Progression of Stargardt Disease as Determined by Fundus Autofluorescence Over a 12-Month Period: ProgStar Report No. 11

Genetic and Clinical Features of ABCA4-Associated Retinopathy in a Japanese Nationwide Cohort

PURPOSE

To clarify the genetic and clinical features of Japanese patients with ABCA4-associated retinopathy.

DESIGN

Retrospective, multicenter cohort study.

METHODS

Patients with retinal degeneration and biallelic ABCA4 variants were recruited from 13 different hospitals. Whole exome sequencing analysis was used for genetic testing. Comprehensive ophthalmic examinations were performed on matched patients. The primary outcome measure was identifying multimodal retinal imaging findings associated with disease progression.

RESULTS

This study included 63 patients: 19 with missense/missense, 23 with missense/truncation, and 21 with truncation/truncation genotypes. In total, 62 variants were identified, including 29 novel variants. Six patients had a mild phenotype characterized by foveal-sparing or preserved foveal structure, including 4 with missense/missense and 2 with missense/truncation genotypes. The p.Arg212His variant was the most frequent in patients with mild phenotypes (4/12 alleles). Clinical findings showed a disease duration-dependent worsening of the phenotypic stage. Patients with the truncation/truncation genotype exhibited rapid retinal degeneration within a few years and definite fundus autofluorescence imaging patterns, including hyper autofluorescence at the macula and few or no flecks.

CONCLUSIONS

Our results indicate that missense/missense or missense/truncation genotypes, including the p.Arg212His variant, are associated with a relatively mild phenotype. In contrast, the truncation/truncation genotype causes rapid and severe retinal degeneration in Japanese patients with ABCA4-associated retinopathy. These data are vital in predicting patient prognosis, guiding genetic counseling, and stratifying patients for future clinical trials.

Phenotyping and genotyping inherited retinal diseases: Molecular genetics, clinical and imaging features, and therapeutics of macular dystrophies, cone and cone-rod dystrophies, rod-cone dystrophies, Leber congenital amaurosis, and cone dysfunction syndromes

Inherited retinal diseases (IRD) are a leading cause of blindness in the working age population and in children. The scope of this review is to familiarise clinicians and scientists with the current landscape of molecular genetics, clinical phenotype, retinal imaging and therapeutic prospects/completed trials in IRD. Herein we present in a comprehensive and concise manner: (i) macular dystrophies (Stargardt disease (ABCA4), X-linked retinoschisis (RS1), Best disease (BEST1), PRPH2-associated pattern dystrophy, Sorsby fundus dystrophy (TIMP3), and autosomal dominant drusen (EFEMP1)), (ii) cone and cone-rod dystrophies (GUCA1A, PRPH2, ABCA4, KCNV2 and RPGR), (iii) predominant rod or rod-cone dystrophies (retinitis pigmentosa, enhanced S-Cone syndrome (NR2E3), Bietti crystalline corneoretinal dystrophy (CYP4V2)), (iv) Leber congenital amaurosis/early-onset severe retinal dystrophy (GUCY2D, CEP290, CRB1, RDH12, RPE65, TULP1, AIPL1 and NMNAT1), (v) cone dysfunction syndromes (achromatopsia (CNGA3, CNGB3, PDE6C, PDE6H, GNAT2, ATF6), X-linked cone dysfunction with myopia and dichromacy (Bornholm Eye disease; OPN1LW/OPN1MW array), oligocone trichromacy, and blue-cone monochromatism (OPN1LW/OPN1MW array)). Whilst we use the aforementioned classical phenotypic groupings, a key feature of IRD is that it is characterised by tremendous heterogeneity and variable expressivity, with several of the above genes associated with a range of phenotypes.

Clinical, Genotypic, and Imaging Characterization of the Spectrum of ABCA4 Retinopathies

PURPOSE

To investigate the clinical and genotypic differences in the spectrum of ABCA4-associated retinopathies (ABCA4Rs).

DESIGN

Observational, cross sectional case series.

PARTICIPANTS

Sixty-six patients (132 eyes) carrying biallelic ABCA4 variants.

METHODS

Patients underwent visual acuity measurement and multimodal imaging. Clinical records were reviewed for age at onset, presenting symptoms, genetic variants, and electroretinogram (ERG). Each eye was assigned to a phenotype based on age at onset, imaging and ERG: cone dystrophy-bull's-eye maculopathy (CD-BEM, 40 eyes), cone-rod dystrophy (CRD, 12 eyes), Stargardt disease (SD, 28 eyes), late-onset SD (LO-SD, 38 eyes), and fundus flavimaculatus (14 eyes). Images were analyzed for: peripapillary sparing, retinal pigment epithelium (RPE) atrophy (definitely decreased autofluorescence, DDAF), flecks patterns using autofluorescence; type of atrophy according to Classification of Atrophy Meeting reports, macular and choroidal thickness on OCT; and choriocapillaris flow deficits on OCT angiography.

MAIN OUTCOME MEASURES

Primary outcome was to report the demographic, genotypic, and imaging characteristics of the different ABCA4R phenotypes. Secondary objectives included the assessment of imaging biomarkers as outcome measures for clinical trials.

RESULTS

Age at onset was lower in CRD (12 ± 8 years) and higher in patients with LO-SD (59 ± 9 years) (all P < 0.01). Central vision loss was a common presenting symptom in CD-BEM and SD, whereas patients with LO-SD primarily complained of difficult dark adaptation. Missense variants were more frequent in CD-BEM, and splice site in CRD and LO-SD (P < 0.05). Peripapillary sparing was absent in 3 eyes with LO-SD (8%). Cone dystrophy-bull's-eye maculopathy eyes typically had complete outer retinal atrophy alterations (98%), whereas CRD and SD eyes showed both complete outer retinal atrophy and complete RPE and outer retinal atrophy (cRORA) (71%-100%). Patients with LO-SD had larger areas of DDAF (100% cRORA) and of choriocapillaris flow deficits (all P < 0.01). Repeatability of DDAF measurements was low for some phenotypes (CD-BEM and CRD) and atrophic areas <7.5 mm2. Resorbed flecks were significantly associated with CRD and LO-SD (P < 0.01).

CONCLUSIONS

This research provides a thorough evaluation of the spectrum of ABCA4R. Our findings suggest that certain phenotypes show preferential photoreceptor degeneration (e.g., CD-BEM), whereas others have substantial RPE and choriocapillaris alterations (e.g., LO-SD). We recommend that clinical trial end points take into consideration these imaging features to improve the interpretation of their results.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

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.

Quantification of Fundus Autofluorescence Features in a Molecularly Characterized Cohort of More Than 3000 Inherited Retinal Disease Patients from the United Kingdom

Purpose

To quantify relevant fundus autofluorescence (FAF) image features cross-sectionally and longitudinally in a large cohort of inherited retinal diseases (IRDs) patients.

Design

Retrospective study of imaging data (55-degree blue-FAF on Heidelberg Spectralis) from patients.

Participants

Patients with a clinical and molecularly confirmed diagnosis of IRD who have undergone FAF 55-degree imaging at Moorfields Eye Hospital (MEH) and the Royal Liverpool Hospital (RLH) between 2004 and 2019.

Methods

Five FAF features of interest were defined: vessels, optic disc, perimacular ring of increased signal (ring), relative hypo-autofluorescence (hypo-AF) and hyper-autofluorescence (hyper-AF). Features were manually annotated by six graders in a subset of patients based on a defined grading protocol to produce segmentation masks to train an AI model, AIRDetect, which was then applied to the entire imaging dataset.

Main Outcome Measures

Quantitative FAF imaging features including area in mm 2 and vessel metrics, were analysed cross-sectionally by gene and age, and longitudinally to determine rate of progression. AIRDetect feature segmentation and detection were validated with Dice score and precision/recall, respectively.

Results

A total of 45,749 FAF images from 3,606 IRD patients from MEH covering 170 genes were automatically segmented using AIRDetect. Model-grader Dice scores for disc, hypo-AF, hyper-AF, ring and vessels were respectively 0.86, 0.72, 0.69, 0.68 and 0.65. The five genes with the largest hypo-AF areas were CHM , ABCC6 , ABCA4 , RDH12 , and RPE65 , with mean per-patient areas of 41.5, 30.0, 21.9, 21.4, and 15.1 mm 2 . The five genes with the largest hyper-AF areas were BEST1 , CDH23 , RDH12 , MYO7A , and NR2E3 , with mean areas of 0.49, 0.45, 0.44, 0.39, and 0.34 mm 2 respectively. The five genes with largest ring areas were CDH23 , NR2E3 , CRX , EYS and MYO7A, with mean areas of 3.63, 3.32, 2.84, 2.39, and 2.16 mm 2 . Vessel density was found to be highest in EFEMP1 , BEST1 , TIMP3 , RS1 , and PRPH2 (10.6%, 10.3%, 9.8%, 9.7%, 8.9%) and was lower in Retinitis Pigmentosa (RP) and Leber Congenital Amaurosis genes. Longitudinal analysis of decreasing ring area in four RP genes ( RPGR, USH2A, RHO, EYS ) found EYS to be the fastest progressor at -0.18 mm 2 /year.

