Extinguished ERGs And Retinal Function In Usher Syndrome

Abstract

Purpose: : Patients suffering from Usher Syndrome, a genetic disorder, which impairs auditory, vestibular and visual senses, often have an extinguished electroretinogram (ERG). Our aim in this study was to ascertain what other measures can still detect retinal function in such patients. The existence of preserved function is of importance when selecting patients for initial testing of future therapies for retinal degenerations.

Methods: : From a cohort of 61 Usher patients examined, 49 had prima vista "non-recordable" scotopic (0.001 cd/m2) and photopic (3 cd/m2) ERGs and were used for further analyses. They were aged between 12 and 59 years (mean 36.98+/-12.4); 10 were Usher type 1, 39 were Usher type 2. Kinetic visual fields were measured with the Goldmann III4e marker and the preserved area calculated. ERG responses to 31Hz flicker (3 cd/m2) were recorded and the response Fourier analyzed, furthermore, multifocal ERGs (mfERG) were recorded (100cd/m2) and peak amplitudes and latencies of P1 for the central element (0.4deg diameter) were used for analysis. Finally, spectral domain OCT imaging was performed and the foveal thickness calculated.

Results: : Preserved areas of visual field could be measured in 96 eyes (median visual field: 471 deg2). Of the 98 eyes with extinguished ERGs 23 eyes (23.5%) showed a significant response to 31Hz flicker. The central mfERG response showed remaining function in over 50% of eyes (mean centre amplitude, 16.7 μV). The median foveal retinal thickness was 219 μm. We found a significant correlation between 31 Hz flicker responses and foveal thickness (p=0.03). Furthermore, there was also a strong correlation between foveal thickness and the amplitude of response to the central mfERG element (p=0.01).

Conclusions: : We investigated a large cohort of Usher patients with extinguished Ganzfeld ERG responses. Despite advanced retinal disease, remaining cone function could still be detected and correlated well with the preserved retinal structure. OCT imaging along with kinetic visual field measurement and mfERGs are sensitive methods for recording remaining visual function.

Keywords: retinal degenerations: hereditary • electroretinography: clinical • clinical research methodology