- Umesh Masharani, MB, BS, MRCP(UK)
1. Diabetic cataracts - Premature cataracts occur in diabetic patients and seem to correlate with both the duration of diabetes and the severity of chronic hyperglycemia. Nonenzymatic glycosylation of lens protein is twice as high in diabetic patients as in age-matched nondiabetic persons and may contribute to the premature occurrence of cataracts.
2. Diabetic retinopathy - Three main categories exist: background, or "simple," retinopathy, consisting of microaneurysms, hemorrhages, exudates, and retinal edema; preproliferative retinopathy with arteriolar ischemia manifested as cotton-wool spots (small infarcted areas of retina); and proliferative, or "malignant," retinopathy, consisting of newly formed vessels. Proliferative retinopathy is a leading cause of blindness in the United States, particularly since it increases the risk of retinal detachment.
Vision-threatening retinopathy virtually never appears in type 1 patients in the first 3-5 years of diabetes or before puberty. Up to 20% of patients with type 2 diabetes have retinopathy at the time of diagnosis. Annual consultation with an ophthalmologist should be arranged for patients who have had type 1 diabetes for more than 3-5 years and for all patients with type 2 diabetes, because many were probably diabetic for an extensive period of time before diagnosis.
Patients with any macular edema, severe nonproliferative retinopathy, or any proliferative retinopathy require the care of an ophthalmologist. Extensive "scatter" xenon or argon photocoagulation and focal treatment of new vessels reduce severe visual loss in those cases in which proliferative retinopathy is associated with recent vitreous hemorrhages or in which extensive new vessels are located on or near the optic disk.
Macular edema, which is more common than proliferative retinopathy in patients with type 2 diabetes (up to 20% prevalence), has a guarded prognosis, but it has also responded to scatter therapy with improvement in visual acuity if detected early.
Avoiding tobacco use and correction of associated hypertension are important therapeutic measures in the management of diabetic retinopathy. There is no contraindication to using aspirin in patients with proliferative retinopathy.
3. Glaucoma - Glaucoma occurs in approximately 6% of persons with diabetes. It is responsive to the usual therapy for open-angle disease. Neovascularization of the iris in diabetics can predispose to closed-angle glaucoma, but this is relatively uncommon except after cataract extraction, when growth of new vessels has been known to progress rapidly, involving the angle of the iris and obstructing outflow.