In the KARNS, patients with diabetic retinopathy and NVD of one-third disc area or greater in extent were assigned at random to either argon or krypton laser scatter photocoagulation (panretinal photocoagulation). The null hypothesis was that each treatment would result in a similar proportion of eyes having regression of the NVD by 3 months. The KARNS pilot study affirmed the benefits of argon laser photocoagulation in the treatment of proliferative diabetic retinopathy, as demonstrated in the NEI-supported Diabetic Retinopathy Study conducted a decade ago. (See publication list.) The KARNS study sought to determine whether use of the krypton laser could be as effective as the argon laser in causing regression of diabetic neovascularization, but with fewer side effects (such as smaller loss of central visual acuity).