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

Detailed phenotype and long-term follow-up of RAB28-associated cone-rod dystrophy

PURPOSE

To gain an insight into the pathophysiology of RAB28-associated inherited retinal degeneration through detailed phenotyping and long-term longitudinal follow-up.

METHODS

The patient underwent complete ophthalmic examinations. Visual function was assessed with microperimetry, full-field electroretinography (ffERG), imaging with optical coherence tomography (OCT), short-wave (SW), and near-infrared (NIR) fundus autofluorescence (FAF).

RESULTS

A healthy Haitian woman with homozygous pathogenic variants (c.68C > T; p.Ser23Phe) in RAB28 presented at 16 years of age with a four-year history of blurred vision. Visual acuities were 20/125 in each eye, which remained relatively stable since. At age 27, cone ffERGs were non-detectable and borderline for rod-mediated responses. Kinetic fields were full to a V-4e target, undetectable to a small I-4e stimulus. Microperimetry showed an absolute central scotoma surrounded by a pericentral relative scotoma. SD-OCT showed an undetectable or barely detectable foveal and parafoveal photoreceptor outer nuclear layer (ONL), photoreceptor outer segment (POS), and retinal pigment epithelium (RPE) signals and loss of the SW- and NIR-FAF signals. This atrophic region was separated from a normally laminated retina by a narrow transition zone (TZ) of hyper SW- and NIR-FAF that co-localized with preserved ONL but abnormally thinned POS and RPE. There was minimal centrifugal (<100 μ m) expansion over a six-year period.

CONCLUSION

The cone-rod dystrophy phenotype documented herein supports a critical role of RAB28 for cone function and POS maintenance. Severe central photoreceptor and RPE loss with a predilection for POS loss in TZs suggests possible disruptions of complex mechanisms that maintain central cone photoreceptor and RPE homeostasis.

Progression, reliability, predicting parameters and sample size calculations for quantitative fundus autofluorescence measures in ABCA4-related retinopathy

BACKGROUND/AIMS

To investigate the progression of quantitative autofluorescence (qAF) measures and the potential as clinical trial endpoint in ABCA4-related retinopathy.

METHODS

In this longitudinal monocentre study, 64 patients with ABCA4-related retinopathy (age (mean±SD), 34.84±16.36 years) underwent serial retinal imaging, including optical coherence tomography (OCT) and qAF (488 nm excitation) imaging using a modified confocal scanning laser ophthalmoscope with a mean (±SD) review period of 20.32±10.90 months. A group of 110 healthy subjects served as controls. Retest variability, changes of qAF measures over time and its association with genotype and phenotype were analysed. Furthermore, individual prognostic feature importance was assessed, and sample size calculations for future interventional trials were performed.

RESULTS

Compared with controls, qAF levels of patients were significantly elevated. The test-retest reliability revealed a 95% coefficient of repeatability of 20.37. During the observation time, young patients, patients with a mild phenotype (morphological and functional) and patients with mild mutations showed an absolute and relative increase in qAF values, while patients with advanced disease manifestation (morphological and functional), and homozygous mutations at adulthood revealed a decrease in qAF. Considering these parameters, required sample size and study duration could significantly be reduced.

CONCLUSION

Under standardised settings with elaborated conditions towards operators and analysis to counterbalance variability, qAF imaging might be reliable, suitable for quantifying disease progression and constitutes a potential clinical surrogate marker in ABCA4-related retinopathy. Trial design based on patients' baseline characteristics and genotype has the potential to provide benefits regarding required cohort size and absolute number of visits.

Inner retinal thickness in Stargardt disease

PURPOSE

To analyze the alterations at the level of the inner retina in patients affected by Stargardt disease (STGD1).

METHODS

Cross-sectional investigation involving STGD1 patients with genetically confirmed diagnosis, who underwent optical coherence tomography (OCT), optical coherence tomography angiography (OCTA), and microperimetry.

