diabetic macular edema (DME). The study objective was to evaluate the integrity of individual cone photoreceptors after SML treatment using high-resolution retinal imaging. PATIENTS AND METHODS: An observational cohort study of four subjects with DME treated using SML was followed over time. Cone inner and outer segment lengths and total retinal thicknesses (TRT) were measured as the edema resolved. The primary outcome was the detection of any laser-induced photoreceptor damage / change following the SML treatment using adaptive optics imaging. RESULTS: Individual cones observed pre-treatment remained visible, whereas cones that were initially obscured by the DME became more discernable after the treatment. TRT showed statistically significant thinning in half of the subjects. One subject showed no significant change, whereas another showed a statistically significant increase in TRT despite the treatment. No subject was found to have photoreceptor damage following treatment. CONCLUSIONS: SML at 577 nm did not result in measurable structural damage to the underlying photoreceptor layer, supporting previous work that SML is a safe alternative for treating DME. [Ophthalmic Surg Lasers Imaging Retina. 2018;49:946-954.].

Inner Retinal Changes in Primary Open-Angle Glaucoma Revealed Through Adaptive Optics-Optical Coherence Tomography.

PURPOSE: To examine the microstructural changes in the inner nuclear layer (INL) and ganglion cell layer (GCL) in a primary open-angle glaucoma (POAG) subject at 2 timepoints, 4 months apart. PATIENTS AND METHODS: This case-control study (1 POAG subject and 1 normal control) used the single cell, 3-dimensional volumetric imaging capability of an adaptive optics-optical coherence tomography-scanning laser ophthalmoscopy system to examine the inner retina. RESULTS: At the area of greatest glaucomatous change in the POAG subject [3-degrees temporal (T), 3-degrees inferior (I), right eye], the GCL was greatly thinned at both timepoints, yet retinal ganglion cell soma remained visible amid a meshwork of capillaries. Microcystic lesions in the INL were visible at both timepoints, ranging in diameter from 8 to 43 µm on day 1 to 11 to 64 µm at 4 months, with an average diameter increase of ∼124%. Small hyperreflective features (not seen in the contralateral eye or control subject) at a depth midway through the INL seemed correlated to the development of microcysts. CONCLUSIONS: We demonstrate the ability to image microcystic lesions early in their development and have quantified longitudinal changes. The presence of small hyperreflective structures at a layer midway through the INL seems to be a precursor to their formation and is a potential biomarker for assessing POAG severity and progression. The adaptive optics imaging system is also able to visualize retinal ganglion cells in this subject, despite severe thinning of the GCL.

Volumetric imaging of rod and cone photoreceptor structure with a combined adaptive optics-optical coherence tomography-scanning laser ophthalmoscope.

We have designed and implemented a dual-mode adaptive optics (AO) imaging system that combines spectral domain optical coherence tomography (OCT) and scanning laser ophthalmoscopy (SLO) for in vivo imaging of the human retina. The system simultaneously acquires SLO frames and OCT B-scans at 60 Hz with an OCT volume acquisition time of 4.2 s. Transverse eye motion measured from the SLO is used to register the OCT B-scans to generate three-dimensional (3-D) volumes. Key optical design considerations include: minimizing system aberrations through the use of off-axis relay telescopes, conjugate pupil plane requirements, and the use of dichroic beam splitters to separate and recombine the OCT and SLO beams around the nonshared horizontal scanning mirrors. To demonstrate system performance, AO-OCT-SLO images and measurements are taken from three normal human subjects ranging in retinal eccentricity from the fovea out to 15-deg temporal and 20-deg superior. Also presented are en face OCT projections generated from the registered 3-D volumes. The ability to acquire high-resolution 3-D images of the human retina in the midperiphery and beyond has clinical importance in diseases, such as retinitis pigmentosa and cone-rod dystrophy.

Vision science and adaptive optics, the state of the field.

Adaptive optics is a relatively new field, yet it is spreading rapidly and allows new questions to be asked about how the visual system is organized. The editors of this feature issue have posed a series of question to scientists involved in using adaptive optics in vision science. The questions are focused on three main areas. In the first we investigate the use of adaptive optics for psychophysical measurements of visual system function and for improving the optics of the eye. In the second, we look at the applications and impact of adaptive optics on retinal imaging and its promise for basic and applied research. In the third, we explore how adaptive optics is being used to improve our understanding of the neurophysiology of the visual system.

In vivo imaging of the photoreceptor mosaic in retinal dystrophies and correlations with visual function.

PURPOSE: To relate in vivo microscopic retinal changes to visual function in patients who have various forms of retinal dystrophy. METHODS: The UC Davis Adaptive Optics (AO) fundus camera was used to acquire in vivo retinal images at the cellular level. Visual function tests consisting of visual fields, multifocal electroretinography (mfERG), and contrast sensitivity were measured in all subjects by using stimuli that were coincident with areas imaged. Five patients with different forms of retinal dystrophy and three control subjects were recruited. Cone densities were quantified for all retinal images. RESULTS: In all images of diseased retinas, there were extensive areas of dark space between groups of photoreceptors, where no cone photoreceptors were evident. These irregular features were not seen in healthy retinas, but were apparent in patients with retinal dystrophy. There were significant correlations between functional vision losses and the extent to which these irregularities, quantified by cone density, occurred in retinal images. CONCLUSIONS: AO fundus imaging is a reliable technique for assessing and quantifying the changes in the photoreceptor layer as disease progresses. Furthermore, this technique can be useful in cases where visual function tests provide borderline or ambiguous results, as it allows visualization of individual photoreceptors.

