Photoreceptor cells as a source of fundus autofluorescence in recessive Stargardt disease

Multimodal imaging in autosomal recessive Stargardt's disease

Autosomal recessive Stargardt disease type 1 (STGD-1) is a common inherited retinal disorder caused by mutations in the ABCA4 gene. This case series highlights the role of multimodal imaging (MMI): fundus autofluorescence, optical coherence tomography, optical coherence tomography angiography and fluorescein angiography in diagnosing and staging STGD-1 in three patients with varying disease severities. Imaging revealed characteristic retinal changes, including flecks and atrophic lesions, which were correlated with genotype and clinical presentation. Genotype-phenotype correlation demonstrated the influence of specific ABCA4 mutations on disease severity. MMI proved valuable in detecting subclinical changes, distinguishing disease stages and providing prognostic insights. Genetic analysis remains essential for definitive diagnosis, particularly in atypical presentations. This report emphasises the importance of integrating imaging findings with clinical and genetic data to enhance diagnostic accuracy and patient care, especially in resource-limited settings, where genetic testing may not be readily available.

Near-Infrared Autofluorescence: Early Detection of Retinal Pigment Epithelial Alterations in Inherited Retinal Dystrophies

Near-infrared autofluorescence (NIA) is a non-invasive retinal imaging technique used to examine the retinal pigment epithelium (RPE) based on the autofluorescence of melanin. Melanin has several functions within RPE cells. It serves as a protective antioxidative factor and is involved in the phagocytosis of photoreceptor outer segments. Disorders affecting the photoreceptor-RPE complex result in alterations of RPE cells which are detectable by alterations of NIA. NIA allows us to detect early alterations in various chorioretinal disorders, frequently before they are ophthalmoscopically visible and often prior to alterations in lipofuscin-associated fundus autofluorescence (FAF) or optical coherence tomography (OCT). Although NIA and FAF relate to disorders affecting the RPE, the findings for both imaging methods differ and the area involved has been demonstrated to be larger in NIA compared to FAF in several disorders, especially inherited retinal dystrophies (IRDs), indicating that NIA detects earlier alterations compared to FAF. Foveal alterations can be much more easily detected using NIA compared to FAF. A reduced subfoveal NIA intensity is the earliest sign of autosomal dominant Best disease, when FAF and OCT are still normal. In other IRDs, a preserved subfoveal NIA intensity is associated with good visual acuity. So far, the current knowledge on NIA in IRD has been presented in multiple separate publications but has not been summarized in an overview. This review presents the current knowledge on NIA in IRD and demonstrates NIA biomarkers.

Automated identification of fleck lesions in Stargardt disease using deep learning enhances lesion detection sensitivity and enables morphometric analysis of flecks

PURPOSE

To classify fleck lesions and assess artificial intelligence (AI) in identifying flecks in Stargardt disease (STGD).

METHODS

A retrospective study of 170 eyes from 85 consecutive patients with confirmed STGD. Fundus autofluorescence images were extracted, and flecks were manually outlined. A deep learning model was trained, and a hold-out testing subset was used to compare with manually identified flecks and for graders to assess. Flecks were clustered using K-means clustering.

RESULTS

Of the 85 subjects, 45 were female, and the median age was 37 years (IQR 25-59). A subset of subjects (n=41) had clearly identifiable fleck lesions, and an AI was successfully trained to identify these lesions (average Dice score of 0.53, n=18). The AI segmentation had smaller (0.018 compared with 0.034 mm2, p<0.001) but more numerous flecks (75.5 per retina compared with 40.0, p<0.001), but the total size of flecks was not different. The AI model had higher sensitivity to detect flecks but resulted in more false positives. There were two clusters of flecks based on morphology: broadly, one cluster of small round flecks and another of large amorphous flecks. The per cent frequency of small round flecks negatively correlated with subject age (r=-0.31, p<0.005).

CONCLUSIONS

AI-based detection of flecks shows greater sensitivity than human graders but with a higher false-positive rate. With further optimisation to address current shortcomings, this approach could be used to prescreen subjects for clinical research. The feasibility and utility of quantifying fleck morphology in conjunction with AI-based segmentation as a biomarker of progression require further study.

LONGITUDINAL ADAPTIVE OPTICS SCANNING LASER OPHTHALMOSCOPY REVEALS REGIONAL VARIATION IN CONE AND ROD PHOTORECEPTOR LOSS IN STARGARDT DISEASE

PURPOSE

To investigate the temporal sequence of changes in the photoreceptor cell mosaic in patients with Stargardt disease type 1, using adaptive optics scanning laser ophthalmoscopy.

METHODS

Two brothers with genetically confirmed Stargardt disease type 1 underwent comprehensive eye exams, spectral-domain optical coherence tomography, fundus autofluorescence, and adaptive optics scanning laser ophthalmoscopy imaging 3 times over the course of 28 months. Confocal images of the cones and rods were obtained from the central fovea to 10° inferiorly. Photoreceptors were counted in sampling windows at 100- µ m intervals of 200 µ m × 200 µ m for cones and 50 µ m × 50 µ m for rods, using custom cell marking software with manual correction. Photoreceptor density and spacing were measured and compared across imaging sessions using one-way analysis of variance.

