Photoreceptor-Based Biomarkers in AOSLO Retinal Imaging.

We characterized retinal structure in patients and carriers of choroideremia using adaptive optics and other high resolution modalities. A total of 57 patients and 18 carriers of choroideremia were imaged using adaptive optics scanning light ophthalmoscopy (AOSLO), optical coherence tomography (OCT), autofluorescence (AF), and scanning light ophthalmoscopy (SLO). Cone density was measured in 59 eyes of 34 patients where the full cone mosaic was observed. The SLO imaging revealed scalloped edges of RPE atrophy and large choroidal vessels. The AF imaging showed hypo-AF in areas of degeneration, while central AF remained present. OCT images showed outer retinal tubulations and thinned RPE/interdigitation layers. The AOSLO imaging revealed the cone mosaic in central relatively intact retina, and cone density was either reduced or normal at 0.5 mm eccentricity. The border of RPE atrophy showed abrupt loss of the cone mosaic at the same location. The AF imaging in comparison with AOSLO showed RPE health may be compromised before cone degeneration. Other disease features, including visualization of choroidal vessels, hyper-reflective clumps of cones, and unique retinal findings, were tabulated to show the frequency of occurrence and model disease progression. The data support the RPE being one primary site of degeneration in patients with choroideremia. Photoreceptors also may degenerate independently. High resolution imaging, particularly AOSLO in combination with OCT, allows single cell analysis of disease in choroideremia. These modalities promise to be useful in monitoring disease progression, and in documenting the efficacy of gene and cell-based therapies for choroideremia and other diseases as these therapies emerge. (ClinicalTrials.gov number, NCT01866371.).

The incorporation of adaptive optics to scanning ophthalmoscopes (AOSOs) has allowed for in vivo, noninvasive imaging of the human rod and cone photoreceptor mosaics. Light safety restrictions and power limitations of the current low-coherence light sources available for imaging result in each individual raw image having a low signal to noise ratio (SNR). To date, the only approach used to increase the SNR has been to collect large number of raw images (N >50), to register them to remove the distortions due to involuntary eye motion, and then to average them. The large amplitude of involuntary eye motion with respect to the AOSO field of view (FOV) dictates that an even larger number of images need to be collected at each retinal location to ensure adequate SNR over the feature of interest. Compensating for eye motion during image acquisition to keep the feature of interest within the FOV could reduce the number of raw frames required per retinal feature, therefore significantly reduce the imaging time, storage requirements, post-processing times and, more importantly, subject's exposure to light. In this paper, we present a particular implementation of an AOSO, termed the adaptive optics scanning light ophthalmoscope (AOSLO) equipped with a simple eye tracking system capable of compensating for eye drift by estimating the eye motion from the raw frames and by using a tip-tilt mirror to compensate for it in a closed-loop. Multiple control strategies were evaluated to minimize the image distortion introduced by the tracker itself. Also, linear, quadratic and Kalman filter motion prediction algorithms were implemented and tested and tested using both simulated motion (sinusoidal motion with varying frequencies) and human subjects. The residual displacement of the retinal features was used to compare the performance of the different correction strategies and prediction methods.

The adaptive optics (AO) technique is widely used to compensate for ocular aberrations and improve imaging resolution. However, when affected by intraocular scatter, speckle noise, and other factors, the quality of the retinal image will be degraded. To effectively improve the image quality without increasing the imaging system's complexity, the post-processing method of image deblurring is adopted. In this study, we proposed a conditional adversarial network-based method for directly learning an end-to-end mapping between blurry and restored AO retinal images. The proposed model was validated on synthetically generated AO retinal images and real retinal images. The restoration results of synthetic images were evaluated with the metrics of peak signal-to-noise ratio (PSNR), structural similarity (SSIM), perceptual distance, and error rate of cone counting. Moreover, the blind image quality index (BIQI) was used as the no-reference image quality assessment (NR-IQA) algorithm to evaluate the restoration results on real AO retinal images. The experimental results indicate that the images restored by the proposed method have sharper quality and higher signal-to-noise ratio (SNR) when compared with other state-of-the-art methods, which has great practical significance for clinical research and analysis.

