Glycosylated Hemoglobin and the Risk of Retinopathy in Insulin-Dependent Diabetes Mellitus

To the Editor: Since we found evidence of a threshold for the effect of hyperglycemia on the risk of microalbuminuria in patients with insulin-dependent diabetes mellitus (IDDM),1 we used published data to examine whether there was a similar pattern for diabetic retinopathy. In the Diabetes Control and Complications Trial (DCCT),2 the incidence of the development or progression of retinopathy in the group assigned to intensive treatment fluctuated around 2.0 per 100 person-years in the nine deciles of the hemoglobin A1c distribution below 8.5 percent and rose to 7.0 per 100 person-years in the highest decile, consistent with a threshold . . .