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DIABETIC & ISCHEMIC MACULAR EDEMA TREATMENT OPTIONS Vitreoretinal News for the Medical Community
Thickening of the central macula occurs from leakage of serum products from microaneurysms and dilated capillaries. Diabetic retinopathy, branch and central retinal vein occlusions, and less common diseases such as radiation retinopathy may benefit from judicious retinal laser applications. Clinically significant diabetic macular edema is present when lipid and/or retinal thickening is within 500µ of the fovea, or edema equal to one disc diameter is within one disc diameter of the fovea. Several well designed studies have demonstrated that focal and/or grid macular laser treatment is effective in stabilyzing central vision. Focal treatment applied directly to the microaneurysms and grid treatment to areas of diffuse leakage may eliminate lipid exudates from settling into the fovea. Once lipid has consolidated it is very unlikely that vision will improve. Capillary nonperfusion may complicate diabetic retinopathy causing severe visual loss sometimes out of proportion to the clinical appearance of the fundus. Patients with both diabetes and poorly controlled systolic hypertension appear to be at a much greater risk for macular ischemia. Patients with Type I diabetes mellitus have the greatest visual morbidity. A circinate lipid ring will usually surround an actively leaking microaneurysm. This occurs as fluid is reabsorbed leaving the lipid behind. Focal laser treatment is applied to discreet microaneurysms. Sufficient energy to cause a whitening or darkening of the aneurysm will produce occlusion. Particularly succulent lesions will "frost" after laser treatment. The edema will rapidly reabsorb but the lipid may take months to clear. Diffuse macular edema and leakage caused by capillary ischemia are best treated with a grid pattern. Very light laser spots, almost unperceptible, are applied to the areas of fluorescein leakage. Any focal lesions are treated directly with appropriate energy. Focal treatment may consist of relatively few laser spots whereas it is not unusual for grid laser treatment to require 100 -200 spots. The foveal avascular zone is avoided and any microaneurysms along the edge are treated in those patients with severe leakage. Fluorescein angiography is repeated in 6 - 12 weeks to determine if the goals of treatment were met. Argon green or yellow are the wavelengths of choice. Hemoglobin is not absorbed by red wavelengths and blue-green may damage the macula because of xanthophil absorption. |
