ASSESSING PHOTORECEPTOR STRUCTURE ASSOCIATED WITH ELLIPSOID ZONE DISRUPTIONS VISUALIZED WITH OPTICAL COHERENCE TOMOGRAPHY

Chemically induced cone degeneration in the 13-lined ground squirrel

Animal models of retinal degeneration are critical for understanding disease and testing potential therapies. Inducing degeneration commonly involves the administration of chemicals that kill photoreceptors by disrupting metabolic pathways, signaling pathways, or protein synthesis. While chemically induced degeneration has been demonstrated in a variety of animals (mice, rats, rabbits, felines, 13-lined ground squirrels (13-LGS), pigs, chicks), few studies have used noninvasive high-resolution retinal imaging to monitor the in vivo cellular effects. Here, we used longitudinal scanning light ophthalmoscopy (SLO), optical coherence tomography, and adaptive optics SLO imaging in the euthermic, cone-dominant 13-LGS (46 animals, 52 eyes) to examine retinal structure following intravitreal injections of chemicals, which were previously shown to induce photoreceptor degeneration, throughout the active season of 2019 and 2020. We found that iodoacetic acid induced severe pan-retinal damage in all but one eye, which received the lowest concentration. While sodium nitroprusside successfully induced degeneration of the outer retinal layers, the results were variable, and damage was also observed in 50% of contralateral control eyes. Adenosine triphosphate and tunicamycin induced outer retinal specific damage with varying results, while eyes injected with thapsigargin did not show signs of degeneration. Given the variability of damage we observed, follow-up studies examining the possible physiological origins of this variability are critical. These additional studies should further advance the utility of chemically induced photoreceptor degeneration models in the cone-dominant 13-LGS.

Retinal Imaging Findings in Inherited Retinal Diseases

Inherited retinal diseases (IRDs) represent one of the major causes of progressive and irreversible vision loss in the working-age population. Over the last few decades, advances in retinal imaging have allowed for an improvement in the phenotypic characterization of this group of diseases and have facilitated phenotype-to-genotype correlation studies. As a result, the number of clinical trials targeting IRDs has steadily increased, and commensurate to this, the need for novel reproducible outcome measures and endpoints has grown. This review aims to summarize and describe the clinical presentation, characteristic imaging findings, and imaging endpoint measures that are being used in clinical research on IRDs. For the purpose of this review, IRDs have been divided into four categories: (1) panretinal pigmentary retinopathies affecting rods or cones; (2) macular dystrophies; (3) stationary conditions; (4) hereditary vitreoretinopathies.

Photoreceptor Integrity in MEWDS: Longitudinal Structure-Function Correlations

Purpose

The purpose of this study was to investigate structure-function correlations in multiple evanescent white dot syndrome (MEWDS) using microperimetry (MP) and spectral-domain optical coherence tomography (SD-OCT).

Methods

Single-center prospective observational study including 14 eyes from 13 patients with MEWDS monitored over a median of 49.5 days (interquartile range = 29-92 days). Investigations focused on best-corrected visual acuity (BCVA), foveal granularity, and the Photoreceptor Reflectivity Ratio (PRR) as a measure of photoreceptor integrity. MP assessed average retinal threshold sensitivity (RTS) and bivariate contour ellipse area (BCEA) for fixation stability. A linear mixed model was used to test associations and interactions among RTS, time, and clinical variables. A hierarchical linear mixed model was used to analyze structure-function relationships, addressing both individual and location-specific variations.

Results

Overall, 2340 MP locations were tested. PRR revealed a transient decrease within 30 days post-presentation, indicative of early photoreceptor disruption, followed by a progressive increase, signaling recovery. Significantly lower foveal sensitivity (RTS = 14.8 ± 7.4 vs. 22.5 ± 4.4 decibel [dB], P = 0.04) and increased fixation spread (63% BCEA = 1.26 ± 0.97 vs. 0.48 ± 0.35 deg2, P = 0.06) were noted in eyes with foveal granularity compared to those without. A significant increase in RTS was demonstrated over time (0.066 dB/day, P < 0.001), with a central-to-peripheral gradient of improvement. The interaction between follow-up time and baseline BCVA (P < 0.001) indicated more rapid improvement in eyes with worse initial vision. There was a robust, nonlinear association between PRR and RTS across all tested locations (P < 0.001), becoming asymptotic for sensitivity losses exceeding 20 dB.

Conclusions

Photoreceptor reflectivity accurately aligned with visual function in MEWDS on longitudinal examinations. The central-to-peripheral gradient of improvement may suggest specific vulnerabilities underlying the area around the disc.

The USH3A causative gene clarin1 functions in Müller glia to maintain retinal photoreceptors

Mutations in CLRN1 cause Usher syndrome type IIIA (USH3A), an autosomal recessive disorder characterized by hearing and vision loss, and often accompanied by vestibular balance issues. The identity of the cell types responsible for the pathology and mechanisms leading to vision loss in USH3A remains elusive. To address this, we employed CRISPR/Cas9 technology to delete a large region in the coding and untranslated (UTR) region of zebrafish clrn1. Retina of clrn1 mutant larvae exhibited sensitivity to cell stress, along with age-dependent loss of function and degeneration in the photoreceptor layer. Investigation revealed disorganization in the outer retina in clrn1 mutants, including actin-based structures of the Müller glia and photoreceptor cells. To assess cell-specific contributions to USH3A pathology, we specifically re-expressed clrn1 in either Müller glia or photoreceptor cells. Müller glia re-expression of clrn1 prevented the elevated cell death observed in larval clrn1 mutant zebrafish exposed to high-intensity light. Notably, the degree of phenotypic rescue correlated with the level of Clrn1 re-expression. Surprisingly, high levels of Clrn1 expression enhanced cell death in both wild-type and clrn1 mutant animals. However, rod- or cone-specific Clrn1 re-expression did not rescue the extent of cell death. Taken together, our findings underscore three crucial insights. First, clrn1 mutant zebrafish exhibit key pathological features of USH3A; second, Clrn1 within Müller glia plays a pivotal role in photoreceptor maintenance, with its expression requiring controlled regulation; third, the reliance of photoreceptors on Müller glia suggests a structural support mechanism, possibly through direct interactions between Müller glia and photoreceptors mediated in part by Clrn1 protein.

Adaptive optics imaging in inherited retinal diseases: A scoping review of the clinical literature

Adaptive optics (AO) imaging enables direct, objective assessments of retinal cells. Applications of AO show great promise in advancing our understanding of the etiology of inherited retinal disease (IRDs) and discovering new imaging biomarkers. This scoping review systematically identifies and summarizes clinical studies evaluating AO imaging in IRDs. Ovid MEDLINE and EMBASE were searched on February 6, 2023. Studies describing AO imaging in monogenic IRDs were included. Study screening and data extraction were performed by 2 reviewers independently. This review presents (1) a broad overview of the dominant areas of research; (2) a summary of IRD characteristics revealed by AO imaging; and (3) a discussion of methodological considerations relating to AO imaging in IRDs. From 140 studies with AO outcomes, including 2 following subretinal gene therapy treatments, 75% included fewer than 10 participants with AO imaging data. Of 100 studies that included participants' genetic diagnoses, the most common IRD genes with AO outcomes are CNGA3, CNGB3, CHM, USH2A, and ABCA4. Confocal reflectance AO scanning laser ophthalmoscopy was the most reported imaging modality, followed by flood-illuminated AO and split-detector AO. The most common outcome was cone density, reported quantitatively in 56% of studies. Future research areas include guidelines to reduce variability in the reporting of AO methodology and a focus on functional AO techniques to guide the development of therapeutic interventions.

Relation of interdigitation zone changes and right-angle vessels in Macular Telangiectasia Type-2 (MacTel)

BACKGROUND

To study the relation between interdigitation zone (IDZ) and right-angle vessel (RAV) in Macular Telangiectasia Type-2 (MacTel).

