To determine whether photocoagulation helps prevent severe visual loss from proliferative diabetic retinopathy.

To determine whether a difference exists in the efficacy and safety of argon versus xenon photocoagulation for proliferative diabetic retinopathy.

By the 1950s, diabetic retinopathy had become a leading cause of blindness and visual disability in the United States. The use of photocoagulation to treat proliferative retinopathy gained widespread use in ophthalmic practice following its introduction in 1959. However, only a few studies of photocoagulation incorporated any of the basic principles of controlled clinical trials, and these involved inadequate numbers of patients. Consequently, there has been inadequate evidence of the actual value of the procedure. Because of the clinical importance of diabetic retinopathy and the increasing use of photocoagulation in its management, the Diabetic Retinopathy Study (DRS) was begun in 1971. This randomized, controlled clinical trial involved more than 1,700 patients enrolled at 15 medical centers.

One eye of each patient was randomly assigned to immediate photocoagulation and the other to followup without treatment, regardless of the course followed by either eye. The eye chosen for photocoagulation was randomly assigned to either of two treatment techniques, one using an argon laser and the other a xenon arc photocoagulator. Patients were followed at 4-month intervals according to a protocol that provided for measurement of best corrected visual acuity.

Treatment was usually completed in one or two sittings and included scatter (panretinal) photocoagulation extending to or beyond the vortex vein ampulae. The argon treatment technique specified 800 to 1,600, 500-micron scatter burns of 0.1 second duration and direct treatment of new vessels whether on or within one disc diameter of the optic disc (NVD) or outside this area (NVE). Focal treatment was also applied to microaneurysms or other lesions thought to be causing macular edema. Followup treatment was applied as needed at 4-month intervals. The xenon technique was similar, but scatter burns were fewer in number, generally of longer duration, and stronger, and direct treatment was applied only to NVE on the surface of the retina.

Patients were eligible if they had best corrected visual acuity of 20/100 or better in each eye and the presence of proliferative diabetic retinopathy in at least one eye or severe nonproliferative retinopathy in both eyes. They could not have had prior treatment with photocoagulation or pituitary ablation, and both eyes had to be suitable for photocoagulation. All eligible patients were younger than 70 years, and the examining physician assessed the outlook for survival and availability for 5 years of followup to be good.