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)
Objective—To characterize lysosomal storage body
accumulation in the retina and brain of Tibetan Terriers
with ceroid-lipofuscinosis and determine whether the
disease in these dogs is accompanied by impaired
retinal function and retinal degeneration.
Animals—Three 7- to 10-year-old Tibetan Terriers with
ceroid-lipofuscinosis and 1 healthy 5-year-old Tibetan
Procedure—Owners completed a questionnaire to
identify behavioral and physical signs indicative of
ceroid-lipofuscinosis. Neurologic, behavioral, and
ophthalmologic evaluations, including full-field electroretinograms,
were performed on each dog.
Fluorescence, light, and electron microscopy were
performed on specimens of retina, cerebral cortex,
and cerebellum of all dogs postmortem.
Results—Behavioral assessments of the affected
dogs revealed moderate visual impairment in lowlight
conditions but good vision in bright light. On
funduscopic evaluation of these dogs, abnormalities
detected ranged from none to signs of moderately
advanced retinal degeneration. Compared with findings
in the control dog, electroretinography revealed
depressed rod cell function with some impairment
of cone cell function in the affected dogs.
Morphologically, disease-specific storage bodies
were detected in retinal Müller cells and neurons,
particularly in ganglion cells, and in cells of the cerebral
cortex and cerebellum in affected dogs.
Substantial photoreceptor cell loss and disruption of
photoreceptor outer segment morphology appeared
to develop late in the disease.
Conclusions and Clinical Relevance—The similarities
between ceroid-lipofuscinosis in Tibetan Terriers and
some forms of ceroid-lipofuscinosis in humans suggest
that the canine disease may have a genetic and
biochemical basis similar to that of one of the ceroidlipofuscinosis
disorders in humans. (Am J Vet Res 2005;66:67–76)
Objective—To characterize the effects of oral administration of a high dose of enrofloxacin to cats.
Animals—24 (12 male and 12 female) young healthy cats.
Procedures—Cats were allocated on the basis of sex into 2 groups (4 males and 4 females/ group) from which 3 subgroups for 3 durations (3, 5, or 7 days) of enrofloxacin (50 mg/kg, PO, q 24 h) or control solution (1 mL of water, PO, q 24 h) administration that began on day −1 were created. Funduscopic examinations were performed daily. Electroretinography (ERG) was performed before and every 2 to 3 days after the start of oral administration. Four cats/study group were euthanized on days 3, 5, and 7, and eyes were collected for light and electron microscopic evaluations.
Results—Neurologic, funduscopic, and ERG abnormalities were evident only in cats administered enrofloxacin. Funduscopic changes (granular appearance or graying of the area centralis) were noticed on or before day 3 (after only 3 days of enrofloxacin administration), with subsequent similar changes along the visual streak. Vascular attenuation (between days 2 and 4) and generalized tapetal hyperreflectivity (between days 5 and 7) followed. Reduction in b-wave ERG amplitude preceded funduscopic changes. Morphologic changes in the photoreceptor layers correlated with duration of enrofloxacin administration, with generalized degenerative changes evident after 3 doses.
Conclusions and Clinical Relevance—The study indicated that a high dose of enrofloxacin (50 mg/kg/d, PO) induced retinal and systemic changes. Enrofloxacin at 10 times the recommended dosage is acutely toxic to the outer retina of clinically normal cats.