Page 1193 - Problem-Based Feline Medicine

57 – THE BLIND CAT OR CAT WITH RETINAL DISEASE 1185

Fundoscopy may show a bulging of the retina, and ketamine hydrochloride, has also been associated with
some pigment change such as a brownish appear- this syndrome.
ance. Retinal detachment may occur as the neoplasia ● Ketamine also increases cerebral oxygen demand,
extends through the choroid into the intra-retinal space. and the visual cortex is the most sensitive area
of the brain to hypoxia. Hypotension associated
The most common metastatic neoplasia in the eye
with acepromazine especially intravenous adminis-
include lymphosarcoma, and adenocarcinoma from
tration, and high doses of isoflurane, or other anes-
lung, uterus and undetermined origin.
thetic agents, and mask delivery of anesthetic
agents all exacerbate the hypoxia. Hypoxia of the
Diagnosis visual cortex can result in cortical blindness follow-
ing anesthesia.
An initial tentative diagnosis is based on the most
common presentation of iris swelling, distortion of the Pupils become dilated and unresponsive to light.
retina and signs of uveitis.
Pathology is characterized by photoreceptor and outer
Fine-needle biopsies may help to obtain a diagnosis. nuclear layer degeneration.
Chest and abdominal radiology should be done to
Diagnosis
find primary adenocarcinomas.
A tentative diagnosis is based on clinical signs and
Examination of the buffy coat for abnormal lympho-
history of either:
cytes can be done in cases with lymphosarcoma.
● Sudden blindness after administration of methylni-
Fine-needle biopsies of enlarged lymph nodes may trosourea and ketamine.
be diagnostic. ● Sudden blindness after administration of enro-
floxacin, especially at a higher dose (20 mg/kg q 24
h) than the recommended rate of 5 mg/kg q 24 h.
TOXIC RETINAL DEGENERATION

Classical signs LIPEMIA RETINALIS
● Rapid loss of vision within 5 days with
Classical signs
dilated pupils.
● History of administration of ● Retinal blood vessels appear enlarged, and
methylnitrosurea in combination with may have a yellow to orange hue.
ketamine hydrochloride. ● Rare in cats.
● High doses of fluoroquinalones,
particularly enrofloxacin, may cause See main reference on page 569 (The Cat With Hyper-
blindness in cats. lipidemia).

Clinical signs
Clinical signs Cats do not show visual impairment with lipemia
retinalis, so this condition is usually seen as an inci-
There are few cases reported of toxic retinal degener-
dental finding.
ation in the cat.
Ophthalmosopic examination reveals enlarged retinal
There is rapid loss of vision over approximately
blood vessels, which have a yellow to orange col-
5 days, usually in cats that have been administered spe-
oration. There may be some haziness surrounding the
cific drugs. This syndrome is associated with high
major vessels from lipid leakage, and this may cause
doses of fluoroquinalones, particularly enrofloxacin,
a local inflammation.
although it has also occurred as an idiosyncratic reac-
tion in cats given less than the recommended dose of Lipemia retinalis is seen in cats that have increased
5 mg/kg q 24 h. Methylnitrosurea, in combination with fasting triglycerides, which is most commonly