Conclusions

We have conducted the first large-scale cross-sectional and longitudinal quantitative analysis of FAF features across a diverse range of IRDs using a novel AI approach.

Stargardt macular dystrophy and therapeutic approaches

Stargardt macular dystrophy (Stargardt disease; STGD1; OMIM 248200) is the most prevalent inherited macular dystrophy. STGD1 is an autosomal recessive disorder caused by multiple pathogenic sequence variants in the large ABCA4 gene (OMIM 601691). Major advances in understanding both the clinical and molecular features, as well as the underlying pathophysiology, have culminated in many completed, ongoing and planned human clinical trials of novel therapies.The aims of this concise review are to describe (1) the detailed phenotypic and genotypic characteristics of the disease, multimodal imaging findings, natural history of the disease, and pathogenesis, (2) the multiple avenues of research and therapeutic intervention, including pharmacological, cellular therapies and diverse types of genetic therapies that have either been investigated or are under investigation and (3) the exciting novel therapeutic approaches on the translational horizon that aim to treat STGD1 by replacing the entire 6.8 kb ABCA4 open reading frame.

Deep phenotyping of PROM1-associated retinal degeneration

BACKGROUND/AIMS

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

METHODS

Four eyes from four subjects (three with AD and one with AR) PROM1-RD were investigated by ophthalmic examination including best-corrected visual acuity (BCVA) and multimodal retinal imaging: fundus autofluorescence (FAF), spectral-domain optical coherence tomography (SD-OCT) and adaptive optics scanning light ophthalmoscopy. Quantitative assessment of atrophic lesions determined by FAF, thickness of individual retinal layers and cone photoreceptor quantification was performed.

RESULTS

BCVA ranged from 20/16 to 20/200. Initial pathological changes included the presence of hyperautofluorescent spots on FAF imaging, while later stages demonstrated discrete areas of atrophy. In all patients, thinning of the outer retinal layers on SD-OCT with varying degrees of atrophy could be detected depending on disease-causing variants and age. Cone density was quantified both in central and/or at different eccentricities from the fovea. Longitudinal assessments were possible in two patients.

CONCLUSIONS

PROM1-RD comprises a wide range of clinical phenotypes. Depending on the stage of disease, the cone mosaic in PROM1-RD is relatively preserved and can potentially be targeted by cone-directed interventions.

Multimodal Phenomap of Stargardt Disease Integrating Structural, Psychophysical, and Electrophysiologic Measures of Retinal Degeneration

Objective

To cluster the diverse phenotypic features of Stargardt disease (STGD) using unsupervised clustering of multimodal retinal structure and function data.

Design

Retrospective cross-sectional study.

Subjects

Eyes of subjects with STGD and fundus autofluorescence (FAF), OCT, electroretinography (ERG), and microperimetry (MP) data available within 1 year of the baseline evaluation.

Methods

A total of 46 variables from FAF, OCT, ERG, and MP results were recorded for subjects with STGD as defined per published criteria. Factor analysis of mixed data identified the most informative variables. Unsupervised hierarchical clustering and silhouette analysis identified the optimal number of clusters to classify multimodal phenotypes.

Main Outcome Measures

Phenotypic clusters of STGD subjects and the corresponding cluster features.

Results

We included 52 subjects and 102 eyes with a mean visual acuity (VA) at the time of multimodal testing of 0.69 ± 0.494 logarithm of minimum angle of resolution (20/63 Snellen). We identified 4 clusters of eyes. Compared to the other clusters, cluster 1 (n = 16) included younger subjects, VA greater than that of clusters 2 and 3, normal or moderately low total macular volume (TMV), greater preservation of scotopic and photopic ERG responses and fixation stability, less atrophy, and fewer flecks. Cluster 2 (n = 49) differed from cluster 1 mainly with less atrophy and relatively stable fixation. Cluster 3 (n = 10) included older subjects than clusters 1 and 2 and showed the lowest VA, TMV, ERG responses, and fixation stability, with extensive atrophy. Cluster 4 (n = 27) showed better VA, TMV similar to clusters 1 and 2, moderate ERG activity, stable fixation, and moderate-high atrophy and flecks.

Conclusions

Reflecting the phenotypic complexity of STGD, an unsupervised clustering approach incorporating phenotypic measures can be used to categorize STGD eyes into distinct clusters. The clusters exhibit differences in structural and functional measures including quantity of flecks, extent of retinal atrophy, visual fixation accuracy, and ERG responses, among other features. If novel pharmacologic, gene, or cell therapy modalities become available in the future, the multimodal phenomap approach may be useful to individualize treatment decisions, and its utility in aiding prognostication requires further evaluation.

Financial Disclosures

Proprietary or commercial disclosure may be found after the references.

Gene Therapy for Inherited Retinal Diseases: From Laboratory Bench to Patient Bedside and Beyond

This comprehensive review provides a thorough examination of inherited retinal diseases (IRDs), encompassing their classification, genetic underpinnings, and the promising landscape of gene therapy trials. IRDs, a diverse group of genetic conditions causing vision loss through photoreceptor cell death, are explored through various angles, including inheritance patterns, gene involvement, and associated systemic disorders. The focal point is gene therapy, which offers hope for halting or even reversing the progression of IRDs. The review highlights ongoing clinical trials spanning retinal cell replacement, neuroprotection, pharmacological interventions, and optogenetics. While these therapies hold tremendous potential, they face challenges like timing optimization, standardized assessment criteria, inflammation management, vector refinement, and raising awareness among vision scientists. Additionally, translating gene therapy success into widespread adoption and addressing cost-effectiveness are crucial challenges to address. Continued research and clinical trials are essential to fully harness gene therapy's potential in treating IRDs and enhancing the lives of affected individuals.

Local progression kinetics of macular atrophy in recessive Stargardt disease

BACKGROUND

To determine the effect of lesion topography on progression in Stargardt disease (STGD1).

METHODS

Fundus autofluoresence (excitation 488 nm) images of 193 eyes in patients with proven ABCA4 mutation were semi-automatically segmented for autofluoresence changes: (DDAF) and questionably decreased autofluoresence (QDAF), which are proxies for retinal pigment epithelial (RPE) atrophy. We calculated topographic incidence of DDAF and DDAF + QDAF, as well as velocity of progression of the border of lesions using Euclidean distance mapping.

RESULTS

Incidence of atrophy was highest near the fovea, then decreased in incidence with increased foveal eccentricity. However, the rate of atrophy progression followed the opposite pattern; rate of atrophy increased with distance from foveal center. The mean growth rate 500 microns from the foveal center for DDAF + QDAF was 39 microns per year (95% CI = 28-49), whereas the mean growth rate 3000 microns from the foveal center was 342 microns per year (95% CI = 194-522). No difference in growth rate was noted by axis around the fovea.

CONCLUSIONS

Incidence and progression of atrophy by fundus autofluorescence follow opposite patterns in STGD1. Further, atrophy progression increases significantly with distance from foveal center, which should be taken into consideration in clinical trials.

Prognostication in Stargardt Disease Using Fundus Autofluorescence: Improving Patient Care

PURPOSE

To explore fundus autofluorescence (FAF) imaging as an alternative to electroretinography as a noninvasive, quick, and readily interpretable method to predict disease progression in Stargardt disease (STGD).

DESIGN

Retrospective case series of patients who attended Moorfields Eye Hospital (London, United Kingdom).

PARTICIPANTS

Patients with STGD who met the following criteria were included: (1) biallelic disease-causing variants in ABCA4, (2) electroretinography testing performed in house with an unequivocal electroretinography group classification, and (3) ultrawidefield (UWF) FAF imaging performed up to 2 years before or after the electroretinography.

METHODS

Patients were divided into 3 electroretinography groups based on retinal function and 3 FAF groups according to the extent of hypoautofluorescence and retinal background appearance. Fundus autofluorescence images of 30° and 55° were reviewed subsequently.

MAIN OUTCOME MEASURES

Electroretinography and FAF concordance and its association with baseline visual acuity (VA) and genetics.