RESULTS

Overall, 31 patients (62 eyes) with genetically confirmed STGD1 were included in the study. Mean inner retinal thickness, vessel density of plexa, and retinal sensitivity resulted significantly reduced in STGD patients, compared with healthy controls (p < 0.05), both in the outer and in the inner ETDRS rings. Overall, 43% of eyes revealed an inner retinal thinning, whereas 21% and 35% showed a thicker or within normal range inner retina.

CONCLUSIONS

Inner retina is irregularly altered in STGD1, showing variable quantitative alterations as detected on OCT. Inner retinal status might represent a useful biomarker to better characterize STGD1 and to ascertain the effects of new treatment approaches.

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.

Longitudinal Changes in Scotopic and Mesopic Macular Function as Assessed with Microperimetry in Patients With Stargardt Disease: SMART Study Report No. 2

PURPOSE

To estimate and compare cross-sectional scotopic versus mesopic macular sensitivity losses measured by microperimetry, and to report and compare the longitudinal rates of scotopic and mesopic macular sensitivity losses in ABCA4 gene-associated Stargardt disease (STGD1).

DESIGN

This was a multicenter prospective cohort study.

METHODS

Participants comprised 127 molecularly confirmed STGD1 patients enrolled from 6 centers in the United States and Europe and followed up every 6 months for up to 2 years. The Nidek MP-1S device was used to measure macular sensitivities of the central 20° under mesopic and scotopic conditions. The mean deviations (MD) from normal for mesopic macular sensitivity for the fovea (within 2° eccentricity) and extrafovea (4°-10° eccentricity), and the MD for scotopic sensitivity for the extrafovea, were calculated. Linear mixed effects models were used to estimate mesopic and scotopic changes. Main outcome measures were baseline mesopic mean deviation (mMD) and scotopic MD (sMD) and rates of longitudinal changes in the mMDs and sMD.

RESULTS

At baseline, all eyes had larger sMD, and the difference between extrafoveal sMD and mMD was 10.7 dB (P < .001). Longitudinally, all eyes showed a statistically significant worsening trend: the rates of foveal mMD and extrafoveal mMD and sMD changes were 0.72 (95% CI = 0.37-1.07), 0.86 (95% CI = 0.58-1.14), and 1.12 (95% CI = 0.66-1.57) dB per year, respectively.

CONCLUSIONS

In STGD1, in extrafovea, loss of scotopic macular function preceded and was faster than the loss of mesopic macular function. Scotopic and mesopic macular sensitivities using microperimetry provide alternative visual function outcomes for STGD1 treatment trials.

Kinetics of Heterogeneous Background in Stargardt’s Disease over Time

Stargardt’s disease (STGD1) is caused by mutations in the ABCA4 gene. Different lesions characterised by decreased autofluorescence levels are found in fundus autofluorescence (FAF) from STGD1 patients and could be used as outcome indicators for disease progression. We investigated the fate of foci with reduced autofluorescence (FRA) within the heterogeneous background of STGD1 patients using FAF imaging. Genetically confirmed STGD1 patients presenting heterogeneous background autofluorescence on high-quality FAF images at a minimum of two visits at least 12 months apart were chosen. A grid centred on the fovea was used to define five different zones. Within each zone, five FRA were randomly selected for each eye. The eccentricity of foci was determined at different time points for each patient. Analysis of 175 randomly chosen FRA showed consistent centrifugal displacement over time, most notably in eyes showing areas with definitely decreased autofluorescence. Interestingly, FRA did not leave an area of hypo-autofluorescence on FAF in locations where they were previously located. These findings may help to better understand STGD1 progression, improve FAF interpretation, and shed light on the nature of heterogeneous background.

Comparisons Among Optical Coherence Tomography and Fundus Autofluorescence Modalities as Measurements of Atrophy in ABCA4-Associated Disease

Purpose

In ABCA4-associated retinopathy, central atrophy was assessed by spectral domain optical coherence tomography (SD-OCT) and by short-wavelength (SW-AF) and near-infrared (NIR-AF) autofluorescence.

