Common Cares

Diabetic eyes -Cataract.

Introduction

Sight is one of basic senses affected by diabetes in the long term . There are various reasons for the loss of sight in diabetics ,some being retinopathy , cataracts and glaucoma. Most important among them is called diabetic retinopathy caused because of growth of new blood vessels in the retina .the diabetic cataract comes next in the list and finally the rarer glaucoma.

These diabetic cataracts seem to be indistinguishable from senile cataracts in the nondiabetic population, however their incidence seems to be increased and the age of onset decreased. The mechanisms leading to diabetic cataracts are thought to be multi-faceted.

• The polyol pathway, in the presence of raised glucose levels in diabetics, becomes particularly active in the lens of the eye, leading to increased concentrations of sorbitol and other polyols. This has two main effects: an increase in osmolality leading to an influx of water, and a reduction in glutathione levels in the lens (a chemical important in the proper structure and function of the lens).
• Glycosylation of the crystallins (proteins in the lens cells which give the lens its unique properties) also seems to be important in cataract formation.

Cataracts develop sooner in diabetic patients than in patients who do not have diabetes. In fact, fluctuating vision and rapid-onset myopia caused by shifts in the glucose, electrolyte, and water balance within the lens are early symptoms of diabetes. These metabolic imbalances predispose the lens to cataract formation.

Diabetic cataracts are considered to be caused by hyperglycemia associated with disturbed glucose metabolism. Diabetes mellitus often involves abnormal lipid metabolism in addition to abnormal glucose metabolism. To date, however, very few studies have counted hyperlipidemia as a risk factor for diabetic cataracts.

The present study was undertaken to determine whether this abnormal lipid metabolism is a risk factor for diabetic cataracts in rats.

• Cataracts were caused by streptozocin (STZ) administration in the ordinary diet or cholesterol rich diet fed rats.
• When rats with STZ (65 mg/kg)-induced diabetes mellitus were fed an ordinary diet, cataracts became evident at 9 weeks in 26.7% of animals, and increased to an incidence of 53.3% after 10 weeks of STZ treatment.
• However, in rats with STZ-induced diabetes mellitus that were fed a cholesterol rich diet to induce severe hyperlipidemia and low high density lipoprotein (HDL) cholesterol, cataracts were observed one week earlier, after 8 weeks of treatment, in 40.0% of animals, with an increase to a 53.3% incidence and an 86.7% incidence after 9 and 10 weeks of STZ treatment, respectively.
• Plasma glucose levels did not differ between the groups.

These results suggest that hyperlipidemia and low HDL cholesterol are associated with an earlier onset and an elevated incidence of diabetic cataracts. Researchers then investigated the relationship between plasma lipids and cataracts by STZ (45-85 mg/kg) administration. The onset of cataracts correlated positively with plasma total cholesterol, triglyceride, non-HDL cholesterol and glucose levels, and negatively with HDL cholesterol levels.

Hyperlipidemia and low HDL cholesterol levels may be risk factors for the onset of diabetic cataracts and that diabetic cataracts may be accelerated by hyperlipidemia and low HDL cholesterol in rats.

Diabetic retinopathy may also contribute to vision loss, and fundoscopic findings include dot-and-blot hemorrhages, microaneurysms, exudates, dilated and tortuous vessels, and neovascularization of the disk and retina. Cataracts often obscure the fundus, making assessment of diabetic retinopathy difficult.

The study of diabetic cataracts has led to the elucidation of the role of aldose reductase (AR) in the development of diabetic complications. AR is the enzyme involved in the formation of polyols, some of which (sorbitol and galactitol) are implicated in the development of diabetic complications.

The use of drugs, which inhibit aldose reductase, such as sorbinil, has led to improvement in some individuals with diabetes. Flavonoids, such as quercetin, are potent inhibitors of polyol accumulation which are, but still, to be widely studied before going to the market, at least officially.