Spectral-domain OCT peripapillary retinal nerve fibre layer thickness measurements in patients with Stargardt disease

OCT Intensity of the Region between Outer Retina Band 2 and Band 3 as a Biomarker for Retinal Degeneration and Therapy

Optical coherence tomography (OCT) is widely used to probe retinal structure and function. This study investigated the outer retina band (ORB) pattern and reflective intensity for the region between bands 2 and 3 (Dip) in three mouse models of inherited retinal degeneration (Rs1KO, TTLL5KO, RPE65KO) and in human AMD patients from the A2A database. OCT images were manually graded, and reflectivity signals were used to calculate the Dip ratio. Qualitative analyses demonstrated the progressive merging band 2 and band 3 in all three mouse models, leading to a reduction in the Dip ratio compared to wildtype (WT) controls. Gene replacement therapy in Rs1KO mice reverted the ORB pattern to one resembling WT and increased the Dip ratio. The degree of anatomical rescue in these mice was highly correlated with level of transgenic RS1 expression and with the restoration of ERG b-wave amplitudes. While the inner retinal cavity was significantly enlarged in dark-adapted Rs1KO mice, the Dip ratio was not altered. A reduction of the Dip ratio was also detected in AMD patients compared with healthy controls and was also positively correlated with AMD severity on the AMD score. We propose that the ORB and Dip ratio can be used as non-invasive early biomarkers for retina health, which can be used to probe therapeutic gene expression and to evaluate the effectiveness of therapy.

Investigation of Structural Alterations in Inherited Retinal Diseases: A Quantitative SD-OCT-Analysis of Retinal Layer Thicknesses in Light of Underlying Genetic Mutations

Inherited retinal diseases can result from various genetic defects and are one of the leading causes for blindness in the working-age population. The present study aims to provide a comprehensive description of changes in retinal structure associated with phenotypic disease entities and underlying genetic mutations. Full macular spectral domain optical coherence tomography scans were obtained and manually segmented in 16 patients with retinitis pigmentosa, 7 patients with cone−rod dystrophy, and 7 patients with Stargardt disease, as well as 23 age- and sex-matched controls without retinal disease, to assess retinal layer thicknesses. As indicated by generalized least squares models, all IRDs were associated with retinal thinning (p < 0.001), especially of the outer nuclear layer (ONL, p < 0.001). Except for the retinal nerve fiber layer, such thinning was associated with a reduced visual acuity (p < 0.001). These advances in our understanding of ultrastructural retinal changes are important for the development of gene-, cell-, and optogenetic therapy. Longitudinal studies are warranted to describe the temporal component of those changes.

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.

Thinner temporal peripapillary retinal nerve fibre layer in Stargardt disease detected by optical coherence tomography

Purpose

To evaluate peripapillary retinal nerve fibre layer (RNFL) thickness measured by spectral domain optical coherence tomography (OCT) in patients with Stargardt disease (STGD).

Methods

A cross-sectional, monocentric, observational case-control study. Twenty patients (39 eyes) with ABCA4 mutations graded according to the Fishman STGD classification were included. RNFL measurement was performed using Heidelberg Spectralis SD-OCT. RNFL thickness in STGD patients was compared to age-matched data of healthy individuals provided by the device’s manufacturer. A manual readjustment of the optic disc-fovea angle was performed when needed.

Results

The mean age at first diagnosis of STGD was 22.9 years (range 9 to 50) and 39.1 years (range 18 to 74) at the time of examination. Thirty-nine percent of eyes (15 eyes) needed manual adjustment of the optic disc-fovea angle due to malfixation of the patients during OCT. The temporal quadrant corresponding to the macula showed a RNFL 16% thinner than controls (mean − 12 μm, 95%CI − 9 to −15 μm). However, global RNFL thickness did not differ from controls due to increased RNFL thickness of 12% in the nasal sectors. Duration and stage of STGD were not correlated to thinner RNFL.

Conclusion

STGD seems to be associated with thinner peripapillary RNFL in the sector of axons projecting to the degenerated macular area. It is yet unclear as to whether this results from anterograde transneuronal degeneration of direct injury to retinal ganglion cells.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00417-020-04992-2.

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.

STARGARDT DISEASE: Beyond Flecks and Atrophy

PURPOSE

To identify changes in the outer retina in areas without atrophy or flecks of Stargardt disease (STGD) using spectral-domain optical coherence tomography.

METHODS

Twenty-three STGD patients and 26 control subjects were assessed for outer retina (from the outer border of Bruch membrane [BrM] to the inner border of the inner segment ellipsoid zone [EZ]), BrM-retinal pigment epithelium apex, the EZ thickness, and apical process interdigitation zone.

