Twenty-five years of clinical applications using adaptive optics ophthalmoscopy [Invited]

Abstract

Twenty-five years ago, adaptive optics (AO) was combined with fundus photography, thereby initiating a new era in the field of ophthalmic imaging. Since that time, clinical applications of AO ophthalmoscopy to investigate visual system structure and function in both health and disease abound. To date, AO ophthalmoscopy has enabled visualization of most cell types in the retina, offered insight into retinal and systemic disease pathogenesis, and been integrated into clinical trials. This article reviews clinical applications of AO ophthalmoscopy and addresses remaining challenges for AO ophthalmoscopy to become fully integrated into standard ophthalmic care.

Fig. 1.

Adaptive optics ophthalmoscopy. (A) Schematic of aberration measurement and correction provided through an AO loop to enable aberration-corrected imaging of the living eye. (B) Individual AO images of the photoreceptor mosaic in a normal-sighted eye illustrating the advantage provided by AO (B1: AO off, B2: AO on). Figure courtesy of Stephen Burns.

Fig. 2.

The normal photoreceptor mosaic imaged with AO. (A) AOFIO image of the normal cone mosaic at 1° superior to fixation. (B) AOSLO images of the photoreceptor mosaic in the parafovea using confocal imaging at 1° and 10° temporal to fixation using confocal and non-confocal split-detection. Individual cone and rod photoreceptors can be identified in the images (blue dots: cones, orange dots: rods). Confocal and non-confocal split-detection images show outer segment waveguiding and inner segments correspond one-to-one. (C) AOOCT enables visualization of the parafoveal cone mosaic in three dimensions [92]. Aligned B-scans (left) can be segmented to visualize the inner segment/outer segment (IS/OS) junction and cone outer segment tips (COST) en face (C-scans, middle). B-scans at the level of the photoreceptors (right) show each cone contains a reflection at the IS/OS junction and COST. Panel (C) courtesy of Ravi Jonnal.

Fig. 3.

Confocal and non-confocal split-detection AOSLO images (1 and 2) of the foveal region in inherited retinal diseases: (A) achromatopsia, (B) choroideremia, and (C) GUCA1A-mediated cone-rod dystrophy. Yellow asterisks mark the fovea. (3 and 4) Confocal and non-confocal split-detection images, respectively of the region within the white square in (1 and 2). For achromatopsia (A), cone density is reduced, and the cones visible in the non-confocal split detection image do not exhibit waveguided reflectance in the confocal image (blue arrows). Red arrows point to rods which maintain waveguided reflectance. For choroideremia (B), the cone mosaic is relatively intact within the central region out to the atrophic border (yellow arrow). Orange asterisk: an outer retinal tubulation. Blue and red arrows point to clumps of hypo- and hyper-reflective cones, respectively. Yellow arrow marks the sharp border of atrophy. For GUCA1A-mediated cone-rod dystrophy (C), cone density is reduced, only a subset of the cones observed in non-confocal split-detection exhibit waveguided reflectance on confocal. Red arrows point to cone locations that exhibit waveguided reflectance, blue arrows point to cones with abnormal, reduced waveguiding.

Fig. 4.

(A) The cone mosaic surrounding a subretinal drusenoid deposit in a 73-year-old male with non-neovascular AMD [101]. Using confocal AOSLO, waveguiding cones are visualized around the subretinal drusenoid deposit, the edge of which appears as a dark ring. Panel (A) courtesy of Yuhua Zhang. (B) Drusen, observed as hyper-reflective rings, in a 65-year-old patient with intermediate AMD revealed by gaze dependent AOFIO imaging [109].

Fig. 5.

Multi-modal AOSLO imaging in retinitis pigmentosa reveals the transition zone between the intact photoreceptor mosaic and loss of the photoreceptors. Blue arrows show the cone mosaic in both confocal and non-confocal split-detection AOSLO images. White and yellow arrows point to locations where the cone mosaic is no longer intact, and the RPE becomes visible both in confocal and dark-field imaging modalities.