METHODS

A total of 43 eyes of 38 patients with presence of definite RAV on colour fundus photograph (Gass and Blodi-only stage-3) were confirmed on multimodal imaging. The relation of IDZ changes and associated ellipsoid zone (EZ) alterations on spectral-domain optical coherence tomography (OCT) with RAV were studied at baseline and these OCT changes were followed up in 15 eyes over a mean of 3.86 years.

RESULTS

A total of 58 RAVs were found in the 43 eyes and 53/58 (91.3%) RAVs were associated with IDZ alterations in 39 eyes. On follow-up, IDZ attenuation progressed to IDZ loss and subsequent EZ attenuation and loss. A pre-existing IDZ loss was associated with subsequent EZ defect (P = 0.002). In 36 eyes that had OCT angiography, eyes with RAV showed deep capillary plexus telangiectasia in all 36 (100%) eyes and 32/36 (89%) eyes showed IDZ changes with or without EZ loss.

CONCLUSIONS

IDZ attenuation and/or loss are associated with RAV and may serve as predictor of EZ loss in MacTel.

Blue cone monochromacy and gene therapy

Blue cone monochromacy (BCM) is a congenital vision disorder characterized by complete loss or severely reduced long- and middle-wavelength cone function, caused by mutations in the OPN1LW/OPN1MW gene cluster on the X-chromosome. BCM patients typically suffer from poor visual acuity, severely impaired color discrimination, myopia, and nystagmus. In this review, we cover the genetic causes of BCM, clinical features of BCM patients, genetic testing, and clinical outcome measurements for future BCM clinical trials. However, our emphasis is on detailing the animal models for BCM and gene therapy using adeno-associated vectors (AAV). We describe two mouse models resembling the two most common causes of BCM, current progress in proof-of-concept studies to treat BCM with deletion mutations, the challenges we face, and future directions.

Clinical and Genetic Features of Korean Patients with Achromatopsia

This multicenter study aimed to characterize Korean patients with achromatopsia. The patients' genotypes and phenotypes were retrospectively evaluated. Twenty-one patients (with a mean age at the baseline of 10.9 years) were enrolled and followed up for a mean of 7.3 years. A targeted gene panel or exome sequencing was performed. The pathogenic variants of the four genes and their frequencies were identified. CNGA3 and PDE6C were equally the most prevalent genes: CNGA3 (N = 8, 38.1%), PDE6C (N = 8, 38.1%), CNGB3 (N = 3, 14.3%), and GNAT2 (N = 2, 9.5%). The degree of functional and structural defects varied among the patients. The patients' age exhibited no significant correlation with structural defects. During the follow-up, the visual acuity and retinal thickness did not change significantly. In CNGA3-achromatopsia patients, a proportion of patients with a normal foveal ellipsoid zone on the OCT was significantly higher than that of patients with other causative genes (62.5% vs. 16.7%; p = 0.023). In PDE6C-achromatopsia patients, the same proportion was significantly lower than that of patients with other causative genes (0% vs. 58.3%; p = 0.003). Korean patients with achromatopsia showed similar clinical features but a higher prevalence of PDE6C variants than those of other ethnic groups. The retinal phenotypes of the PDE6C variants were more likely to be worse than those of other genes.

Extracting spacing-derived estimates of rod density in healthy retinae

Quantification of the rod photoreceptor mosaic using adaptive optics scanning light ophthalmoscopy (AOSLO) remains challenging. Here we demonstrate a method for deriving estimates of rod density and rod:cone ratio based on measures of rod spacing, cone numerosity, and cone inner segment area. Twenty-two AOSLO images with complete rod visualization were used to validate this spacing-derived method for estimating density. The method was then used to estimate rod metrics in an additional 105 images without complete rod visualization. The spacing-derived rod mosaic metrics were comparable to published data from histology. This method could be leveraged to develop large normative databases of rod mosaic metrics, though limitations persist with intergrader variability in assessing cone area and numerosity.

Visual function and retinal changes after voretigene neparvovec treatment in children with biallelic RPE65-related inherited retinal dystrophy

To report quantitative retinal changes assessed by spectral-domain optical coherence tomography (SD-OCT) in children treated with voretigene neparvovec (VN) at a single center in Italy. Retrospective review of six consecutive pediatric patients with biallelic RPE65-related dystrophy treated bilaterally with VN. SD-OCT scans were analyzed to extract Early Treatment Diabetic Retinopathy Study (ETDRS) thickness maps of the whole retina and the outer nuclear layer (ONL). Changes in visual function were assessed by best-corrected visual acuity (BCVA) and retinal morphology at Days 30/45 and 180. BCVA significantly improved at Day 30/45 and 6 months (both P < 0.001). Central foveal retinal thickness and central foveal ONL thickness tended to increase (6.4 ± 19.2 µm; P = 0.080 and 3.42 ± 7.68 µm; P = 0.091, respectively). ONL thickness of the internal ETDRS-ring significantly increased at day 30/45 (4.7 ± 8.4 µm; P < 0.001) and day 180 (5.0 ± 5.7 µm; P = 0.009). Intra-operative foveal detachment was not associated with a higher function gain in terms of BCVA, but with a mild thinning of foveal ONL after treatment. The improvement of BCVA and thickening of the ONL layer suggest that improvement of visual acuity could be related to partial recovery of retinal morphology in the perifoveal ring.

Reflectance adaptive optics findings in a patient with Vogt-Koyanagi-Harada disease

Purpose

To describe the reflectance adaptive optics scanning laser ophthalmoscopy (AOSLO) findings in different stages of Vogt-Koyanagi-Harada (VKH) disease and correlate them to visual gain post treatment. Confocal (cAOSLO) and non-confocal split-detector AOSLO (sdAOSLO) were used to assess longitudinally the status of the photoreceptors in a patient with VKH managed on corticosteroid and immunomodulatory therapy.

Observation

A 32-year-old Japanese American female presented with a 2-week history of blurred vision in both eyes (OU) and worsening headache previously diagnosed as a case of VKH and treated with high dose oral prednisone. At the time of presentation, though vision was improving, and frank serous retinal detachments were absent, spectral domain optical coherence tomography (SD-OCT) showed presence of residual subretinal fluid with disruption of the photoreceptor inner segments and outer segments (IS/OS) involving OU. The photoreceptor mosaic at the foveal center appeared very sparse with large areas devoid of visible photoreceptors on cAOSLO, in agreement with the SD-OCT data. sdAOSLO imaging over the same location shows a higher number of contiguous photoreceptors. After imaging, the patient was started on mycophenolate mofetil as steroid-sparing long-term therapy. Three months later, visual acuity improved to 20/20 OU, and SD-OCT showed almost complete resolution of subretinal fluid with significant improvement of the IS/OS SD-OCT signal, OU. cAOSLO imaging revealed a contiguous photoreceptor mosaic without gaps and of normal appearance.

Conclusions and Importance

VKH patients may demonstrate transient photoreceptor abnormalities on SD-OCT and cAOSLO imaging. sdAOSLO imaging revealed intact photoreceptor segments in areas that appeared as voids on cAOSLO, which later showed structural recovery on SD-OCT and cAOSLO. Therefore, sdAOSLO may predict potential for improvement in patients wherein there appears to be photoreceptor loss in cAOSLO and/or SD-OCT.

Early-stage macular telangiectasia type 2 vascular abnormalities are associated with interdigitation zone disruption

PURPOSE

To investigate the relationship between disruption in different photoreceptor layers and deep capillary plexus (DCP) telangiectasias in eyes with macular telangiectasia type 2 (MacTel).

METHODS

35 eyes (21 patients) with MacTel imaged with optical coherence tomography angiography (OCTA) were included. Circumscribed areas of DCP telangiectasia were traced from OCTA slabs and the corresponding spectral-domain OCT (SD-OCT) slabs were used to visualize the photoreceptor layer interdigitation zone (IZ) and ellipsoid zone (EZ). IZ attenuation, IZ loss, and EZ loss were graded by reviewing en face SD-OCT slabs for hypo-reflective areas and confirming their status on cross-sectional views. Total area of photoreceptor disruption and overlap with DCP telangiectasia were evaluated with respect to OCT-based MacTel stage. Longitudinal changes were evaluated in a subset of patients with follow-up imaging.