RESULTS

Adaptive optics scanning laser ophthalmoscopy revealed the younger brother had a 30% decline in foveal cone density after 8 months, followed by complete loss of foveal cones at 28 months; the older brother had no detectable foveal cones at baseline. In the peripheral macula, cone and rod spacings were greater than normal in both patients. The ratio of the cone spacing to rod spacing was greater than normal across all eccentricities, with a greater divergence closer to the foveal center.

CONCLUSION

Cone cell loss may be an early pathogenetic step in Stargardt disease. Adaptive optics scanning laser ophthalmoscopy provides the capability to track individual photoreceptor changes longitudinally in Stargardt disease.

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.

Retinoid Synthesis Regulation by Retinal Cells in Health and Disease

Vision starts in retinal photoreceptors when specialized proteins (opsins) sense photons via their covalently bonded vitamin A derivative 11cis retinaldehyde (11cis-RAL). The reaction of non-enzymatic aldehydes with amino groups lacks specificity, and the reaction products may trigger cell damage. However, the reduced synthesis of 11cis-RAL results in photoreceptor demise and suggests the need for careful control over 11cis-RAL handling by retinal cells. This perspective focuses on retinoid(s) synthesis, their control in the adult retina, and their role during retina development. It also explores the potential importance of 9cis vitamin A derivatives in regulating retinoid synthesis and their impact on photoreceptor development and survival. Additionally, recent advancements suggesting the pivotal nature of retinoid synthesis regulation for cone cell viability are discussed.

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.

Subretinal autofluorescent deposits: A review and proposal for clinical classification

Subretinal autofluorescent deposits (SADs) may be found in the posterior pole, associated with very various conditions. These disorders usually present a typical pattern of autofluorescent lesions seen on short-wavelength fundus autofluorescence. We describe SADs according to their putative pathophysiological origin and also according to their clinical pattern, i.e., number, shape, and usual location. Five main putative pathophysiological origins of SADs were identified in disorders associated with an intrinsic impairment of phagocytosis and protein transportation, with excess of retinal pigment epithelium phagocytic capacity, with direct or indirect retinal pigment epithelium injury, and/or disorders associated with long-standing serous retinal detachment with mechanical separation between the retinal pigment epithelium and the photoreceptor outer segments. Clinically, however, they could be classified into eight subclasses of SADs, as observed on fundus autofluorescence as follows: single vitelliform macular lesion, multiple roundish or vitelliform lesions, multiple peripapillary lesions, flecked lesions, leopard-spot lesions, macular patterned lesions, patterned lesions located in the same area as the causal disorder, or nonpatterned lesions. Thus, if multimodal imaging may be required to diagnose the cause of SADs, the proposed classification based on noninvasive, widely available short-wavelength fundus autofluorescence could guide clinicians in making their diagnosis decision tree before considering the use of more invasive tools.

Primary versus Secondary Elevations in Fundus Autofluorescence

The method of quantitative fundus autofluorescence (qAF) can be used to assess the levels of bisretinoids in retinal pigment epithelium (RPE) cells so as to aid the interpretation and management of a variety of retinal conditions. In this review, we focused on seven retinal diseases to highlight the possible pathways to increased fundus autofluorescence. ABCA4- and RDH12-associated diseases benefit from known mechanisms whereby gene malfunctioning leads to elevated bisretinoid levels in RPE cells. On the other hand, peripherin2/RDS-associated disease (PRPH2/RDS), retinitis pigmentosa (RP), central serous chorioretinopathy (CSC), acute zonal occult outer retinopathy (AZOOR), and ceramide kinase like (CERKL)-associated retinal degeneration all express abnormally high fundus autofluorescence levels without a demonstrated pathophysiological pathway for bisretinoid elevation. We suggest that, while a known link from gene mutation to increased production of bisretinoids (as in ABCA4- and RDH12-associated diseases) causes primary elevation in fundus autofluorescence, a secondary autofluorescence elevation also exists, where an impairment and degeneration of photoreceptor cells by various causes leads to an increase in bisretinoid levels in RPE cells.

A model eye for fluorescent characterization of retinal cultures and tissues

Many human neural or neurodegenerative diseases strongly affect the ocular and retinal environment showing peculiar alterations which can be employed as specific disease biomarkers. The noninvasive optical accessibility of the retina makes the ocular investigation a potentially competitive strategy for screening, thus the development of retinal biomarkers is rapidly growing. Nevertheless, a tool to study and image biomarkers or biological samples in a human-like eye environment is still missing. Here we report on a modular and versatile eye model designed to host biological samples, such as retinal cultures differentiated from human induced pluripotent stem cells and ex-vivo retinal tissue, but also suited to host any kind of retinal biomarkers. We characterized the imaging performance of this eye model on standard biomarkers such as Alexa Fluor 532 and Alexa Fluor 594.

