Page 127 - Clinical Small Animal Internal Medicine

12 Diabetes Mellitus in Dogs and Cats 95

Hepatomegaly sorbitol occurs more rapidly than its degradation into
VetBooks.ir Insulin promotes storage of lipid in adipose tissue. Relative fructose. In the diabetic eye, a large amount of sor bitol is
produced and acts as an osmotic agent within the lens fib-
or absolute lack of insulin promotes lipid catabolism into
fatty acids, which are transported to the liver. The liver ers, drawing water into the lens, leading to lens swelling,
lens fiber collapse, and ultimately cataract formation.
uses this excess of fatty acids to produce and store triglyc- Lens‐induced uveitis is common in diabetic dogs due
erides (lipids), leading to hepatic lipidosis and hepatomeg- to the rapid onset of the cataracts. Lens‐induced uveitis
aly. In the diabetic liver, excess fatty acids are also used for occurs when the lens becomes swollen and the stretched
gluconeogenesis, which worsens hyperglycemia, and are lens capsule allows leakage of cataract lens proteins into
converted into ketone bodies, which cause ketoacidosis.
the anterior and posterior chambers. This, in turn,
causes iris and ciliary body vasculitis, resulting in serum
Cataracts protein leakage into the aqueous humor and prostaglan-
din release from the iris, which continue the uveitis.
The pathogenesis of cataracts in diabetics is multifac torial Diabetic cataracts are found in 80% of diabetic dogs
and incompletely understood. The enzyme aldose reduc- within 16 months (Figure 12.1). Diabetic cats are rarely
tase catalyzes the conversion of glucose to sorbitol, and clinical for cataracts, though recent studies suggest that
the enzyme sorbitol dehydrogenase catalyzes the conver- mild diabetes‐associated lens opacity is more common
sion of sorbitol to fructose. In the eye, the formation of than previously thought. Topical administration of

(a) (b)

(c)

Figure 12.1 Diabetic cataracts in a dog. (a) An 11‐year‐old cross‐bred dog photographed shortly after diagnosis of diabetes mellitus.
(b) The same dog three months later. Diabetic cataracts had developed rapidly and the owners reported sudden vision loss. (c) The same
dog following phacoemulsification surgery to remove the cataract from the right eye. Source: Fleeman and Rand 2000. Reproduced with
permission.