Turning to larger clinical trials, the Protein Kinase C β Inhibitor Diabetic Retinopathy Study (PKC-DRS) multicenter randomized clinical trial tested the effect of 32 mg/day RBX vs. placebo in 252 patients with nonproliferative diabetic retinopathy, and found that while RBX was well tolerated without significant adverse effects, RBX treatment had no effect on the primary endpoint of progression to proliferative DR; however, RBX treatment did show a clinical benefit in delaying time to occurrence of moderate vision loss (150). This evidence concerns the gene PRRT2 and non-proliferative diabetic retinopathy.