Retinal branch vein occlusion (BVO) is the second most common retinal vascular disease after diabetic retinopathy. Many treatments for this disorder were attempted before 1977, but none were proven to be effective. The only treatment that seemed at all promising in preventing visual loss from BVO was laser photocoagulation.

Approximately 500 patients were enrolled in the study. One-half were randomly assigned to treatment with argon laser photocoagulation; the other one-half remained untreated as controls. For BVO with or without neovascularization, scatter treatment of 100 to 400 laser burns was applied in the drainage area of the occluded vein site, avoiding the fovea and optic disc. Individual laser burns were 200 to 500 microns in diameter with an exposure time of 0.1 to 0.2 seconds. For macular edema, burns of 50 to 100 microns in diameter with exposure time of 0.05 to 0.1 seconds were used. A fluorescein angiogram less than 1 month old had to have been available for each patient. Treatment was performed under topical anesthesia using the argon laser to achieve a grid pattern over the area of capillary leakage identified by fluorescein in the macular region. Photocoagulation was extended no closer to the fovea than the edge of the foveal avascular zone and did not extend peripherally beyond the major vascular arcade. The efficacy of treatment was judged on the basis of visual acuity measurements as well as assessment of the subsequent development of neovascularization and/or vitreous hemorrhage. Patients were followed for at least 3 years.