RESULTS

Two hundred thirty-four patients were included in the cohort. One hundred seventy patients (73%) were in electroretinography and FAF groups of the same severity, 33 (14%) were in a milder FAF than electroretinography group, and 31 (13%) were in a more severe FAF than electroretinography group. Children < 10 years of age (n = 23) showed the lowest electroretinography and FAF concordance at 57% (9 of the 10 with discordant electroretinography and FAF showed milder FAF than electroretinography), and adults with adult onset showed the highest (80%). In 97% and 98% of patients, 30° and 55° FAF imaging, respectively, matched with the group defined by UWF FAF.

CONCLUSIONS

We demonstrated that FAF imaging is an effective method to determine the extent of retinal involvement and thereby inform prognostication by comparing FAF with the current gold standard of electroretinography. In 80% of patients in our large molecularly proven cohort, we were able to predict if the disease was confined to the macula or also affected the peripheral retina. Children assessed at a young age, with at least 1 null variant, early disease onset, poor initial VA, or a combination thereof may have wider retinal involvement than predicted by FAF alone, may progress to a more severe FAF phenotype over time, or both.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Endpoints for clinical trials in ophthalmology

With the identification of novel targets, the number of interventional clinical trials in ophthalmology has increased. Visual acuity has for a long time been considered the gold standard endpoint for clinical trials, but in the recent years it became evident that other endpoints are required for many indications including geographic atrophy and inherited retinal disease. In glaucoma the currently available drugs were approved based on their IOP lowering capacity. Some recent findings do, however, indicate that at the same level of IOP reduction, not all drugs have the same effect on visual field progression. For neuroprotection trials in glaucoma, novel surrogate endpoints are required, which may either include functional or structural parameters or a combination of both. A number of potential surrogate endpoints for ophthalmology clinical trials have been identified, but their validation is complicated and requires solid scientific evidence. In this article we summarize candidates for clinical endpoints in ophthalmology with a focus on retinal disease and glaucoma. Functional and structural biomarkers, as well as quality of life measures are discussed, and their potential to serve as endpoints in pivotal trials is critically evaluated.

ABCA4 Variant c.5714+5G>A in Trans With Null Alleles Results in Primary RPE Damage

Purpose

To determine the disease pathogenesis associated with the frequent ABCA4 variant c.5714+5G>A (p.[=,Glu1863Leufs*33]).

Methods

Patient-derived photoreceptor precursor cells were generated to analyze the effect of c.5714+5G>A on splicing and perform a quantitative analysis of c.5714+5G>A products. Patients with c.5714+5G>A in trans with a null allele (i.e., c.5714+5G>A patients; n = 7) were compared with patients with two null alleles (i.e., double null patients; n = 11); with a special attention to the degree of RPE atrophy (area of definitely decreased autofluorescence and the degree of photoreceptor impairment (outer nuclear layer thickness and pattern electroretinography amplitude).

Results

RT-PCR of mRNA from patient-derived photoreceptor precursor cells showed exon 40 and exon 39/40 deletion products, as well as the normal transcript. Quantification of products showed 52.4% normal and 47.6% mutant ABCA4 mRNA. Clinically, c.5714+5G>A patients displayed significantly better structural and functional preservation of photoreceptors (thicker outer nuclear layer, presence of tubulations, higher pattern electroretinography amplitude) than double null patients with similar degrees of RPE loss, whereas double null patients exhibited signs of extensive photoreceptor ,damage even in the areas with preserved RPE.

Conclusions

The prototypical STGD1 sequence of events of primary RPE and secondary photoreceptor damage is congruous with c.5714+5G>A, but not the double null genotype, which implies different and genotype-dependent disease mechanisms. We hypothesize that the relative photoreceptor sparing in c.5714+5G>A patients results from the remaining function of the ABCA4 transporter originating from the normally spliced product, possibly by decreasing the direct bisretinoid toxicity on photoreceptor membranes.

Characteristics of Rare Inherited Retinal Dystrophies in Adaptive Optics-A Study on 53 Eyes

Inherited retinal dystrophies (IRDs) are genetic disorders that lead to the bilateral degeneration of the retina, causing irreversible vision loss. These conditions often manifest during the first and second decades of life, and their primary symptoms can be non-specific. Diagnostic processes encompass assessments of best-corrected visual acuity, fundoscopy, optical coherence tomography, fundus autofluorescence, fluorescein angiography, electrophysiological tests, and genetic testing. This study focuses on the application of adaptive optics (AO), a non-invasive retinal examination, for the assessment of patients with IRDs. AO facilitates the high-quality, detailed observation of retinal photoreceptor structures (cones and rods) and enables the quantitative analysis of parameters such as cone density (DM), cone spacing (SM), cone regularity (REG), and Voronoi analysis (N%6). AO examinations were conducted on eyes diagnosed with Stargardt disease (STGD, N=36), cone dystrophy (CD, N=9), and cone-rod dystrophy (CRD, N=8), and on healthy eyes (N=14). There were significant differences in the DM, SM, REG, and N%6 parameters between the healthy and IRD-affected eyes (p<0.001 for DM, SM, and REG; p=0.008 for N%6). The mean DM in the CD, CRD, and STGD groups was 8900.39/mm2, 9296.32/mm2, and 16,209.66/mm2, respectively, with a significant inter-group difference (p=0.006). The mean SM in the CD, CRD, and STGD groups was 12.37 μm, 14.82 μm, and 9.65 μm, respectively, with a significant difference observed between groups (p=0.002). However, no significant difference was found in REG and N%6 among the CD, CRD, and STGD groups. Significant differences were found in SM and DM between CD and STGD (p=0.014 for SM; p=0.003 for DM) and between CRD and STGD (p=0.027 for SM; p=0.003 for DM). Our findings suggest that AO holds significant potential as an impactful diagnostic tool for IRDs.

Natural History of Stargardt Disease: The Longest Follow-Up Cohort Study

Long-term natural history studies are important in rare disease research. This study aimed to assess electrophysiological and fundus autofluorescence (FAF) progression rate in 18 genetically confirmed Stargardt disease (STGD1) patients with a minimum follow-up of 10 years. Age at the first and last exams, age at onset, Snellen decimal visual acuity (VA), electroretinography (ERG), and FAF images were evaluated. Patients were classified into four Fishman stages and three electroretinography groups, and areas of definitely decreased autofluorescence (DDAF) were measured. Patients were further substratified based on genotype, and phenotype-genotype correlations were performed. The median follow-up was 18 (range 10-26) years. The median yearly VA loss was 0.009 (range 0.002-0.071), while the median progression rate of the DDAF area was 0.354 (range 0.002-4.359) mm² per year. Patients harbouring p.(Gly1961Glu) or p.(Asn1868Ile) allele had significantly slower DDAF area progression when compared to patients with other genotypes (0.07 mm² vs. 1.03 mm², respectively), as well as significantly later age at onset (20 years vs. 13 years, respectively). Results showed that structural and functional parameters, together with genotype, should be considered when counselling patients regarding prognosis and monitoring disease progression. Patients harbouring hypomorphic variants p.(Gly1961Glu) or p.(Asn1868Ile) presented with overall milder disease than patients with other genotypes.

Monitoring Lesion Area Progression in Stargardt Disease: A Comparison of En Face Optical Coherence Tomography and Fundus Autofluorescence

Purpose

To compare longitudinal changes in en face spectral domain-optical coherence tomography (SD-OCT) measurements of ellipsoid zone (EZ) and retinal pigment epithelium (RPE) loss to changes in the hypoautofluorescent and hyperautofluorescent (AF) areas detected with short-wavelength (SW)-AF in ABCA4-associated retinopathy.

Methods

SD-OCT volume scans were obtained from 20 patients (20 eyes) over 2.6 ± 1.2 years (range 1-5 years). The EZ, and RPE/Bruch's membrane boundaries were segmented, and en face slab images generated. SubRPE and EZ slab images were used to measure areas of atrophic RPE and EZ loss. These were compared to longitudinal measurements of the hypo- and abnormal AF (hypoAF and surrounding hyperAF) areas.

Results

At baseline, the en face area of EZ loss was significantly larger than the subRPE atrophic area, and the abnormal AF area was significantly larger than the hypoAF area. The median rate of EZ loss was significantly greater than the rate of increase in the subRPE atrophic area (1.2 mm2/yr compared to 0.5 mm2/yr). The median rate of increase in the abnormal AF area was significantly greater than the increase in the hypoAF area (1.6 mm2/yr compared to 0.6 mm2/yr).

Conclusions

En face SD-OCT can be used to quantify changes in RPE atrophy and photoreceptor integrity. It can be a complementary or alternative technique to SW-AF with the advantage of monitoring EZ loss. The SW-AF results emphasize the importance of measuring changes in the hypo- and abnormal AF areas.

Translational Relevance

The findings are relevant to the selection of outcome measures for monitoring ABCA4-associated retinopathy.

Progression of Stargardt Disease as Determined by Fundus Autofluorescence Over a 24-Month Period (ProgStar Report No. 17)

PURPOSE

To estimate the progression rate of atrophic lesions in Stargardt disease derived from fundus autofluorescence (FAF).

