Macular cone abnormalities in retinitis pigmentosa with preserved central vision using adaptive optics scanning laser ophthalmoscopy

Multimodal High-Resolution Imaging in Retinitis Pigmentosa: A Comparison Between Optoretinography, Cone Density, and Visual Sensitivity

Purpose

Retinitis pigmentosa (RP), the most common inherited retinal disease, is characterized by progressive photoreceptor degeneration. It remains unknown to what extent surviving photoreceptors transduce light and support vision in RP. To address this, we correlated structure and functional measures using adaptive optics scanning laser ophthalmoscopy (AOSLO), adaptive optics microperimetry, and adaptive optics optical coherence tomography (AO-OCT)-based optoretinograms (ORGs).

Methods

Four patients with RP were imaged with AOSLO across the visual field covering the transition zone (TZ) of normal to diseased retina. Cone density was estimated in discrete regions spanning the TZ. Visual sensitivity was assessed by measuring increment thresholds for a 3-arcmin stimulus targeted via active eye tracking in AOSLO. ORGs were measured at the same locations using AO-OCT to assess the cones' functional response to a 528 ± 20-nm stimulus. Individual cone outer segment (COS) lengths were measured from AO-OCT in each subject.

Results

Cone density was significantly reduced in patients with RP. Density reduction correlated with TZ location in 3 patients with RP, while a fourth had patches of reduced density throughout the retina. ORG amplitude was reduced in regions of normal and reduced cone density in all patients with RP. ORG response and COS length were positively correlated in controls but not in patients with RP. Despite deficits in cone density and ORG, visual sensitivity remained comparable to controls in three of four patients with RP.

Conclusions

ORG-based measures of retinal dysfunction may precede deficits in cone structure and visual sensitivity. ORG is a sensitive measure of RP disease status and has significant potential to provide insight into disease progression and treatment efficacy.

Optimization-Based Pairwise Interaction Point Process (O-PIPP): A Precise and Universal Retinal Mosaic Modeling Approach

Purpose

A retinal mosaic, the spatial organization of a population of homotypic neurons, is thought to sample a specific visual feature into the feedforward visual pathway. The purpose of this study was to propose a universal modeling approach for precisely generating retinal mosaics and overcoming the limitations of previous models, especially in modeling abnormal mosaic patterns under disease conditions.

Methods

Here, we developed the optimization-based pairwise interaction point process (O-PIPP). It incorporates optimization techniques into previous simulation approaches, enabling directional control of the simulation process according to the user-designed optimization target. For the convenience of the community, we implemented the O-PIPP approach into a Python package and a website application.

Results

We showed that the O-PIPP can generate more precise neural spatial patterns of healthy and diseased mosaics compared to previous phenomenological approaches. Notably, through modeling the retinal neural circuitry with O-PIPP-simulated retinitis pigmentosa cone mosaics, we elucidated how the cone mosaic rearrangement impacted the information processing of ganglion cells.

Conclusions

The O-PIPP provides a precise and universal tool to simulate realistic mosaics, which could help to investigate the function of retinal mosaics in vision.

Adaptive optics retinal imaging in patients with usher syndrome

Purpose

To determine the structure of the cone photoreceptor mosaic in the macula in eyes with retinitis pigmentosa related to Usher syndrome using adaptive optics fundus (AO) imaging and to correlate these findings with those of the standard clinical diagnostics.

Methods

Ten patients with a genetically confirmed retinitis pigmentosa in Usher syndrome due to biallelic variants in MYO7A or USH2A were enrolled in the study. All patients underwent a complete ophthalmological examination including best corrected visual acuity (BCVA), spectral-domain optical coherence tomography (SD-OCT) with fundus autofluorescence photography (FAF), full-field (ffERG) and multifocal electroretinography (mfERG) and Adaptive Optics Flood Illuminated Ophthalmoscopy (AO, rtx1™, Imagine Eyes, Orsay, France). The cone density was assessed centrally and at each 0.5 degree horizontally and vertically from 1-4 degree of eccentricity.

Results

In the AO images, photoreceptor cell death was visualized as a disruption of the cone mosaic and low cone density. In the early stage of the disease, cones were still visible in the fovea, whereas outside the fovea a loss of cones was recognizable by blurry, dark patches. The blurry patches corresponded to the parafoveal hypofluorescent ring in the FAF images and the beginning loss of the IS/OS line and external limiting membrane in the SD-OCT images. FfERGs were non-recordable in 7 patients and reduced in 3. The mfERG was reduced in all patients and correlated significantly (p <0.001) with the cone density. The kinetic visual field area, measured with III4e and I4e, did not correlate with the cone density.

Conclusion

The structure of the photoreceptors in Usher syndrome patients were detectable by AO fundus imaging. The approach of using high-resolution technique to assess the photoreceptor structure complements the established clinical examinations and allows a more sensitive monitoring of early stages of retinitis pigmentosa in Usher syndrome.

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.

Pearls and Pitfalls of Adaptive Optics Ophthalmoscopy in Inherited Retinal Diseases

Adaptive optics (AO) retinal imaging enables individual photoreceptors to be visualized in the clinical setting. AO imaging can be a powerful clinical tool for detecting photoreceptor degeneration at a cellular level that might be overlooked through conventional structural assessments, such as spectral-domain optical coherence tomography (SD-OCT). Therefore, AO imaging has gained significant interest in the study of photoreceptor degeneration, one of the most common causes of inherited blindness. Growing evidence supports that AO imaging may be useful for diagnosing early-stage retinal dystrophy before it becomes apparent on fundus examination or conventional retinal imaging. In addition, serial AO imaging may detect structural disease progression in early-stage disease over a shorter period compared to SD-OCT. Although AO imaging is gaining popularity as a structural endpoint in clinical trials, the results should be interpreted with caution due to several pitfalls, including the lack of standardized imaging and image analysis protocols, frequent ocular comorbidities that affect image quality, and significant interindividual variation of normal values. Herein, we summarize the current state-of-the-art AO imaging and review its potential applications, limitations, and pitfalls in patients with inherited retinal diseases.

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

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

Importance of two-dimensional gaze analyses in the assessment of reading performance in patients with retinitis pigmentosa

The causes of reading difficulties in people with peripheral visual field loss are not fully understood. We conducted a two-dimensional gaze analysis on eye movements during reading in patients with retinitis pigmentosa to investigate the causes of reading difficulties in relation to the central visual field using a binocular eye mark recorder (EMR-9). Twenty-seven patients with retinitis pigmentosa whose central visual field narrowed to ≤ 20° using Goldmann kinetic perimetry (I/4 target) and this present study included eight healthy participants. The participants' visual acuities were corrected to better than +0.4 logMAR. Correlations and multivariate regression analyses were investigated between the number of letters read correctly, the I/4 central visual field, V/4 perifoveal and peripheral visual field, and visual acuity. Multivariate regression analysis revealed that all these parameters played almost equal roles in the number of letters read correctly. In the two-dimensional gaze analysis, the task performance time of patients during reading increased as the I/4 central visual field narrowed. The task performance time was more clearly correlated with the rotation saccade (r = 0.428, p <0.05) and the distance of the vertical direction (ΣY) of eye movements (r = 0.624, p < 0.01), but not with regressive saccade and the distance of the horizontal direction (ΣX). Visual acuity was correlated with the task performance time (-0.436, <0.05) but not with eye movement directionality. Reading difficulties in patients with retinitis pigmentosa result from impaired eye movement directionality. Understanding eye measurements for people with tunnel vision required a two-dimensional gaze analysis. The two-dimensional gaze analysis also showed that the involvement of the perifoveal and peripheral visual fields, visual acuity, and I/4 central visual field was important for reading in people with tunnel vision.

