<qa>  What is the maximum number of laser treatments?Participants will be randomly assigned to take 1600 IU of vitamin E or placebo an inactive, look-alike pill daily. After taking the pills for 3 months or more, patients who require laser treatment will be randomly assigned to one of the two laser therapies. Patients with macular edema in both eyes will receive both treatments, one in each eye. For these procedures, eye drops are put in the eye to numb the surface and a contact lens is placed on the eye during the laser beam application. Several visits may be required for additional laser treatments. The maximum number of treatments depends on how well they are working. Patients will return for follow-up visits 1, 3, and 6 months after the first treatment, and then every 6 months until either the patient returns for a 3-year visit; the last enrolled patient returns for the 1-year visit; or the patient requests to leave the study. During the follow-up visits, patients response to treatment will be evaluated with repeat tests of several of the screening exams. 