DESIGN

International, multicenter, prospective cohort study.

METHODS

A total of 259 participants aged ≥6 years with disease-causing variants in the ABCA4 gene were enrolled from 9 centers and followed over a 24-month period. FAF images were obtained every 6 months, and areas of definitely decreased autofluorescence (DDAF) and decreased autofluorescence (DAF) were quantified. Progression rates were estimated from linear mixed models with time as the independent variable.

RESULTS

A total of 488 study eyes of 259 participants (88.8% with both eyes) were enrolled and images from 432 eyes were followed for 24 months. The overall estimated progression of DDAF was 0.74 mm²/y (95% CI 0.64-0.85, P < .0001) and that of DAF was 0.64 mm²/y (95% CI 0.57-0.71) over a 24-month period in univariate analysis. Growth rates were strongly dependent on baseline lesion area. After square root transformation, the DDAF growth rate was not dependent on baseline lesion radius (P = .11), whereas the DAF growth rate was dependent (P < .0001). Genotype was not found to significantly impact the growth rate of DDAF or DAF lesions.

CONCLUSIONS

FAF may serve as a convenient monitoring tool and suitable end point for interventional clinical trials that aim to slow disease progression. DDAF and DAF lesion sizes at baseline are strong predicting factors for lesion area growth and can be partially accounted for by square root transformation.

Repeatability of Quantitative Autofluorescence Imaging in a Multicenter Study Involving Patients With Recessive Stargardt Disease 1

Purpose

This study assesses the repeatability of quantitative autofluorescence (qAF) in a multicenter setting and evaluates qAF as the end point for clinical trials in recessive Stargardt disease 1 (STGD1).

Methods

A total of 102 patients with STGD1 underwent qAF imaging as part of the Stargardt Remofuscin Treatment Trial (STARTT; EudraCT No. 2018-001496-20). For 166 eyes, we obtained qAF imaging at 2 visits, with 2 recordings per visit. The qAF8 values were independently determined by the study site and a central reading center. Intra- and inter-visit reproducibility, as well as interobserver (study site versus reading center) reproducibility were obtained using intraclass correlation (ICC), one-sample t-test, and Bland-Altman coefficient of repeatability.

Results

The qAF repeatability was ± 26.1% for intra-visit, ± 40.5% for inter-visit, and ± 20.2% for the interobserver reproducibility measures. Intra-visit repeatability was good to excellent for all sites (ICC of 0.88-0.96). Variability between visits was higher with an overall ICC of 0.76 (0.69-0.81). We observed no significant difference in qAF values across sites between visits (7.06 ± 93.33, P = 0.238).

Conclusions

Real-life test-retest variability of qAF is higher in this set of data than previously reported in single center settings. With improved operator training and by selecting the better of two recordings for evaluation, qAF serves as a useful method for assessing changes in autofluorescence signal.

Translational Relevance

The qAF can be adopted as a clinical trial end point, but steps to counterbalance variability should be considered.

Genotype-Phenotype Association in ABCA4-Associated Retinopathy

Stargardt disease (STGD1) is the most common inherited retina degeneration. It is caused by biallelic ABCA4 variants, and no treatment is available to date. STGD1 shows marked phenotypic variability, especially regarding the age of onset. The underlying genotype can partially explain this variability. Notably, a subset of ABCA4 variants was previously associated with an earlier disease onset than truncating ABCA4 variants, pointing toward pathogenic mechanisms beyond the loss of gene function in these patients. On the other end of the spectrum, variants such as p.Gly1961Glu were associated with markedly slower extrafoveal disease progression. Given that these drastic differences in phenotype are based on genotype (resulting in important prognostic implications for patients), this chapter reviews previous approaches to genotype-phenotype correlation analyses in STGD1.

Automated Segmentation of Autofluorescence Lesions in Stargardt Disease

OBJECTIVE

To train a deep learning (DL) algorithm to perform fully automated semantic segmentation of multiple autofluorescence lesion types in Stargardt disease.

DESIGN

Cross-sectional study with retrospective imaging data.

SUBJECTS

The study included 193 images from 193 eyes of 97 patients with Stargardt disease.

METHODS

Fundus autofluorescence images obtained from patient visits between 2013 and 2020 were annotated with ground-truth labels. Model training and evaluation were performed using fivefold cross-validation.

MAIN OUTCOMES MEASURES

Dice similarity coefficients, intraclass correlation coefficients, and Bland-Altman analyses comparing algorithm-predicted and grader-labeled segmentations.

RESULTS

The overall Dice similarity coefficient across all lesion classes was 0.78 (95% confidence interval [CI], 0.69-0.86). Dice coefficients were 0.90 (95% CI, 0.85-0.94) for areas of definitely decreased autofluorescence (DDAF), 0.55 (95% CI, 0.35-0.76) for areas of questionably decreased autofluorescence (QDAF), and 0.88 (95% CI, 0.73-1.00) for areas of abnormal background autofluorescence (ABAF). Intraclass correlation coefficients comparing the ground-truth and automated methods were 0.997 (95% CI, 0.996-0.998) for DDAF, 0.863 (95% CI, 0.823-0.895) for QDAF, and 0.974 (95% CI, 0.966-0.980) for ABAF.

CONCLUSIONS

A DL algorithm performed accurate segmentation of autofluorescence lesions in Stargardt disease, demonstrating the feasibility of fully automated segmentation as an alternative to manual or semiautomated labeling methods.

Prevalence, multimodal imaging and genotype-phenotype assessment of trauma related subretinal fibrosis in stargardt disease

Background and Objectives

Stargardt disease produces lipofuscin accumulation predisposing to subretinal fibrosis (SRFib) after ocular trauma. Noninvasive imaging techniques allow in vivo assessment. The purpose of this study is to determine the prevalence of SRFib in a cohort of Stargardt patients, the presence of history of ocular trauma, the clinical features and possible genotype-phenotype associations in Stargardt patients with SRFib.

Methods

We evaluated retrospectively 106 Stargardt patients and analysed the multimodal imaging and the genotype of patients with SRFib.

Results

Six patients exhibited SRFib, three of them with history of ocular trauma. Multimodal imaging showed extensive SRFib principally in the temporal midperipheral retina with no fluid associated. SRFib was better defined by short wavelength autofluorescence and spectral domain optical coherence tomography and appeared clinically stable over time. There was no particular genotype associated to SRFib.

Conclusion

SRFib occurs in a significant percentage of patients with Stargardt disease and can be diagnosed through multimodal imaging regardless the history of trauma, further sustaining the importance of an appropriate imaging in such patients. No genotype-phenotype association has been established, supporting the traumatic etiology in half of cases. The remaining cases may be classified as idiopathic or have a minimal trauma occurring early in life that may be not recalled by the patients.

Photoreceptor degeneration in ABCA4-associated retinopathy and its genetic correlates

BACKGROUND

Outcome measures sensitive to disease progression are needed for ATP-binding cassette, sub-family A, member 4–associated (ABCA4-associated) retinopathy. We aimed to quantify ellipsoid zone (EZ) loss and photoreceptor degeneration beyond EZ-loss in ABCA4-associated retinopathy and investigate associations between photoreceptor degeneration, genotype, and age.

METHODS

We analyzed 132 eyes from 66 patients (of 67 enrolled) with molecularly confirmed ABCA4-associated retinopathy from a prospective natural history study with a median [IQR] follow-up of 4.2 years [3.1, 5.1]. Longitudinal spectral-domain optical coherence tomography volume scans (37 B-scans, 30° × 15°) were segmented using a deep learning (DL) approach. For genotype-phenotype analysis, a model of ABCA4 variants was applied with the age of criterion EZ-loss (6.25 mm²) as the dependent variable.

RESULTS

Patients exhibited an average (square-root-transformed) EZ-loss progression rate of [95% CI] 0.09 mm/y [0.06, 0.11]. Outer nuclear layer (ONL) thinning extended beyond the area of EZ-loss. The average distance from the EZ-loss boundary to normalization of ONL thickness (to ±2 z score units) was 3.20° [2.53, 3.87]. Inner segment (IS) and outer segment (OS) thinning was less pronounced, with an average distance from the EZ-loss boundary to layer thickness normalization of 1.20° [0.91, 1.48] for the IS and 0.60° [0.49, 0.72] for the OS. An additive model of allele severity explained 52.7% of variability in the age of criterion EZ-loss.

CONCLUSION

Patients with ABCA4-associated retinopathy exhibited significant alterations of photoreceptors outside of EZ-loss. DL-based analysis of photoreceptor laminae may help monitor disease progression and estimate the severity of ABCA4 variants.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT01736293.