Aim: The objective of this project was to evaluate high resolution images from an adaptive optics retinal imager through comparisons with standard film-based and standard digital fundus imagers. Methods: A clinical prototype adaptive optics fundus imager (AOFI) was used to collect retinal images from subjects with various forms of retinopathy to determine whether improved visibility into the disease could be provided to the clinician. The AOFI achieves low-order correction of aberrations through a closed-loop wavefront sensor and an adaptive optics system. The remaining high-order aberrations are removed by direct deconvolution using the point spread function (PSF) or by blind deconvolution when the PSF is not available. An ophthalmologist compared the AOFI images with standard fundus images and provided a clinical evaluation of all the modalities and processing techniques. All images were also analyzed using a quantitative image quality index. Results: This system has been tested on three human subjects (one normal and two with retinopathy). In the diabetic patient vascular abnormalities were detected with the AOFI that cannot be resolved with the standard fundus camera. Very small features, such as the fine vascular structures on the optic disc and the individual nerve fiber bundles are easily resolved by the AOFI. Conclusion: This project demonstrated that adaptive optic images have great potential in providing clinically significant detail of anatomical and pathological structures to the ophthalmologist.

ObjectiveIdiopathic macular telangiectasia (MacTel) is considered primarily a vascular disease affecting juxtafoveal retinal capillaries. However, recent evidence suggests that neuronal changes may occur early in disease development. We used high-resolution...

PurposeMice are highly used in retinal research because, like humans, mice have vascularized retinas and choroidal circulation. Although the retinal circulation has been well-characterized in development, its stability during adulthood is less understood. To examine this network, we quantified several key metrics of the trilaminar vasculature.MethodsWe used mice (n = 15) with transgenic fluorescent NG2-DsRed (JX: #00824), a vascular-associated label in the retina. One eye per mouse was imaged using confocal microscopy (Nikon A1 Ti2 Eclipse) and traced with ImageJ SNT tools. Using an adaptive optics scanning light ophthalmoscope, additional mice (n = 3) were imaged at single-cell resolution within the living eye to measure the same vasculature.ResultsAcross mice, we found a stable retinal circulation that formed and maintained a trilaminar stratification throughout early adulthood at all eccentricities. Bridging these layers, microvessels had five distinct anatomical branching patterns. The superficial, intermediate, and deep plexuses increased in density with depth: 16.14 ± 3.61 mm/mm2, 22.14 ± 6.86 mm/mm2, and 31.01 ± 6.24 mm/mm2, respectively. This patterning was not impacted by eccentricity or age (13–61 weeks). Similar metrics were achieved using adaptive optics scanning light ophthalmoscope in vivo with the same analysis pipeline.ConclusionsThe mouse retinal vasculature was stable up to 50 weeks of age, providing a robust and extensive baseline dataset with which models of retinal vascular and neural disease may be compared. Vessels connecting the laminae were more complex than previously reported and represented a uniquely vulnerable population due to their relatively low density.

Background/aimsThe purpose of this study was to investigate retinal structure in detail of subjects with autosomal-dominant (AD) and autosomal-recessive (AR) PROM1-associated retinal degeneration (PROM1-RD), study design: institutional, cross-sectional study.MethodsFour eyes...

Fast and reliable quantification of cone photoreceptors is a bottleneck in the clinical utilization of adaptive optics scanning light ophthalmoscope (AOSLO) systems for the study, diagnosis, and prognosis of retinal diseases. To-date, manual grading has been the sole reliable source of AOSLO quantification, as no automatic method has been reliably utilized for cone detection in real-world low-quality images of diseased retina. We present a novel deep learning based approach that combines information from both the confocal and non-confocal split detector AOSLO modalities to detect cones in subjects with achromatopsia. Our dual-mode deep learning based approach outperforms the state-of-the-art automated techniques and is on a par with human grading.