RESULTS

Overlap of DCP telangiectasia with IZ attenuation significantly decreased with MacTel severity, while overlap with IZ and EZ loss significantly increased. Overlap with IZ loss peaked in moderate MacTel (Stages 3-5). Longitudinal imaging showed that new EZ loss at 6 months was largely predicted by baseline IZ loss.

CONCLUSIONS

Worsening MacTel severity is characterized by greater overlap between DCP telangiectasia and zones of increasing severity of photoreceptor disruption, with EZ loss enlarging over time within areas of preexisting IZ disruption. We suggest that IZ disruption may indicate early photoreceptor dysfunction that eventually progresses to EZ loss, with IZ loss being a more reliable metric than IZ attenuation. Additional studies will be necessary to further explore long-term photoreceptor changes and evaluate their relationship with visual function in MacTel.

Gene Therapy in Inherited Retinal Diseases: An Update on Current State of the Art

Background: Gene therapy cannot be yet considered a far perspective, but a tangible therapeutic option in the field of retinal diseases. Although still confined in experimental settings, the preliminary results are promising and provide an overall scenario suggesting that we are not so far from the application of gene therapy in clinical settings. The main aim of this review is to provide a complete and updated overview of the current state of the art and of the future perspectives of gene therapy applied on retinal diseases.

Methods: We carefully revised the entire literature to report all the relevant findings related to the experimental procedures and the future scenarios of gene therapy applied in retinal diseases. A clinical background and a detailed description of the genetic features of each retinal disease included are also reported.

Results: The current literature strongly support the hope of gene therapy options developed for retinal diseases. Although being considered in advanced stages of investigation for some retinal diseases, such as choroideremia (CHM), retinitis pigmentosa (RP), and Leber's congenital amaurosis (LCA), gene therapy is still quite far from a tangible application in clinical practice for other retinal diseases.

Conclusions: Gene therapy is an extremely promising therapeutic tool for retinal diseases. The experimental data reported in this review offer a strong hope that gene therapy will be effectively available in clinical practice in the next years.

Challenges Associated With Ellipsoid Zone Intensity Measurements Using Optical Coherence Tomography

Translational Relevance

Qualitative evaluation of the ellipsoid zone band on optical coherence tomography is a valuable clinical tool for assessing photoreceptor structure, though more quantitative metrics are emerging. Awareness of the challenges involved in interpreting quantitative metrics is important for their clinical translation.

Defining inclusion criteria and endpoints for clinical trials: a prospective cross-sectional study in CRB1-associated retinal dystrophies

Purpose

To investigate the retinal structure and function in patients with CRB1‐associated retinal dystrophies (RD) and to explore potential clinical endpoints.

Methods

In this prospective cross‐sectional study, 22 patients with genetically confirmed CRB1‐RD (aged 6–74 years), and who had a decimal best‐corrected visual acuity (BCVA) ≥ 0.05 at the last visit, were studied clinically with ETDRS BCVA, corneal topography, spectral‐domain optical coherence tomography (SD‐OCT), fundus autofluorescence, Goldmann visual field (VF), microperimetry, full‐field electroretinography (ERG) and full‐field stimulus testing (FST). Ten patients were from a genetic isolate (GI).

Results

Patients had retinitis pigmentosa (n = 19; GI and non‐GI), cone‐rod dystrophy (n = 2; GI) or macular dystrophy (n = 1; non‐GI). Median age at first symptom onset was 3 years (range 0.8–49). Median decimal BCVA in the better and worse‐seeing eye was 0.18 (range 0.05–0.83) and 0.08 (range light perception‐0.72), respectively. Spectral‐domain optical coherence tomography (SD‐OCT) showed cystoid maculopathy in 8 subjects; inner retinal thickening (n = 20), a well‐preserved (para)foveal outer retina (n = 7) or severe (para)foveal outer retinal atrophy (n = 14). All retinal layers were discernible in 13/21 patients (62%), with mild to moderate laminar disorganization in the others. Nanophthalmos was observed in 8 patients (36%). Full‐field stimulus testing (FST) provided a subjective outcome measure for retinal sensitivity in eyes with (nearly) extinguished ERG amplitudes.

Conclusions

Despite the generally severe course of CRB1‐RDs, symptom onset and central visual function are variable, even at advanced ages. Phenotypes may vary within the same family. Imaging and functional studies in a prospective longitudinal setting should clarify which endpoints may be most appropriate in a clinical trial.

Comparison of confocal and non-confocal split-detection cone photoreceptor imaging

Quadrant reflectance confocal and non-confocal scanning light ophthalmoscope images of the photoreceptor mosaic were recorded in a subject with congenital achromatopsia (ACHM) and a normal control. These images, captured with various circular and annular apertures, were used to calculate split-detection images, revealing two cone photoreceptor contrast mechanisms. The first contrast mechanism, maximal in the non-confocal 5.5-10 Airy disk diameter annular region, is unrelated to the cone reflectivity in confocal or flood illumination imaging. The second mechanism, maximal for confocal split-detection, is related to the cone reflectivity in confocal or flood illumination imaging that originates from the ellipsoid zone and/or inner-outer segment junction. Seeking to maximize image contrast, split-detection images were generated using various quadrant detector combinations, with opposite (diagonal) quadrant detectors producing the highest contrast. Split-detection generated with the addition of adjacent quadrant detector pairs, shows lower contrast, while azimuthal split-detection images, calculated from adjacent quadrant detectors, showed the lowest contrast. Finally, the integration of image pairs with orthogonal split directions was used to produce images in which the photoreceptor contrast does not change with direction.

ASSESSING THE ABILITY OF PREOPERATIVE QUANTITATIVE SPECTRAL-DOMAIN OPTICAL COHERENCE TOMOGRAPHY CHARACTERISTICS TO PREDICT VISUAL OUTCOME IN IDIOPATHIC MACULAR HOLE SURGERY

PURPOSE

To determine which spectral domain optical coherence tomography biomarkers of idiopathic macular hole (MH) correlate with the postoperative best-corrected visual acuity (BCVA) in anatomically closed MH.

METHODS

Retrospective analysis of spectral domain optical coherence tomography scans of 44 patients presenting with MH followed for a mean of 17 months. Widths of MH aperture, base, and ellipsoid zone disruption were calculated from presenting foveal spectral domain optical coherence tomography B-scans. Macular hole base area and ellipsoid zone disruption area were calculated through the custom in-house software.

RESULTS

Poorer postoperative BCVA correlated with increased preoperative choroidal hypertransmission (r = 0.503, P = 0.0005), minimum diameter (r = 0.491, P = 0.0007), and base diameter (r = 0.319, P = 0.0348), but not with preoperative ellipsoid zone width (r = 0.199, P = 0.2001). Applying en-face analysis, the BCVA correlated weakly with preoperative ellipsoid zone loss area (r = 0.380, P = 0.013), but not with preoperative MH base area (r = 0.253, P = 0.1058).

CONCLUSION

Increased MH minimum diameter, base diameter, base area, and choroidal hypertransmission are correlated with a poorer postoperative BCVA. Ellipsoid zone loss measurements were not consistently correlated with a BCVA. Choroidal hypertransmission width may be an easy-to-visualize predictive imaging biomarker in MH surgery.