Fig. 6.

RPE imaging in health and disease. Healthy RPE cells can be visualized using (A) short-wavelength autofluorescence AOSLO [9], (B) near-infrared autofluorescence AOSLO [17], (C) dark-field imaging AOSLO [17], (D) AOOCT [127], (E) ICG fluorescence AOSLO [16], and (F) transscleral AOFIO imaging [128]. In all modalities, RPE cells appear as a in a honeycomb pattern of tightly packed cells. (G) Enlarged RPE cells with hypofluorescent nuclei are visualized with ICG fluorescence in Bietti Crystalline Dystrophy [129]. (H) Transscleral AOFIO near the fovea reveals pigmentary clumps in the RPE layer of a 78-year-old female patient with geographic atrophy with foveal sparing. (I) Foveal mosaic of enlarged RPE cells visualized using near infra-red autofluorescence in a case of radiation retinopathy that caused loss of photoreceptors at the same location [115]. Panels (B), (C), (D), (E), and (G) courtesy of Johnny Tam. Panel (H) courtesy of Kiyoko Gocho.

Fig. 7.

Retinal ganglion cells resolved with AOOCT in a 54-year-old healthy control subject (left) compared to a 51-year-old glaucoma subject (right) at 12° temporal retina. Note the lower density and enlarged cells in the glaucomatous eye [137]. Figure courtesy of Zhuolin Liu.

Fig. 8.

Progression of peripapillary retinal nerve fiber bundle defect over 17.3 months in a 46-year-old patient with glaucomatous damage at the inferior region imaged using confocal AOSLO [156]. (A) Montage of the peripapillary AOSLO images obtained at 17.3 months superimposed upon the fundus photograph of the right eye. The regions within the green and red rectangles obtained at the baseline and 17.3 months are magnified in B1 and C1 and B2 and C2, respectively. (B1 and B2) Superior region shows relatively healthy retinal nerve fiber bundles and stable surface reflectively over time. (C1 and C2) Inferior region shows progression of a focal retinal nerve fiber bundle defect over 17.3 months. Defect widths are shown in the inferior region at both visits.

Fig. 9.

Imaging of the normal foveal capillary network and FAZ. (A) Confocal AOSLO imaging shows the microvascular structure at the fovea. (B) Confocal fluorescein angiography perfusion map obtained using oral fluorescein. (C) Motion contrast perfusion map generated based on the blood cell flow induced reflectivity variation from registered non-confocal offset pinhole videos [159]. (A-C) show the foveal capillary network of the same subject. (D) AOOCT-A image taken by the multi-modal multiscale system created in the European MERLIN project. Panel (D) Courtesy of Kiyoko Gocho.

Fig. 10.

An arteriole located in the optic disc of a 26-year-old healthy subject imaged using non-confocal offset pinhole AOSLO. The outer diameter and inner diameter are indicated by the red and cyan line, respectively. Wall to lumen ratio is computed as the difference between the outer and inner diameters divided by the inner diameter [177]. Yellow arrows indicate examples of mural cells along the blood vessel walls [193].

Fig. 11.

Imaging of parafoveal microvasculature in human retina using non-confocal offset pinhole AOSLO. (A) Parafoveal capillary network in a 25-year-old healthy subject. (B) A 43-year-old diabetic patient with focal retinal microvascular changes such as capillary wall thickening (red arrow), capillary dilation (yellow arrows), and microaneurysm (cyan arrow).

Fig. 12.

Hyalocytes imaging in a 32-year-old healthy subject using non-confocal quadrant-detection AOSLO. (A and B) Arrows indicate two ramified hyalocytes imaged at two time points with their somas and processes varying in shape and orientation noticeably. Time of acquisition in the lower-left corner denotes the hrs:mins:secs. (C) Red-green overlay shows hyalocytes at two time points. Yellow indicates stationary structures that appeared in both time points due to the combined contributions of red and green. The entire image sequences of these cells over 2 hours are shown in Visualization 5.

Fig. 13.