Fundus autofluorescence imaging using red excitation light

Retinal disease accounts significantly for visual impairment and blindness. An important role in the pathophysiology of retinal disease and aging is attributed to lipofuscin, a complex of fluorescent metabolites. Fundus autofluorescence (AF) imaging allows non-invasive mapping of lipofuscin and is a key technology to diagnose and monitor retinal disease. However, currently used short-wavelength (SW) excitation light has several limitations, including glare and discomfort during image acquisition, reduced image quality in case of lens opacities, limited visualization of the central retina, and potential retinal light toxicity. Here, we establish a novel imaging modality which uses red excitation light (R-AF) and overcomes these drawbacks. R-AF images are high-quality, high-contrast fundus images and image interpretation may build on clinical experience due to similar appearance of pathology as on SW-AF images. Additionally, R-AF images may uncover disease features that previously remained undetected. The R-AF signal increases with higher abundance of lipofuscin and does not depend on photopigment bleaching or on the amount of macular pigment. Improved patient comfort, limited effect of cataract on image quality, and lack of safety concerns qualify R-AF for routine clinical monitoring, e.g. for patients with age-related macular degeneration, Stargardt disease, or for quantitative analysis of AF signal intensity.

Optical Coherence Tomography and Optical Coherence Tomography Angiography in Pediatric Retinal Diseases

Indirect ophthalmoscopy and handheld retinal imaging are the most common and traditional modalities for the evaluation and documentation of the pediatric fundus, especially for pre-verbal children. Optical coherence tomography (OCT) allows for in vivo visualization that resembles histology, and optical coherence tomography angiography (OCTA) allows for non-invasive depth-resolved imaging of the retinal vasculature. Both OCT and OCTA were extensively used and studied in adults, but not in children. The advent of prototype handheld OCT and OCTA have allowed for detailed imaging in younger infants and even neonates in the neonatal care intensive unit with retinopathy of prematurity (ROP). In this review, we discuss the use of OCTA and OCTA in various pediatric retinal diseases, including ROP, familial exudative vitreoretinopathy (FEVR), Coats disease and other less common diseases. For example, handheld portable OCT was shown to detect subclinical macular edema and incomplete foveal development in ROP, as well as subretinal exudation and fibrosis in Coats disease. Some challenges in the pediatric age group include the lack of a normative database and the difficulty in image registration for longitudinal comparison. We believe that technological improvements in the use of OCT and OCTA will improve our understanding and care of pediatric retina patients in the future.

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.

Novel Pathogenic Mutations Identified from Whole-Genome Sequencing in Unsolved Cases of Patients Affected with Inherited Retinal Diseases

Inherited retinal diseases (IRDs) are a diverse set of visual disorders that collectively represent a major cause of early-onset blindness. With the reduction in sequencing costs in recent years, whole-genome sequencing (WGS) is being used more frequently, particularly when targeted gene panels and whole-exome sequencing (WES) fail to detect pathogenic mutations in patients. In this study, we performed mutation screens using WGS for a cohort of 311 IRD patients whose mutations were undetermined. A total of nine putative pathogenic mutations in six IRD patients were identified, including six novel mutations. Among them, four were deep intronic mutations that affected mRNA splicing, while the other five affected protein-coding sequences. Our results suggested that the rate of resolution of unsolved cases via targeted gene panels and WES can be further enhanced with WGS; however, the overall improvement may be limited.

The big warp: Registration of disparate retinal imaging modalities and an example overlay of ultrawide-field photos and en-face OCTA images

PURPOSE

To develop an algorithm and scripts to combine disparate multimodal imaging modalities and show its use by overlaying en-face optical coherence tomography angiography (OCTA) images and Optos ultra-widefield (UWF) retinal images using the Fiji (ImageJ) plugin BigWarp.

METHODS

Optos UWF images and Heidelberg en-face OCTA images were collected from various patients as part of their routine care. En-face OCTA images were generated and ten (10) images at varying retinal depths were exported. The Fiji plugin BigWarp was used to transform the Optos UWF image onto the en-face OCTA image using matching reference points in the retinal vasculature surrounding the macula. The images were then overlayed and stacked to create a series of ten combined Optos UWF and en-face OCTA images of increasing retinal depths. The first algorithm was modified to include two scripts that automatically aligned all the en-face OCTA images.

RESULTS

The Optos UWF image could easily be transformed to the en-face OCTA images using BigWarp with common vessel branch point landmarks in the vasculature. The resulting warped Optos image was then successfully superimposed onto the ten Optos UWF images. The scripts more easily allowed for automatic overlay of the images.

CONCLUSIONS

Optos UWF images can be successfully superimposed onto en-face OCTA images using freely available software that has been applied to ocular use. This synthesis of multimodal imaging may increase their potential diagnostic value. Script A is publicly available at https://doi.org/10.6084/m9.figshare.16879591.v1 and Script B is available at https://doi.org/10.6084/m9.figshare.17330048.

Choroideremia Carriers: Dark-Adapted Perimetry and Retinal Structures

Purpose

In choroideremia (CHM) carriers, scotopic sensitivity was assessed by dark adapted chromatic perimetry (DACP) and outer retinal structure was evaluated by multimodal imaging.

