Adaptive Optics (AO) retinal imaging has provided revolutionary tools to scientists and clinicians for studying retinal structure and function in the living eye. From animal models to clinical patients, AO imaging is changing the way scientists are approaching the study of the retina. By providing cellular and subcellular details without the need for histology, it is now possible to perform large scale studies as well as to understand how an individual retina changes over time. Because AO retinal imaging is non-invasive and when performed with near-IR wavelengths both safe and easily tolerated by patients, it holds promise for being incorporated into clinical trials providing cell specific approaches to monitoring diseases and therapeutic interventions. AO is being used to enhance the ability of OCT, fluorescence imaging, and reflectance imaging. By incorporating imaging that is sensitive to differences in the scattering properties of retinal tissue, it is especially sensitive to disease, which can drastically impact retinal tissue properties. This review examines human AO retinal imaging with a concentration on the use of the Adaptive Optics Scanning Laser Ophthalmoscope (AOSLO). It first covers the background and the overall approaches to human AO retinal imaging, and the technology involved, and then concentrates on using AO retinal imaging to study the structure and function of the retina.
PurposeTo investigate distances from retinal capillaries to arterioles or venules noninvasively.MethodsAn adaptive optics scanning laser ophthalmoscope (AOSLO) and optical coherence tomography angiography (OCTA) imager acquired detailed maps of retinal vasculature. Using OCTA, we quantified the distance from the edge of an arteriole or venule to the middle of the nearest capillaries (periarteriole or perivenule capillary-free zones, respectively) within the superficial vascular plexus of 20 young healthy subjects with normal axial lengths. These distances were compared to AOSLO images for three subjects. We tested the relation between the peripheral capillary-free zones and FAZ horizontal, vertical, effective diameters, and asymmetry indices in the deep vascular plexus. We examined enlargement with OCTA of capillary-free zones in a type 2 diabetic patient.ResultsThe periarteriole capillary-free zone (67.2 ± 25.3 μm) was readily visible and larger than the perivenule capillary-free zone (42.7 ± 14.4 μm), F(1, 998) = 771, P < 0.0001. The distance from foveal center (P = 0.003) and diameter (P = 0.048) were predictive of perivenule capillary-free zone values. OCTA and AOSLO corresponded for arterioles. FAZ effective diameter was positively associated with asymmetry indices, r = 0.49, P = 0.028, but not peripheral capillary-free zones, although focal enlargements were found in a diabetic patient.ConclusionsFor normal retinas, periarteriole and perivenule capillary-free zones are readily visible with OCTA and AOSLO. Periarteriole capillary-free zones were larger, consistent with arterioles carrying oxygen rich blood that diffuses to support the retina.
PurposeWe measured localized changes occurring in the foveal cone photoreceptors and related defects in the cone mosaic to alterations in the nearby retinal vasculature.MethodsThe central 4° of the retina of 54 diabetic (53.7 ± 12.5 years) and 85 control (35.8 ± 15.2 years) participants were imaged with the Indiana adaptive optics scanning laser ophthalmoscope. Foveal cones and overlying retinal capillaries were imaged and infrared scanning laser ophthalmoscopy (IR SLO) images and optical coherence tomography (OCT) B-scans were obtained. Follow-up imaging sessions were performed with intervals from 4 to 50 months for 22 of the 54 diabetic participants.ResultsThe foveal cone mosaics of 49 of 54 diabetic participants were of sufficient quality to assess the absence or presence of small localized defects in the cone mosaic. In 13 of these 49 diabetic participants we found localized defects, visualized as sharp-edged areas of cones with diminished reflectivity. These small, localized areas ranged in size from 10 × 10 μm to 75 × 30 μm. Of these 13 participants with cone defects, 11 were imaged over periods from 4 to 50 months and the defects remained relatively stable. These dark regions were not shadows of overlying retinal vessels, but all participants with these localized defects had alterations in the juxtafoveal capillary network.ConclusionsThe foveal cone mosaic can show localized areas of dark cones that persist over time, that apparently correspond to either missing or nonreflecting cones, and may be related to local retinal ischemia.
In adaptive optics scanning laser ophthalmoscope (AOSLO) systems, capturing multiply scattered light can increase the contrast of the retinal microvasculature structure, cone inner segments, and retinal ganglion cells. Current systems generally use either a split detector or offset aperture approach to collect this light. We tested the ability of a spatial light modulator (SLM) as a rapidly configurable aperture to use more complex shapes to enhance the contrast of retinal structure. Particularly, we varied the orientation of a split detector aperture and explored the use of a more complex shape, the half annulus, to enhance the contrast of the retinal vasculature. We used the new approach to investigate the influence of scattering distance and orientation on vascular imaging.
PurposeTo investigate outer retinal tubulation (ORT) using spectral domain optical coherence tomography (SD-OCT) and an adaptive optics scanning laser ophthalmoscope (AOSLO). To document the frequency of ORT in atrophic retinal conditions and quantify ORT dimensions versus adjacent retinal layers.MethodsSD-OCT images were reviewed for the presence of retinal atrophy, scarring, and/or exudation. The greatest width of each ORT was quantified. Inner and outer retinal thicknesses adjacent to and within the area of ORT were measured for 18 patients. AOSLO imaged ORTs in five subjects with direct and scattered light imaging.ResultsORT was identified in 47 of 76 subjects (61.8%) and in 65 eyes via SD-OCT in a wide range of conditions and ages, and in peripapillary atrophy. ORTs appeared as finger-like projections in atrophy, seen in the en face images. AOSLO showed some ORTs with bright cones that guide light within atrophic areas. Multiply scattered light mode AOSLO visualized variegated lines (18–35 μm) radiating from ORTs. The ORTs’ width on OCT b-scan images varied from 70 to 509 μm. The inner retina at the ORT was significantly thinner than the adjacent retina, 135 vs.170 μm (P = .004), whereas the outer retina was significantly thicker, 115 vs. 80 μm (P = .03).ConclusionsORTs are quite common in eyes with retinal atrophy in various disorders. ORTs demonstrate surviving photoreceptors in tubular structures found within otherwise nonsupportive atrophic areas that lack retinal pigment epithelium and choriocapillaris.
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