The KARNS was a randomized clinical trial designed to compare the effectiveness of argon and krypton laser photocoagulation in causing the regression of preexisting neovascularization on the disc (NVD) in diabetic retinopathy. The main theoretical advantage for the krypton laser in the treatment of diabetic retinopathy is that the red laser beam penetrates blood and may be more effective in making burns in the pigment epithelium in eyes with vitreous hemorrhage.