Promises and pitfalls of evaluating photoreceptor-based retinal disease with adaptive optics scanning light ophthalmoscopy (AOSLO)

Adaptive optics scanning light ophthalmoscopy (AOSLO) allows visualization of the living human retina with exquisite single-cell resolution. This technology has improved our understanding of normal retinal structure and revealed pathophysiological details of a number of retinal diseases. Despite the remarkable capabilities of AOSLO, it has not seen the widespread commercial adoption and mainstream clinical success of other modalities developed in a similar time frame. Nevertheless, continued advancements in AOSLO hardware and software have expanded use to a broader range of patients. Current devices enable imaging of a number of different retinal cell types, with recent improvements in stimulus and detection schemes enabling monitoring of retinal function, microscopic structural changes, and even subcellular activity. This has positioned AOSLO for use in clinical trials, primarily as exploratory outcome measures or biomarkers that can be used to monitor disease progression or therapeutic response. AOSLO metrics could facilitate patient selection for such trials, to refine inclusion criteria or to guide the choice of therapy, depending on the presence, absence, or functional viability of specific cell types. Here we explore the potential of AOSLO retinal imaging by reviewing clinical applications as well as some of the pitfalls and barriers to more widespread clinical adoption.

Topographic Relationship between Telangiectasia and Cone Mosaic Disruption in Macular Telangiectasia Type 2

In this cross-sectional observational study, we investigated the relationship between photoreceptor layer disruption and telangiectasia in patients diagnosed with early stage macular telangiectasia type 2 (MacTel). A total of 31 eyes (17 patients) with MacTel were imaged with adaptive optics scanning laser ophthalmoscopy (AOSLO) and optical coherence tomography angiography (OCTA). Confocal AOSLO was used to visualize dark regions of nonwaveguiding outer segments, which we refer to as “photoreceptor lesions”. En-face OCTA images of the deep capillary plexus (DCP) were used in conjunction with confocal AOSLO to evaluate the topographic relationship between areas of capillary telangiectasias and photoreceptor lesions. Among seven eyes with early stage MacTel (stage 0–2 based on OCT), we identified ten photoreceptor lesions, all of which were located within parafoveal quadrants containing DCP telangiectasia on OCTA. Seven of the lesions corresponded to the intact ellipsoid zone on spectral-domain OCT (SD-OCT), and three of these also corresponded to the intact interdigitation zone. This work demonstrates a topographic relationship between AOSLO photoreceptor lesions and DCP telangiectasias, and it also suggests that these lesions with normal SD-OCT appearance may represent areas of photoreceptors at risk for dysfunction. Thus, confocal AOSLO may have a meaningful role in detecting early photoreceptor abnormalities in eyes with MacTel.

Longitudinal Assessment of Remnant Foveal Cone Structure in a Case Series of Early Macular Telangiectasia Type 2

Purpose

To determine the extent of remnant cone structure within early foveal ellipsoid zone (EZ) lesions in macular telangiectasia type 2 longitudinally using both confocal and split detector adaptive optics scanning light ophthalmoscopy (AOSLO).

Methods

Spectral domain optical coherence tomography (SDOCT), confocal and split detector AOSLO were acquired from seven patients (10 eyes) with small (early) EZ lesions on SDOCT secondary to macular telangiectasia type 2 at baseline, 6 months, and 12 months. The presence of cone structure on AOSLO in areas of EZ loss as well as cones at 1° eccentricity, and their change over time were quantified.

Results

By split detector AOSLO, remnant cone structure was identified within and on the borders of all foveal EZ lesions. Within the extent of these lesions, cone spacing ranged from 4.97 to 9.95 µm at baseline, 5.30 to 6.10 µm at 6 months, and 4.99 to 7.12 µm at 12 months. Four eyes with significantly smaller EZ lesions showed evidence of recovery of EZ reflectivity on SDOCT B-scans. Remnant cone structure was identified in some areas where EZ reflectivity recovered at the following time point. Eyes that showed recovery of EZ reflectivity had a continuous external limiting membrane.

Conclusions

Remnant cone structure can persist within small SDOCT-defined EZ lesions, which can wax and wane in appearance over time. AOSLO can help to inform the interpretation of SDOCT imaging.

Translational Relevance

The absence of EZ in early macular telangiectasia type 2 and other retinal conditions needs careful interpretation because it does not always indicate an absence of underlying cone structure. The integrity of the external limiting membrane may better predict the presence of remnant cone structure and recovery of EZ reflectivity.

Foveal Therapy in Blue Cone Monochromacy: Predictions of Visual Potential From Artificial Intelligence

Novel therapeutic approaches for treating inherited retinal degenerations (IRDs) prompt a need to understand which patients with impaired vision have the anatomical potential to gain from participation in a clinical trial. We used supervised machine learning to predict foveal function from foveal structure in blue cone monochromacy (BCM), an X-linked congenital cone photoreceptor dysfunction secondary to mutations in the OPN1LW/OPN1MW gene cluster. BCM patients with either disease-associated large deletion or missense mutations were studied and results compared with those from subjects with other forms of IRD and various degrees of preserved central structure and function. A machine learning technique was used to associate foveal sensitivities and best-corrected visual acuities to foveal structure in IRD patients. Two random forest (RF) models trained on IRD data were applied to predict foveal function in BCM. A curve fitting method was also used and results compared with those of the RF models. The BCM and IRD patients had a comparable range of foveal structure. IRD patients had peak sensitivity at the fovea. Machine learning could successfully predict foveal sensitivity (FS) results from segmented or un-segmented optical coherence tomography (OCT) input. Application of machine learning predictions to BCM at the fovea showed differences between predicted and measured sensitivities, thereby defining treatment potential. The curve fitting method provided similar results. Given a measure of visual acuity (VA) and foveal outer nuclear layer thickness, the question of how many lines of acuity would represent the best efficacious result for each BCM patient could be answered. We propose that foveal vision improvement potential in BCM is predictable from retinal structure using machine learning and curve fitting approaches. This should allow estimates of maximal efficacy in patients being considered for clinical trials and also guide decisions about dosing.

CHANGES IN VISUAL ACUITY AND PHOTORECEPTOR DENSITY USING ADAPTIVE OPTICS AFTER RETINAL DETACHMENT REPAIR

PURPOSE

To quantify changes in photoreceptor density using adaptive optics fundus camera in patients after retinal detachment (RD) and to correlate them with macular involvement and best-corrected visual acuity.

METHODS

At 1 and 3 months (M1 and M3) after vitrectomy, 194 patients underwent adaptive optics imagery in both eyes, at 5 locations, that we matched between time points using anatomical landmarks. Twenty-two patients (10 fovea-OFF [OFF] and 12 fovea-ON [ON]) had matched and analyzable adaptive optics images. We used analysis of variance for repeated measures.

RESULTS

Best-corrected visual acuity (logarithm of the minimum angle of resolution and Snellen equivalent [SE]) was significantly different between OFF and ON RDs at baseline: 2.0 (2.3-0.95) (SE: 20/2000) versus 0 (0.1-0) (SE: 20/20); at M1: 0.35 (0.5-0.1) (SE: 20/40) versus 0.05 (0-0.1) (SE: 20/25); and at M3: 0.25 (0.3-0.1) (SE: 20/32) versus 0 (0-0) (SE: 20/20). We observed that cone density was stable in fellow eyes between M1 and M3 (P = 0.67); decreased in treated eyes than in fellow eyes (P < 0.05); and increased postoperatively in the ON group (P = 0.02) but not in the OFF group (P = 0.97). Visual acuity and RD type were independently correlated with cone density (P = 0.004, P = 0.000).

CONCLUSION

Postoperative cone density was reduced in OFF RD, but also in the ON group, although the drop recovered during the 3-month follow-up. Cone density was significantly correlated with both visual acuity and type of RD at both time points.