Methods

Nine carriers (18 eyes) and 13 healthy controls (13 eyes) underwent DACP testing with cyan and red stimuli. Analysis addressed peripapillary (4 test locations closest to the optic disc), macular (52 locations), and peripheral (60 locations outside the macula) regions. Responses were considered to be rod-mediated when cyan relative to red sensitivity was >5 dB. Fundus imaging included spectral domain optical coherence tomography (SD-OCT), short-wavelength (SW-AF), near-infrared (NIR-AF), ultrawide-field (200 degrees) pseudocolor fundus imaging, and quantitative (qAF) fundus autofluorescence.

Results

Detection of the cyan stimulus was rod mediated in essentially all test locations (99.7%). In the macular and peripheral areas, DACP sensitivity values were not significantly different from healthy eyes. In the peripapillary area, sensitivities were significantly decreased (P < 0.05). SD-OCT imaging ranged from hyper-reflective lesions and discontinuities of the outer retinal bands to hypertransmission of signal. SW-AF and NIR-AF images presented with peripapillary atrophy in seven patients (14 eyes). Mosaicism was detectable in SW-AF images in seven patients and in NIR-AF images in five patients. Frank hypo-autofluorescence was visible in eight patients with distinct chorioretinopathy in seven patients. The qAF values were below the 95% confidence interval (CI) of healthy age-matched individuals in 12 eyes.

Conclusions

Rod mediated scotopic sensitivity was comparable to that in control eyes in macular and peripheral areas but was decreased in the peripapillary area where changes in retinal structure were also most severe.

Nahinfrarot-Autofluoreszenz: klinische Anwendung und diagnostische Relevanz

Die Nahinfrarot-Autofluoreszenz (NIA) ist ein nicht-invasives Verfahren zur Untersuchung des retinalen Pigmentepithels (RPE) basierend auf der Darstellung des antioxidativen Schutzfaktors Melanin in den RPE-Zellen. Die NIA verbessert die Früherkennung chorioretinaler Erkrankungen, da bei vielen dieser Erkrankungen mit der NIA Strukturveränderungen des RPE nachweisbar sind, bevor sich in anderen Untersuchungen Krankheitszeichen erkennen lassen.

[Near-infrared Fundus Autofluorescence: Clinical Application and Diagnostic Relevance]

Near-infrared autofluorescence (NIA) is a non-invasive retinal imaging technique for examination of the retinal pigment epithelium (RPE) based on the autofluorescence of melanin. Melanin has several functions within the RPE cells, in one of them it serves as a protective antioxidative factor within the RPE cells and is involved in the phagocytosis of photoreceptor outer segments. Disorders that affect the photoreceptor-RPE complex result in alterations of RPE cells which are detectable by alterations of NIA. Therefore, NIA allows to detect early alterations in inherited and acquired chorioretinal disorders, frequently prior to ophthalmoscopical visualisation and often prior to alterations in lipofuscin associated fundus autofluorescence (FAF) or optical coherence tomography (OCT). Although NIA and FAF relate to disorders affecting the RPE, findings between both imaging methods differ and the area involved has been demonstrated to be larger in NIA compared to FAF in several disorders (e.g., age-related macular degeneration, retinitis pigmentosa, ABCA4-gene associated Stargardt disease and cone-rod dystrophy, light damage), indicating that NIA detects earlier alterations compared to FAF. In addition, due to the absence of blue-light filtering which limits foveal visualisation in FAF, foveal alterations can be much better detected using NIA. A reduced subfoveal NIA intensity is the earliest sign of autosomal dominant BEST1-associated disease, when FAF and OCT are still normal. In other disorders, a normal subfoveal NIA intensity is associated with good visual acuity. This review summarizes the present knowledge on NIA and demonstrates biomarkers for various chorioretinal disorders.

Animal Models of LED-Induced Phototoxicity. Short- and Long-Term In Vivo and Ex Vivo Retinal Alterations

Phototoxicity animal models have been largely studied due to their degenerative communalities with human pathologies, e.g., age-related macular degeneration (AMD). Studies have documented not only the effects of white light exposure, but also other wavelengths using LEDs, such as blue or green light. Recently, a blue LED-induced phototoxicity (LIP) model has been developed that causes focal damage in the outer layers of the superior-temporal region of the retina in rodents. In vivo studies described a progressive reduction in retinal thickness that affected the most extensively the photoreceptor layer. Functionally, a transient reduction in a- and b-wave amplitude of the ERG response was observed. Ex vivo studies showed a progressive reduction of cones and an involvement of retinal pigment epithelium cells in the area of the lesion and, in parallel, an activation of microglial cells that perfectly circumscribe the damage in the outer retinal layer. The use of neuroprotective strategies such as intravitreal administration of trophic factors, e.g., basic fibroblast growth factor (bFGF), brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF) or pigment epithelium-derived factor (PEDF) and topical administration of the selective alpha-2 agonist (Brimonidine) have demonstrated to increase the survival of the cone population after LIP.