FUNDING

National Eye Institute Intramural Research Program and German Research Foundation grant PF950/1-1.

Clinical Observation and Genotype-Phenotype Analysis of ABCA4- Related Hereditary Retinal Degeneration before Gene Therapy

BACKGROUND

Hereditary retinal degeneration (HRD) is an irreversible eye disease that results in blindness in severe cases. It is most commonly caused by variants in the ABCA4 gene. HRD presents a high degree of clinical and genetic heterogeneity. We determined genotypic and phenotypic correlations, in the natural course of clinical observation, of unrelated progenitors of HRD associated with ABCA4.

OBJECTIVE

To analyze the relationship between the phenotypes and genotypes of ABCA4 variants.

METHODS

A retrospective clinical study of five cases from the ophthalmology department of the People's Hospital of Wuhan University from January 2019 to October 2020 was conducted. We tested for ABCA4 variants in the probands. We performed eye tests, including the best-corrected visual acuity, super-wide fundus photography and spontaneous fluorescence photography, optical coherence tomography, and electrophysiological examination.

RESULTS

Disease-causing variants were identified in the ABCA4 genes of all patients. Among these, seven ABCA4 variants were novel. All patients were sporadic cases; only one patient had parents who were relatives, and the other four patients were offspring of unrelated parents. Two patients presented with Stargardt disease, mainly with macular lesions, two presented with retinitis pigmentosa (cone-rod type), and one presented with cone dystrophy. The visual acuity and visual field of the five patients showed varying degrees of deterioration and impairment.

CONCLUSION

The same ABCA4 mutation can lead to different clinical phenotypes, and there is variation in the degree of damage to vision, visual field, and electrophysiology among different clinical phenotypes. Clinicians must differentiate between and diagnose pathologies resulting from this mutation.

Longitudinal Changes of Fixation Stability and Location Within 24 Months in Stargardt Disease: ProgStar Report No. 16

PURPOSE

Stargardt disease type 1 (STGD1) is the most common macular dystrophy. The assessment of fixation describes an important dimension of visual function, but data on its progression over time are limited. We present longitudinal changes and investigate its usefulness for clinical trials.

DESIGN

International, multicenter, prospective cohort study.

METHODS

Included were 239 individuals with genetically confirmed STGD1 (one or more disease-causing ATP binding cassette subfamily A member 4 [ABCA4] variant). We determined the fixation stability (FS) using 1 SD of the bivariate contour ellipse area (1 SD-BCEA) and fixation location (FL) using the eccentricity of fixation from the fovea during five study visits every 6 months.

RESULTS

At baseline, 239 patients (105 males [44%]) and 459 eyes, with a median age of 32 years, were included. The baseline mean logBCEA was 0.70 ± 1.41 log deg² and the mean FL was 6.25° ± 4.40°. Although the mean logBCEA did not monotonically increase from visit to visit, the overall yearly increase in the logBCEA was 0.124 log deg² (95% CI, 0.063-0.185 log deg²). The rate of change was not different between the 2 years but increased faster in eyes without flecks outside of the vascular arcades and depended on baseline logBCEA. FL did not change statistically significantly over time.

CONCLUSIONS

Fixation parameters are unlikely to be sensitive outcome measures for clinical trials in STGD1 but may provide useful ancillary information in selected cases to longitudinally describe and understand an eye's visual function.

Structure and function of ABCA4 and its role in the visual cycle and Stargardt macular degeneration

ABCA4 is a member of the superfamily of ATP-binding cassette (ABC) transporters that is preferentially localized along the rim region of rod and cone photoreceptor outer segment disc membranes. It uses the energy from ATP binding and hydrolysis to transport N-retinylidene-phosphatidylethanolamine (N-Ret-PE), the Schiff base adduct of retinal and phosphatidylethanolamine, from the lumen to the cytoplasmic leaflet of disc membranes. This ensures that all-trans-retinal and excess 11-cis-retinal are efficiently cleared from photoreceptor cells thereby preventing the accumulation of toxic retinoid compounds. Loss-of-function mutations in the gene encoding ABCA4 cause autosomal recessive Stargardt macular degeneration, also known as Stargardt disease (STGD1), and related autosomal recessive retinopathies characterized by impaired central vision and an accumulation of lipofuscin and bis-retinoid compounds. High resolution structures of ABCA4 in its substrate and nucleotide free state and containing bound N-Ret-PE or ATP have been determined by cryo-electron microscopy providing insight into the molecular architecture of ABCA4 and mechanisms underlying substrate recognition and conformational changes induced by ATP binding. The expression and functional characterization of a large number of disease-causing missense ABCA4 variants have been determined. These studies have shed light into the molecular mechanisms underlying Stargardt disease and a classification that reliably predicts the effect of a specific missense mutation on the severity of the disease. They also provide a framework for developing rational therapeutic treatments for ABCA4-associated diseases.

Structural evaluation in inherited retinal diseases

Ophthalmic genetics is a field that has been rapidly evolving over the last decade, mainly due to the flourishing of translational medicine for inherited retinal diseases (IRD). In this review, we will address the different methods by which retinal structure can be objectively and accurately assessed in IRD. We review standard-of-care imaging for these patients: colour fundus photography, fundus autofluorescence imaging and optical coherence tomography (OCT), as well as higher-resolution and/or newer technologies including OCT angiography, adaptive optics imaging, fundus imaging using a range of wavelengths, magnetic resonance imaging, laser speckle flowgraphy and retinal oximetry, illustrating their utility using paradigm genotypes with on-going therapeutic efforts/trials.

The Progression of Stargardt Disease Using Volumetric Hill of Vision Analyses Over 24 Months: ProgStar Report No.15

PURPOSE

To report the yearly rate of change in macular function in patients with Stargardt disease type 1 (STGD1) over 24 months and to establish a new volumetric visual function index for use in clinical trials investigating the efficacy on retinal sensitivity.

METHODS

Design: International, multicenter, prospective cohort study with 5 study visits every 6 months over 24 months.

PARTICIPANTS

A total of 233 individuals with genetically confirmed STGD1 (≥1 disease-causing ABCA4 variant).

MAIN OUTCOME MEASURES

The total volume (V_TOT) beneath the sensitivity surface of a 3-D model of the hill of vision and mean sensitivity (MS) derived from mesopic microperimetry performed with a white stimulus. Changes of V_TOT over time and its correlation with the ABCA4 genotype and baseline features.

RESULTS

At baseline, 440 eyes (233 patients) with a mean (SD) age of 33.7 (15.0) years, mean (SD) visual acuity of 46.08 (16.03) ETDRS letters were analyzed with an average V_TOT of 0.91 decibel-steradian (dB-sr) and an MS of 10.73 dB. The overall mean rate of decrease in sensitivity [95% confidence interval] was 0.077 [0.064, 0.090] dB-sr/y for V_TOT and 0.87 [0.72, 1.02] dB/year for MS. The progression rate of V_TOT depended on baseline visual function (0.029 dB-sr/year for low and 0.120 dB-sr/year for high baseline V_TOT; P < .001) and exhibited a difference in the first vs second year of follow-up (0.065 dB-sr/year vs 0.089 dB-sr/year, respectively; P < .001). The absence of pigmentary abnormalities of the retinal pigment epithelium at baseline was found to be associated with a faster progression rate (P < .001), whereas a significant association with the genotype was not detected (P = .7).

CONCLUSION

In STGD1, both microperimetric outcomes demonstrate statistically significant and clinically meaningful changes after relatively short follow-up periods. Volumetric modeling may be useful in future interventional clinical trials that aim to improve retinal sensitivity or to slow down its decline and for structure-function correlations.

A phase I clinical trial of human embryonic stem cell-derived retinal pigment epithelial cells for early-stage Stargardt macular degeneration: 5-years' follow-up

Objectives

To evaluate the long‐term biosafety and efficacy of transplantation of human embryonic stem cells‐derived retinal pigment epithelial (hESC‐RPE) cells in early‐stage of Stargardt macular degeneration (STGD1).

Materials and methods

Seven patients participated in this prospective clinical study, where they underwent a single subretinal transplantation of 1 × 10⁵ hESC‐RPE cells in one eye, whereas the fellow eye served as control. These patients were reassessed for a 60‐month follow‐up through systemic and ophthalmic examinations.

Results

None of the patients experienced adverse reactions systemically or locally, except for two who had transiently high intraocular pressure post‐operation. Functional assessments demonstrated that all of the seven operated eyes had transiently increased or stable visual function 1‐4 months after transplantation. At the last follow‐up visit, two of the seven eyes showed visual function loss than the baseline; however, one of them showed a stable visual acuity when compared with the change of fellow eye. Obvious small high reflective foci in the RPE layer were displayed after the transplantation, and maintained until the last visit. Interestingly, three categories of patients who were classified based on autofluorescence, exhibited distinctive patterns of morphological and functional change.

