Abstract
Purpose:
A breeding colony of cats with a previously undescribed autosomal recessive retinal degeneration affecting the area centralis (AC) and the visual streak (VS) was established. The AC and VS are central regions of high photoreceptor density. The AC is the feline equivalent of the human macula. The purpose of this study was to investigate the phenotype of this new feline model for macular degeneration.
Methods:
Animals from the colony (affected and unaffected littermates) were followed over time by fundoscopy, spectral-domain optical coherence tomography (SD-OCT) and electroretinography (ERG).
Results:
Initial changes in the AC and VS were apparent from as early as 5 months of age. On SD-OCT there was a loss of definition of the external limiting membrane, photoreceptor inner segment ellipsoid and photoreceptor outer segment-retinal pigment epithelium (RPE) bands. On fundus imaging, there was tapetal hyporeflectivity and increasing autofluorescence affecting the AC and extending along the VS. With progression, the outer nuclear layer (ONL) progressively thinned in the center of the AC. The ONL thinning was accompanied by reduced autofluorescence of the center of the AC but this was still surrounded by a ring of increased autofluorescence. Concurrently, ophthalmoscopy showed the presence of tapetal hyperreflectivity in the center of the AC; an ophthalmoscopic indication of retinal thinning. Retinal regions outside of the AC and VS appeared to be unaffected. ERG revealed that with disease progression a significant decrease in the cone mediated a-wave developed whereas rod-mediated responses were maintained.
Conclusions:
This unique autososomal recessive feline retinopathy shows similarities to human macular degenerations with autofluorescence changes similar to those described in Stargardt disease patients. Initial changes in the photoreceptor inner/outer segment region on SD-OCT were followed by a marked degeneration of the photoreceptors within the regions of highest photoreceptor density. This represents a new and potentially valuable large animal model of macular degeneration.