A Deep Learning Approach to Denoise Optical Coherence Tomography Images of the Optic Nerve Head

Optical coherence tomography (OCT) has become an established clinical routine for the in vivo imaging of the optic nerve head (ONH) tissues, that is crucial in the diagnosis and management of various ocular and neuro-ocular pathologies. However, the presence of speckle noise affects the quality of OCT images and its interpretation. Although recent frame-averaging techniques have shown to enhance OCT image quality, they require longer scanning durations, resulting in patient discomfort. Using a custom deep learning network trained with 2,328 'clean B-scans' (multi-frame B-scans; signal averaged), and their corresponding 'noisy B-scans' (clean B-scans + Gaussian noise), we were able to successfully denoise 1,552 unseen single-frame (without signal averaging) B-scans. The denoised B-scans were qualitatively similar to their corresponding multi-frame B-scans, with enhanced visibility of the ONH tissues. The mean signal to noise ratio (SNR) increased from 4.02 ± 0.68 dB (single-frame) to 8.14 ± 1.03 dB (denoised). For all the ONH tissues, the mean contrast to noise ratio (CNR) increased from 3.50 ± 0.56 (single-frame) to 7.63 ± 1.81 (denoised). The mean structural similarity index (MSSIM) increased from 0.13 ± 0.02 (single frame) to 0.65 ± 0.03 (denoised) when compared with the corresponding multi-frame B-scans. Our deep learning algorithm can denoise a single-frame OCT B-scan of the ONH in under 20 ms, thus offering a framework to obtain superior quality OCT B-scans with reduced scanning times and minimal patient discomfort.

A Mouse Model of Retinal Recovery From Photo-Oxidative/Photo-Inflammatory Injury: Nrf2, SOD1, DJ-1, and Parkin Are Not Essential to Recovery

Purpose

To determine if there is structural and functional recovery of the retina from light induced retinal degeneration, and to evaluate the role of the oxidative stress response elements Nrf2, SOD1, DJ-1, and Parkin in such a recovery process.

Methods

Eyes from C57BL/6J (B6J) mice and from oxidative stress response-deficient strains of mice were treated with intense light using the fundus camera-delivered light-induced retinal degeneration (FCD-LIRD) model. Fundus photographs, optical coherence tomography (OCT) images, and electroretinography (ERG) responses were obtained before the injury, during the "maximal injury phase" (days 4-7) and during the "recovery phase" (days 14-16) post light exposure and were evaluated for retinal damage and assessed for evidence of recovery from the injury.

Results

We demonstrate that mice treated with a sub-lethal FCD-LIRD protocol show an initial acute retina injury phase peaking between days 4 to 7 followed by a recovery phase in which the outer retinal thickness/volume and retinal function partially recover. These observations are reproduced in B6J mice and in mice lacking oxidative stress response enzymes (SOD1, DJ-1, and Parkin) or the oxidative stress response master regulator Nrf2.

Conclusions

Our data indicate that retinal recovery from injury can proceed via pathways that are independent from the common oxidative stress response elements Nrf2, SOD1, DJ-1, and Parkin. Furthermore, the model of retinal recovery from injury that we describe here mimics changes seen in a variety of clinical entities and may provide an excellent platform for dissecting general pathways of retinal recovery from sub-lethal injury.

Detection and characterisation of optic nerve and retinal changes in primary congenital glaucoma using hand-held optical coherence tomography

Objective

To investigate (1) the feasibility of scanning the optic nerve (ON) and central retina with hand-held optical coherence tomography (HH-OCT) without sedation or anaesthesia in primary congenital glaucoma (PCG), (2) the characteristics of ON changes in comparison with adult primary open-angle glaucoma (POAG) in comparison with matched controls, (3) the sensitivity and specificity of ON parameters for diagnosis, and (4) changes of foveal morphology.

Methods and analysis

HH-OCT (Envisu 2300; Leica Microsystems) was used to investigate ON and foveal morphology of 20 children with PCG (mean age 4.64±2.79) and 10 adult patients with POAG (mean age 66.8±6.94), and compared with age-matched, gender-matched and ethnicity-matched healthy controls without sedation or anaesthesia.

Results

HH-OCT yielded useful data in 20 out of 24 young children with PCG. Patients with PCG had significantly deeper cup changes than patients with POAG (vs respective age-matched controls, p=0.014). ON changes in PCG are characterised by significant increase in cup depth (165%), increased cup diameter (159%) and reduction in rim area (36.4%) as compared with controls with high sensitivity (81.5, 74.1% and 88.9%, respectively) and specificity (85.0, 80.0% and 75.0%, respectively). Patients with PCG have a significantly smaller width of the macula pit (p<0.001) with non-detectable external limiting membrane.

Conclusion

HH-OCT has the potential to be a useful tool in glaucoma management for young children. We have demonstrated the use of HH-OCT in confirming a diagnosis of glaucoma within the studied cohort and found changes in disc morphology which characterise differently in PCG from POAG.

Longitudinal Assessment of Retinal Structure in Achromatopsia Patients With Long-Term Follow-up

Purpose

To longitudinally characterize structural retinal changes in achromatopsia (ACHM) over extended follow-up.

Methods

Fifty molecularly confirmed ACHM subjects underwent serial spectral-domain optical coherence tomography (SD-OCT) and fundus autofluorescence (FAF) imaging. Foveal structure on SD-OCT was graded and compared for evidence of progression, and foveal total retinal thickness (FTRT) and outer nuclear layer (ONL) thickness were serially measured. FAF patterns were characterized and compared over time.

Results

Mean SD-OCT follow-up was 61.6 months (age range at baseline, 6-52 years). Forty-five of the subjects had serial FAF (mean follow-up: 48.5 months). Only 6 (12%) of the subjects demonstrated qualitative change on serial foveal SD-OCT scans. Among the entire cohort, there was no statistically significant change over time in FTRT (P = 0.2459) or hyporeflective zone (HRZ) diameter (P = 0.3737). There was a small-but statistically significant-increase in ONL thickness (P = 0.0084). Three different FAF patterns were observed: centrally increased FAF (13/45), normal FAF (14/45), and well-demarcated reduced FAF (18/45), with the latter group displaying a small gradual increase in the area of reduced FAF of 0.055 mm2 over 43.4 months (P = 0.0011).

Conclusions

This longitudinal study of retinal structure in ACHM represents the largest cohort and longest follow-up period to date. Our findings support the presiding notion that ACHM is essentially a stationary condition regarding retinal structure, and any change over time is likely to be small, slow, and variable across patients. This may potentially afford a wider window for therapeutic intervention.

Residual Cone Structure in Patients With X-Linked Cone Opsin Mutations

Purpose

To assess residual cone structure in subjects with mutations in exon 2, 3, and 4 of the OPN1LW or OPN1MW opsin.

Methods

Thirteen males had their OPN1LW/OPN1MW opsin genes characterized. The cone mosaic was imaged using both confocal and nonconfocal split-detection adaptive optics scanning light ophthalmoscopy (AOSLO), and retinal thickness was evaluated using optical coherence tomography (OCT). Six subjects completed serial imaging over a maximum period of 18 months and cone density was measured across imaging sessions.

Results

Ten subjects had an OPN1LW/OPN1MW "interchange" opsin mutation designated as LIAVA or LVAVA, which both introduce exon 3 splicing defects leading to a lack of functional photopigment in cones expressing LIAVA and greatly reduced functional photopigment in cones expressing LVAVA. Despite disrupted cone reflectivity and reduced numerosity, residual inner segments could be visualized. Similar patterns were observed in individuals with an exon 2 insertion, or an exon 4 splice defect, both of which are also expected to produce cones that are devoid of functional opsin protein. OCT revealed variably reduced retinal thickness. A significant inverse relationship was found between the proportion of waveguiding cones and axial length.

Conclusions

Split-detection imaging revealed that the altered appearance of the cone mosaic in confocal images for subjects with exon 2, 3, and 4 mutations was generally due to disrupted waveguiding, rather than structural loss, making them possible candidates for gene therapy to restore cone function. The relative fraction of waveguiding cones was highly variable across subjects, which appears to influence emmetropization in these subjects.

Adaptive Optics Retinal Imaging in CNGA3-Associated Achromatopsia: Retinal Characterization, Interocular Symmetry, and Intrafamilial Variability

Purpose

To investigate retinal structure in subjects with CNGA3-associated achromatopsia and evaluate disease symmetry and intrafamilial variability.