Conclusions

Subretinal transplantation of hESC‐RPE in early‐stage STGD1 is safe and tolerated in the long term. Further investigation is needed for choosing proper subjects according to the multi‐model image and function assessments.

Fundus Autofluorescence and Clinical Applications

Fundus autofluorescence (FAF) has allowed in vivo mapping of retinal metabolic derangements and structural changes not possible with conventional color imaging. Incident light is absorbed by molecules in the fundus, which are excited and in turn emit photons of specific wavelengths that are captured and processed by a sensor to create a metabolic map of the fundus. Studies on the growing number of FAF platforms has shown each may be suited to certain clinical scenarios. Scanning laser ophthalmoscopes, fundus cameras, and modifications of these each have benefits and drawbacks that must be considered before and after imaging to properly interpret the images. Emerging clinical evidence has demonstrated the usefulness of FAF in diagnosis and management of an increasing number of chorioretinal conditions, such as age-related macular degeneration, central serous chorioretinopathy, retinal drug toxicities, and inherited retinal degenerations such as retinitis pigmentosa and Stargardt disease. This article reviews commercial imaging platforms, imaging techniques, and clinical applications of FAF.

Stargardt disease: Multimodal imaging: A review

Stargardt disease (STGD1) is an autosomal recessive retinal dystrophy, characterised by bilateral progressive central vision loss and subretinal deposition of lipofuscin-like substances. Recent advances in molecular diagnosis and therapeutic options are complemented by the increasing recognition of new multimodal imaging biomarkers that may predict genotype and disease progression. Unique non-invasive imaging features of STDG1 are useful for gene variant interpretation and may even provide insight into the underlying molecular pathophysiology. In addition, pathognomonic imaging features of STGD1 have been used to train neural networks to improve time efficiency in lesion segmentation and disease progression measurements. This review will discuss the role of key imaging modalities, correlate imaging signs across varied STGD1 presentations and illustrate the use of multimodal imaging as an outcome measure in determining the efficacy of emerging STGD1 specific therapies.

Correlation of Morphology and Function of Flecks Using Short-Wave Fundus Autofluorescence and Microperimetry in Patients With Stargardt Disease

Purpose

The purpose of this study was to evaluate the functional relevance of longitudinal changes in hyperautofluorescent areas and flecks in Stargardt disease (STGD1) using short-wavelength autofluorescence (SW-AF) imaging.

Methods

In this prospective, longitudinal study, 31 patients with STGD1 (56 eyes) underwent microperimetry (MP) and SW-AF imaging twice in 3 to 5 years. A total of 760 MP test points were included in the statistical analysis based on stable fixation and accurate alignment of SW-AF and MP. Autofluorescence intensity was qualitatively assessed in all MP test points. Small circumscriptive hyperautofluorescent lesions were defined as flecks. Longitudinal imaging characteristics observed on SW-AF were classified into the following categories: appearing, disappearing, and stable flecks, stable hyperautofluorescent, and stable background autofluorescence. The relationship between SW-AF intensity changes and MP changes was analyzed using a linear mixed model corrected for baseline sensitivity.

Results

Retinal sensitivity declined most in locations without change in SW-AF intensity. Functional decline per year was significantly larger in flecks that disappeared (−0.72 ± 1.30 dB) compared to flecks that appeared (−0.34 ± 0.65 dB), if baseline sensitivity was high (≥10 dB; P < 0.01). The correlation between the change observed on SW-AF and the sensitivity change significantly depended on the sensitivity at baseline (P = 0.000).

Conclusions

Qualitative longitudinal assessment of SW-AF poorly reflected the retinal sensitivity loss observed over the course of 3 to 5 years.

Translational Relevance

When aiming to assess treatment effect on lesion level, a multimodal end point including MP focused on hyperautofluorescent lesions appears essential but needs further studies on optimizing MP grids, eye-tracking systems, and alignment software.

Tackling the Challenges of Product Development Through a Collaborative Rare Disease Network: The Foundation Fighting Blindness Consortium

The Foundation Fighting Blindness, a 501(c)(3) nonprofit organization, established an international consortium of inherited retinal disease specialists in 2016, with a mission to accelerate the development of treatments for rare, inherited retinal degenerations, such as retinitis pigmentosa, Stargardt disease, Leber congenital amaurosis, Usher syndrome, choroideremia, and achromatopsia. The Consortium accomplishes its mission by evaluating novel outcome measures, sharing standardized study protocols and datasets, and disseminating findings. Having established research infrastructure in the first 3 years, including 39 global research sites, the network is now poised to expand its infrastructure for trials of new therapies in partnership with industry. This model represents an innovative approach to overcome challenges of therapeutic development for rare diseases.

Atrophy Expansion Rates in Stargardt Disease Using Ultra-Widefield Fundus Autofluorescence

Purpose

Design

Participants

Methods

Main Outcome Measures

Results

Conclusions

Quantitative Fundus Autofluorescence in ABCA4-Related Retinopathy -Functional Relevance and Genotype-Phenotype Correlation

PURPOSE

To investigate lipofuscin-related quantitative autofluorescence measures and their association with demographic characteristics, retinal structure, retinal function and genotype in ABCA4-related retinopathy (Stargardt disease 1).

DESIGN

Cross-sectional study with age-matched healthy control subjects.

METHODS

A total of 77 patients with ABCA4-related retinopathy and 110 control subjects underwent quantitative fundus autofluorescence (qAF) imaging using a confocal scanning laser ophthalmoscope equipped with an internal fluorescent reference to measure qAF as surrogate for lipofuscin accumulation. Measures of qAF were correlated with demographic characteristics, structural alterations on optical coherence tomography and fundus autofluorescence imaging, retinal function assessed by full-field electroretinography (ERG) and fundus-controlled perimetry, and genotype.

RESULTS

Most patients (76.6%) had qAF levels >95% prediction interval of the age-related control group, with best discrimination between cases and control subjects in younger patients. Reduced discrimination based on qAF measures was associated with mild disease, more advanced disease with dark flecks, or older age because of the physiological age-related increase in qAF and a ceiling effect in patients. Nullizygous patients presented with high qAF levels earlier in life compared with those with at least 1 milder ABCA4 variant. Within the sectors of qAF measurements, at approximately 7-9° eccentricity, increased qAF without flecks or with only bright flecks was associated with topographically related preserved retinal thickness and fundus-controlled perimetry results, and with normal full-field ERG recordings. All 3 parameters were increasingly abnormal with the development of dark flecks and decreasing qAF.

CONCLUSIONS

The accumulation of lipofuscin depends on the severity of ABCA4 variants, precedes other structural changes, and may remain without clinically relevant effect on retinal function.

Longitudinal Microperimetric Changes of Macular Sensitivity in Stargardt Disease After 12 Months: ProgStar Report No. 13

Importance

Functional end points for clinical trials investigating the efficacy of emerging treatments for Stargardt disease type 1 (STGD1) are needed.

Objective

To assess the yearly rate of change of macular function in patients with STGD1 using microperimetry.

Design, Setting, and Participants

This multicenter prospective cohort study was conducted in an international selection of tertiary referral centers from October 21, 2013, to February 15, 2017. The study included participants with ABCA4-related STGD1 who were enrolled in the Natural History of the Progression of Atrophy Secondary to Stargardt Disease (ProgStar) study at baseline. Data were analyzed from February 16, 2017, to December 1, 2019.

Exposure

ABCA4-related STGD1 with a minimum lesion size on fundus autofluorescence and a minimum visual acuity.

Main Outcomes and Measures

Changes in overall macular sensitivity (MS), deep scotoma count, number of points that tested normal, and location-specific sensitivity changes.

Results

Among the 359 eyes from 200 patients (87 [43.5%] men; mean [SD] age, 33.3 [15.2] years) who underwent microperimetry examination graded at baseline and month 12, the mean (SD) yearly change in MS was -0.68 (2.04) dB (95% CI, -0.89 to -0.47 dB; P < .001), and deep scotoma points increased by a mean (SD) of 1.56 (5.74) points per year. The points with sensitivity of 12 dB or higher decreased in sensitivity by a mean (SD) of -3.01 (9.84) dB (95% CI, -4.03 to -1.99 dB; P < .001). The mean (SD) yearly change in MS was not significantly different between the eyes with a grading of good or fair pattern placement at both visits (-0.67 [2.1] dB) and the eyes with a poor pattern placement during at least 1 visit (-0.64 [2.2] dB) (P = .91).

Conclusions and Relevance

This study showed that MS and the number of deep scotoma points had measurably changed after follow-up of approximately 1 year. Microperimetry may serve as a useful functional outcome parameter for clinical trials aimed at slowing the progression of STGD1.

