OCULAR MANIFESTATIONS OF DIABETES-MELLITUS - DIABETIC CATARACTS IN DOGS

Ocular manifestations of diabetes mellitus commonly occur in the dog. Increased aqueous humor glucose concentration causes cataract formatio n and corneal endothelial cell loss. Prolonged hyperglycemia, even if only intermittent, causes retinal vascular damage acid results in a se quence of retinal changes termed diabetic retinopathy. In humans, loss of vision may result from diabetic retinopathy occurring over the cou rse of many years. Retinopathic changes in dogs, by comparison, are mi nor and limited to formation of microaneurysms due to loss of pericyte s from retinal capillary walls, along with some other morphologic chan ges in the retinal veins.(30) (See Munana, this issue.) Pathologic cha nges documented in the corneal endothelial cells of diabetic dogs incl ude cellular polymegathism (variation in cell size) and pleomorphism ( decrease in percentage of normal hexagonal cells) as a result of cell loss.(31) These changes are detectable with a slit lamp and, although not clinically noticeable, might theoretically contribute to corneal e dema after cataract surgery, By far the most common ocular manifestati on of diabetes in the dog is cataract formation. The incidence of cata racts in diabetic dogs is very high, in one survey 38 of 56 dogs (68%) diagnosed with diabetes mellitus had cataracts.(29) The majority of d iabetic dogs will develop cataracts, and many will progress rapidly to ward blindness. Surgical removal of the cataract by phacoemulsificatio n offers the best chance of vision restoration. Ocular signs of hyperg lycemia are rare in cats, although early cataract formation occasional ly is detected.(22)