Methods

Patients exhibited a central atrophic lesion characterized by hypoautofluorescence (hypoAF) surrounded either by hyperautofluorescent (hyperAF) rings in both AF images (group 1, 4 patients); or a hyperAF ring in SW-AF but not in NIR-AF images (group 2, 11 patients); or hyperAF rings in neither AF images (group 3, 11 patients). Choroidal hypertransmission and widths of ellipsoid zone (EZ) loss were measured in foveal SD-OCT scans, and in AF images hypoAF and total hypo+hyperAF widths were measured along the same axis. Bland-Altman and repeated measures analysis of variance with Tukey post hoc were applied.

Results

For all groups, hypertransmission widths were significantly smaller than EZ loss widths. In Groups 1 and 2, hypertransmission width was not significantly different than SW-hypoAF width, but hypertransmission was narrower than the width of SW-hypo+hyperAF (groups 1, 2) and NIR-hypo+hyperAF (group 1). In group 3, the hypertransmission width was also significantly less than the width of SW-hypoAF and NIR-hypoAF. The EZ loss widths were not significantly different than measurements of total lesion size, the latter being the widths of SW-hypo+hyperAF and NIR-hypo+hyperAF (group 1); widths of NIR-hypoAF and SW-hypo+hyperAF (group 2); and widths of NIR-hypoAF and SW-hypoAF (group 3).

Conclusions

Hypertransmission and SW-hypoAF (except when reflecting total lesion width) underestimate lesion size detected by EZ loss, SW-hypoAF+hyperAF, and NIR-hypo+hyperAF.

Translational Relevance

The findings are significant to the selection of outcome measures in clinical studies.

Stargardt disease and progress in therapeutic strategies

Background: Stargardt disease (STGD1) is an autosomal recessive retinal dystrophy due to mutations in ABCA4, characterized by subretinal deposition of lipofuscin-like substances and bilateral centrifugal vision loss. Despite the tremendous progress made in the understanding of STGD1, there are no approved treatments to date. This review examines the challenges in the development of an effective STGD1 therapy.Materials and Methods: A literature review was performed through to June 2021 summarizing the spectrum of retinal phenotypes in STGD1, the molecular biology of ABCA4 protein, the in vivo and in vitro models used to investigate the mechanisms of ABCA4 mutations and current clinical trials.Results: STGD1 phenotypic variability remains an challenge for clinical trial design and patient selection. Pre-clinical development of therapeutic options has been limited by the lack of animal models reflecting the diverse phenotypic spectrum of STDG1. Patient-derived cell lines have facilitated the characterization of splice mutations but the clinical presentation is not always predicted by the effect of specific mutations on retinoid metabolism in cellular models. Current therapies primarily aim to delay vision loss whilst strategies to restore vision are less well developed.Conclusions: STGD1 therapy development can be accelerated by a deeper understanding of genotype-phenotype correlations.

Gene Therapy for Rdh12-Associated Retinal Diseases Helps to Delay Retinal Degeneration and Vision Loss

Purpose

The aim of study was to establish Rdh12-associated inherited retinal disease (Rdh12-IRD) mouse model and to identify the best timepoint for gene therapy.

Methods

We induced retinal degeneration in Rdh12^-/- mice using a bright light. We clarified the establishment of Rdh12-IRD mouse model by analyzing the thickness of retinal layers and electroretinography (ERG). Rdh12-IRD mice received a subretinal injection of adeno-associated virus 2/8-packaged Rdh12 cDNA for treatment. We evaluated the visual function and retinal structure in the treated and untreated eyes to identify the best timepoint for gene therapy.