Near-Infrared Reflectance Imaging in Retinal Diseases Affecting Young Patients

Near-infrared reflectance (NIR) is a noninvasive, contactless, and rapid in vivo imaging technique for visualizing subretinal alterations in the photoreceptor layer, retinal pigment epithelium, and choroid. The present report describes the application of this imaging method in retinal and choroidal pathologies affecting young patients where scarce cooperation, poor fixation, and intense glare sensation can result in a challenging clinical examination. A literature search of the MEDLINE database was performed using the terms "near-infrared reflectance" and "spectral-domain optical coherence tomography." Articles were selected if they described the diagnostic use of NIR in children or young adults. Of 700 publications, 42 manuscripts published between 2005 and 2020 were inherent to children or young adults and were considered in this narrative literature review. The first disease category is the phakomatoses where NIR is essential in visualizing choroidal alterations recognized as cardinal biomarkers in neurofibromatosis type 1, microvascular retinal alterations, and retinal astrocytic hamartomas. Another diagnostic application is the accurate visualization of crystals of various nature, including the glistening crystals that characterize Bietti crystalline dystrophy. Acute macular neuropathy and paracentral acute middle maculopathy represent a further disease category with young adulthood onset where NIR is not only diagnostic but also essential to monitor disease progression. A further interesting clinical application is to facilitate the detection of laser-induced maculopathy where funduscopic examination can be normal or subnormal. In conclusion, NIR imaging has a noninterchangeable role in diagnosing certain retinal diseases, especially in children and young adults where there is scarce collaboration and a lack of evident clinical findings. Moreover, this technique can reveal unique retinal and choroidal biomarkers highly specific to rare conditions.

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.

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.

Shared Features in Retinal Disorders With Involvement of Retinal Pigment Epithelium

When using spectral domain optical coherence tomography (SD-OCT) to inform the status of outer retina, we have noted discrete hyperreflective lesions extending through photoreceptor-attributable bands that have a similar presentation in multiple retinal diseases. These lesions present as either corrugated thickenings of interdigitation zone and ellipsoid zone bands or in later stages as rectangular or pyramidal shaped foci that extend radially through photoreceptor cell-attributable bands. In ABCA4-related and peripherin-2/RDS-disease (PRPH2/RDS), monogenic forms of retinopathy caused by mutations in proteins expressed in photoreceptor cells, these punctate lesions colocalize with fundus flecks in en face images. In fundus albipunctatus and retinitis punctata albescens, diseases caused by mutations in genes (retinol dehydrogenase 5, RDH5; and retinaldehyde-binding protein 1, RLBP1) encoding proteins of the visual cycle, these lesions manifest as white dot-like puncta. Similar aberrations in photoreceptor cell-attributable SD-OCT reflectivity layers manifest as reticular pseudodrusen (RPD) in short-wavelength fundus autofluorescence and near-infrared fundus autofluorescence fundus images and are linked to age-related macular degeneration a complex disease. Despite differences in the etiologies of retinal diseases presenting as fundus flecks, dots and RPD, underlying degenerative processes in photoreceptor cells are signified in SD-OCT scans by the loss of structural features that would otherwise define healthy photoreceptor cells at these foci.

Retinal Manifestations of Mitochondrial Oxidative Phosphorylation Disorders

Purpose

The purpose of this paper was to discuss manifestations of primary mitochondrial dysfunctions and whether the retinal pigment epithelium or the photoreceptors are preferentially affected.

Methods

A retrospective analysis was performed of patients with clinically and laboratory confirmed diagnoses of maternally inherited diabetes and deafness (MIDD) or Kearns–Sayre syndrome (KSS). Patients underwent full ophthalmic examination, full-field electroretinogram, and multimodal imaging studies, including short-wavelength autofluorescence, spectral domain-optical coherence tomography, and color fundus photography.

Results

A total of five patients with MIDD and four patients with KSS were evaluated at two tertiary referral centers. Mean age at initial evaluation was 50.3 years old. Nascent outer retinal tubulations corresponding with faint foci of autofluorescence were observed in two patients with MIDD. Characteristic features of this cohort included a foveal sparing phenotype observed in 13 of 18 eyes (72%), global absence of intraretinal pigment migration, and preserved retinal function on full-field electroretinogram testing in 12 of 16 eyes (75%). One patient diagnosed with MIDD presented with an unusual pattern of atrophy surrounding the parapapillary region and one patient with KSS presented with an atypical choroideremia-like phenotype.

Conclusions

MIDD and KSS are phenotypically heterogeneous disorders. Several features of disease suggest that primary mitochondrial dysfunction may first affect the retinal pigment epithelium followed by secondary photoreceptor loss. Similarities between primary mitochondrial degenerations and retinal disorders, such as age-related macular degeneration may suggest a primary role of mitochondria in the pathogenesis of these oligogenic disorders.

