Early-Onset Progressive Degeneration of the Area Centralis in RPE65-Deficient Dogs

Retinal epithelium-specific protein 65 kDa (RPE65)-deficient dogs are a valuable large animal model species that have been used to refine gene augmentation therapy for Leber congenital amaurosis type-2 (LCA2). Previous studies have suggested that retinal degeneration in the dog model is slower than that observed in humans. However, the area centralis of the dog retina is a cone and rod photoreceptor rich region comparable to the human macula, and the effect of RPE65 deficiency specifically on this retinal region, important for high acuity vision, has not previously been reported. Spectral-domain optical coherence tomography, fundus photography, and immunohistochemistry of retinal wholemounts and sagittal frozen sections were used to define the time-course and cell-types affected in degeneration of the area centralis in affected dogs. Area centralis photoreceptor degeneration was evident from 6 weeks of age, and progressed to involve the inner retina. Immunohistochemistry showed that RPE65-deficient dogs developed early loss of S-cone outer segments, with slower loss of L/M-cone outer segments and rods. Early-onset severe photoreceptor degeneration in the area centralis of dogs with RPE65-deficiency offers a model of the early foveal/perifoveal degeneration in some patients with LCA2. This model could be used to refine interventions aiming to improve function and halt the progression of foveal/perifoveal photoreceptor degeneration.