Methods

Thirty-eight molecularly confirmed subjects underwent ocular examination, optical coherence tomography (OCT), and nonconfocal split-detection adaptive optics scanning light ophthalmoscopy (AOSLO). OCT scans were used for evaluating foveal hypoplasia, grading foveal ellipsoid zone (EZ) disruption, and measuring outer nuclear layer (ONL) thickness. AOSLO images were used to quantify peak foveal cone density, intercell distance (ICD), and the coefficient of variation (CV) of ICD.

Results

Mean (±SD) age was 25.9 (±13.1) years. Mean (± SD) best corrected visual acuity (BCVA) was 0.87 (±0.14) logarithm of the minimum angle of resolution. Examination with OCT showed variable disruption or loss of the EZ. Seven subjects were evaluated for disease symmetry, with peak foveal cone density, ICD, CV, ONL thickness, and BCVA not differing significantly between eyes. A cross-sectional evaluation of AOSLO imaging showed a mean (±SD) peak foveal cone density of 19,844 (±13,046) cones/mm2. There was a weak negative association between age and peak foveal cone density (r = -0.397, P = 0.102), as well as between EZ grade and age (P = 0.086).

Conclusions

The remnant cone mosaics were irregular and variably disrupted, with significantly lower peak foveal cone density than unaffected individuals. Variability was also seen among subjects with identical mutations. Therefore, subjects should be considered on an individual basis for stratification in clinical trials. Interocular symmetry suggests that both eyes have comparable therapeutic potential and the fellow eye can serve as a valid control. Longitudinal studies are needed, to further examine the weak negative association between age and foveal cone structure observed here.

Cell-Based Therapy for Retinal Disease: The New Frontier

The availability of noninvasive high-resolution imaging technology, the immune-suppressive nature of the subretinal space, and the existence of surgical techniques that permit transplantation surgery to be a safe procedure all render the eye an ideal organ in which to begin cell-based therapy in the central nervous system. A number of early stage clinical trials are underway to assess the safety and feasibility of cell-based therapy for retinal blindness. Cell-based therapy using embryonic stem cell-derived differentiated cells (e.g., retinal pigment epithelium (RPE)), neural progenitor cells, photoreceptor precursors, and bone marrow-derived hematopoietic stem/progenitor cells has demonstrated successful rescue and/or replacement in preclinical models of human retinal degenerative disease. Additional research is needed to identify the mechanisms that control synapse formation/disjunction (to improve photoreceptor transplant efficacy), to identify factors that limit RPE survival in areas of geographic atrophy (to improve RPE transplant efficacy in eyes with age-related macular degeneration), and to identify factors that regulate immune surveillance of the subretinal space (to improve long-term photoreceptor and RPE transplant survival).

Dysflective Cones

Retinal imaging has advanced to enable noninvasive in vivo visualization of macular photoreceptors with cellular resolution. Images of retinal structure are best interpreted in the context of visual function, but clinical measures of visual function lack resolution on the scale of individual cells. Combined with cross-sectional measures of retinal structure acquired with optical coherence tomography (OCT), macular photoreceptor function can be evaluated using visual acuity and fundus-guided microperimetry, but the resolution of these measures is limited to relatively large retinal areas. By incorporating adaptive optics correction of aberrations in light entering and exiting the pupil, individual photoreceptors can be visualized and stimulated to assess structure and function. Discrepancy between structural images and visual function can shed light on the origin of visible features and their relation to visual function. Dysflective cones, cones with abnormal waveguiding properties on confocal adaptive optics scanning laser ophthalmoscopy (AOSLO) images and measurable function, provide insight into the visual significance of features in retinal images and may facilitate identification of patients who could benefit from therapies.

Adaptive optics imaging of the human retina

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.

Cellular-scale evaluation of induced photoreceptor degeneration in the living primate eye

Progress is needed in developing animal models of photoreceptor degeneration and evaluating such models with longitudinal, noninvasive techniques. We employ confocal scanning laser ophthalmoscopy, optical coherence tomography (OCT) and high-resolution retinal imaging to noninvasively observe the retina of non-human primates with induced photoreceptor degeneration. Photoreceptors were imaged at the single-cell scale in three modalities of adaptive optics scanning light ophthalmoscopy: traditional confocal reflectance, indicative of waveguiding; a non-confocal offset aperture technique visualizing scattered light; and two-photon excited fluorescence, the time-varying signal of which, at 730 nm excitation, is representative of visual cycle function. Assessment of photoreceptor structure and function using these imaging modalities revealed a reduction in retinoid production in cone photoreceptor outer segments while inner segments appeared to remain present. Histology of one retina confirmed loss of outer segments and the presence of intact inner segments. This unique combination of imaging modalities can provide essential, clinically-relevant information on both the structural integrity and function of photoreceptors to not only validate models of photoreceptor degeneration but potentially evaluate the efficacy of future cell and gene-based therapies for vision restoration.

Assessing photoreceptor structure in patients with traumatic head injury

Objective

Previous work using adaptive optics scanning light ophthalmoscopy (AOSLO) imaging has shown photoreceptor disruption to be a common finding in head and ocular trauma patients. Here an expanded trauma population was examined using a novel imaging technique, split-detector AOSLO, to assess remnant cone structure in areas with significant disruption on confocal AOSLO imaging and to follow photoreceptor changes longitudinally.

Methods and Analysis

Eight eyes from seven subjects with head and/or ocular trauma underwent imaging with spectral domain optical coherence tomography, confocal AOSLO and split-detector AOSLO to assess foveal and parafoveal photoreceptor structure.

Results

Confocal AOSLO imaging revealed hyporeflective foveal regions in two of eight eyes. Split-detector imaging within the hyporeflective confocal areas showed both remnant and absent inner-segment structure. Both of these eyes were imaged longitudinally and showed variation of the photoreceptor mosaic over time. Four other eyes demonstrated subclinical regions of abnormal waveguiding photoreceptors on multimodal AOSLO imagery but were otherwise normal. Two eyes demonstrated normal foveal cone packing without disruption.

Conclusion

Multimodal imaging can detect subtle photoreceptor abnormalities not necessarily detected by conventional clinical imaging. The addition of split-detector AOSLO revealed the variable condition of inner segments within confocal photoreceptor disruption, confirming the usefulness of dual-modality AOSLO imaging in assessing photoreceptor structure and integrity. Longitudinal imaging demonstrated the dynamic nature of the photoreceptor mosaic after trauma. Multimodal imaging with dual-modality AOSLO improves understanding of visual symptoms and photoreceptor structure changes in patients with head and ocular trauma.

Intraobserver Repeatability and Interobserver Reproducibility of Ellipsoid Zone Measurements in Retinitis Pigmentosa

Purpose

To examine repeatability and reproducibility of ellipsoid zone (EZ) width measurements in patients with retinitis pigmentosa (RP) using a longitudinal reflectivity profile (LRP) analysis.

Methods

We examined Bioptigen optical coherence tomography (OCT) scans from 48 subjects with RP or Usher syndrome. Nominal scan lengths were 6, 7, or 10 mm, and the lateral scale of each scan was calculated using axial length measurements. LRPs were generated from OCT line scans, and the peak corresponding to EZ was manually identified using ImageJ. The locations at which the EZ peak disappeared were used to calculate EZ width. Each scan was analyzed twice by each of two observers, who were masked to their previous measurements and those of the other observer.

Results

On average, horizontal width (HW) was significantly greater than vertical width (VW), and there was high interocular symmetry for both HW and VW. We observed excellent intraobserver repeatability with intraclass correlation coefficients (ICCs) ranging from 0.996 to 0.998 for HW and VW measurements. Interobserver reproducibility was also excellent for both HW (ICC = 0.989; 95% confidence interval [CI] = 0.983–0.995) and VW (ICC = 0.991; 95% CI = 0.985–0.996), with no significant bias observed between observers.