High-resolution, in vivo retinal imaging using adaptive optics and its future role in ophthalmology.

Until recently it was impossible to fully realize the optical resolution afforded by the human eye due to the inherent optical aberrations. These aberrations limit the ability to see fine structure in the retinal layers and visual perception of the outside world. A conventional spectacle or contact lens refraction only provides a static amelioration of the lowest order aberrations, namely defocus and astigmatism. In addition, all of these distortions are constantly evolving due to changes in accommodation and head/eye movements. The technique of adaptive optics not only corrects all of the static spatial modes but also measures and corrects any dynamic changes. Such systems have allowed for routine in vivo cellular imaging, the classification of individual photoreceptor cells and have enabled psychophysical testing of human visual function at the neural level. This review introduces the principle of adaptive optics and the key hardware required to implement such a scheme. The integration of adaptive optics into different imaging modalities is presented along with descriptions of current systems in use today and the experimental results obtained to date. Finally, the review concludes by discussing future technology and gives the author's prediction of how the field will evolve over the coming years.

The locus of fixation and the foveal cone mosaic.

High-resolution retinal imaging with adaptive optics was used to record the position of a light stimulus on the cone mosaic, with an error at least five times smaller than the diameter of the smallest foveal cones. We discuss the factors that limit the accuracy with which absolute retinal position can be determined. In five subjects, the standard deviation of fixation positions measured in discrete trials ranged from 2.1 to 6.3 arcmin, with an average of 3.4 arcmin (about 17 microm), in agreement with previous studies (R. W. Ditchburn, 1973; R. M. Steinman, G. M. Haddad, A. A. Skavenski, & D. Wyman, 1973). The center of fixation, based on the mean retinal position for each of three subjects, was displaced from the location of highest foveal cone density by an average of about 10 arcmin (about 50 microm), indicating that cone density alone does not drive the location on the retina selected for fixation. This method can be used in psychophysical studies or medical applications requiring submicron registration of stimuli with respect to the retina or in delivering light to retinal features as small as single cells.

James Webb Space Telescope segment phasing using differential optical transfer functions.

Differential optical transfer function (dOTF) is an image-based, noniterative wavefront sensing method that uses two star images with a single small change in the pupil. We describe two possible methods for introducing the required pupil modification to the James Webb Space Telescope, one using a small (<λ/4) displacement of a single segment's actuator and another that uses small misalignments of the NIRCam's filter wheel. While both methods should work with NIRCam, the actuator method will allow both MIRI and NIRISS to be used for segment phasing, which is a new functionality. Since the actuator method requires only small displacements, it should provide a fast and safe phasing alternative that reduces the mission risk and can be performed frequently for alignment monitoring and maintenance. Since a single actuator modification can be seen by all three cameras, it should be possible to calibrate the non-common-path aberrations between them. Large segment discontinuities can be measured using dOTFs in two filter bands. Using two images of a star field, aberrations along multiple lines of sight through the telescope can be measured simultaneously. Also, since dOTF gives the pupil field amplitude as well as the phase, it could provide a first approximation or constraint to the planned iterative phase retrieval algorithms.

Measurement of the photoreceptor pointing in the living chick eye.

The chick eye is used in the study of ocular growth and emmetropization; however optical aberrations in the lens and cornea limit the ability to visualize fine retinal structure in living eyes. These aberrations can be corrected using adaptive optics (AO) allowing for cellular level imaging in vivo. Here, this capability is extended to measure the angular tuning properties of individual photoreceptors. The left eyes from two White Leghorn chicks (Gallus gallus domesticus) labeled chick A and chick B, were imaged using an AO flood illuminated fundus camera. By translating the entrance pupil position, the same retinal location was illuminated with light of varying angles allowing for the measurement of individual photoreceptor pointing. At 30° nasal from the pecten tip, the pointing direction for both chicks was towards the pupil center with a narrow distribution. These particular chicks were found to have a temporal (T) and inferior (I) bias in the alignment with peak positions of (0.81 T, 0.23 I) and (0.57 T, 0.18 I) mm from the pupil center for chicks A and B respectively. The rho, ρ, values for the major, ρL, and minor, ρs, axes were 0.14 and 0.17mm(-2) for chick A and 0.09 and 0.20mm(-2) for chick B. The small disarray in the alignment of the chick photoreceptors implies that the photoreceptors are aligned to optimize the light entering the eye through the central portion of the pupil aperture. The ability to measure pointing properties of individual photoreceptors will have application in the study of eye growth and various retinal disorders.