Retinal Pigment Epithelium Atrophy in Recessive Stargardt Disease as Measured by Short-Wavelength and Near-Infrared Autofluorescence

Purpose

To compare the detection of retinal pigment epithelium (RPE) atrophy in short-wavelength (SW-AF) and near-infrared autofluorescence (NIR-AF) images in Stargardt disease (STGD1) patients.

Methods

SW-AF and NIR-AF images (115 eyes from 115 patients) were analyzed by two independent graders. Hypoautofluorescent (hypoAF) areas, indicative of RPE atrophy, were measured, and the two modalities were compared.

Results

Patients were segregated into four groups: nascent (6 [5%]), widespread (21 [18%]), discrete (55 [48%]), and chorioretinal atrophy (33 [29%]). The areas of hypoAF were larger in NIR-AF compared to SW-AF images in discrete (3.9 vs. 2.2 mm², P < 0.001) and chorioretinal atrophy (12.7 vs. 11.4 mm², P = 0.015). Similar findings were observed qualitatively in nascent and widespread atrophy patients. Using the area linear model (ALM), lesion area increased at similar rates in SW-AF and NIR-AF images of discrete atrophy (0.20 vs. 0.32 mm²/y, P = 0.275) and chorioretinal atrophy (1.30 vs. 1.74 mm²/y, P = 0.671). Using the radius linear model (RLM), the lesion effective radius also increased similarly in SW-AF and NIR-AF images in discrete (0.03 vs. 0.05 mm²/y, P = 0.221) and chorioretinal atrophy (0.08 vs. 0.10 mm²/y, P = 0.754) patients.

Conclusions

NIR-AF reveals a larger area of RPE atrophy in STGD1 patients compared to SW-AF images, but rates of lesion enlargement in the two modalities are similar.

Translational Relevance

Measurements of RPE atrophy by AF imaging are crucial for monitoring STGD1 disease progression and given our findings we advocate greater use of NIR-AF for patients.

The role of multimodal imaging and vision function testing in ABCA4-related retinopathies and their relevance to future therapeutic interventions

The aim of this review article is to describe the specific features of Stargardt disease and ABCA4 retinopathies (ABCA4R) using multimodal imaging and functional testing and to highlight their relevance to potential therapeutic interventions. Standardised measures of tissue loss, tissue function and rate of change over time using formal structured deep phenotyping in Stargardt disease and ABCA4R are key in diagnosis, and prognosis as well as when selecting cohorts for therapeutic intervention. In addition, a meticulous documentation of natural history will be invaluable in the future to compare treated with untreated retinas. Despite the familiarity with the term Stargardt disease, this eponymous classification alone is unhelpful when evaluating ABCA4R, as the ABCA4 gene is associated with a number of phenotypes, and a range of severity. Multimodal imaging, psychophysical and electrophysiologic measurements are necessary in diagnosing and characterising these differing retinopathies. A wide range of retinal dystrophy phenotypes are seen in association with ABCA4 mutations. In this article, these will be referred to as ABCA4R. These different phenotypes and the existence of phenocopies present a significant challenge to the clinician. Careful phenotypic characterisation coupled with the genotype enables the clinician to provide an accurate diagnosis, associated inheritance pattern and information regarding prognosis and management. This is particularly relevant now for recruiting to therapeutic trials, and in the future when therapies become available. The importance of accurate genotype-phenotype correlation studies cannot be overemphasised. This approach together with segregation studies can be vital in the identification of causal mutations when variants in more than one gene are being considered as possible. In this article, we give an overview of the current imaging, psychophysical and electrophysiological investigations, as well as current therapeutic research trials for retinopathies associated with the ABCA4 gene.

Geographic Atrophy Growth Is Strongly Related to Lesion Perimeter: Unifying Effects of Lesion Area, Number, and Circularity on Growth

PURPOSE

To investigate the underlying reason for the previously observed impact of baseline lesion size, number, and circularity on geographic atrophy (GA) growth rate.

DESIGN

Retrospective analysis of a multicenter, prospective, randomized controlled trial.

PARTICIPANTS

Age-Related Eye Disease Study participants with GA secondary to nonexudative age-related macular degeneration.

METHODS

We manually delineated atrophic lesions on color fundus photographs of 318 eyes with GA followed up over at least 2 visits (mean follow-up duration, 5.1 ± 3.0 years). We calculated GA area growth rate for each eye based on the first and last visit. GA perimeter-adjusted growth rate was defined as the ratio between GA area growth rate and mean GA perimeter between the first and last visit for each eye.

MAIN OUTCOME MEASURES

GA area growth rate, growth rate of the square root of GA area, and GA perimeter-adjusted growth rate.

RESULTS

GA area growth rate was correlated strongly with mean GA perimeter (r² = 0.66). GA area growth rate was associated with baseline GA area (r² = 0.39; P < 0.001), lesion number (r² = 0.10; P < 0.001), and circularity index (r² = 0.28; P < 0.001). The use of the square root of GA area reduced the influence of baseline GA area (but not lesion number or circularity) on GA growth rate. In comparison, GA perimeter-adjusted growth rate (0.098 ± 0.062 mm/year) was not correlated with baseline GA area (r² = 0.005; P = 0.20), lesion number (r² = 0.00009; P = 0.86), or circularity index (r² = 0.007; P = 0.14). GA perimeter-adjusted growth rate was 50.0% higher in eyes whose fellow eyes showed GA at any visit (0.102 ± 0.062 mm/year) than in eyes whose fellow eyes never demonstrated GA during follow-up (0.068 ± 0.049 mm/year).

CONCLUSIONS

The growth rate of GA area is associated strongly with lesion perimeter. This relationship explains the previously observed influences of baseline GA size, lesion number, and circularity on GA growth rate. GA perimeter-adjusted growth rate is uncorrelated with the 3 morphologic factors and may serve as a surrogate outcome measure to monitor GA progression in future studies.

Analysis of retinal sublayer thicknesses and rates of change in ABCA4-associated Stargardt disease

Stargardt disease, the most common inherited macular dystrophy, is characterized by vision loss due to central retinal atrophy. Although clinical trials for Stargardt are currently underway, the disease is typically slowly progressive, and objective, imaging-based biomarkers are critically needed. In this retrospective, observational study, we characterize the thicknesses of individual retinal sublayers by macular optical coherence tomography (OCT) in a large cohort of patients with molecularly-confirmed, ABCA4-associated Stargardt disease (STGD1) relative to normal controls. Automated segmentation of retinal sublayers was performed with manual correction as needed, and thicknesses in various macular regions were compared using mixed effects models. Relative to controls (42 eyes, 40 patients), STGD1 patients (107 eyes, 63 patients) had slight thickening of the nerve fiber layer and retinal pigment epithelium-Bruch’s membrane, with thinning in other sublayers, especially the outer nuclear layer (ONL) (p < 0.0015). When comparing the rate of retinal sublayer thickness change over time (mean follow-up 3.9 years for STGD1, 2.5 years for controls), STGD1 retinas thinned faster than controls in the outer retina (ONL to photoreceptor outer segments). OCT-based retinal sublayer thickness measurements are feasible in STGD1 patients and may provide objective measures of disease progression or treatment response.

Retinal imaging in inherited retinal diseases

Inherited retinal diseases (IRD) are a leading cause of blindness in the working age population. The advances in ocular genetics, retinal imaging and molecular biology, have conspired to create the ideal environment for establishing treatments for IRD, with the first approved gene therapy and the commencement of multiple therapy trials. The scope of this review is to familiarize clinicians and scientists with the current landscape of retinal imaging in IRD. Herein we present in a comprehensive and concise manner the imaging findings of: (I) macular dystrophies (MD) [Stargardt disease (ABCA4), X-linked retinoschisis (RS1), Best disease (BEST1), pattern dystrophy (PRPH2), Sorsby fundus dystrophy (TIMP3), and autosomal dominant drusen (EFEMP1)], (II) cone and cone-rod dystrophies (GUCA1A, PRPH2, ABCA4 and RPGR), (III) cone dysfunction syndromes [achromatopsia (CNGA3, CNGB3, PDE6C, PDE6H, GNAT2, ATF6], blue-cone monochromatism (OPN1LW/OPN1MW array), oligocone trichromacy, bradyopsia (RGS9/R9AP) and Bornholm eye disease (OPN1LW/OPN1MW), (IV) Leber congenital amaurosis (GUCY2D, CEP290, CRB1, RDH12, RPE65, TULP1, AIPL1 and NMNAT1), (V) rod-cone dystrophies [retinitis pigmentosa, enhanced S-Cone syndrome (NR2E3), Bietti crystalline corneoretinal dystrophy (CYP4V2)], (VI) rod dysfunction syndromes (congenital stationary night blindness, fundus albipunctatus (RDH5), Oguchi disease (SAG, GRK1), and (VII) chorioretinal dystrophies [choroideremia (CHM), gyrate atrophy (OAT)].