Ophthalmic and Genetic Features of Bardet Biedl Syndrome in a German Cohort

The aim of this study was to characterize the ophthalmic and genetic features of Bardet Biedl (BBS) syndrome in a cohort of patients from a German specialized ophthalmic care center. Sixty-one patients, aged 5−56 years, underwent a detailed ophthalmic examination including visual acuity and color vision testing, electroretinography (ERG), visually evoked potential recording (VEP), fundus examination, and spectral domain optical coherence tomography (SD-OCT). Adaptive optics flood illumination ophthalmoscopy was performed in five patients. All patients had received diagnostic genetic testing and were selected upon the presence of apparent biallelic variants in known BBS-associated genes. All patients had retinal dystrophy with morphologic changes of the retina. Visual acuity decreased from ~0.2 (decimal) at age 5 to blindness 0 at 50 years. Visual field examination could be performed in only half of the patients and showed a concentric constriction with remaining islands of function in the periphery. ERG recordings were mostly extinguished whereas VEP recordings were reduced in about half of the patients. The cohort of patients showed 51 different likely biallelic mutations—of which 11 are novel—in 12 different BBS-associated genes. The most common associated genes were BBS10 (32.8%) and BBS1 (24.6%), and by far the most commonly observed variants were BBS10 c.271dup;p.C91Lfs*5 (21 alleles) and BBS1 c.1169T>G;p.M390R (18 alleles). The phenotype associated with the different BBS-associated genes and genotypes in our cohort is heterogeneous, with diverse features without genotype−phenotype correlation. The results confirm and expand our knowledge of this rare disease.

Short term morphological rescue of the fovea after gene therapy with voretigene neparvovec

PURPOSE

Leber congenital amaurosis type 2 (LCA2) and early-onset severe retinal dystrophy (EOSRD) are linked to visual impairment with nyctalopia and visual acuity reduction in early childhood. In 2017, the first gene therapy voretigene neparvovec (Luxturna™) for patients with LCA and EOSRD cause by bi-allelic mutations in the RPE65 gene has been approved. Here we report on an example of short-term change in the foveal morphology after functionally successful gene therapy with voretigene neparvovec in a 15-year old patient.

METHODS

The clinical examinations included best corrected visual acuity (BCVA), spectral domain optical coherence tomography (OCT) and adaptive optics retinal imaging.

RESULTS

During follow-up over a period of 3 months after the treatment, an improvement of the central foveal morphology could be observed in OCT, with a clear demarcation of the external limiting membrane and changes in the photoreceptor mosaic on adaptive optics retinal imaging. These morphological rescue parameters correlated in part with the improvement in foveal-mediated vision after the treatment and adaptive optics imaging. Although the visual acuity improved only slightly at month 3, objective central cone evaluation with chromatic pupil campimetry showed an increase in the central sensitivity. In daily life, the patient reported her visional experience after the treatment as 'brighter'.

CONCLUSION

Rapid changes in the correlates of photoreceptor morphology after successful gene therapy in patients with LCA/EORD can be quantifiable on individual level.

Application of Adaptive Optics in Ophthalmology

The eye, the photoreceptive organ used to perceive the external environment, is of great importance to humans. It has been proven that some diseases in humans are accompanied by fundus changes; therefore, the health status of people may be interpreted from retinal images. However, the human eye is not a perfect refractive system for the existence of ocular aberrations. These aberrations not only affect the ability of human visual discrimination and recognition, but restrict the observation of the fine structures of human eye and reduce the possibility of exploring the mechanisms of eye disease. Adaptive optics (AO) is a technique that corrects optical wavefront aberrations. Once integrated into ophthalmoscopes, AO enables retinal imaging at the cellular level. This paper illustrates the principle of AO in correcting wavefront aberrations in human eyes, and then reviews the applications and advances of AO in ophthalmology, including the adaptive optics fundus camera (AO-FC), the adaptive optics scanning laser ophthalmoscope (AO-SLO), the adaptive optics optical coherence tomography (AO-OCT), and their combined multimodal imaging technologies. The future development trend of AO in ophthalmology is also prospected.

Investigating Biomarkers for USH2A Retinopathy Using Multimodal Retinal Imaging

Pathogenic mutations in USH2A are a leading cause of visual loss secondary to non-syndromic or Usher syndrome-associated retinitis pigmentosa (RP). With an increasing number of RP-targeted clinical trials in progress, we sought to evaluate the photoreceptor topography underlying patterns of loss observed on clinical retinal imaging to guide surrogate endpoint selection in USH2A retinopathy. In this prospective cross-sectional study, twenty-five patients with molecularly confirmed USH2A-RP underwent fundus autofluorescence (FAF), spectral-domain optical coherence tomography (SD-OCT) and adaptive optics scanning laser ophthalmoscopy (AOSLO) retinal imaging. Analysis comprised measurement of FAF horizontal inner (IR) and outer (OR) hyperautofluorescent ring diameter; SD-OCT ellipsoid zone (EZ) and external limiting membrane (ELM) width, normalised EZ reflectance; AOSLO foveal cone density and intact macular photoreceptor mosaic (IMPM) diameter. Thirty-two eyes from 16 patients (mean age ± SD, 36.0 ± 14.2 years) with USH2A-associated Usher syndrome type 2 (n = 14) or non-syndromic RP (n = 2) met the inclusion criteria. Spatial alignment was observed between IR-EZ and OR-ELM diameters/widths (p < 0.001). The IMPM border occurred just lateral to EZ loss (p < 0.001), although sparser intact photoreceptor inner segments were detected until ELM disruption. EZ width and IR diameter displayed a biphasic relationship with cone density whereby slow cone loss occurred until retinal degeneration reached ~1350 μm from the fovea, beyond which greater reduction in cone density followed. Normalised EZ reflectance and cone density were significantly associated (p < 0.001). As the strongest correlate of cone density (p < 0.001) and best-corrected visual acuity (p < 0.001), EZ width is the most sensitive biomarker of structural and functional decline in USH2A retinopathy, rendering it a promising trial endpoint.

Phenotype Heterogeneity and the Association Between Visual Acuity and Outer Retinal Structure in a Cohort of Chinese X-Linked Juvenile Retinoschisis Patients

Purpose: X-linked juvenile retinoschisis (XLRS), caused by mutations in the RS1 gene, is an X-linked recessive inherited disease that typically involves both eyes in the first 2 decades of life. Recently, the phenotype heterogeneity of this condition has drawn increasing attention. We reported various phenotypes caused by RS1 gene mutations in eleven patients from ten Chinese families.

Methods: Data on the medical history of the patients from ten Han families of central China were collected. Ophthalmic examinations including best-corrected visual acuity (BCVA), fundus photography, ultra-wide-angle sweep source optical coherence tomography (SS-OCT), and electroretinography (ERG) were performed. Adaptive optics (AO) images were acquired to evaluate the cone photoreceptor mosaic when applicable. Venous blood of the probands and their family members was collected, and DNA was subjected to sequencing based on next-generation sequencing with a custom-designed targeted gene panel PS400 for inherited retinal diseases. Validation was performed by Sanger sequencing and cosegregation. Pathogenicity was determined in accordance with the American College of Medical Genetics and Genomics (ACMG) guidelines.

Results: Ten RS1 mutations, including eight missense mutations and two terminator mutations, were identified in 10 XLRS families. c.657C > A (p.C219X) was a novel mutation in this cohort. These patients showed a variety of clinical phenotypes, including fovea schisis, bullous retinoschisis, and macular or peripheral atrophy. Fifteen eyes of eight patients exhibited macular retinoschisis, and twelve eyes of seven patients exhibited peripheral retinoschisis. In addition, three patients showed asymmetrical fundus manifestations. Of importance, three patients without macular retinoschisis were misdiagnosed until genetic testing results were obtained. AO showed a decrease in cone density and loss of regularity in the cystic schisis macular of XLRS. Furthermore, the BCVA was associated with the photoreceptor inner segment and outer segment (IS/OS) thickness.

Conclusion: With complicated clinical manifestations, a considerable portion of XLRS patients may present various phenotypes. It should be noted that asymmetry in fundus appearance in both eyes could lead to misdiagnosis easily. Thus, genetic testing is crucial for making a final diagnosis in those patients who are suspected of having amblyopia, bilateral or unilateral macular atrophy, or conditions presenting an asymmetric fundus appearance. In addition, the residual cone photoreceptor structure was critical for the maintenance of useful vision.