Results

Rdh12-IRD mice showed significant differences in ERG amplitudes and photoreceptor survival compared to Rdh12^+/+ mice. Preventive gene therapy not only maintained normal visual function but also prevented photoreceptor loss. Salvage gene therapy could not reverse the retinal degeneration phenotype of Rdh12-IRD mice, but it could slow down the loss of visual function.

Conclusion

The light-induced retinal degeneration in our Rdh12^-/- mice indicated that a defect in Rdh12 alone was sufficient to cause visual dysfunction and photoreceptor degeneration, which reproduced the phenotypes observed in RDH12-IRD patients. This model is suitable for gene therapy studies. Early treatment of the primary Rdh12 defect helps to delay the later onset of photoreceptor degeneration and maintains visual function in Rdh12-IRD mice.

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.

Targeted next-generation sequencing identifies ABCA4 mutations in Chinese families with childhood-onset and adult-onset Stargardt disease

Background: Stargardt disease (STGD) is the most common form of juvenile macular dystrophy associated with progressive central vision loss, and is agenetically and clinically heterogeneous disease. Molecular diagnosis is of great significance in aiding the clinical diagnosis, helping to determine the phenotypic severity and visual prognosis. In the present study, we determined the clinical and genetic features of seven childhood-onset and three adult-onset Chinese STGD families. We performed capture next-generation sequencing (NGS) of the probands and searched for potentially disease-causing genetic variants in previously identified retinal or macular dystrophy genes.

Methods: In all, ten unrelated Chinese families were enrolled. Panel-based NGS was performed to identify potentially disease-causing genetic variants in previously identified retinal or macular dystrophy genes, including the five known STGD genes (ABCA4, PROM1, PRPH2, VMD2, and ELOVL4). Variant analysis, Sanger validation, and segregation tests were utilized to validate the disease-causing mutations in these families.

Results: Using systematic data analysis with an established bioinformatics pipeline and segregation analysis, 17 pathogenic mutations in ABCA4 were identified in the 10 STGD families. Four of these mutations were novel: c.371delG, c.681T > G, c.5509C > T, and EX37del. Childhood-onset STGD was associated with severe visual loss, generalized retinal dysfunction and was due to more severe variants in ABCA4 than those found in adult-onset disease.

Conclusions: We expand the existing spectrum of STGD and reveal the genotype–phenotype relationships of the ABCA4 mutations in Chinese patients. Childhood-onset STGD lies at the severe end of the spectrum of ABCA4-associated retinal phenotypes.

Diagnosis of Inherited Retinal Diseases

Inherited retinal diseases are a frequent cause of severe visual impairment or blindness in children and adults of working age. Across this group of diseases, there is great variability in the degree of visual impairment, the impact on everyday life, disease progression, and the suitability to therapeutic intervention. Therefore, an early and precise diagnosis is crucial for patients and their families. Characterizing inherited retinal diseases involves a detailed medical history, clinical examination with testing of visual function, multimodal retinal imaging as well as molecular genetic testing. This may facilitate a distinction between different inherited retinal diseases, as well as a differentiation from monogenic systemic diseases with retinal involvement, and from mimicking diseases.

Reliability of Retinal Pathology Quantification in Age-Related Macular Degeneration: Implications for Clinical Trials and Machine Learning Applications

Purpose

To investigate the interreader agreement for grading of retinal alterations in age-related macular degeneration (AMD) using a reading center setting.

Methods

In this cross-sectional case series, spectral-domain optical coherence tomography (OCT; Topcon 3D OCT, Tokyo, Japan) scans of 112 eyes of 112 patients with neovascular AMD (56 treatment naive, 56 after three anti-vascular endothelial growth factor injections) were analyzed by four independent readers. Imaging features specific for AMD were annotated using a novel custom-built annotation platform. Dice score, Bland-Altman plots, coefficients of repeatability, coefficients of variation, and intraclass correlation coefficients were assessed.

