Abstract
Objective—To develop a method to electrophysiologically differentiate heterozygous-carrier Abyssiniancrossbred cats from homozygous-affected Abyssiniancrossbred cats before clinical onset of inherited rodcone retinal degeneration.
Animals—14 back-crossed Abyssinian-crossbred cats of unknown genotype (homozygous or heterozygous) for inherited rod-cone retinal degeneration, 24 agematched mixed-breed control cats, 6 age-matched heterozygous Abyssinian-crossbred cats, and 6 homozygous Abyssinian cats.
Procedure—Electroretinography (ERG) of heterozygous and homozygous cats revealed differences, especially for scotopic recordings. Frequent ophthalmoscopy and ERG (2 to 5 times; at intervals of 3 to 6 months) of back-crossed cats were performed. Amplitudes and implicit times were analyzed by use of a graphic representation of results. Ratios for amplitudes of the b-waves to amplitudes of the awaves (b-wave:a-wave) were compared.
Results—8 back-crossed cats had decreased a-wave amplitudes, increased b-wave implicit times, and abnormal ERG waveforms. Values for the b-wave:awave for the highest scotopic light intensity were significantly higher for those same 8 cats.
Conclusions and Clinical Relevance—The 8 back-crossed Abyssinian-crossbred cats with abnormal results developed fundus changes over time consistent with disease. A graphic representation of ERG results can be used to differentiate between genotypes prior to funduscopic changes. Values for the b-wave:a-wave ratio provide confirmation. These ERG analyses may be applied clinically in the diagnosis of retinal degenerations in various species.
Impact for Human Medicine—Cats with hereditary rod-cone degeneration may be a useful model for comparative studies in relation to retinitis pigmentosa in humans. Similar evaluations of ERG results could possibly be used for humans with suspected generalized retinal degeneration. (Am J Vet Res 2005;66:1914–1921)