Retinal imaging capable of resolving individual photoreceptors cannot be obtained with conventional ophthalmoscopy but requires compensation of the individual optical aberrations that blur the optical image from the fundus. This optical compensation is normally accomplished by adaptive optics. We built a retinal imaging system based on adaptive optics can image individual cone photoreceptors. The system uses infrared radiation from a superluminescent diode (SLD) and a Hartman-Shack wavefront sensor to measure eye aberrations. An ophthalmoscope channel with a digital camera is integrated with the system to visualize the retina. A deformable mirror is used to partially compensate the aberrations of the light from the eye thereby improving the image quality and optical resolution. Images from the fundus were obtained from one healthy retina at about 0.5–1.0 deg eccentricity. The cone photoreceptor mosaic is visible and individual photoreceptors can be inspected.

Adaptive optics full-filed OCT (FFOCT) with a transmissive liquid crystal spatial light modulator (LCSLM) as wavefront corrector is used without strict plane conjugation for low order aberrations corrections. We validated experimentally that FFOCT resolution is independent of aberrations and only reduce the signal level. A signal based sensorless algorithm was thus applied for wavefront distortion compensation. Image quality improvements by the wavefront sensorless control of the LCSLM were evaluated on in vitro samples. By replacing the FFOCT sample arm objective with an artificial eye used to train ophthalmologists, adaptive optics retinal imaging was achieved. In vivo experiments using a liquid lens to correct focus and astigmatism are underway.

To compare images of photoreceptor layer disruptions obtained with optical coherence tomography (OCT) and adaptive optics scanning light ophthalmoscopy (AOSLO) in a variety of pathologic states. Five subjects with photoreceptor ellipsoid zone disruption as per OCT and clinical diagnoses of closed-globe blunt ocular trauma (n = 2), macular telangiectasia type 2 (n = 1), blue-cone monochromacy (n = 1), or cone-rod dystrophy (n = 1) were included. Images were acquired within and around photoreceptor lesions using spectral domain OCT, confocal AOSLO, and split-detector AOSLO. There were substantial differences in the extent and appearance of the photoreceptor mosaic as revealed by confocal AOSLO, split-detector AOSLO, and spectral domain OCT en face view of the ellipsoid zone. Clinically available spectral domain OCT, viewed en face or as B-scan, may lead to misinterpretation of photoreceptor anatomy in a variety of diseases and injuries. This was demonstrated using split-detector AOSLO to reveal substantial populations of photoreceptors in areas of no, low, or ambiguous ellipsoid zone reflectivity with en face OCT and confocal AOSLO. Although it is unclear if these photoreceptors are functional, their presence offers hope for therapeutic strategies aimed at preserving or restoring photoreceptor function.

To characterize the photoreceptors and choroidal morphology of heterozygous female carriers of choroideremia who typically do not have any visual defects but can have severe funduscopic changes. This was a clinical case series study. Detailed ophthalmic examinations were performed on six female carriers from four families with choroideremia. The subfoveal choroidal thickness (SFCT) was determined by spectral-domain optical coherence tomography (SD-OCT) and the cone photoreceptor density by adaptive optics (AO) retinal imaging. SFCT and cone densities of the carriers were compared to that of normal eyes of healthy subjects. The mean age of the carriers was 42.5 years. Fundus photographs showed diffuse, patchy depigmentation; however, the SFCT was within the normal limits. AO retinal imaging revealed preserved cone densities at temporal eccentricities from 2 to 8 angular degrees. The findings indicate that despite the presence of distinctive depigmentation of the retinal pigment epithelium in female carriers of choroideremia, their cone photoreceptor densities and SFCT are well-preserved. These observations may account for the good visual acuity and lack of an awareness of visual disturbances. [Ophthalmic Surg Lasers Imaging Retina. 2019;50:76-85.].

