Abnormal dark-adapted ERG in cats heterozygous for a recessively inherited rod-cone degeneration

Purpose To study retinal function in cats homozygous and heterozygous for a recessively inherited rod-cone degeneration. Methods Dark-adapted electroretinograms (ERGs) were performed on early affected, heterozygous (ophthalmoscopically normal), and clinically normal, nonrelated cats. Responses to blue stimuli over a 3.9-log unit range were recorded. Results Lower b-wave amplitudes than normal were observed in heterozygotes and early affected cats. The amplitudes of the heterozygotes took an intermediate position between normal and early affected cats. Normalized amplitude/intensity data suggest a normal dynamic range in carriers. B-wave implicit times in carriers were comparable to those of normal cats. Conclusions These results show that heterozygotes have an altered retinal function, although they are ophthalmoscopically normal. It is difficult to electrophysiologically differentiate heterozygotes from affected cats with the very early stage of retinal degeneration.