Conclusions

EZ width can be measured using LRPs with excellent repeatability and reproducibility. Our observation of greater HW than VW is consistent with previous observations in RP, though the reason for this anisotropy remains unclear.

Translational Relevance

We describe repeatability and reproducibility of a method for measuring EZ width in patients with RP or Usher syndrome. This approach could facilitate measurement of retinal band thickness and/or intensity.

Deep longitudinal transfer learning-based automatic segmentation of photoreceptor ellipsoid zone defects on optical coherence tomography images of macular telangiectasia type 2

Photoreceptor ellipsoid zone (EZ) defects visible on optical coherence tomography (OCT) are important imaging biomarkers for the onset and progression of macular diseases. As such, accurate quantification of EZ defects is paramount to monitor disease progression and treatment efficacy over time. We developed and trained a novel deep learning-based method called Deep OCT Atrophy Detection (DOCTAD) to automatically segment EZ defect areas by classifying 3-dimensional A-scan clusters as normal or defective. Furthermore, we introduce a longitudinal transfer learning paradigm in which the algorithm learns from segmentation errors on images obtained at one time point to segment subsequent images with higher accuracy. We evaluated the performance of this method on 134 eyes of 67 subjects enrolled in a clinical trial of a novel macular telangiectasia type 2 (MacTel2) therapeutic agent. Our method compared favorably to other deep learning-based and non-deep learning-based methods in matching expert manual segmentations. To the best of our knowledge, this is the first automatic segmentation method developed for EZ defects on OCT images of MacTel2.

Assessment of Outer Retinal Remodeling in the Hibernating 13-Lined Ground Squirrel

Purpose

We examined outer retinal remodeling of the euthermic and torpid cone-dominant 13-lined ground squirrel (13-LGS) retina using optical coherence tomography (OCT) imaging and histology.

Methods

Retinas and corneas of living 13-LGSs were imaged during euthermic and torpid physiological states using OCT. Retinal layer thickness was measured at the visual streak from registered and averaged vertical B-scans. Following OCT, some retinas were collected immediately for postmortem histologic comparison using light microscopy, immunofluorescence, or transmission electron microscopy.

Results

Compared to OCT images from euthermic retinae, OCT images of torpid retinae revealed significantly thicker inner and outer nuclear layers, as well as increases in the distances between outer retinal reflectivity bands 1 and 2, and bands 3 and 4. A significant decrease in the distance between bands 2 and 3 also was seen, alongside significant thinning of the choriocapillaris and choroid. OCT image quality was reduced in torpid eyes, partly due to significant thickening of the corneal stroma during this state.

Conclusions

The torpid retina of the hibernating 13-LGS undergoes structural changes that can be detected by OCT imaging. Comparisons between in vivo OCT and ex vivo histomorphometry may offer insight to the origin of hyperreflective OCT bands within the outer retina of the cone-dominant 13-LGS.

LONGITUDINAL CORRELATION OF ELLIPSOID ZONE LOSS AND FUNCTIONAL LOSS IN MACULAR TELANGIECTASIA TYPE 2

PURPOSE

To compare ellipsoid zone (EZ) loss and functional loss in macular telangiectasia (MacTel) type 2 longitudinally.

METHODS

Prospective natural history study. Ellipsoid zone loss was measured in en-face images created from spectral domain optical coherence tomography. Functional loss was assessed by best-corrected visual acuity and microperimetry, counting the number of test points with impaired function.

RESULTS

A total of 56 eyes of 31 participants were followed for 4.5 ± 1.2 years. Ellipsoid zone loss was 18,600 ± 3,917.3 pixel at baseline (≈0.59 mm) and increased 2,627.8 ± 427.9 pixel (≈0.08 mm) per year. Best-corrected visual acuity decreased 2.2 ± 0.9 letters per year. Change in EZ loss correlated significantly with change in relative and absolute scotomas (r = 0.62; P-value < 0.0001 and r = 0.72; P-value < 0.0001), but not with loss of best-corrected visual acuity. Functional loss showed a similar frequency of progression as EZ loss, but a higher rate of "regression," likely due to higher variability of the measurement, assuming a progressive neurodegenerative disease.

CONCLUSION

The results of the authors support EZ loss as surrogate measure for visual function in MacTel type 2. Being objective, EZ loss might be considered more suitable than microperimetry as primary end point in future interventional trials.

Achromatopsia: clinical features, molecular genetics, animal models and therapeutic options

Achromatopsia is an autosomal recessive condition, characterised by reduced visual acuity, impaired colour vision, photophobia and nystagmus. The symptoms can be profoundly disabling, and there is no cure currently available. However, the recent development of gene-based interventions may lead to improved outcomes in the future. This article aims to provide a comprehensive review of the clinical features of the condition, its genetic basis and the underlying pathogenesis. We also explore the insights derived from animal models, including the implications for gene supplementation approaches. Finally, we discuss current human gene therapy trials.

Inspection of the Human Retina by Optical Coherence Tomography

Optical coherence tomography (OCT) is a high-resolution, three-dimensional, noninvasive imaging modality to examine the human retina. Since the introduction of spectral domain (SD-) OCT-the currently most used variant of OCT-previously unknown details of in vivo retinal morphology of a broad variety of pathologies have become visible. This chapter explains the basic principles of the OCT technology, deals with possible pitfalls in OCT examination or analysis, and hints at the use of OCT technology in functional imaging.

Adaptive optics imaging of inherited retinal diseases

Adaptive optics (AO) ophthalmoscopy allows for non-invasive retinal phenotyping on a microscopic scale, thereby helping to improve our understanding of retinal diseases. An increasing number of natural history studies and ongoing/planned interventional clinical trials exploit AO ophthalmoscopy both for participant selection, stratification and monitoring treatment safety and efficacy. In this review, we briefly discuss the evolution of AO ophthalmoscopy, recent developments and its application to a broad range of inherited retinal diseases, including Stargardt disease, retinitis pigmentosa and achromatopsia. Finally, we describe the impact of this in vivo microscopic imaging on our understanding of disease pathogenesis, clinical trial design and outcome metrics, while recognising the limitation of the small cohorts reported to date.

Imaging the adult zebrafish cone mosaic using optical coherence tomography

Zebrafish (Danio rerio) provide many advantages as a model organism for studying ocular disease and development, and there is great interest in the ability to non-invasively assess their photoreceptor mosaic. Despite recent applications of scanning light ophthalmoscopy, fundus photography, and gonioscopy to in vivo imaging of the adult zebrafish eye, current techniques either lack accurate scaling information (limiting quantitative analyses) or require euthanizing the fish (precluding longitudinal analyses). Here we describe improved methods for imaging the adult zebrafish retina using spectral domain optical coherence tomography (OCT). Transgenic fli1:eGFP zebrafish were imaged using the Bioptigen Envisu R2200 broadband source OCT with a 12-mm telecentric probe to measure axial length and a mouse retina probe to acquire retinal volume scans subtending 1.2 × 1.2 mm nominally. En face summed volume projections were generated from the volume scans using custom software that allows the user to create contours tailored to specific retinal layer(s) of interest. Following imaging, the eyes were dissected for ex vivo fluorescence microscopy, and measurements of blood vessel branch points were compared to those made from the en face OCT images to determine the OCT lateral scale as a function of axial length. Using this scaling model, we imaged the photoreceptor layer of five wild-type zebrafish and quantified the density and packing geometry of the UV cone submosaic. Our in vivo cone density measurements agreed with measurements from previously published histology values. The method presented here allows accurate, quantitative assessment of cone structure in vivo and will be useful for longitudinal studies of the zebrafish cone mosaics.

EXPLORING PHOTORECEPTOR REFLECTIVITY THROUGH MULTIMODAL IMAGING OF OUTER RETINAL TUBULATION IN ADVANCED AGE-RELATED MACULAR DEGENERATION

PURPOSE

To investigate the microscopic structure of outer retinal tubulation (ORT) and optical properties of cone photoreceptors in vivo, we studied ORT appearance by multimodal imaging, including spectral domain optical coherence tomography (SD-OCT) and adaptive optics scanning laser ophthalmoscopy.