RESULTS

Patients with STGD had increased BrM-EZ thickness in areas without apparent disease versus control subjects at 1,000, 1,500, 2,000, and 2,500 μm superior and 1,500 μm, 2,000 μm, and 2,500 μm inferior to the fovea (P < 0.05 to P < 0.001), greatest difference (3.4 μm) at 2,500 μm superiorly. The BrM-retinal pigment epithelium segment showed larger fractional contribution of 0.48 to 0.51 to the overall BrM-EZ thickness compared with 0.35 to 0.42 in control subjects. The thickness of EZ and the interspace between the retinal pigment epithelium apex and EZ were smaller in the STGD patients (P < 0.05 to P < 0.001). Patients with STGD displayed an interrupted interdigitation zone in 16 (84.2%) of 19 eyes versus 6 (23.1%) of 26 eyes of the control subjects (P < 0.001). The BrM-EZ segment of the outer retina of STGD patients lacked the typical normal trilaminar pattern.

CONCLUSION

Subtle changes are present within the BrM-EZ segment of the outer retina of STGD patients in areas that are devoid of atrophy and flecks. These findings suggest that pathologic changes in STGD are more widespread than that seen by clinical examination.

Early impairment of the full-field photopic negative response in patients with Stargardt disease and pathogenic variants of the ABCA4 gene

BACKGROUND

To study the photopic negative response of the full-field photopic electroretinography (ERG) in Stargardt patients with pathogenic variants in the ABCA4 gene.

METHODS

A retrospective analysis of 35 Stargardt patients with ABCA4 gene pathogenic variants, compared to normal age-matched controls. Patients were clinically followed at the Ophthalmology Department of Fondazione Policlinico Universitario A. Gemelli/Università Cattolica del Sacro Cuore, Rome, Italy.

RESULTS

The photopic negative response of the full-field photopic ERG was compromised in most Stargardt patients. In the presence of a normal B-wave, the amplitude ratio between the photopic negative response and the B-wave displayed a 97% accuracy in detecting diseased eyes (receiver operating characteristic curves).

CONCLUSIONS

In Stargardt patients with ABCA4 pathogenic mutations, the photopic negative response of the full-field photopic ERG is a very sensitive disease read-out. Its inclusion in standard ERG analysis would be a no-cost addition of practical consequence in the follow-up of Stargardt disease. The early impairment of the photopic negative response suggests that inner retinal function might be affected in Stargardt disease earlier than previously acknowledged.

Objective Analysis of Hyperreflective Outer Retinal Bands Imaged by Optical Coherence Tomography in Patients With Stargardt Disease

PURPOSE

To develop and apply an objective algorithm for analyzing outer retinal layers imaged by spectral-domain optical coherence tomography (SD-OCT) in patients with Stargardt disease (STGD1).

METHODS

Horizontal macular B-scans were acquired from 20 visually normal controls and 20 genetically confirmed stage 1 STGD1 patients. The number of outer retinal bands was quantified using a semiautomated algorithm that detected bands using the second derivative of longitudinal reflectivity profiles. The present analysis focused on the three outermost bands, currently associated with the ellipsoid zone (EZ), cone outer segment interdigitation zone (IZ), and retinal pigment epithelium (RPE) complex.

RESULTS

The RPE complex and EZ bands were detected throughout the B-scan in all controls. The RPE complex was detected throughout the B-scan in all patients, but was atrophic appearing in some locations. The EZ band was detected only outside the central lesion. Interdigitation zone band detection varied as a function of eccentricity for both groups, with detection for controls being highest in the para- and perifovea and lowest in the fovea and near periphery. In patients, the IZ band was generally not present in the fovea or para- or perifovea due to the central lesion. Outside of the lesion, the IZ band was detected in 26% of patients (mean detection across the near periphery), which was approximately half of the detection in controls.

CONCLUSIONS

An objective approach for quantifying the number of outer retinal OCT bands found reduced IZ detection in STGD1 patients. This occurred even outside the central lesion, demonstrating an inability to image the IZ, possibly due to enhanced RPE reflectivity or abnormal outer retinal structure.

Multimodal characterization of proliferative diabetic retinopathy reveals alterations in outer retinal function and structure

PURPOSE

To identify changes in retinal function and structure in persons with proliferative diabetic retinopathy (PDR), including the effects of panretinal photocoagulation (PRP).

DESIGN

Cross-sectional study.

PARTICIPANTS

Thirty adults who underwent PRP for PDR, 15 adults with untreated PDR, and 15 age-matched controls.

METHODS

Contrast sensitivity, frequency doubling perimetry (FDP), Humphrey visual fields, photostress recovery, and dark adaptation were assessed. Fundus photography and macular spectral-domain optical coherence tomography (SD OCT) were performed. To quantify retinal layer thicknesses, SD OCT scans were segmented semiautomatically.

MAIN OUTCOME MEASURES

Visual function measures were compared among patients with PDR and PRP, untreated patients with PDR, and controls. Mean retinal layer thicknesses were compared between groups. Correlation analyses were performed to evaluate associations between visual function measures and retinal layer thicknesses.