Results

Loss of ellipsoid zone, pigment epithelium detachment, subretinal fluid, and drusen were the most abundant features in our cohort. Subretinal fluid, intraretinal fluid, hypertransmission, descent of the outer plexiform layer, and pigment epithelium detachment showed highest interreader agreement, while detection and measures of loss of ellipsoid zone and retinal pigment epithelium were more variable. The agreement on the size and location of the respective annotation was more consistent throughout all features.

Conclusions

The interreader agreement depended on the respective OCT-based feature. A selection of reliable features might provide suitable surrogate markers for disease progression and possible treatment effects focusing on different disease stages.

Translational Relevance

This might give opportunities for a more time- and cost-effective patient assessment and improved decision making as well as have implications for clinical trials and training machine learning algorithms.

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.

Inferred retinal sensitivity in recessive Stargardt disease using machine learning

Spatially-resolved retinal function can be measured by psychophysical testing like fundus-controlled perimetry (FCP or 'microperimetry'). It may serve as a performance outcome measure in emerging interventional clinical trials for macular diseases as requested by regulatory agencies. As FCP constitute laborious examinations, we have evaluated a machine-learning-based approach to predict spatially-resolved retinal function ('inferred sensitivity') based on microstructural imaging (obtained by spectral domain optical coherence tomography) and patient data in recessive Stargardt disease. Using nested cross-validation, prediction accuracies of (mean absolute error, MAE [95% CI]) 4.74 dB [4.48-4.99] were achieved. After additional inclusion of limited FCP data, the latter reached 3.89 dB [3.67-4.10] comparable to the test-retest MAE estimate of 3.51 dB [3.11-3.91]. Analysis of the permutation importance revealed, that the IS&OS and RPE thickness were the most important features for the prediction of retinal sensitivity. 'Inferred sensitivity', herein, enables to accurately estimate differential effects of retinal microstructure on spatially-resolved function in Stargardt disease, and might be used as quasi-functional surrogate marker for a refined and time-efficient investigation of possible functionally relevant treatment effects or disease progression.

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.

Laser Pointer: A Possible Risk for the Retina

In recent years, an increasing incidence of laser pointer-associated retinal injuries has been observed, likely due to easy access to incorrectly classified laser pointers, their labelling as toys, and lack of awareness concerning the associated risk. Laser pointer exposure can lead to irreversible retinal damage and associated vision loss, depending on the wavelength, radiation power, duration of exposure, localization, and spot size. Pronounced retinal laser damage is especially seen in children and teenagers. The structural appearance of retinal laser pointer damage varies and, in some cases, may be a diagnostic challenge. Besides often subtle findings on optical coherence tomography examination, characteristic alterations on near-infrared autofluorescence imaging may be valuable for the diagnosis of retinal laser pointer injuries and for differentiating other retinal lesions with similar appearance. The increase in laser pointer injuries indicates that regulatory actions and increased public awareness are required regarding the dangers of laser pointers.

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.

Structural Features Associated With the Development and Progression of RORA Secondary to Maternally Inherited Diabetes and Deafness

PURPOSE

To investigate the development and progression of retinal pigment epithelial and outer retinal atrophy (RORA) secondary to maternally inherited diabetes and deafness (MIDD).

DESIGN

Retrospective observational case series.

METHODS

Thirty-six eyes of 18 patients (age range, 22.4-71.6 years) with genetically proven MIDD and serial optical coherence tomography (OCT) images were included. As proposed reference standard to diagnose and stage atrophy, OCT images were longitudinally evaluated and analyzed for presence and precursors of RORA. RORA was defined as an area of (1) hypertransmission, (2) disruption of the retinal pigment epithelium, (3) photoreceptor degeneration, and (4) absence of other signs of a retinal pigment epithelial tear.

