Petersen L, et al. – This trial inspected the extent to which the post–hypoxic recovery of the diameter of retinal arterioles depended on nitric oxide (NO) and cyclo–oxygenase (COX) products in normal persons and in diabetic patients. The data reported that it depended on NO and COX products. It appeared to be impaired in diabetic patients, prior to the development of retinopathy. This disturbance could lead to the development of diabetic retinopathy. Its treatment and prevention aspects warranted additional research.