METHODS

Four eyes of four subjects with advanced age-related macular degeneration underwent color fundus photography, infrared reflectance imaging, SD-OCT, and adaptive optics scanning laser ophthalmoscopy with a high-resolution research instrument. Outer retinal tubulation was identified in closely spaced (11 μm) SD-OCT volume scans.

RESULTS

Outer retinal tubulation in cross-sectional and en face SD-OCT was a hyporeflective area representing a lumen surrounded by a hyperreflective border consisting of cone photoreceptor mitochondria and external limiting membrane, per previous histology. In contrast, ORT by adaptive optics scanning laser ophthalmoscopy was a hyporeflective structure of the same shape as in en face SD-OCT but lacking visualizable cone photoreceptors.

CONCLUSION

Lack of ORT cone reflectivity by adaptive optics scanning laser ophthalmoscopy indicates that cones have lost their normal directionality and waveguiding property due to loss of outer segments and subsequent retinal remodeling. Reflective ORT cones by SD-OCT, in contrast, may depend partly on mitochondria as light scatterers within inner segments of these degenerating cells, a phenomenon enhanced by coherent imaging. Multimodal imaging of ORT provides insight into cone degeneration and reflectivity sources in optical coherence tomography.

PHOTORECEPTOR INNER SEGMENT MORPHOLOGY IN BEST VITELLIFORM MACULAR DYSTROPHY

Supplemental Digital Content is Available in the Text.

Outer retinal cellular structure in best vitelliform macular dystrophy was assessed using novel adaptive optics retinal imaging, revealing that photoreceptor morphology is highly variable depending on the stage of disease. Photoreceptor structure is still present even at advanced stages of disease, and longitudinal assessment shows that the photoreceptor mosaic is not static.

Purpose:

To characterize outer retina structure in best vitelliform macular dystrophy (BVMD) and to determine the effect of macular lesions on overlying and adjacent photoreceptors.

Methods:

Five individuals with BVMD were followed prospectively with spectral domain optical coherence tomography and confocal and nonconfocal split-detector adaptive optics scanning light ophthalmoscopy (AOSLO). The AOSLO cone photoreceptor mosaic images were obtained within and around retinal lesions. Cone density was measured inside and outside lesions. In 2 subjects, densities were compared with published measurements acquired ∼2.5 years before. One subject was imaged 3 times over a 5-month period.

Results:

The AOSLO imaging demonstrated that photoreceptor morphology within BVMD retinal lesions was highly variable depending on the disease stage, with photoreceptor structure present even in advanced disease. The AOSLO imaging was repeatable even in severe disease over short-time and long-time intervals. Photoreceptor density was normal in retinal areas immediately adjacent to lesions and stable over ∼2.5 years. Mobile disk-like structures possibly representing subretinal macrophages were also observed.

Conclusion:

Combined confocal and nonconfocal split-detector AOSLO imaging reveals substantial variability within clinical lesions in all stages of BVMD. Longitudinal cellular photoreceptor imaging could prove a powerful tool for understanding disease progression and monitoring emerging therapeutic treatment response in inherited degenerations such as BVMD.

High-Resolution Imaging of Intraretinal Structures in Active and Resolved Central Serous Chorioretinopathy

Purpose

To improve our understanding of central serous chorioretinopathy (CSC), we performed an analysis of noninvasive, high-resolution retinal imaging in patients with active and resolved CSC.

Methods

Adaptive optics scanning light ophthalmoscopy (AOSLO) and spectral-domain optical coherence tomography (SD-OCT) were performed on five subjects with CSC. A custom AOSLO system was used to simultaneously collect confocal and split-detector images. Spectral domain–OCT volume scans were used to create en face views of various retinal layers, which then were compared to montaged AOSLO images after coregistration.

Results

Three distinct types of intraretinal hyperreflective clusters were seen with AOSLO. These clusters had a well-demarcated, round, and granular appearance. Clusters in active CSC over areas of serous retinal detachment were termed type-1. They were found primarily in the outer nuclear layer (ONL) and were associated with large defects in the photoreceptor mosaic and ellipsoid zone. Clusters in areas where the retina had reattached were termed type-2. They also were located primarily in the ONL but showed stability in location over a period of at least 8 months. Smaller clusters in the inner retina along retinal capillaries were termed type-3.

Conclusions

Retinal imaging in CSC using en face OCT and AOSLO allows precise localization of intraretinal structures and detection of features that cannot be seen with SD-OCT alone. These findings may provide greater insight into the pathophysiology of the active and resolved phases of the disease, and support the hypothesis that intraretinal hyperreflective foci on OCT in CSC are cellular in nature.

Assessing Photoreceptor Structure in Retinitis Pigmentosa and Usher Syndrome

Purpose

The purpose of this study was to examine cone photoreceptor structure in retinitis pigmentosa (RP) and Usher syndrome using confocal and nonconfocal split-detector adaptive optics scanning light ophthalmoscopy (AOSLO).

Methods

Nineteen subjects (11 RP, 8 Usher syndrome) underwent ophthalmic and genetic testing, spectral-domain optical coherence tomography (SD-OCT), and AOSLO imaging. Split-detector images obtained in 11 subjects (7 RP, 4 Usher syndrome) were used to assess remnant cone structure in areas of altered cone reflectivity on confocal AOSLO.

Results

Despite normal interdigitation zone and ellipsoid zone appearance on OCT, foveal and parafoveal cone densities derived from confocal AOSLO images were significantly lower in Usher syndrome compared with RP. This was due in large part to an increased prevalence of non-waveguiding cones in the Usher syndrome retina. Although significantly correlated to best-corrected visual acuity and foveal sensitivity, cone density can decrease by nearly 38% before visual acuity becomes abnormal. Aberrantly waveguiding cones were noted within the transition zone of all eyes and corresponded to intact inner segment structures. These remnant cones decreased in density and increased in diameter across the transition zone and disappeared with external limiting membrane collapse.

Conclusions

Foveal cone density can be decreased in RP and Usher syndrome before visible changes on OCT or a decline in visual function. Thus, AOSLO imaging may allow more sensitive monitoring of disease than current methods. However, confocal AOSLO is limited by dependence on cone waveguiding, whereas split-detector AOSLO offers unambiguous and quantifiable visualization of remnant cone inner segment structure. Confocal and split-detector thus offer complementary insights into retinal pathology.

Cone Photoreceptor Structure in Patients With X-Linked Cone Dysfunction and Red-Green Color Vision Deficiency

Purpose

Mutations in the coding sequence of the L and M opsin genes are often associated with X-linked cone dysfunction (such as Bornholm Eye Disease, BED), though the exact color vision phenotype associated with these disorders is variable. We examined individuals with L/M opsin gene mutations to clarify the link between color vision deficiency and cone dysfunction.

Methods

We recruited 17 males for imaging. The thickness and integrity of the photoreceptor layers were evaluated using spectral-domain optical coherence tomography. Cone density was measured using high-resolution images of the cone mosaic obtained with adaptive optics scanning light ophthalmoscopy. The L/M opsin gene array was characterized in 16 subjects, including at least one subject from each family.

Results

There were six subjects with the LVAVA haplotype encoded by exon 3, seven with LIAVA, two with the Cys203Arg mutation encoded by exon 4, and two with a novel insertion in exon 2. Foveal cone structure and retinal thickness was disrupted to a variable degree, even among related individuals with the same L/M array.

Conclusions

Our findings provide a direct link between disruption of the cone mosaic and L/M opsin variants. We hypothesize that, in addition to large phenotypic differences between different L/M opsin variants, the ratio of expression of first versus downstream genes in the L/M array contributes to phenotypic diversity. While the L/M opsin mutations underlie the cone dysfunction in all of the subjects tested, the color vision defect can be caused either by the same mutation or a gene rearrangement at the same locus.