MAPPING THE DENSE SCOTOMA AND ITS ENLARGEMENT IN STARGARDT DISEASE

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

PURPOSE

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

METHODS

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

PARTICIPANTS

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

MAIN OUTCOME MEASURES

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

RESULTS

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

CONCLUSION

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

Outer nuclear layer relevance in visual function correlated to quantitative enface OCT parameters in Stargardt disease

PURPOSE

To evaluate the correlation between Best Corrected Visual Acuity (BCVA) and the following parameters in Stargardt Disease (STGD): Central Retinal Thickness (CR-T), Central Outer Nuclear Layer Thickness (C-ONL-T), Areas of macular Photoreceptor loss (PHRa), and Retinal Pigment Epithelium (RPE) loss (RPEa).

METHODS

A total of 64 eyes of 32 STGD patients were included in the study. All patients received a comprehensive ophthalmological examination, color fundus photographs, fundus auto-fluorescence imaging, and Optical Coherence Tomography (OCT). The CR-T and C-ONL-T were evaluated from standard SD-OCT scans. The PHRa and RPEa were calculated from enface OCT scans (sub RPE slab and photoreceptor slab). The collected OCT parameters were evaluated for possible association with BCVA.

RESULTS

The mean macular PHRa and RPEa was 16.16 ± 13.36 and 12.05 ± 12.57 mm² respectively. The mean CR-T measured 120.78 ± 41.49 μm while the mean C-ONL-T was assessed at 4.60 ± 13.73 μm. BCVA showed the highest correlation with the C-ONL-T (r = -0.72; p < 0.001) while there was no correlation with the CR-T (r = -0.17; p = 1.00).

CONCLUSIONS

Enface OCT permits a rapid and precise quantitative evaluation of the macular PHR and RPE atrophy area in STGD. Nonetheless, the OCT parameter that showed the highest correlation with visual acuity in STGD was the ONL thickness.

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

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

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

PURPOSE

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

DESIGN

Multicenter, international, prospective cohort study: ProgStar Study.

METHODS

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

RESULTS

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

CONCLUSIONS

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

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.

Abnormal Visual Function Outside the Area of Atrophy Defined by Short-Wavelength Fundus Autofluorescence in Stargardt Disease

Purpose

To examine the extent of visual function abnormality outside the dark lesion on short-wavelength fundus autofluorescence (SW-AF), and its correlation with background SW-AF features and optical coherence tomography (OCT) in recessive Stargardt disease (STGD1).

Methods

Forty-nine eyes of 25 participants in the ProgStar (the Natural History of the Progression of Atrophy Secondary to Stargardt Disease) study at our center were included. Patients underwent microperimetry (both threshold and dense scotoma mapping), OCT, SW-AF, and visual acuity testing. The Fisher's exact test, the χ2 test, and unpaired t-tests were used to analyze the data.

Results

Of 40 eyes without central fixation, 33 (82%) placed fixation remote (most ≥5°) from the dense scotoma edge, despite good intervening retinal sensitivity. OCT findings accounted for the remote fixation in 75%. Eighteen (37%) of all 49 eyes had dense scotoma extending past the dark lesion border. OCT was not adequate to define the edge of the scotoma. Of the 49 eyes, 28 (57%) had the mottled background pattern, 10 (20%) had the uniform pattern, and 11 (22%) had the other pattern, with >75% of eyes in each pattern having remote fixation. The dense scotoma exceeded the dark lesion primarily in the mottled pattern. The two eyes of each patient were concordant in all features.

Conclusions

Functional abnormalities in STGD1 extend past the SW-AF dark lesion. The disruption of the ellipsoid zone shows that photoreceptor abnormality extends peripheral to the dark lesion, and it explains in part the remote fixation pattern and the dense scotoma exceeding the dark lesion. This has implications for clinical trials for STGD1.

Correlation between Choriocapillaris Density and Retinal Sensitivity in Stargardt Disease

The aim of this work was to characterize the choriocapillaris (CC) in patients with Stargardt disease (STGD) using the swept source widefield optical coherence tomography angiography (SS WF OCTA) and to compare CC perfusion density to retinal sensitivity, analyzed using microperimetry (MP). This cross-sectional study included 9 patients (18 eyes) with STGD and central CC atrophy (stage 3 STGD). The CC was analyzed using SS WF OCTA and areas of different CC impairment were quantified and correlated with retinal sensitivity analyzed using MP. The main outcome measures were the percent perfused choriocapillaris area (PPCA), retinal sensitivity, and correlation between PPCA and retinal sensitivity. Seventeen eyes of 9 patients suffering from stage 3 STGD were analyzed. SS WF OCTA revealed a vascular rarefaction in central atrophic zones and a near atrophy halo of choriocapillaris impairment. In all eyes were noticed a central atrophy (CA) area with absolute absence of CC that corresponded to 0 dB points at MP, a near atrophy (NA) zone of PPCA impairment that included points with decreased sensitivity at MP and a distant from atrophy (DA) zone with higher PPCA and retinal sensitivity values. The mean difference of PPCA and retinal sensitivity between NA and CA and DA and CA was statistical significantly different (p < 0.01), the latter showing higher values. A direct relationship between PPCA and retinal sensitivity was found (p < 0.001). Choriocapillaris damage evaluated using SS WF OCTA correlates with MP, these data suggest that CC impairment may be a predictor of retinal function in patients with STGD.