Cone photoreceptor dysfunction in retinitis pigmentosa revealed by optoretinography

Retinitis pigmentosa (RP) is the most common group of inherited retinal degenerative diseases, whose most debilitating phase is cone photoreceptor death. Perimetric and electroretinographic methods are the gold standards for diagnosing and monitoring RP and assessing cone function. However, these methods lack the spatial resolution and sensitivity to assess disease progression at the level of individual photoreceptor cells, where the disease originates and whose degradation causes vision loss. High-resolution retinal imaging methods permit visualization of human cone cells in vivo but have only recently achieved sufficient sensitivity to observe their function as manifested in the cone optoretinogram. By imaging with phase-sensitive adaptive optics optical coherence tomography, we identify a biomarker in the cone optoretinogram that characterizes individual cone dysfunction by stimulating cone cells with flashes of light and measuring nanometer-scale changes in their outer segments. We find that cone optoretinographic responses decrease with increasing RP severity and that even in areas where cone density appears normal, cones can respond differently than those in controls. Unexpectedly, in the most severely diseased patches examined, we find isolated cones that respond normally. Short-wavelength-sensitive cones are found to be more vulnerable to RP than medium- and long-wavelength-sensitive cones. We find that decreases in cone response and cone outer-segment length arise earlier in RP than changes in cone density but that decreases in response and length are not necessarily correlated within single cones.

Characterization and allogeneic transplantation of a novel transgenic cone-rich donor mouse line

OBJECTIVES

Cone photoreceptor transplantation is a potential treatment for macular diseases. The optimal conditions for cone transplantation are poorly understood, partly because of the scarcity of cones in donor mice. To facilitate allogeneic cone photoreceptor transplantation studies in mice, we aimed to create and characterize a donor mouse model containing a cone-rich retina with a cone-specific enhanced green fluorescent protein (EGFP) reporter.

METHODS

We generated OPN1LW-EGFP/NRL-/- mice by crossing NRL-/- and OPN1LW-EGFP mice. We characterized the anatomical phenotype of OPN1LW-EGFP/NRL-/- mice using multimodal confocal scanning laser ophthalmoscopy (cSLO) imaging, immunohistology, and transmission electron microscopy. We evaluated retinal function using electroretinography (ERG), including 465 and 525 nm chromatic stimuli. Retinal sheets and cell suspensions from OPN1LW-EGFP/NRL-/- mice were transplanted subretinally into immunodeficient Rd1 mice.

RESULTS

OPN1LW-EGFP/NRL-/- retinas were enriched with OPN1LW-EGFP+ and S-opsin+ cone photoreceptors in a dorsal-ventral distribution gradient. Cone photoreceptors co-expressing OPNL1W-EGFP and S-opsin significantly increased in OPN1LW-EGFP/NRL-/- compared to OPN1LW-EGFP mice. Temporal dynamics of rosette formation in the OPN1LW-EGFP/NRL-/- were similar as the NRL-/- with peak formation at P15. Rosettes formed preferentially in the ventral retina. The outer retina in P35 OPN1LW-EGFP/NRL-/- was thinner than NRL-/- controls. The OPN1LW-EGFP/NRL-/- ERG response amplitudes to 465 nm stimulation were similar to, but to 535 nm stimulation were lower than, NRL-/- controls. Three months after transplantation, the suspension grafts showed greater macroscopic degradation than sheet grafts. Retinal sheet grafts from OPN1LW-EGFP/NRL-/- mice showed greater S-opsin + cone survival than suspension grafts from the same strain.

CONCLUSIONS

OPN1LW-EGFP/NRL-/- retinae were enriched with S-opsin+ photoreceptors. Sustained expression of EGFP facilitated the longitudinal tracking of transplanted donor cells. Transplantation of cone-rich retinal grafts harvested prior to peak rosette formation survived and differentiated into cone photoreceptor subtypes. Photoreceptor sheet transplantation may promote greater macroscopic graft integrity and S-opsin+ cone survival than cell suspension transplantation, although the mechanism underlying this observation is unclear at present. This novel cone-rich reporter mouse strain may be useful to study the influence of graft structure on cone survival.

Detection Sensitivity of Retinitis Pigmentosa Progression Using Static Perimetry and Optical Coherence Tomography

Purpose

To compare the detection sensitivities of the progression of retinitis pigmentosa (RP) by automated perimetry to obtain the mean deviation (MD) and total point score and by optical coherence tomography (OCT) to determine the residual ellipsoid zone (EZ) length and thickness of retinal layers.

Methods

Twenty-two eyes of 22 patients with RP who underwent annual automated perimetry (Humphrey Field Analyzer 10-2) and OCT examinations during the same period more than four times were included. Disease progression was evaluated using linear regression analysis with the least-squares method. The disease progression speed and interinspection fluctuations for the different examinations were compared using standardized values. The progression detection ability factor, defined as the average of the least squares divided by the square of annual change, was used to compare the sensitivities of the examinations for detecting the progression of RP.

Results

EZ length showed a high correlation with MD (R = 0.87; P = 1.12E-07) at baseline. Disease progression was detected more frequently using EZ length (12/22 eyes) than using MD (3/22 eyes; P = 0.004) or central retinal thickness (1/11 eyes; P = 0.012). Linear regression using standardized values showed that the EZ length had the fastest annual change, with the smallest least absolute values. EZ length was more sensitive for detecting RP progression than MD, total point score, visual acuity, or central retinal thickness.

Conclusions

EZ measurement was sensitive for detecting RP progression, and the results of this study indicate that EZ length is appropriate for end points in clinical trials.

Translational Relevance

The study provides a basis for conducting future clinical trials.

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.

Macular Changes in a Mucopolysaccharidosis Type I Patient with Earlier Systemic Therapies

Purpose

To describe retinal findings in a patient with mucopolysaccharidosis type I (MPS I) that underwent an early treatment with hematopoietic stem cell transplantation (HSCT) and enzyme replacement therapy (ERT). Case Report. We describe a case of a 12-year-old female with a biochemical and genetic diagnosis of MPS I. She underwent HSCT and ERT on the first year of life. The visual acuity was 5/10 in both eyes and she had bilateral grade 2 corneal haze. Spectral domain optical coherence tomography (SD-OCT) revealed thickening of the external limiting membrane (ELM) at the fovea. In the parafoveal and perifoveal regions, SD-OCT displayed a loss of the interdigitation, ellipsoid, and myoid zones and of the ELM accompanied by progressive thinning of the outer nuclear layer. Fundus infrared imaging revealed a hyperreflective ring centred on the fovea and hyporeflective areas in temporal parafoveal regions in both eyes. En face OCT imaging revealed two hyperreflective rings on the outer retinal level.

Conclusion

This patient developed macular changes with foveal deposition of hyperreflective material and parafoveal thinning, despite early systemic treatment. Systemic therapies can provide an increase in life expectancy and stabilize visual acuity and corneal clouding, although their effect on retinal degeneration is unknown.

Multimodal Imaging in Retinitis Pigmentosa: Correlations among Microvascular Changes, Macular Function and Retinal Structure

Purpose:

To analyze microvascular changes in patients with retinitis pigmentosa (RP) with relatively preserved visual acuity (VA), using swept source optical coherence tomography (SS-OCT) angiography to correlate results to macular function and structure.

Methods:

This was a case–control study conducted over 70 eyes of 35 RP patients with relatively preserved VA. All patients underwent a complete ophthalmic examination, including SS-OCT, OCT angiography (OCT-A), fundus autofluorescence (FAF), and multifocal electroretinogram (mfERG). Thirty-four eyes of 34 healthy controls of age-, sex-, and axial length-matched (control group), were also analyzed. The main outcome measures were foveal and parafoveal vascular densities (FVDs and PFVDs) in the superficial capillary plexus (SCP) and deep capillary plexus (DCP), foveal avascular zone (FAZ) and its enlargement coefficient and their correlation with macular function (by means of VA and mfERG), and structure (by means of FAF and SS-OCT).