Quantitative autofluorescence: Review of Current Technical Aspects and Applications in Chorioretinal Disease

Purpose: In this review we discuss the broad clinical application of qAF and provide a descriptive summary of the phenotypic findings of different chorioretinal pathologies.Background: Quantitative Fundus autofluorescence (qAF) is a novel developing technology that can aid in diagnosis and longitudinal disease monitoring by measuring and comparing autofluorescence intensities. Fundus autofluorescence (FAF) is a noninvasive imaging method that creates a density map of the fluorophores of the ocular fundus and provides both functional and topographic anatomic information about retinal cells. Fluorophores are molecules that have the ability to temporarily absorb irradiated light, and emit a small amount of light of a different wavelength. Different endogenous fluorophores can be found in the ocular fundus. Changes in accumulation of retinal fluorophores usually indicate retinal pathology and create characteristic patterns of hyper-autofluorescence and hypo-autofluorescence that help establish a diagnosis.Conclusion: qAF allows a safe non-invasive visualization of the retina, enables a standard for AF intensities comparison and aids to the understanding of the genotype-phenotype correlations.

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.

Deep learning segmentation of hyperautofluorescent fleck lesions in Stargardt disease

Stargardt disease is one of the most common forms of inherited retinal disease and leads to permanent vision loss. A diagnostic feature of the disease is retinal flecks, which appear hyperautofluorescent in fundus autofluorescence (FAF) imaging. The size and number of these flecks increase with disease progression. Manual segmentation of flecks allows monitoring of disease, but is time-consuming. Herein, we have developed and validated a deep learning approach for segmenting these Stargardt flecks (1750 training and 100 validation FAF patches from 37 eyes with Stargardt disease). Testing was done in 10 separate Stargardt FAF images and we observed a good overall agreement between manual and deep learning in both fleck count and fleck area. Longitudinal data were available in both eyes from 6 patients (average total follow-up time 4.2 years), with both manual and deep learning segmentation performed on all (n = 82) images. Both methods detected a similar upward trend in fleck number and area over time. In conclusion, we demonstrated the feasibility of utilizing deep learning to segment and quantify FAF lesions, laying the foundation for future studies using fleck parameters as a trial endpoint.

Phenotype-genotype correlations in a pseudodominant Stargardt disease pedigree due to a novel ABCA4 deletion-insertion variant causing a splicing defect

BACKGROUND

Deletion-insertion (delins) variants in the retina-specific ATP-binding cassette transporter gene, subfamily A, member 4 (ABCA4) accounts for <1% in Stargardt disease. The consequences of these delins variants on splicing cannot be predicted with certainty without supporting in vitro data.

METHODS

Candidate ABCA4 variants were revealed by genetic and segregation analysis of a family with pseudodominant Stargardt disease using a commercial panel and Sanger sequencing. RNA extracted from patient-derived fibroblasts was analyzed by RT-PCR to evaluate splicing behavior of the ABCA4 variants.

RESULTS

Affected members carrying the novel c.6031_6044delinsAGTATTTAACCAATATTT variant in exon 44 presented with contrasting phenotypes; from early-onset cone-rod dystrophy to late-onset macular dystrophy. This variant resulted in a 56-nucleotide deletion in the mutant allele by activation of a cryptic splice acceptor site which disrupts the reading frame and results in a premature termination codon (p.Ile2003LeufsTer41). If translated, the crucial functional domains near the C-terminus would be truncated from the ABCA4 protein.

CONCLUSION

This work demonstrates the intrafamilial phenotypic variability in a pseudodominant Stargardt disease pedigree and the use of patient-derived fibroblasts to evaluate the effect of a novel ABCA4 delins variant on splicing to complement in silico pathogenicity assessment.

Clinical spectrum, genetic complexity and therapeutic approaches for retinal disease caused by ABCA4 mutations

The ABCA4 protein (then called a “rim protein”) was first identified in 1978 in the rims and incisures of rod photoreceptors. The corresponding gene, ABCA4, was cloned in 1997, and variants were identified as the cause of autosomal recessive Stargardt disease (STGD1). Over the next two decades, variation in ABCA4 has been attributed to phenotypes other than the classically defined STGD1 or fundus flavimaculatus, ranging from early onset and fast progressing cone-rod dystrophy and retinitis pigmentosa-like phenotypes to very late onset cases of mostly mild disease sometimes resembling, and confused with, age-related macular degeneration. Similarly, analysis of the ABCA4 locus uncovered a trove of genetic information, including >1200 disease-causing mutations of varying severity, and of all types – missense, nonsense, small deletions/insertions, and splicing affecting variants, of which many are located deep-intronic. Altogether, this has greatly expanded our understanding of complexity not only of the diseases caused by ABCA4 mutations, but of all Mendelian diseases in general. This review provides an in depth assessment of the cumulative knowledge of ABCA4-associated retinopathy – clinical manifestations, genetic complexity, pathophysiology as well as current and proposed therapeutic approaches.

Functional Relevance and Structural Correlates of Near Infrared and Short Wavelength Fundus Autofluorescence Imaging in ABCA4-Related Retinopathy

Purpose

To evaluate the functional relevance and structural correlates of autofluorescence (AF) alterations under short-wavelength (SW) and near-infrared (NIR) excitation light in ABCA4-related retinopathy.

Methods

In this prospective, cross-sectional case series, 88 eyes of 44 patients with ABCA4-related retinopathy (mean age, 37.6 years; range, 9-77 years) underwent SW-AF and NIR-AF imaging. The AF images were graded for disease characteristic patterns by two independent readers and correlated with alterations in optical coherence tomography (OCT) and impairment of retinal sensitivity along a foveo-papillary line assessed by fundus-controlled microperimetry.

