An epidemiologic approach to the study of retinopathy: the Pittsburgh diabetic morbidity and retinopathy studies.

Diabetic retinopathy was studied in two cohorts of insulin-dependent diabetics (IDDs) from the Children's Hospital of Pittsburgh. The first cohort (n = 696) consisted of IDDs of long duration. Severe retinopathy was self-reported in 70% of this cohort by 30 years duration of diabetes. Associations between severe retinopathy, hypertension and smoking were observed. In order to examine the relationship between metabolic control and early diabetic retinopathy, a second cohort of adolescent IDDs (n = 58) were referred for standardized fluorescein angiography. Sixty-four percent had early retinopathy. None had proliferative changes. Significant differences in individual mean whole blood glycosylated hemoglobin (GHb), averaged over 3 years before angiography, were consistently seen between those with and without early retinopathy. Also, the number of microaneurysms was positively correlated with individual mean GHb. Before the advent of GHb testing, those IDDs who later had retinopathy were more likely to have experienced at least one hospitalization for diabetic ketoacidosis. These observations provide strong support that poor metabolic control preceded the development of diabetic retinopathy. Results are consistent with the hypothesis that improvement of metabolic control early in the course of IDDM may prevent or delay the development of the early changes of diabetic retinopathy.