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.

Comparison of Green Versus Blue Fundus Autofluorescence in ABCA4-Related Retinopathy

Purpose

To investigate the interreader and intermodality agreement for grading of retinal pigment epithelium (RPE) atrophy lesion size in ABCA4-related retinopathy using green (GAF) and blue fundus autofluorescence (BAF) imaging.

Methods

In this cross-sectional case series, 97 eyes of 49 patients with RPE atrophy secondary to ABCA4-related retinopathy underwent GAF- (518 nm excitation light) and BAF- (488 nm excitation light) imaging using confocal scanning laser ophthalmoscopy (Spectralis HRA, Heidelberg Engineering, Heidelberg, Germany). Lesions with definitely decreased autofluorescence (DDAF) and questionably decreased autofluorescence (QDAF) in GAF and BAF imaging were analyzed separately by five independent readers using semiautomated software (RegionFinder, Heidelberg Engineering). Intermodality and interreader agreements were assessed for the square-root lesion size, lesion perimeter, and circularity.

Results

GAF- and BAF-based measurements of DDAF and QDAF showed high intermodality and interreader agreement concerning square-root lesion size, as well as shape descriptive parameters (perimeter and circularity). Interreader agreement of square-root lesion size was slightly, hence not significantly higher for GAF-based grading ([95% coefficients of repeatability, intraclass correlation coefficient] DDAF: 0.215 mm, 0.997; QDAF: 0.712 mm, 0.981) compared to BAF-based grading (DDAF: 0.232 mm, 0.997; QDAF: 0.764 mm, 0.978). However, DDAF-measurements revealed distinctly more reproducible results than QDAF-measurements. Foveal sparing did not interfere with intermodality agreement.

Conclusions

Both GAF- and BAF-based quantification of RPE atrophy showed very reliable results with possible superiority of GAF in the context of less energetic excitation light.

Translational Relevance

The high interreader agreement qualifies the use of DDAF progression in GAF and BAF imaging as potential morphologic outcome measure for interventional clinical trials and disease monitoring.

Peripheral Visual Fields in ABCA4 Stargardt Disease and Correlation With Disease Extent on Ultra-widefield Fundus Autofluorescence

PURPOSE

To evaluate the disease extent on ultra-widefield fundus autofluorescence (UWF-FAF) in patients with ABCA4 Stargardt disease (STGD) and correlate these data with functional outcome measures.

DESIGN

Retrospective cross-sectional study.

METHODS

Setting: Kellogg Eye Center, University of Michigan.

STUDY POPULATION

Sixty-five patients with clinical diagnosis and proven pathogenic variants in the ABCA4 gene. Observational Procedures: The UWF-FAF images were obtained using Optos (200 degrees) and classified into 3 types. Functional testing included kinetic widefield perimetry, full-field electroretinogram (ffERG), and visual acuity (VA). All results were evaluated with respect to UWF-FAF classification.

MAIN OUTCOME MEASURES

Classification of UWF-FAF; area comprising the I4e, III4e, and IV4e isopters; ffERG patterns; and VA.

RESULTS

For UWF-FAF, 27 subjects (41.5%) were classified as type I, 17 (26.2%) as type II, and 21 (32.4%) as type III. The area of each isopter correlated inversely with the extent of the disease and all isopters were able to detect differences among UWF-FAF types (IV4e, P = .0013; III4e, P = .0003; I4e, P < .0001 = 3.93e^-8). ffERG patterns and VA were also different among the 3 UWF-FAF types (P < .001 = 6.61e-⁶ and P < .001 = 7.3e^-5, respectively).

CONCLUSION

Patients with widespread disease presented with more constriction of peripheral visual fields and had more dysfunction on ffERG and worse VA compared to patients with disease confined to the macula. UWF-FAF images may provide information for estimating peripheral and central visual function in STGD.

Juvenile Macular Degenerations

In this article, we review the following 3 common juvenile macular degenerations: Stargardt disease, X-linked retinoschisis, and Best vitelliform macular dystrophy. These are inherited disorders that typically present during childhood, when vision is still developing. They are sufficiently common that they should be included in the differential diagnosis of visual loss in pediatric patients. Diagnosis is secured by a combination of clinical findings, optical coherence tomography imaging, and genetic testing. Early diagnosis promotes optimal management. Although there is currently no definitive cure for these conditions, therapeutic modalities under investigation include pharmacologic treatment, gene therapy, and stem cell transplantation.

Macular hole in Stargardt disease: Clinical and ultra-structural observation

PURPOSE

To report for the first time a case report of a Stargardt disease patient who developed a macular hole (MH) which was treated with a surgical approach.

METHOD

Case report.

RESULTS

After vitrectomy a complete closure of the MH was obtained and the best-corrected visual acuity remained stable. No complications were reported after one year of follow-up. An ultra-structural examination of the removed internal limiting membrane (ILM) and epiretinal membrane (ERM) was carried out under electron microscopy.

CONCLUSION

Vitreo-retinal surgery could represent a therapeutic option to treat vitreo-retinal interface abnormalities associated with inherited retinal diseases.