Page 1293 - Problem-Based Feline Medicine

62 – THE CAT WITH ABNORMAL PUPIL SIZE, SHAPE OR RESPONSE 1285

Clinical signs Taurine deficiency is regarded as being the primary fac-
tor leading to photoreceptor degeneration.
Acute onset of bilaterally dilated pupils that are non-
responsive to light. The syndromes feline central retinal degeneration
(FCRD) and taurine deficiency retinopathy are re-
Acute onset of vision loss.
garded by many authors as being the same disease. The
There is a history of recent use of a fluoroquinolone, disease is still occasionally seen in cats which appear
especially at higher than recommended dose rate. to have adequate levels of dietary taurine, but the
Blindness may also occur at the recommended dose, overall incidence of the disease throughout the world
and appears to be an idiosyncratic reaction to the drug. appears to have declined as the taurine content of com-
● Anecdotal personal communication suggests that mercial diets has been increased.
the problem is seen frequently when Enrofloxacin
Taurine deficiency also causes dilated cardiomyopa-
is given at a daily dose rate of 20 mg/kg (the stan-
thy. See main references on page 151 for details (The
dard recommended dose rate is 5 mg/kg q 24 h).
Cat With Abnormal Heart Sounds and/or an Enlarged
The retina has a normal appearance on fundoscopy. Heart).

Diagnosis Clinical signs
Diagnosis is based on the acute onset of the clinical Vision loss occurs in the later stages of the disease,
signs and the history of recent use of a fluoro- and is associated with a poor pupil light reflex.
quinolone, especially at a higher than recommended Characteristic retinal lesions are evident on fundo-
dose. scopy.
● Focal degeneration occurs in the area centralis at
Prognosis first. The area centralis at first develops a granular
appearance, then becomes hyper-reflective.
Prognosis for vision is usually guarded, but may be ● A second hyper-reflective lesion then develops
improved if the toxicity is recognized in the early nasal to the optic disc, which eventually coalesces
stages and the drug withdrawn immediately. with the area centralis lesion to form a broad hyper-
reflective band dorsal to the optic disc.
TAURINE DEFICIENCY ● Finally, generalized retinal degeneration devel-
RETINOPATHY* ops, with generalized tapetal hyper-reflectivity and
retinal vessel attenuation.
FELINE CENTRAL RETINAL
DEGENERATION (FCRD) Diagnosis
Diagnosis is based on clinical signs, in particular obser-
Classical signs vation of the typical retinal lesions.
● Vision loss in advanced cases. Electroretinography (ERG) can be performed to identify
● Typical ophthalmoscopic signs starting in altered photoreceptor function. Cones appear to be
the area centralis progressing to involve affected more than rods, so these cats will have
the whole of the retina. reduced b waves in photopic (light) conditions and bet-
● History of inadequate diet. ter responses in scotopic (dark-adapted) conditions.

Pathogenesis Treatment
The disease occurs in cats fed an inadequate diet, Administer taurine supplementation. A minimum
especially cats fed commercial dog foods, or a diet high intake of 110 mg/kg body weight per day is needed
in plant fiber. for maintenance of normal retinal function.