Results:

In the RP group, PFVD was 25.99 ± 5.2% in the SCP and 34.47 ± 2.37% in the DCP and were significantly lower as compared to control group (P < 0.0001; P = 0.0026, respectively). Enlargement coefficient of FAZ was 1.78 ± 0.79. We found a statistically significant correlation between VA and PFVD in the DCP (P < 0.0001), FAZ disruption in the SCP (P = 0.006) and enlargement coefficient of FAZ (P = 0.01). The parafoveal DCP density was significantly correlated with P1 amplitude (P = 0.005) in rings 2, 3, 4, and 5 of the mfERG. We found a statistically significant correlation between parafoveal density in the DCP, thickness of ganglion cell complex (GCC) (P = 0.001), and the width of ellipsoid band (P = 0.041). Parafoveal SCP density was also correlated to GCC (P = 0.033).

Conclusions:

We showed that vascular alteration in RP begins at the level of the DCP, which affects the outer retina and leads to a narrowing of the ellipsoid. The alteration of the SCP would occur later in the evolution of the disease. Vascular changes occur early during RP and were highly correlated to retinal function and structure. OCT-A seems to be a good tool to quantify vascular network loss and could play a central role in staging, prognosis, and monitoring disease progression.

Cone Identification in Choroideremia: Repeatability, Reliability, and Automation Through Use of a Convolutional Neural Network

Purpose

Adaptive optics imaging has enabled the visualization of photoreceptors both in health and disease. However, there remains a need for automated accurate cone photoreceptor identification in images of disease. Here, we apply an open-source convolutional neural network (CNN) to automatically identify cones in images of choroideremia (CHM). We further compare the results to the repeatability and reliability of manual cone identifications in CHM.

Methods

We used split-detection adaptive optics scanning laser ophthalmoscopy to image the inner segment cone mosaic of 17 patients with CHM. Cones were manually identified twice by one experienced grader and once by two additional experienced graders in 204 regions of interest (ROIs). An open-source CNN either pre-trained on normal images or trained on CHM images automatically identified cones in the ROIs. True and false positive rates and Dice's coefficient were used to determine the agreement in cone locations between data sets. Interclass correlation coefficient was used to assess agreement in bound cone density.

Results

Intra- and intergrader agreement for cone density is high in CHM. CNN performance increased when it was trained on CHM images in comparison to normal, but had lower agreement than manual grading.

Conclusions

Manual cone identifications and cone density measurements are repeatable and reliable for images of CHM. CNNs show promise for automated cone selections, although additional improvements are needed to equal the accuracy of manual measurements.

Translational Relevance

These results are important for designing and interpreting longitudinal studies of cone mosaic metrics in disease progression or treatment intervention in CHM.

Expansion of retinal nerve fiber bundle narrowing in glaucoma: An adaptive optics scanning laser ophthalmoscopy study

Purpose

To investigate longitudinal changes in the retinal nerve fiber bundle in eyes with primary open angle glaucoma using adaptive optics scanning laser ophthalmoscopy.

Methods

A prospective observational case series. Fourteen eyes from 12 patients with primary open angle glaucoma that exhibited retinal nerve fiber layer defects on fundus photography were imaged with adaptive optics scanning laser ophthalmoscopy over time.

Results

The expansion of retinal nerve fiber bundle narrowing was observed on adaptive optics scanning laser ophthalmoscopy in 8 eyes (57.1%) over a period of 1.44 ± 0.42 years. Retinal nerve fiber bundle narrowing expanded horizontally in 2 eyes and vertically in 6 eyes. In 3 eyes, changes in the retinal nerve fiber layer were only detectable on adaptive optics scanning laser ophthalmoscopy images.

Conclusions and Importance

The expansion of retinal nerve fiber bundle narrowing was observed using adaptive optics scanning laser ophthalmoscopy. Accordingly, this tool may be a useful tool for detecting glaucoma-related changes in retinal nerve fibers in a short time.

Posterior staphylomas in non-highly myopic eyes with retinitis pigmentosa

PURPOSE

Our aim was to highlight the presence and the frequency of posterior staphyloma (PS) in non-highly myopic retinitis pigmentosa (RP) patients and to study the relationship between PS and choroidal thickness (CT).

METHODS

This was a retrospective case-control study of 77 eyes (39 patients) with RP, axial length inferior to 26 mm and clinically preserved macular area. All patients underwent fundus photography, A- and B-scan ocular ultrasonography, fundus autofluorescence (FAF) and swept source optical coherence tomography (SS-OCT). PS was defined by an outward bowing of the sclera on SS-OCT and B-scans. The relationship between the PS and SS-OCT layers thicknesses was determined.

RESULTS

Over 77 RP eyes of 39 patients studied, a PS was identified in 17 eyes (22%) of nine patients. Fifteen eyes had a narrow macular staphyloma (NMS), and two eyes had a wide macular staphyloma (WMS). Mean age in this group was 34.2 years (range 19-53 years), mean axial length was 23.60 ± 0.61 mm and mean CT was 185.7 ± 71 um versus 259.7 um in eyes without PS. The staphyloma edges corresponded to area of outer retina loss on SS-OCT and were larger than the hyperautofluorescent ring on FAF. We found a significant association between PS and CT in our RP patients (p = 0.003). The mean CT was significantly thinner in PS eyes compared to eyes without staphyloma. There was no significant association between PS and with visual acuity, years of progression, retinal thickness nor FAF findings.

CONCLUSIONS

PS was present in 22% of non-highly myopic eyes with RP. Narrow macular staphyloma was the most common type observed in our series. A marked thinning of the choroid was noted in PS eyes when compared to RP eyes without PS, as well as the outer retina degeneration.

Cellular imaging of inherited retinal diseases using adaptive optics

Adaptive optics (AO) is an insightful tool that has been increasingly applied to existing imaging systems for viewing the retina at a cellular level. By correcting for individual optical aberrations, AO offers an improvement in transverse resolution from 10-15 μm to ~2 μm, enabling assessment of individual retinal cell types. One of the settings in which its utility has been recognised is that of the inherited retinal diseases (IRDs), the genetic and clinical heterogeneity of which warrants better cellular characterisation. In this review, we provide a summary of the basic principles of AO, its integration into multiple retinal imaging modalities and its clinical applications, focusing primarily on IRDs. Furthermore, we present a comprehensive summary of AO-based cellular findings in IRDs according to their associated disease-causing genes.

Automatic Detection of Cone Photoreceptors With Fully Convolutional Networks

PURPOSE

To develop a fully automatic method, based on deep learning algorithms, for determining the locations of cone photoreceptors within adaptive optics scanning laser ophthalmoscope images and evaluate its performance against a dataset of manually segmented images.

METHODS

A fully convolutional network (FCN) based on U-Net architecture was used to generate prediction probability maps and then used a localization algorithm to reduce the prediction map to a collection of points. The proposed method was trained and tested on two publicly available datasets of different imaging modalities, with Dice overlap, false discovery rate, and true positive reported to assess performance.

RESULTS

The proposed method achieves a Dice coefficient of 0.989, true positive rate of 0.987, and false discovery rate of 0.009 on the first confocal dataset; and a Dice coefficient of 0.926, true positive rate of 0.909, and false discovery rate of 0.051 on the second split detector dataset. Results compare favorably with a previously proposed method, but this method provides quicker (25 times faster) evaluation performance.

CONCLUSIONS

The proposed FCN-based method demonstrates that deep learning algorithms can achieve accurate cone localizations, almost comparable to a human expert, while labeling the images.

TRANSLATIONAL RELEVANCE

Manual cone photoreceptor identification is a time-consuming task due to the large number of cones present within a single image; using the proposed FCN-based method could support the image analysis task, drastically reducing the need for manual assessment of the photoreceptor mosaic.