AO-guided microperimetry in conjunction with confocal (A) and non-confocal split-detection (B) AOSLO imaging in choroideremia reveals a sharp transition in retinal sensitivity at the atrophic border and along an outer retinal tabulation [211]. Circled dots show the test-locations and are scaled to the size of the stimulus on the retina. Figure courtesy of William S. Tuten.

Fig. 14.

AO densitometry reveals the three cone classes in the normal retina [220]. (A) Shows a histogram of the number of cones versus the change in intensity between fully bleached and dark adapted photopigment. S-cones show little change in intensity following a full bleach, while L- and M- cones show a larger change. Blue and yellow lines depict Gaussian fits to the histogram and denote the S- and L-/M- cones respectively. (B) Histogram of the number of cones versus the angular coordinate of the change in intensity for a selective L-cone bleach verses a selective M-cone bleach. Red and green lines show Gaussian fits to the histogram and denote the L- and M- cones respectively. (C) Psuedo-colored cone mosaic depicting the L-, M-, and S- cones in a normal trichromat in red, green and blue, respectively. Figure courtesy of Ramkumar Sabesan.

Fig. 15.

AO optoretinography reveals cone function and enables classification of L-, M-, and S-cones [231,234]. (A) Cone mosaic revealed with line-scan AOOCT. (B) Pseudo-colored cone mosaic depicting the L-, M-, and S-cones in red, green, and blue, respectively. Cone type was assigned based on the magnitude of ΔOPL following a 660 nm visible stimulus. (C) ΔOPL versus time after the stimulus onset. L-cones exhibit the strongest ΔOPL following the stimulus. (D) Histogram showing the number of cones versus the ΔOPL for the 660 nm stimulus. Blue, green, and red lines show three Gaussian fits to the data, and represent the cones that constitute the S-, M- and L-cones respectively. Figure courtesy of Ramkumar Sabesan.

Fig. 16.

Imaging parafoveal capillary flow in a subject with type I diabetes [256]. (A) Shows an OCT-A image acquired using a commercial device (Heidelberg Spectralis). Foveal avascular zone is located at the lower right. (B) Motion contrast map acquired with an AOFIO at 400 fps with 593 nm imaging beam superimposed upon the corresponding region of the background OCT-A image. Image sequence of the red box region is shown in Visualization 6. (C) Velocity mapping using pixel intensity cross-correlation, in the same region as (B). Velocity color map ranges from 0 to 4.5-mm/s. Figure courtesy of Phillip Bedggood and Andrew Metha.

Fig. 17.

Cone inner segment mosaic visible using non-confocal split-detection AOSLO imaging before (top) and after (bottom) subretinal injection of AAV2.hCHM gene therapy in a patient with choroideremia [267]. Global alignment of the montages shows the same retinal features (yellow arrows) before and after application of the experimental therapeutic. Regions of interest (colored boxes) show magnified images of the photoreceptor mosaic; cone densities between baseline and one-month post injection timepoints were not significantly different. The data provide evidence supporting the safety of subretinal injections of AAV2.hCHM. Yellow asterisk denotes the location of the fovea.

Fig. 18.

(A) Right eye fundus photo of a sickle cell disease patient, a treatment-naïve 31-year-old female with HbSS genotype and non-proliferative sickle cell retinopathy. White box indicates a region imaged at two visits using non-confocal quadrant-detection AOSLO [271]. (B) At the baseline visit, single frame image revealed two thrombi of blood cells within the same capillary (cyan arrow). A sludged erythrocyte (white arrow) and a fully perfused capillary (yellow arrow) were also visualized. (C) At the second visit, 2 months following initiation of oral hydroxyurea treatment, single frame image showed resolution of the thrombi (cyan arrow), and restoration of normal flow through the previously non-perfused capillary (white arrow). Interestingly, non-perfusion of a previously perfused capillary segment (yellow arrow) was also evident two months after treatment. Perfused blood vessels are tinted in red based on the corresponding motion contrast perfusion maps. See also Visualization 7.