Page 1282 - Problem-Based Feline Medicine

1274 PART 15 CAT WITH EYE PROBLEMS

Pathogenesis Classical signs—Cont’d

Diabetic cataract forms because the lens is bathed in a ● Cloudy vitreous with red areas of
solution that is very high in glucose. The lens cells can- hemorrhage.
not metabolize the excess glucose by normal anaerobic
glycolysis, and therefore uses aerobic glycolysis using See the main reference on page 1171 (The Blind Cat or
the sorbitol pathway and the enzyme aldose reductase Cat With Retinal Disease).
as the catalyst. The by-product of this process is sugar
alcohol (sorbitol), which kills the cell. The sugar alco- Pathogenesis
hol is a large molecule that cannot escape through the
cell wall, and results in a more concentrated intracellular Hypertension causes vasoconstriction of pre-capil-
fluid than the surrounding fluid. Water is therefore lary retinal arterioles. Hypoxia of the arteriole causes
imbibed into the cell, which causes it to swell and rup- smooth muscle necrosis, which leads to vascular dilata-
ture. This in turn causes an immune reaction within the tion, and leakage of serum and blood.
eye called lens-induced uveitis.
Leakage from vessels causes serous retinal detach-
Diabetic cataracts are rare in cats. This is thought to be ment, and subretinal, intraretinal or preretinal hemor-
due to low levels of the enzyme aldose reductase in rhage.
old cats, which prevents the lens cells from using the
Retinal blood vessels may rupture, causing hemor-
sorbitol pathway to the same degree as other animals.
rhage into the vitreous.
Hypertensive retinopathy occurs most commonly sec-
Clinical signs
ondary to chronic renal disease and hyperthyroidism.
Cloudy lens and poor vision in a cat with diabetes
mellitus.
Clinical signs
Classical signs are acute onset of vision loss in an
Diagnosis
old cat, which is usually bilateral. The cat suddenly
A tentative diagnosis is based on the signs of a cloudy starts to bump into things, appears to be lost, and has
lens consistent with an immature to mature cataract in very cautious movements.
a cat with diabetes mellitus.
The pupils are usually dilated, and non-responsive or
poorly responsive light.
Treatment
Affected eyes appear slightly cloudy, and there may
Cataract surgery can be done successfully by a trained be focal red areas visible through the pupil, as a result
ophthalmologist. of retinal hemorrhage. The vitreous may appear red.
Early cases may show hemorrhage along the larger reti-
DISEASES CAUSING A CLOUDY nal blood vessels.
VITREOUS It is difficult to visualize the retina on fundoscopic
examination, as it appears out of focus. This is caused
CLOUDY VITREOUS ASSOCIATED WITH by retinal detachment, with the retina ballooning into
SYSTEMIC HYPERTENSION*** the vitreous, and appears as a thin veil of pale tissue.
These cats may have cardiomegaly, and left ventricu-
Classical signs lar hypertrophy.
● Acute onset of vision loss in an old cat, There may be other signs suggestive of hypertension,
usually bilateral. for example, a bounding cardiac apex beat.
● Dilated pupils, non-responsive or poorly
responsive to light. Systolic arterial blood pressure is usually greater
than 160 mmHg.