A 2-Year Longitudinal Study of Normal Cone Photoreceptor Density

Purpose

Despite the potential for adaptive optics scanning light ophthalmoscopy (AOSLO) to quantify retinal disease progression at the cellular level, there remain few longitudinal studies investigating changes in cone density as a measure of disease progression. Here, we undertook a prospective, longitudinal study to investigate the variability of cone density measurements in normal subjects during a 2-year period.

Methods

Fourteen eyes of nine subjects with no known ocular pathology were imaged both at a baseline and a 2-year follow-up visit by using confocal AOSLO at five retinal locations. Two-year affine-registered images were created to minimize the effects of intraframe distortions. Regions of interest were cropped from baseline, 2-year manually aligned, and 2-year affine-registered images. Cones were identified (graded masked) and cone density was extracted.

Results

Mean baseline cone density (cones/mm²) was 87,300, 62,200, 45,500, 28,700, and 18,200 at 190, 350, 500, 900, and 1500 μm, respectively. The mean difference (± standard deviation [SD]) in cone density from baseline to 2-year affine-registered images was 1400 (1700), 100 (1800), 300 (800), 400 (800), and 1000 (2400) cones/mm² at the same locations. The mean difference in cone density during the 2-year period was lower for affine-registered images than manually aligned images.

Conclusions

There was no meaningful change in normal cone density during a 2-year period. Intervisit variability in cone density measurements decreased when intraframe distortions between time points were minimized. This variability must be considered when planning prospective longitudinal clinical trials using changes in cone density as an outcome measure for assessing retinal disease progression.

Cone Spacing Correlates With Retinal Thickness and Microperimetry in Patients With Inherited Retinal Degenerations

Purpose

To determine whether high-resolution retinal imaging measures of macular structure correlate with visual function over 36 months in retinal degeneration (RD) patients and normal subjects.

Methods

Twenty-six eyes of 16 RD patients and 16 eyes of 8 normal subjects were studied at baseline; 15 eyes (14 RD) and 11 eyes (6 normal) were studied 36 months later. Adaptive Optics Scanning Laser Ophthalmoscopy (AOSLO) was used to identify regions of interest (ROIs) with unambiguous cones at baseline to measure cone spacing. AOSLO images were aligned with spectral-domain optical coherence tomography (SD-OCT) and fundus-guided microperimetry results to correlate structure and function at the ROIs. SD-OCT images were segmented to measure inner segment (IS) and outer segment (OS) thickness. Correlations between cone spacing, IS and OS thickness and sensitivity were assessed using Spearman correlation coefficient ρ with bootstrap analyses clustered by person.

Results

Cone spacing (ρ = 0.57, P < 0.001) and macular sensitivity (ρ = 0.19, P = 0.14) were significantly correlated with eccentricity in patients. Controlling for eccentricity, cone spacing Z-scores were inversely correlated with IS (ρ = −0.29, P = 0.002) and OS thickness (ρ = −0.39, P < 0.001) in RD patients only, and with sensitivity in normal subjects (ρ = −0.22, P < 0.001) and RD patients (ρ = −0.38, P < 0.001). After 36 months, cone spacing increased (P < 0.001) and macular sensitivity decreased (P = 0.007) compared to baseline in RD patients.

Conclusions

Cone spacing increased and macular sensitivity declined significantly in RD patients over 36 months. High resolution images of cone structure correlated with retinal sensitivity, and may be appropriate outcome measures for clinical trials in RD.

Repeatability of Adaptive Optics Automated Cone Measurements in Subjects With Retinitis Pigmentosa and Novel Metrics for Assessment of Image Quality

Purpose

We determine the intersession repeatability of cone measurements via flood-illuminated adaptive optics (AO) imaging in patients with retinitis pigmentosa (RP), to better differentiate variation due to imaging inaccuracies versus pathology-driven change.

Methods

A total of 25 4° × 4° AO images were acquired three times on the same day in 10 subjects with RP, registered in i2K Retina, and cones were identified using a custom-built MATLAB algorithm. Nine equally spaced regions of interest were selected for each imaging set. A subset of subjectively “poor” and “good” quality images was selected by three independent graders, analyzed using cone density, cone location similarity (CLS) and cone spacing, and compared to age-matched normals.

Results

The coefficient of variation (CoV), repeatability, and percent repeatability of automated cone density were slightly higher in patients with RP compared to age-matched normals, but showed no statistically significant difference. The standard deviation of CLS and cone spacing of nearest-neighbor distance demonstrated a statistically significant difference between good- and poor-quality images.

Conclusions

Repeatability of automated cone density measurements in patients with RP is comparable to normals. Misidentification of cones due to image quality variability is a major limitation of automated cone counting algorithms in patients with RP. Our study suggests that CLS and cone spacing metrics could be used to help define image quality and, thus, increase confidence in automated cone counts in patients with RP.

Translational Relevance

The novel AO image quality assessment metrics described in our study could help to improve patient image interpretation, prognosis, and longitudinal care.

Automated identification of cone photoreceptors in adaptive optics optical coherence tomography images using transfer learning

Automated measurements of the human cone mosaic requires the identification of individual cone photoreceptors. The current gold standard, manual labeling, is a tedious process and can not be done in a clinically useful timeframe. As such, we present an automated algorithm for identifying cone photoreceptors in adaptive optics optical coherence tomography (AO-OCT) images. Our approach fine-tunes a pre-trained convolutional neural network originally trained on AO scanning laser ophthalmoscope (AO-SLO) images, to work on previously unseen data from a different imaging modality. On average, the automated method correctly identified 94% of manually labeled cones when compared to manual raters, from twenty different AO-OCT images acquired from five normal subjects. Voronoi analysis confirmed the general hexagonal-packing structure of the cone mosaic as well as the general cone density variability across portions of the retina. The consistency of our measurements demonstrates the high reliability and practical utility of having an automated solution to this problem.

Optical coherence tomography angiography in patients with retinitis pigmentosa who have normal visual acuity

PURPOSE

To investigate flow area changes measured using optical coherence tomography angiography (OCTA; RTVue XR Avanti^® ) in patients with retinitis pigmentosa (RP) with preserved visual acuity (VA).

METHODS

This was an age- and refraction-matched case-control study. Consecutive patients with a best-corrected visual acuity (BCVA) of ≥20/20 and normal subjects were recruited. Fifty eyes (32 patients) and 22 eyes (12 controls) were included. The flow area and foveal avascular zone (FAZ) were measured in both superficial and deep layers within a 3 × 3 mm central area of the fovea. Association between OCTA parameters and the length of the inner segment ellipsoid (ISe) and external limiting membrane (ELM), the area without abnormal fluorescence in fundus autofluorescence (normal FAF area ratio) and the area of I-2e of the Goldmann perimeter were analysed using mixed-effects regression analysis.

RESULTS

Foveal avascular zones were significantly smaller in patients with RP than in controls in superficial (p = 0.004) but not in deep layers (p = 0.25). The flow area in superficial (p = 0.007) and deep layers (p = 0.004) was significantly smaller in patients with RP than in controls. In patients with RP, flow areas in the superficial layers, but not in the deep layers, were significantly associated with the lengths of ISe (p = 0.001) and ELM (p = 0.002) and the I-2e area (p = 0.036), but not with the normal FAF area ratio (p = 0.399).

CONCLUSION

Optical coherence tomography angiography (OCTA)-measured flow area in superficial layers gradually reduced with RP progression and may be a useful parameter of RP pathogenesis.

Peripheral Cone Dystrophy: Expanded Clinical Spectrum, Multimodal and Ultrawide-Field Imaging, and Genomic Analysis

PURPOSE

To present new clinical features, multimodal and ultrawide-field imaging characteristics of peripheral cone dystrophy (PCD), and results of laboratory and genetic investigation to decipher the etiology.

METHODS

Retrospective observational case-series.