RESULTS

The majority of patients revealed areas of RORA in a circular area around the fovea of between 5° and 15° eccentricity. Over the observation time (range, 0.5-8.5 years), evidence for a consistent sequence of OCT features from earlier disease stages to the end stage of RORA could be found, starting with loss of ellipsoid zone and subretinal deposits, followed by loss of external limiting membrane and loss of retinal pigment epithelium with hypertransmission of OCT signal into the choroid, and leading to loss of the outer nuclear layer bordered by hyporeflective wedges. Outer retinal tabulations seemed to develop in regions of coalescent areas of RORA.

CONCLUSIONS

The development and progression of RORA could be tracked in MIDD patients using OCT images, allowing potential definition of novel surrogate markers. Similarities to OCT features in age-related macular degeneration, where mitochondrial dysfunction has been implicated in the pathogenesis, support wide-ranging benefits from proof-of-concept studies in MIDD.

Prediction of Function in ABCA4-Related Retinopathy Using Ensemble Machine Learning

Full-field electroretinogram (ERG) and best corrected visual acuity (BCVA) measures have been shown to have prognostic value for recessive Stargardt disease (also called “ABCA4-related retinopathy”). These functional tests may serve as a performance-outcome-measure (PerfO) in emerging interventional clinical trials, but utility is limited by variability and patient burden. To address these limitations, an ensemble machine-learning-based approach was evaluated to differentiate patients from controls, and predict disease categories depending on ERG (‘inferred ERG’) and visual impairment (‘inferred visual impairment’) as well as BCVA values (‘inferred BCVA’) based on microstructural imaging (utilizing spectral-domain optical coherence tomography) and patient data. The accuracy for ‘inferred ERG’ and ‘inferred visual impairment’ was up to 99.53 ± 1.02%. Prediction of BCVA values (‘inferred BCVA’) achieved a precision of ±0.3LogMAR in up to 85.31% of eyes. Analysis of the permutation importance revealed that foveal status was the most important feature for BCVA prediction, while the thickness of outer nuclear layer and photoreceptor inner and outer segments as well as age of onset highly ranked for all predictions. ‘Inferred ERG’, ‘inferred visual impairment’, and ‘inferred BCVA’, herein, represent accurate estimates of differential functional effects of retinal microstructure, and offer quasi-functional parameters with the potential for a refined patient assessment, and investigation of potential future treatment effects or disease progression.

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.

Retinal light sensitivity as outcome measure in recessive Stargardt disease

BACKGROUND/AIMS

To evaluate the applicability of mesopic light sensitivity measurements obtained by fundus-controlled perimetry (FCP, also termed 'microperimetry') as clinical trial endpoint in Stargardt disease (STGD1).

METHODS

In this retrospective, monocentre cohort study, 271 eyes of 136 patients (age, 37.1 years) with STGD1 and 87 eyes of 54 healthy controls (age, 41.0 years) underwent mesopic FCP, using a pattern of 50 stimuli (achromatic, 400-800 nm) centred on the fovea. The concurrent validity of mesopic FCP testing using the MAIA device (CenterVue, Italy), the retest variability and its determinants, and the progression of sensitivity loss over time were investigated using mixed-model analyses. The main outcomes were the average pointwise sensitivity loss in dependence of patients' demographic, functional and imaging characteristics, the intrasession 95% coefficient of repeatability, and the pointwise sensitivity loss over time.

RESULTS

Pointwise sensitivity loss was on average (estimate (95% CI)) 13.88 dB (12.55 to 15.21) along the horizontal meridian and was significantly associated with the electrophysiological subgroup, presence/absence of foveal sparing, best-corrected visual acuity and disease duration. The 95% coefficient of repeatability was 12.15 dB (10.78 to 13.38) and varied in dependence of the underlying mean sensitivity and local sensitivity slope. The global progression rate for the sensitivity loss was 0.45 dB/year (0.13 to 0.78) and was higher for the central and inner ETDRS subfields compared with more peripheral regions.

CONCLUSIONS

Mesopic light sensitivity measured by FCP is reliable and susceptible for functional changes. It constitutes a potential clinical outcome for both natural history studies as well as future interventional studies in patients with STGD1.