Objective—To develop a method to electrophysiologically
differentiate heterozygous-carrier Abyssiniancrossbred
cats from homozygous-affected Abyssiniancrossbred
cats before clinical onset of inherited rodcone
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
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)