Diabetic retinopathy is the most common and one of the most serious manifestations of diabetes mellitus. It can result in severe visual impairment due to complications including macular edema, macular ischemia, traction detachment of the macula and neovascular glaucoma. Two stages are recognized: nonproliferative retinopathy (NPDR) and the more advanced proliferative stage (PDR).
Mild NPDR is characterized by the presence of microaneurysms, retinal edema and hard exudates. The Early Treatment Diabetic Retinopathy Study (ETDRS) coined the term “clinically significant macular edema” (CSME) to describe when edema or hard exudates were likely to threaten the most visually important part of the central retina, called the fovea.
More severe NPDR presents with the additional features of cotton-wool spots, IRMAs and venous beading. PDR is said to develop with the formation of new blood vessels on the optic disc or elsewhere on the retina. These new vessels are abnormally prone to bleeding and can result in vitreous and preretinal hemorrhages. Advanced PDR is associated with recurrent vitreous hemorrhage, retinal detachment, neovascular glaucoma and a serious threat of vision loss progressing to blindness.
Treatment of diabetic retinopathy involves careful monitoring of all diabetics for signs of NPDR and PDR. This monitoring is performed annually for diabetics who have never had any sign of retinopathy, and is more frequent for those with signs of retinopathy, based on the severity of their disease. An examination of the retina is usually conducted 10 to 15 minutes after drops that dilate the pupils are given, allowing for a better view of the retina. Fundus photography is often performed to document clinical observations and to allow for future review of examination findings that leads to an understanding of the rapidity of progression of the disease.
Medical treatment of diabetes influences the development of diabetic retinopathy and its progression. Good metabolic control helps to prevent retinopathy and slows progression of the disease. Monitoring of the hemoglobin A1C level is useful in understanding the degree of control of blood sugar regulation, and is advised. NPDR usually requires no treatment if CSME does not exist. CSME, if present, can be treated with injections of medication referred to as VEGF inhibitors, which are made directly into the posterior segment of the eye, and with laser photocoagulation. The VEGF inhibitors used include Avastin and Lucentis, and a variety of steroids can also be injected therapeutically. Photocoagulation is commonly performed with lasers emitting light in the green wave band. This treatment technique involves directly aiming the laser beam at bleeding vessels (focal treatment) or creating a grid pattern in the central retina.
PDR is also treated with a combination of medication injected directly into the posterior segment of the eye and laser photocoagulation. VEGF inhibitors act powerfully on neovascular blood vessels, resulting in their regression. Scatter (pan-retinal) photocoagulation is used for PDR and was proven effective by the landmark Diabetic Retinopathy Study. The treatment technique consists of the creation of 1,200 to 1,600 burn spots on the midperipheral and peripheral portions of the retina. Regression of neovascularization is usually apparent within weeks of the laser treatment. Additional scatter treatments are sometimes performed if the regression is initially incomplete. The complications of photocoagulation are generally mild and include a decrease in light sensitivity, contraction of the peripheral visual field and blurred reading vision. More severe complications sometimes follow intense treatments.
There are several surgical options for complications of diabetic retinopathy, which include cataract removal, vitrectomy, retinal membrane peeling, scleral buckle and other techniques for repair of retinal detachment, and tube shunts for treatment of neovascular glaucoma. The surgeries are chosen based on the complications that have arisen. Vitreous hemorrhage accompanying proliferative retinopathy may obstruct vision and necessitate the removal of blood with a vitrectomy. The Diabetic Retinopathy Vitrectomy Study showed the value of vitrectomy in severe proliferative disease and the benefit of early vitrectomy in type I diabetics.
Diabetic retinopathy poses a major threat of blindness to patients with diabetes mellitus. With early detection of retinopathy and proper control of the disease, blindness is preventable in most cases. All diabetes patients should have an annual comprehensive eye examination. If retinopathy is seen, then more frequent examination by an ophthalmologist is indicated in order to initiate specialized care, such as photocoagulation, injection of VEGF inhibitors or surgery.