RESULTS

Three patients with PCD presented with bilateral paracentral scotomas and a mean visual acuity of 20/25. All exhibited confluent macular hyperautofluorescence with a central bull's eye lesion. Spectral-domain optical coherence tomography revealed loss of outer retinal elements, particularly the inner segment ellipsoid band and external limiting membrane, within the area of macular hyperautofluorescence. This area corresponded with a lightened fundus appearance and variable retinal pigment epithelium (RPE) abnormalities. Full field and multifocal electroretinography distinguished PCD from other photoreceptor dystrophies. Ultrawide-field imaging revealed irregular peripheral retinal lesions in a distribution greater nasally than temporally and not contiguous with the macular lesion. Functional and anatomic testing remained stable over a mean follow-up of 3 years. Laboratory investigation for causes of uveitis was negative. Whole exome sequencing identified rare variants in genes associated with macular or cone dystrophy or degeneration.

CONCLUSIONS

In contrast to the original description, the funduscopic and fluorescein angiographic appearance of PCD is abnormal, although the defects are subtle. Peripheral lesions may be observed in some patients. Bilateral, symmetric, macular hyperautofluorescence associated with outer retinal atrophy that spares the fovea is a characteristic of PCD. Pathogenic variants in the same gene were not shared across the cohort, suggesting genetic heterogeneity. Further evaluation is warranted.

Adaptive optics scanning laser ophthalmoscopy in fundus imaging, a review and update

Adaptive optics scanning laser ophthalmoscopy (AO-SLO) has been a promising technique in funds imaging with growing popularity. This review firstly gives a brief history of adaptive optics (AO) and AO-SLO. Then it compares AO-SLO with conventional imaging methods (fundus fluorescein angiography, fundus autofluorescence, indocyanine green angiography and optical coherence tomography) and other AO techniques (adaptive optics flood-illumination ophthalmoscopy and adaptive optics optical coherence tomography). Furthermore, an update of current research situation in AO-SLO is made based on different fundus structures as photoreceptors (cones and rods), fundus vessels, retinal pigment epithelium layer, retinal nerve fiber layer, ganglion cell layer and lamina cribrosa. Finally, this review indicates possible research directions of AO-SLO in future.

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.

In Vivo Imaging of Cx3cr1gfp/gfp Reporter Mice with Spectral-domain Optical Coherence Tomography and Scanning Laser Ophthalmoscopy

Spectral domain optical coherence tomography (SD-OCT) and scanning laser ophthalmoscopy (SLO) are extensively used in experimental ophthalmology. In the present protocol, mice expressing green fluorescent protein (gfp) under the promoter of Cx3cr1 (BALB/c-Cx3cr1^gfp/gfp) were used to image microglia cells in vivo in the retina. Microglia are resident macrophages of the retina and have been implicated in several retinal diseases^1,2,3,4,5,6. This protocol provides a detailed approach for generation of retinal B-scans, with SD-OCT, and imaging of microglia cell distribution in Cx3cr1^gfp/gfp mice with SLO in vivo, using an ophthalmic imaging platform system. The protocol can be used in several reporter mouse lines. However, there are some limitations to the protocol presented here. First, both SLO and SD-OCT, when used in the high-resolution mode, collect data with high axial resolution but the lateral resolution is lower (3.5 µm and 6 µm, respectively). Moreover, the focus and saturation level in SLO is highly dependent on parameter selection and correct alignment of the eye. Additionally, using devices designed for human patients in mice is challenging due to the higher total optical power of the mouse eye compared to the human eye; this can lead to lateral magnification inaccuracies⁷, which are also dependent on the magnification by the mouse lens among others. However, despite that the axial scan position is dependent upon lateral magnification, the axial SD-OCT measurements are accurate⁸.

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.

Cell type-specific changes in retinal ganglion cell function induced by rod death and cone reorganization in rats

We have determined the impact of rod death and cone reorganization on the spatiotemporal receptive fields (RFs) and spontaneous activity of distinct retinal ganglion cell (RGC) types. We compared RGC function between healthy and retinitis pigmentosa (RP) model rats (S334ter-3) at a time when nearly all rods were lost but cones remained. This allowed us to determine the impact of rod death on cone-mediated visual signaling, a relevant time point because the diagnosis of RP frequently occurs when patients are nightblind but daytime vision persists. Following rod death, functionally distinct RGC types persisted; this indicates that parallel processing of visual input remained largely intact. However, some properties of cone-mediated responses were altered ubiquitously across RGC types, such as prolonged temporal integration and reduced spatial RF area. Other properties changed in a cell type-specific manner, such as temporal RF shape (dynamics), spontaneous activity, and direction selectivity. These observations identify the extent of functional remodeling in the retina following rod death but before cone loss. They also indicate new potential challenges to restoring normal vision by replacing lost rod photoreceptors.NEW & NOTEWORTHY This study provides novel and therapeutically relevant insights to retinal function following rod death but before cone death. To determine changes in retinal output, we used a large-scale multielectrode array to simultaneously record from hundreds of retinal ganglion cells (RGCs). These recordings of large-scale neural activity revealed that following the death of all rods, functionally distinct RGCs remain. However, the receptive field properties and spontaneous activity of these RGCs are altered in a cell type-specific manner.

Optical Coherence Tomography Angiography to Estimate Retinal Blood Flow in Eyes with Retinitis Pigmentosa

Ophthalmologists sometimes face difficulties in identifying the origin of visual acuity (VA) loss in a retinitis pigmentosa (RP) patient, particularly before cataract surgery: cataract or the retinal disease state. Therefore, it is important to identify the significant factors correlating with VA. Nowadays, retinal blood flow in superficial and deep layers can be estimated non-invasively using optical coherence tomography angiography (OCTA). We estimated blood flow per retinal layer by using OCTA; investigated the correlation between VA and other parameters including blood flow and retinal thickness; and identified the most associated factor with VA in patients with RP. OCTA images in 68 of consecutive 110 Japanese RP patients were analysable (analysable RP group). Thirty-two age- and axial length-matched healthy eyes (control group) were studied. In the analysable RP group, the parafoveal flow density in superficial and deep layers was 47.0 ± 4.9% and 52.4 ± 5.5%, respectively, which was significantly lower than that in controls. Using multivariate analysis, we found that the parafoveal flow density in the deep layer and superficial foveal avascular area were the factors associated with VA. Non-invasive estimation of retinal blood flow per retinal layer using OCTA is useful for predicting VA in RP patients.

An Automated Reference Frame Selection (ARFS) Algorithm for Cone Imaging with Adaptive Optics Scanning Light Ophthalmoscopy

PURPOSE

To develop an automated reference frame selection (ARFS) algorithm to replace the subjective approach of manually selecting reference frames for processing adaptive optics scanning light ophthalmoscope (AOSLO) videos of cone photoreceptors.

METHODS

Relative distortion was measured within individual frames before conducting image-based motion tracking and sorting of frames into distinct spatial clusters. AOSLO images from nine healthy subjects were processed using ARFS and human-derived reference frames, then aligned to undistorted AO-flood images by nonlinear registration and the registration transformations were compared. The frequency at which humans selected reference frames that were rejected by ARFS was calculated in 35 datasets from healthy subjects, and subjects with achromatopsia, albinism, or retinitis pigmentosa. The level of distortion in this set of human-derived reference frames was assessed.

RESULTS

The average transformation vector magnitude required for registration of AOSLO images to AO-flood images was significantly reduced from 3.33 ± 1.61 pixels when using manual reference frame selection to 2.75 ± 1.60 pixels (mean ± SD) when using ARFS (P = 0.0016). Between 5.16% and 39.22% of human-derived frames were rejected by ARFS. Only 2.71% to 7.73% of human-derived frames were ranked in the top 5% of least distorted frames.

CONCLUSION

ARFS outperforms expert observers in selecting minimally distorted reference frames in AOSLO image sequences. The low success rate in human frame choice illustrates the difficulty in subjectively assessing image distortion.

TRANSLATIONAL RELEVANCE

Manual reference frame selection represented a significant barrier to a fully automated image-processing pipeline (including montaging, cone identification, and metric extraction). The approach presented here will aid in the clinical translation of AOSLO imaging.

Cone Integrity in Glaucoma: An Adaptive-Optics Scanning Laser Ophthalmoscopy Study

PURPOSE

To investigate photoreceptor changes in eyes with glaucoma.