In retinal raster imaging modalities, fixational eye movements manifest as image warp, where the relative positions of the beam and retina change during the acquisition of single frames. To remove warp artifacts, strip-based registration methods–in which fast-axis strips from target images are registered to a reference frame–have been applied in adaptive optics (AO) scanning light ophthalmoscopy (SLO) and optical coherence tomography (OCT). This approach has enabled object tracking and frame averaging, and methods have been described to automatically select reference frames with minimal motion. However, inconspicuous motion artifacts may persist in reference frames and propagate themselves throughout the processes of registration, tracking, and averaging. Here we test a previously proposed method for removing movement artifacts in reference frames, using biases in stripwise cross-correlation statistics. We applied the method to synthetic retinal images with simulated eye motion artifacts as well as real AO-SLO images of the cone mosaic and volumetric AO-OCT images, both affected by eye motion. In the case of synthetic images, the method was validated by direct comparison with motion-free versions of the images. In the case of real AO images, performance was validated by comparing the correlation of uncorrected images with that of corrected images, by quantifying the effect of motion artifacts on the image power spectra, and by qualitative examination of AO-OCT B-scans and en face projections. In all cases, the proposed method reduced motion artifacts and produced more faithful images of the retina.

Recent advances in the acquisition of in-vivo high resolution retinal images through the use of Adaptive Optics (AO) have allowed the identification of cellular structures such as cones and rods, in and out of the fovea, in such a way that their histological characteristics can be studied in-vivo and later compared to data obtained post-mortem . In this work, an algorithm is proposed for the detection of photoreceptors; it consists of two stages: Early Cell Detection (ECD), to detect all candidate cells, and Refinement of Cell Detection (RCD), to reduce over-detection of photoreceptors. The algorithm has been tested using synthetic and real images, the latter acquired with an Adaptive Optics Scanning Light Ophthalmoscope (AOSLO). The proposed algorithm was compared against the one developed by Li and Roorda, and both algorithms were tested on synthetic and real images, yielding similar algorithm performance on both kinds of images when they had only cones; however, the algorithm developed by Li and Roorda, when applied to real images having cones and rods, identifies photoreceptors in vascular tissue, in addition to showing low rod detection.

PurposeTo perform deep phenotyping of subjects with PDE6C achromatopsia and examine disease natural history.MethodsEight subjects with disease-causing variants in PDE6C were assessed in detail, including clinical phenotype, best-corrected visual acuity, fundus autofluorescence, and optical coherence tomography. Six subjects also had confocal and nonconfocal adaptive optics scanning light ophthalmoscopy, axial length, international standard pattern and full-field electroretinography (ERG), short-wavelength flash (S-cone) ERGs, and color vision testing.ResultsAll subjects presented with early-onset nystagmus, decreased best-corrected visual acuity, light sensitivity, and severe color vision loss, and five of them had high myopia. We identified three novel disease-causing variants and provide phenotype data associated with nine variants for the first time. No subjects had foveal hypoplasia or residual ellipsoid zone (EZ) at the foveal center; one had an absent EZ, three had a hyporeflective zone, and four had outer retinal atrophy. The mean width of the central EZ lesion on optical coherence tomography at baseline was 1923 μm. The mean annual increase in EZ lesion size was 48.3 μm. Fundus autofluorescence revealed a central hypoautofluorescence with a surrounding ring of increased signal (n = 5). The mean hypoautofluorescent area at baseline was 3.33 mm2 and increased in size by a mean of 0.13 mm2/year. Nonconfocal adaptive optics scanning light ophthalmoscopy revealed residual foveal cones in only one of two cases. Full-field ERGs were consistent with severe generalized cone system dysfunction but with relative preservation of S-cone sensitivity.ConclusionsPDE6C retinopathy is a severe cone dysfunction syndrome often presenting as typical achromatopsia but without foveal hypoplasia. Myopia and slowly progressive maculopathy are common features. There are few (if any) residual foveal cones for intervention in older adults.