Results

A centrifugal sequence of AF patterns from atrophic lesions to homogeneous background was found for both AF modalities. The eccentricity of each AF pattern in NIR-AF was larger compared to those in SW-AF (P < 0.001). Increasing eccentricity of each pattern correlated with increasing retinal sensitivity. The distant border of the zone of hyperfluorescent flecks in SW-AF and hypoautofluorescent flecks in NIR-AF correlated with the margins of the ellipsoid zone loss in OCT (r = 0.979 and r = 0.971, P < 0.001). The expansion of hypofluorescent flecks in SW-AF was associated with the boundaries of external limiting membrane loss (r = 0.933, P < 0.001).

Conclusions

SW-AF and NIR-AF revealed a characteristic sequence of AF patterns that correlated with functional and structural alterations, suggesting different stages in disease progression.

Translational Relevance

Alterations in NIR-AF exceeded those in SW-AF images, substantiating the hypothesis of different AF origins and suggesting NIR-AF as surrogate marker for early disease-related changes.

Age, lipofuscin and melanin oxidation affect fundus near-infrared autofluorescence

Background

Fundus autofluorescence is a non-invasive imaging technique in ophthalmology. Conventionally, short-wavelength autofluorescence (SW-AF) is used for detection of lipofuscin, a byproduct of the visual cycle which accumulates with age or disease in the retinal pigment epithelium (RPE). Furthermore, near-infrared autofluorescence (NIR-AF) is used as a marker for RPE and choroidal melanin, but contribution of lipofuscin to the NIR-AF signal is unclear.

Methods

We employed fluorescence microscopy to investigate NIR-AF properties of melanosomes, lipofuscin and melanolipofuscin granules in histologic sections of wildtype and Abca4^−/− mouse eyes, the latter having increased lipofuscin, as well as aged human donor eyes. Differentiation between these pigments was verified by analytical electron microscopy. To investigate the influence of oxidative and photic stress we used an in vitro model with isolated ocular melanosomes and an in vivo phototoxicity mouse model.

Findings

We show that NIR-AF is not an intrinsic property of melanin, but rather increases with age and after photic or oxidative stress in mice and isolated melanosomes. Furthermore, when lipofuscin levels are high, lipofuscin granules also show NIR-AF, as confirmed by correlative fluorescence and electron microscopy in human tissue. However, lipofuscin in albino Abca4^−/− mice lacks NIR-AF signals.

Interpretation

We suggest that NIR-AF is derived from melanin degradation products that accumulate with time in lipofuscin granules. These findings can help to improve the interpretation of patient fundus autofluorescence data.

Funding

This work was supported by Bundesministerium für Bildung und Forschung, Deutsche Forschungsgemeinschaft and Chinese Scholarship Council. Major instrumentation used in this work was supported by Deutsche Forschungsgemeinschaft, the European Fund for Regional Development and the state of Baden-Württemberg.

Near-infrared autofluorescence in young choroideremia patients

Purpose: To study near-infrared autofluorescence (NIR-AF) and short- wave autofluorescence (SW-AF) imaging modalities in young patients affected with choroideremia (CHM).Methods: NIR-AF and SW-AF images, Optical coherence tomography (OCT) and color fundus images were acquired from 3 young CHM patients (6 eyes) enrolled at the Regional Reference Center for Hereditary Retinal Degenerations of the Eye Clinic in Florence.Results: We studied 3 young CHM patients (6 eyes). The mean age of the patients was 17,3 years. Using NIR-AF, patient P1 was characterized by speckled hypo-autofluorescent areas at the posterior pole with a preserved central hyper-autofluorescence while patient P2 and P3 were characterized by a preserved NIR-AF signal only at the fovea. Using SW-AF, patient P1 was characterized by a normal macular autofluorescence and by a speckled FAF pattern involved the vascular arcades while patient P2 and P3 showed well-demarcated hypo-autofluorescence areas involving the posterior pole with a preserved macular autofluorescence. The differences between NIR-AF and SW-AF were more pronounced in advanced stages. In correspondence of preserved NIR-AF, the OCT examination showed regular and continuous outer retinal hyperreflective bands. We observed abnormal RPE/Bruch's membrane complex and EZ band externally to the NIR-AF signal area.Conclusions: NIR-AF imaging confirms an early RPE involvement allowing us to identify and to quantify the RPE pigment loss in choroideremia. For this reason, NIR-AF imaging can be useful for monitoring the progression of the disease and to study the effect of future treatments.