DESIGN

Cross-sectional study.

METHODS

The study included 35 eyes of 35 patients with primary open-angle glaucoma who had suffered parafoveal visual field loss at least 3 years previously, as well as 21 eyes of 21 normal subjects. Eyes with an axial length ≥26.0 mm were excluded. All subjects underwent a full ophthalmologic examination, including spectral-domain optical coherence tomography (SDOCT) and prototype adaptive-optics scanning laser ophthalmoscopy (AO-SLO) imaging.

RESULTS

As determined using AO-SLO, eyes with glaucoma did not differ significantly from normal eyes in terms of either cone density (26 468 ± 3392 cones/m² vs 26 147 ± 2700 cones/m², respectively; P = .77; measured 0.5 mm from the foveal center) or cone spatial organization (ratio of hexagonal Voronoi domain: 43.7% ± 4.4% vs 44.3% ± 4.9%; P = .76; measured 0.5 mm from the foveal center). Furthermore, SDOCT showed that the 2 groups did not differ significantly in terms of the photoreceptor-related layer thickness, and that the photoreceptor ellipsoid zone band was continuous in all normal and glaucoma eyes. In glaucoma eyes with vertically asymmetric severity, the more affected side did not significantly differ from the less affected side in terms of cone density, cone spatial organization, or photoreceptor-related layer thickness. In 8 eyes (22.9%) with glaucoma, dark, partition-like areas surrounded the cones on the AO-SLO.

CONCLUSIONS

Both AO-SLO and SDOCT showed cone integrity in eyes with glaucoma, even in areas with visual field and nerve fiber loss. In AO-SLO, microcystic lesions in the inner nuclear layer may influence images of the cone mosaic.

Clinical and Genetic Findings of Autosomal Recessive Bestrophinopathy in Japanese Cohort

PURPOSE

To report the clinical and genetic findings of 9 Japanese patients with autosomal recessive bestrophinopathy (ARB).

DESIGN

Retrospective, multicenter observational case series.

METHODS

Nine ARB patients from 7 unrelated Japanese families that were examined in 3 institutions in Japan were studied. A series of ophthalmic examinations including fundus photography, spectral-domain optical coherence tomography, fundus autofluorescence, electrooculography (EOG), electroretinography, and the results of genetic analysis were reviewed.

RESULTS

Genetic analyses identified 7 pathogenic variants in BEST1 including 2 novel variants, c.478G>C (p.A160P) and c.948+1delG. Homozygous variants were found in 4 families and compound heterozygous variants were found in 3 families. Two patients were diagnosed as ARB only after the whole exome sequencing analyses. The Arden ratio of the EOG was less than 1.5 in all 7 patients tested. Vitelliform lesions typical for Best vitelliform macular dystrophy were not seen in any of the patients. Seven patients shared some of the previously described features of ARB: subretinal deposits, extensive subretinal fluid, and cystoid macular edema (CME). However, the other 2 patients with severe retinal degeneration lacked these features. Focal choroidal excavations were present bilaterally in 2 patients. One case had a marked reduction of the CME and expansion of subretinal deposits over an 8-year of follow-up period.

CONCLUSIONS

Japanese ARB patients had some but not all of the previously described features. Genetic analyses are essential to diagnose ARB correctly in consequence of considerable phenotypic variations.

Chromatic Multifocal Pupillometer for Objective Perimetry and Diagnosis of Patients with Retinitis Pigmentosa

PURPOSE

To assess visual field (VF) defects and retinal function objectively in healthy participants and patients with retinitis pigmentosa (RP) using a chromatic multifocal pupillometer.

DESIGN

Cross-sectional study.

PARTICIPANTS

The right eyes of 16 healthy participants and 13 RP patients.

METHODS

Pupil responses to red and blue light (peak, 485 and 625 nm, respectively) presented by 76 light-emitting diodes, 1.8-mm spot size at different locations of a 16.2° VF were recorded. Subjective VFs of RP patients were determined using chromatic dark-adapted Goldmann VFs (CDA-GVFs). Six healthy participants underwent 2 pupillometer examinations to determine test-retest reliability.

MAIN OUTCOME MEASURES

Three parameters of pupil contraction were determined automatically: percentage of change of pupil size (PPC), maximum contraction velocity (MCV; in pixels per second), and latency of MCV (LMCV; in seconds). The fraction of functional VF was determined by CDA-GVF.

RESULTS

In healthy participants, higher PPC and MCV were measured in response to blue compared with red light. The LMCV in response to blue light was relatively constant throughout the VF. Healthy participants demonstrated higher PPC and MCV and shorter LMCV in central compared with peripheral test points in response to red light. Test-retest correlation coefficients were 0.7 for PPC and 0.5 for MCV. In RP patients, test point in which the PPC and MCV were lower than 4 standard errors from the mean of healthy participants correlated with areas that were indicated as nonseeing by CDA-GVF. The mean absolute deviation in LMCV parameter in response to the red light between different test point was significantly higher in RP patients (range, 0.16-0.47) than in healthy participants (range, 0.02-0.16; P < 0.0001) and indicated its usefulness as a diagnostic tool with high sensitivity and specificity (area under the receiver operating characteristic curve (AUC), 0.97, Mann-Whitney-Wilcoxon analysis). Randomly reducing the number of test points to a total of 15 points did not significantly reduce the AUC in RP diagnosis based on this parameter.

CONCLUSIONS

This study demonstrates the feasibility of using a chromatic multifocal pupillometer for objective diagnosis of RP and assessment of VF defects.

The fundus photo has met its match: optical coherence tomography and adaptive optics ophthalmoscopy are here to stay

PURPOSE

Over the past 25 years, optical coherence tomography (OCT) and adaptive optics (AO) ophthalmoscopy have revolutionised our ability to non-invasively observe the living retina. The purpose of this review is to highlight the techniques and human clinical applications of recent advances in OCT and adaptive optics scanning laser/light ophthalmoscopy (AOSLO) ophthalmic imaging.

RECENT FINDINGS

Optical coherence tomography retinal and optic nerve head (ONH) imaging technology allows high resolution in the axial direction resulting in cross-sectional visualisation of retinal and ONH lamination. Complementary AO ophthalmoscopy gives high resolution in the transverse direction resulting in en face visualisation of retinal cell mosaics. Innovative detection schemes applied to OCT and AOSLO technologies (such as spectral domain OCT, OCT angiography, confocal and non-confocal AOSLO, fluorescence, and AO-OCT) have enabled high contrast between retinal and ONH structures in three dimensions and have allowed in vivo retinal imaging to approach that of histological quality. In addition, both OCT and AOSLO have shown the capability to detect retinal reflectance changes in response to visual stimuli, paving the way for future studies to investigate objective biomarkers of visual function at the cellular level. Increasingly, these imaging techniques are being applied to clinical studies of the normal and diseased visual system.

SUMMARY

Optical coherence tomography and AOSLO technologies are capable of elucidating the structure and function of the retina and ONH noninvasively with unprecedented resolution and contrast. The techniques have proven their worth in both basic science and clinical applications and each will continue to be utilised in future studies for many years to come.

Evaluation of Photoreceptors in Bietti Crystalline Dystrophy with CYP4V2 Mutations Using Adaptive Optics Scanning Laser Ophthalmoscopy

PURPOSE

To evaluate photoreceptors in Bietti crystalline dystrophy patients with CYP4V2 mutations using high-resolution images of the macula obtained with adaptive optics scanning laser ophthalmoscopy (AO-SLO).

DESIGN

Prospective observational case series with comparison to healthy controls.

METHODS

Seven eyes of 7 Bietti crystalline dystrophy patients with CYP4V2 mutations and 12 normal eyes of 12 age- and axial length-matched healthy volunteers were studied. All participants underwent ophthalmologic examinations and AO-SLO assessments. All patients underwent spectral-domain optical coherence tomography, fundus autofluorescence, Humphrey field analysis, and electroretinography. AO-SLO images were analyzed 0.5 mm and 1.0 mm from the center of the fovea in the superior, inferior, nasal, and temporal quadrants.