RESULTS

A significant reduction of FDP mean deviation (MD) was exhibited in PRP-treated patients with PDR (MD ± standard deviation, -8.20±5.76 dB; P < 0.0001) and untreated patients (-5.48±4.48 dB; P < 0.0001) relative to controls (1.07±2.50 dB). Reduced log contrast sensitivity compared with controls (1.80±0.14) also was observed in both PRP-treated patients (1.42±0.17; P < 0.0001) and untreated patients (1.56±0.20; P = 0.001) with PDR. Compared with controls, patients treated with PRP demonstrated increased photostress recovery time (151.02±104.43 vs. 70.64±47.14 seconds; P = 0.001) and dark adaptation speed (12.80±5.15 vs. 9.74±2.56 minutes; P = 0.022). Patients who underwent PRP had diffusely thickened nerve fiber layers (P = 0.024) and diffusely thinned retinal pigment epithelium (RPE) layers (P = 0.009) versus controls. Untreated patients with PDR also had diffusely thinned RPE layers (P = 0.031) compared with controls.

CONCLUSIONS

Patients with untreated PDR exhibited inner retinal dysfunction, as evidenced by reduced contrast sensitivity and FDP performance, accompanied by alterations in inner and outer retinal structure. Patients who underwent PRP had more profound changes in outer retinal structure and function. Distinguishing the effects of PDR and PRP may guide the development of restorative vision therapies for patients with advanced diabetic retinopathy.

Clinical and molecular analysis of Stargardt disease with preserved foveal structure and function

PURPOSE

To describe a cohort of patients with Stargardt disease who show a foveal-sparing phenotype.

DESIGN

Retrospective case series.

METHODS

The foveal-sparing phenotype was defined as foveal preservation on autofluorescence imaging, despite a retinopathy otherwise consistent with Stargardt disease. Forty such individuals were ascertained and a full ophthalmic examination was undertaken. Following mutation screening of ABCA4, the molecular findings were compared with those of patients with Stargardt disease but no foveal sparing.

RESULTS

The median age of onset and age at examination of 40 patients with the foveal-sparing phenotype were 43.5 and 46.5 years. The median logMAR visual acuity was 0.18. Twenty-two patients (22/40, 55%) had patchy parafoveal atrophy and flecks; 8 (20%) had numerous flecks at the posterior pole without atrophy; 7 (17.5%) had mottled retinal pigment epithelial changes; 2 (5%) had multiple atrophic lesions, extending beyond the arcades; and 1 (2.5%) had a bull's-eye appearance. The median central foveal thickness assessed with spectral-domain optical coherence tomographic images was 183.0 μm (n = 33), with outer retinal tubulation observed in 15 (45%). Twenty-two of 33 subjects (67%) had electrophysiological evidence of macular dysfunction without generalized retinal dysfunction. Disease-causing variants were found in 31 patients (31/40, 78%). There was a higher prevalence of the variant p.Arg2030Gln in the cohort with foveal sparing compared to the group with foveal atrophy (6.45% vs 1.07%).

CONCLUSIONS

The distinct clinical and molecular characteristics of patients with the foveal-sparing phenotype are described. The presence of 2 distinct phenotypes of Stargardt disease (foveal sparing and foveal atrophy) suggests that there may be more than 1 disease mechanism in ABCA4 retinopathy.

Quantification of peripapillary sparing and macular involvement in Stargardt disease (STGD1)

PURPOSE

To quantify and compare structure and function across the macula and peripapillary area in Stargardt disease (STGD1).

METHODS

Twenty-seven patients (27 eyes) and 12 age-similar controls (12 eyes) were studied. Patients were classified on the basis of full-field electroretinogram (ERG) results: Fundus autofluorescence (FAF) and spectral domain-optical coherence tomography (SD-OCT) horizontal line scans were obtained through the fovea and peripapillary area. The thicknesses of the outer nuclear layer plus outer plexiform layer (ONL+), outer segment (OS), and retinal pigment epithelium (RPE) were measured through the fovea, and peripapillary areas from 1° to 4° temporal to the optic disc edge using a computer-aided, manual segmentation technique. Visual sensitivities in the central 10° were assessed using microperimetry and related to retinal layer thicknesses.

RESULTS

Compared to the central macula, the differences between controls and patients in ONL+, OS, and RPE layer thicknesses were less in the nasal and temporal macula. Relative sparing of the ONL+ and/or OS layers was detected in the nasal (i.e., peripapillary) macula in 8 of 13 patients with extramacular disease on FAF; relative functional sparing was also detected in this subgroup. All 14 patients with disease confined to the central macula, as detected on FAF, showed ONL+ and OS layer thinning in regions of normal RPE thickness.

CONCLUSIONS

Relative peripapillary sparing was detected in STGD1 patients with extramacular disease on FAF. Photoreceptor thinning may precede RPE degeneration in STGD1.