Delivered by Dr. Anne Fulton at the International Symposium on Usher Syndrome.

Download the presentation slides here.

Abstract:
Purpose: To study phototransduction and post receptor retinal processes in pediatric patients with a genetic diagnosis of MYO7A and others with a USH2A. A cilium connects the photoreceptor outer segment (the site of phototransduction) to the more proximal portion of the photoreceptor which synapses with the second order retinal neurons.

Methods: ERG responses to full field stimuli were recorded from 22 patients (MYO7A, n= 9; USH2A, n=13) in scotopic and photopic conditions. We calculated the phototransduction parameters specifying sensitivity and saturated amplitude of the rod and cone photoreceptor response (a-wave) and also the post receptor response sensitivity and saturated amplitude parameters (b-wave) were calculated. The dark adapted visual thresholds were measured in all patients.

Results: Despite attenuated ERG responses, photoreceptor and post receptor parameters could be fully assessed in 11. As anticipated in a ciliopathy, the deficits in post-receptor sensitivity were greater than deficits in photoreceptor sensitivity. The saturated amplitude for outer segment activity was reduced, consistent with the short outer segment length seen on OCT imaging. The deficits in the saturated amplitude of outer segment activity and post-receptor activity were correlated and significantly associated with deficits in dark adapted visual sensitivity.

Conclusions: The activation of phototransdution, occurring in the photoreceptor outer segment is quite normal in those in whom it can be assessed. Deficits in post receptor retinal sensitivity, set proximal to the connecting cilium in the photoreceptor, is associated with visual deficits