Sensitive Subjective and Objective Visual Function Measures in Stargardt Macular Dystrophy

Abstract

Abstract: : Purpose: Stargardt macular dystrophy (SMD) is one of the most frequent causes of macular degeneration (MD) in childhood; to date it has no cure. Current visual function measures, namely visual acuity and the full field electroretinogram (ERG) are not sensitive enough to detect early retinal changes in SMD. The primary aim of this study is to develop a visual function assessment protocol for patients with SMD that is comprehensive, sensitive and reproducible and easy to use in a clinical setting. Methods: To date 35 subjects with SMD (positive ABCR–/–) aged 8–55 years having vision < 1.3 logMAR (0.1–1.3 log MAR) and normal anterior segments have been recruited from the Ocular Genetics Program at The Hospital for Sick Children. Twenty age–matched controls have been recruited. All subjects underwent the following: Visual Acuity, Contrast Sensitivity, Perimetry and Color Vision. All subjects completed a low vision questionnaire which examines perceived visual ability (PVA). To detect early retinal changes in patients with SMD the full field and bright flash rod ERG (ISCEV standards plus bright flash [244 cd.s/ m²] scotopic responses were recorded), kinetic ERG (Rod Dark Adaptation Kinetics at 30 and 50% bleach), and the multifocal ERG (mfERG, average central: 15⁰ P₁ implicit time and P₁ amplitude) were performed. Results: Interim results show that the mfERG was a more sensitive indicator of retinal dysfunction with abnormal findings in 95% of patients with SMD (mean Amp and IT for SMD and controls: 8.81 nV and 31.7 msec, and 38.64 nV and 28.3 msec, respectively) when compared with the bright flash rod ERG, which was abnormal in only in 35% of SMD patients (mean Amp and IT in SMD and controls: 139.41µV and 5 msec and 197.9µV and 4.8 msec, respectively). Subjects with SMD exhibited delayed rod dark adaptation following 30% bleach (mean=13.5min) when compared with age–matched controls (mean=6min) (p<0.05). The questionnaire was sensitive in measuring PVA in patients with SMD (mean=0.49logits) when compared with controls (mean=2.4logits) (p<0.001). Conclusions: In patients with SMD mfERG, kinetic ERG and VA LV VFQ–48 are useful in measuring localized retinal dysfunction, rod–dark adaptation, and PVA respectively. Addition of these tests in routine clinical testing may aid in the early diagnosis and management of SMD.

Keywords: electroretinography: clinical • degenerations/dystrophies • quality of life