RESULTS

Mean ± standard deviation cone density (cells/mm(2)) 0.5 mm from the center of the fovea was 17,209 ± 2276 in patients and 20 493 ± 2758 in controls, which was statistically different (P = .001); however, mean cone density 1.0 mm from the center of the fovea was 15 685 ± 2302 in patients and 15 705 ± 1848 in controls, which was not statistically different (P = .20). There was no correlation between cone density and mean deviation measured using a Humphrey field analysis or visual acuity in patients.

CONCLUSIONS

In Bietti crystalline dystrophy patients with CYP4V2 mutations, cone density remained for visual dysfunction by evaluation using high-resolution AO-SLO. These findings support the theory that disorder of the retinal pigment epithelium and the photoreceptors in the patients are the primary and secondary pathologic changes, respectively. This is consistent with results from previous basic studies.

Necrotic enlargement of cone photoreceptor cells and the release of high-mobility group box-1 in retinitis pigmentosa

Retinitis pigmentosa (RP) refers to a group of inherited retinal degenerations resulting form rod and cone photoreceptor cell death. The rod cell death due to deleterious genetic mutations has been shown to occur mainly through apoptosis, whereas the mechanisms and features of the secondary cone cell death have not been fully elucidated. Our previous study showed that the cone cell death in rd10 mice, an animal model of RP, involves necrotic features and is partly mediated by the receptor interacting protein kinase. However, the relevancy of necrotic cone cell death in human RP patients remains unknown. In the present study, we showed that dying cone cells in rd10 mice exhibited cellular enlargement, along with necrotic changes such as cellular swelling and mitochondrial rupture. In human eyes, live imaging of cone cells by adaptive optics scanning laser ophthalmoscopy revealed significantly increased percentages of enlarged cone cells in the RP patients compared with the control subjects. The vitreous of the RP patients contained significantly higher levels of high-mobility group box-1, which is released extracellularly associated with necrotic cell death. These findings suggest that necrotic enlargement of cone cells is involved in the process of cone degeneration, and that necrosis may be a novel target to prevent or delay the loss of cone-mediated central vision in RP.

Assessment of Different Sampling Methods for Measuring and Representing Macular Cone Density Using Flood-Illuminated Adaptive Optics

PURPOSE

To describe a standardized flood-illuminated adaptive optics (AO) imaging protocol suitable for the clinical setting and to assess sampling methods for measuring cone density.

METHODS

Cone density was calculated following three measurement protocols: 50 × 50-μm sampling window values every 0.5° along the horizontal and vertical meridians (fixed-interval method), the mean density of expanding 0.5°-wide arcuate areas in the nasal, temporal, superior, and inferior quadrants (arcuate mean method), and the peak cone density of a 50 × 50-μm sampling window within expanding arcuate areas near the meridian (peak density method). Repeated imaging was performed in nine subjects to determine intersession repeatability of cone density.

RESULTS

Cone density montages could be created for 67 of the 74 subjects. Image quality was determined to be adequate for automated cone counting for 35 (52%) of the 67 subjects. We found that cone density varied with different sampling methods and regions tested. In the nasal and temporal quadrants, peak density most closely resembled histological data, whereas the arcuate mean and fixed-interval methods tended to underestimate the density compared with histological data. However, in the inferior and superior quadrants, arcuate mean and fixed-interval methods most closely matched histological data, whereas the peak density method overestimated cone density compared with histological data. Intersession repeatability testing showed that repeatability was greatest when sampling by arcuate mean and lowest when sampling by fixed interval.

CONCLUSIONS

We show that different methods of sampling can significantly affect cone density measurements. Therefore, care must be taken when interpreting cone density results, even in a normal population.

Radial fundus autofluorescence in the periphery in patients with X-linked retinitis pigmentosa

Purpose

To describe the peripheral autofluorescence images and clinical features of patients with retinal dystrophy who showed radial fundus autofluorescence (FAF) at the posterior pole.

Methods

The authors retrospectively reviewed pooled wide-field FAF images of 711 patients with retinal dystrophy and 56 family members.

Results

Eleven eyes of seven women exhibited radial FAF at the posterior pole. Wide-field FAF showed extension of the radial pattern to the periphery in all eyes except one. One woman showed radial hyper-FAF only in the periphery, not at the posterior pole. These eight individuals were X-linked retinitis pigmentosa patients or carriers. The tapetal-like reflex was not observed in their color fundus photographs. The peripheral visual field showed wedge-shaped restriction in some individuals.

Conclusion

Wide-field FAF imaging can depict radial FAF not only at the posterior pole but also in the periphery in X-linked retinitis pigmentosa carriers. The authors therefore agree with previous reports that radial FAF may be a hallmark of X-linked retinitis pigmentosa.

Spontaneous remission of acute zonal occult outer retinopathy: follow-up using adaptive optics scanning laser ophthalmoscopy

PURPOSE

The purpose of this study was to report a case of acute zonal occult outer retinopathy (AZOOR) with spontaneous remission that was followed up using adaptive optics scanning laser ophthalmoscopy (AO-SLO).

METHODS

The right eye of a 31-year old myopic man diagnosed with AZOOR was followed up. The patient underwent a full ophthalmologic examination, spectral-domain optical coherence tomography (SD-OCT), multifocal electroretinography (mfERG) and imaging with prototype AO-SLO systems (Canon Inc) at the first visit, 1 month after, and 2 months after. Images focused on the photoreceptor layer were recorded in the area, and a montage of AO-SLO images was created.

RESULTS

The patient presented with acute onset of a blind spot and photopsia in his right eye. On AO-SLO, focal dark areas could be observed on the right eye but not on the left eye at the first examination (cone density 8,589/mm(2), mosaic regularity of cone photoreceptors 38.5 %, cone spacing 0.567). The dark areas on AO-SLO corresponded to areas of disrupted inner segments and outer segments (IS/OS) line or ellipsoid of the IS and abnormal area in mfERG. After 1 and 2 months, his symptoms tended to disappear gradually without any treatment. IS/OS line and mfERG could be nearly normalized. Furthermore, normal cone mosaic could be observed in areas where some focal dark spots could be observed at the first examination (cone density 10,112/mm(2), mosaic regularity of cone photoreceptors 39.9 %, cone spacing 0.606).

CONCLUSION

AO-SLO is a useful tool of diagnosis and follow-up of AZOOR. This study might suggest reversible cone damage could occur in some cases of AZOOR with spontaneous remission.

In vivo imaging of human cone photoreceptor inner segments

PURPOSE

An often overlooked prerequisite to cone photoreceptor gene therapy development is residual photoreceptor structure that can be rescued. While advances in adaptive optics (AO) retinal imaging have recently enabled direct visualization of individual cone and rod photoreceptors in the living human retina, these techniques largely detect strongly directionally-backscattered (waveguided) light from normal intact photoreceptors. This represents a major limitation in using existing AO imaging to quantify structure of remnant cones in degenerating retina.

METHODS

Photoreceptor inner segment structure was assessed with a novel AO scanning light ophthalmoscopy (AOSLO) differential phase technique, that we termed nonconfocal split-detector, in two healthy subjects and four subjects with achromatopsia. Ex vivo preparations of five healthy donor eyes were analyzed for comparison of inner segment diameter to that measured in vivo with split-detector AOSLO.

RESULTS

Nonconfocal split-detector AOSLO reveals the photoreceptor inner segment with or without the presence of a waveguiding outer segment. The diameter of inner segments measured in vivo is in good agreement with histology. A substantial number of foveal and parafoveal cone photoreceptors with apparently intact inner segments were identified in patients with the inherited disease achromatopsia.

CONCLUSIONS

The application of nonconfocal split-detector to emerging human gene therapy trials will improve the potential of therapeutic success, by identifying patients with sufficient retained photoreceptor structure to benefit the most from intervention. Additionally, split-detector imaging may be useful for studies of other retinal degenerations such as AMD, retinitis pigmentosa, and choroideremia where the outer segment is lost before the remainder of the photoreceptor cell.