Clinical and genetic characteristics of Stargardt disease in a large Western China cohort: Report 1

Stargardt disease 1 (STGD1) is the most prevalent retinal dystrophy caused by pathogenic biallelic ABCA4 variants. Forty-two unrelated patients mostly originating from Western China were recruited. Comprehensive ophthalmological examinations, including visual acuity measurements (subjective function), fundus autofluorescence (retinal imaging), and full-field electroretinography (objective function), were performed. Next-generation sequencing (target/whole exome) and direct sequencing were conducted. Genotype grouping was performed based on the presence of deleterious variants. The median age of onset/age was 10.0 (5-52)/29.5 (12-72) years, and the median visual acuity in the right/left eye was 1.30 (0.15-2.28)/1.30 (0.15-2.28) in the logarithm of the minimum angle of resolution unit. Ten patients (10/38, 27.0%) showed confined macular dysfunction, and 27 (27/37, 73.7%) had generalized retinal dysfunction. Fifty-eight pathogenic/likely pathogenic ABCA4 variants, including 14 novel variants, were identified. Eight patients (8/35, 22.8%) harbored multiple deleterious variants, and 17 (17/35, 48.6%) had a single deleterious variant. Significant associations were revealed between subjective functional, retinal imaging, and objective functional groups, identifying a significant genotype-phenotype association. This study illustrates a large phenotypic/genotypic spectrum in a large well-characterized STGD1 cohort. A distinct genetic background of the Chinese population from the Caucasian population was identified; meanwhile, a genotype-phenotype association was similarly represented.

Fundus autofluorescence imaging

Fundus autofluorescence (FAF) imaging is an in vivo imaging method that allows for topographic mapping of naturally or pathologically occurring intrinsic fluorophores of the ocular fundus. The dominant sources are fluorophores accumulating as lipofuscin in lysosomal storage bodies in postmitotic retinal pigment epithelium cells as well as other fluorophores that may occur with disease in the outer retina and subretinal space. Photopigments of the photoreceptor outer segments as well as macular pigment and melanin at the fovea and parafovea may act as filters of the excitation light. FAF imaging has been shown to be useful with regard to understanding of pathophysiological mechanisms, diagnostics, phenotype-genotype correlation, identification of prognostic markers for disease progression, and novel outcome parameters to assess efficacy of interventional strategies in chorio-retinal diseases. More recently, the spectrum of FAF imaging has been expanded with increasing use of green in addition to blue FAF, introduction of spectrally-resolved FAF, near-infrared FAF, quantitative FAF imaging and fluorescence life time imaging (FLIO). This article gives an overview of basic principles, FAF findings in various retinal diseases and an update on recent developments.

Faster Sensitivity Loss around Dense Scotomas than for Overall Macular Sensitivity in Stargardt Disease: ProgStar Report No. 14

PURPOSE

Mean sensitivity (MS) derived from a standard test grid using microperimetry is a sensitive outcome measure in clinical trials investigating new treatments for degenerative retinal diseases. This study hypothesizes that the functional decline is faster at the edge of the dense scotoma (eMS) than by using the overall MS.

DESIGN

Multicenter, international, prospective cohort study: ProgStar Study.

METHODS

Stargardt disease type 1 patients (carrying at least 1 mutation in the ABCA4 gene) were followed over 12 months using microperimetry with a Humphrey 10-2 test grid. Customized software was developed to automatically define and selectively follow the test points directly adjacent to the dense scotoma points and to calculate their mean sensitivity (eMS).

RESULTS

Among 361 eyes (185 patients), the mean age was 32.9 ± 15.1 years old. At baseline, MS was 10.4 ± 5.2 dB (n = 361), and the eMS was 9.3 ± 3.3 dB (n = 335). The yearly progression rate of MS (1.5 ± 2.1 dB/year) was significantly lower (β = -1.33; P < .001) than that for eMS (2.9 ± 2.9 dB/year). There were no differences between progression rates using automated grading and those using manual grading (β = .09; P = .461).

CONCLUSIONS

In Stargardt disease type 1, macular sensitivity declines significantly faster at the edge of the dense scotoma than in the overall test grid. An automated, time-efficient approach for extracting and grading eMS is possible and appears valid. Thus, eMS offers a valuable tool and sensitive outcome parameter with which to follow Stargardt patients in clinical trials, allowing clinical trial designs with shorter duration and/or smaller cohorts.

Progress in treating inherited retinal diseases: Early subretinal gene therapy clinical trials and candidates for future initiatives

Due to improved phenotyping and genetic characterization, the field of 'incurable' and 'blinding' inherited retinal diseases (IRDs) has moved substantially forward. Decades of ascertainment of IRD patient data from Philadelphia and Toronto centers illustrate the progress from Mendelian genetic types to molecular diagnoses. Molecular genetics have been used not only to clarify diagnoses and to direct counseling but also to enable the first clinical trials of gene-based treatment in these diseases. An overview of the recent reports of gene augmentation clinical trials by subretinal injections is used to reflect on the reasons why there has been limited success in this early venture into therapy. These first-in human experiences have taught that there is a need for advancing the techniques of delivery of the gene products - not only for refining further subretinal trials, but also for evaluating intravitreal delivery. Candidate IRDs for intravitreal gene delivery are then suggested to illustrate some of the disorders that may be amenable to improvement of remaining central vision with the least photoreceptor trauma. A more detailed understanding of the human IRDs to be considered for therapy and the calculated potential for efficacy should be among the routine prerequisites for initiating a clinical trial.

Factors Influencing Retinal Pigment Epithelium-Atrophy Progression Rate in Stargardt Disease

Purpose

To evaluate demographic, clinical, imaging, and genetic factors associated with retinal pigment epithelium enlargement in Stargardt disease (STGD1) and to measure the agreement between short-wavelength fundus autofluorescence (SW-FAF) and near-infrared fundus autofluorescence (NIR-FAF).

Methods

Retrospective cohort study of patients with STGD1 with ≥2 gradable SW-FAF images. RPE-atrophy areas were measured on SW-FAF and NIR-FAF at each visit and regressed against time to obtain the rate of RPE-atrophy enlargement. Agreement between SW-FAF and NIR-FAF with regards to baseline atrophic areas and rates of enlargement was evaluated. Baseline factors predictive of faster SW-FAF RPE-atrophy enlargement were investigated with linear mixed models.

Results

Fifty-four eyes of 28 patients (median age: 45 years; 13 males) were included. SW-FAF and NIR-FAF agreed well for slow rates of RPE-atrophy progression, but agreement decreased as the rate increased. Median (interquartile range [IQR]) rate of RPE-atrophy expansion was 0.18 (0.10–0.85) mm²/year on SW-FAF and 0.24 (0.08–0.33) mm²/year on NIR-FAF. Larger baseline RPE-atrophy area (estimate: 0.057 mm²/year, P < 0.001), worse visual acuity (0.305 mm²/year, P = 0.005), multifocal disease (0.401 mm²/year, P = 0.02), and SW-FAF pattern (0.534 mm²/year, P =0 .03) were associated with a faster rate of progression (predictive R²: 0.65).

Conclusions

SW-FAF and NIR-FAF are not interchangeable in the evaluation of RPE-atrophy enlargement, and both imaging modalities may be required for optimal detection of disease progression. A multivariable model based on baseline clinical and imaging information may identify patients at higher risk of fast disease progression.

Translational Relevance

The knowledge of the agreement of different FAF modalities, the estimated rates of RPE-atrophy enlargement, and factors predictive of faster anatomic decay in STGD1 may allow tailored clinical management and better clinical trials design.

Advancing Clinical Trials for Inherited Retinal Diseases: Recommendations from the Second Monaciano Symposium

Major advances in the study of inherited retinal diseases (IRDs) have placed efforts to develop treatments for these blinding conditions at the forefront of the emerging field of precision medicine. As a result, the growth of clinical trials for IRDs has increased rapidly over the past decade and is expected to further accelerate as more therapeutic possibilities emerge and qualified participants are identified. Although guided by established principles, these specialized trials, requiring analysis of novel outcome measures and endpoints in small patient populations, present multiple challenges relative to study design and ethical considerations. This position paper reviews recent accomplishments and existing challenges in clinical trials for IRDs and presents a set of recommendations aimed at rapidly advancing future progress. The goal is to stimulate discussions among researchers, funding agencies, industry, and policy makers that will further the design, conduct, and analysis of clinical trials needed to accelerate the approval of effective treatments for IRDs, while promoting advocacy and ensuring patient safety.