Lessons learned from quantitative fundus autofluorescence

Quantitative fundus autofluorescence (qAF) is an approach that is built on a confocal scanning laser platform and used to measure the intensity of the inherent autofluorescence of retina elicited by short-wavelength (488 nm) excitation. Being non-invasive, qAF does not interrupt tissue architecture, thus allowing for structural correlations. The spectral features, cellular origin and topographic distribution of the natural autofluorescence of the fundus indicate that it is emitted from retinaldehyde-adducts that form in photoreceptor cells and accumulate, under most conditions, in retinal pigment epithelial cells. The distributions and intensities of fundus autofluorescence deviate from normal in many retinal disorders and it is widely recognized that these changing patterns can aid in the diagnosis and monitoring of retinal disease. The standardized protocol employed by qAF involves the normalization of fundus grey levels to a fluorescent reference installed in the imaging instrument. Together with corrections for magnification and anterior media absorption, this approach facilitates comparisons with serial images and images acquired within groups of patients. Here we provide a comprehensive summary of the principles and practice of qAF and we highlight recent efforts to elucidate retinal disease processes by combining qAF with multi-modal imaging.

Multi-platform imaging in ABCA4-Associated Disease

Fundus autofluorescence (FAF) imaging is crucial to the diagnosis and monitoring of recessive Stargardt disease (STGD1). In a retrospective cohort study of 34 patients, we compared FAF imaging platforms varying in field size (30° and 55°: blue/SW-AF and NIR-AF; 200°: ultrawide-field, UWF-AF), excitation wavelength (488 nm, blue/SW-AF; 532 nm, UWF-AF and 787 nm, NIR-AF) and image processing. Due to reduced absorption of 532 nm and 787 nm light by macular pigment, foveal sparing was more readily demonstrable by green/UWF-AF and NIR-AF imaging. Prominent in green/UWF-AF images is a central zone of relatively elevated AF that is continuous inferonasal with a demarcation line bordering lower AF nasally and higher AF temporally. This zone and border are more visible in STGD1 than in healthy eyes and more visible with green/UWF-AF. With the development of AF flecks, inferonasal retina is initially spared. Central atrophic areas were larger in NIR-AF images than in blue/SW-AF and green/UWF-AF images and the presence of a contiguous hyperAF ring varied with imaging modality. Flecks visible as hyperAF foci in blue/SW-AF images were also visible in green/UWF-AF but were often hypoAF in NIR-AF. Since disease in STGD1 often extends beyond the 30° and 55° fields, green/UWF-AF has advantages including for pediatric patients. The imaging platforms examined provided complementary information.

Macular hyperpigmentary changes in ABCA4-Stargardt disease

Background

Stargardt disease (STGD) and age-related macular degeneration (AMD) share clinical and pathophysiological features. In AMD, macular hyperpigmentary changes are associated to a worse prognosis. The purpose of this study was to characterize macular hyperpigmentary changes in patients with STGD and associate them with the severity of phenotype.

Materials and methods

This retrospective cross-sectional study included 141 patients with STGD. Hyperpigmentary changes were evaluated on color fundus photography and spectral-domain optical coherence tomography. Severity of phenotype was assessed by full-field electroretinogram (ffERG) and fundus autofluorescence (FAF) patterns, and visual acuity (VA).

Results

Thirty patients (21.7%) showed macular hyperpigmentary changes in four distinct patterns. Out of seventeen patients who had follow-up images, eleven patients demonstrated increases of the hyperpigmented lesions, and progression of the underlying RPE atrophy overtime. VA remained stable. Of 28 patients who had ffERG, 17 patients presented with reduction of photopic and scotopic responses, while 8 presented with reduction of photopic responses only, and 3 presented with preserved photopic and scotopic responses. Of 25 patients who had FAF available, 12 presented with widespread disease extending anteriorly to the vascular arcades, while eight presented with widespread disease, extending beyond the vascular arcades, and 5 presented with disease confined to the foveal area.

Conclusion

In this study, we demonstrated that patients with STGD with macular hyperpigmented lesions had a severe phenotype. Overtime, hyperpigmented lesions increased in size, spread across the retina, and migrated to different retinal layers. Macular hyperpigmentation may be a marker of advanced stage of the disease.

Stargardt macular dystrophy and evolving therapies

INTRODUCTION

Stargardt macular dystrophy (STGD1) is a hereditary retinal degeneration that lacks effective treatment options. Gene therapy, stem cell therapy, and pharmacotherapy with visual cycle modulators (VCMs) and complement inhibitors are discussed as potential treatments.

AREAS COVERED

Investigational therapies for STGD1 aim to reduce toxic bisretinoids and lipofuscin in the retina and retinal pigment epithelium (RPE). These agents include C20-D3-vitamin A (ALK-001), isotretinoin, VM200, emixustat, and A1120. Avacincaptad pegol is a C5 complement inhibitor that may reduce inflammation-related RPE damage. Animal models of STGD1 show promising data for these treatments, though proof of efficacy in humans is lacking. Fenretinide and emixustat are VCMs for dry AMD and STGD1 that failed to halt geographic atrophy progression or improve vision in trials for AMD. A1120 prevents retinol transport into RPE and may spare side effects typically seen with VCMs (nyctalopia and chromatopsia). Stem cell transplantation suggests potential biologic plausibility in a phase I/II trial. Gene therapy aims to augment the mutated ABCA4 gene, though results of a phase I/II trial are pending.

EXPERT OPINION

Stem cell transplantation, ABCA4 gene therapy, VCMs, and complement inhibitors offer biologically plausible treatment mechanisms for treatment of STGD1. Further trials are warranted to assess efficacy and safety in humans.