Factors protective against retinopathy in insulin-dependent diabetics free of retinopathy for 30 years.

To investigate which factors might protect against the development of retinopathy 40 insulin-dependent diabetics who had remained free from retinopathy despite diabetes of long duration (mean+/-1 SD 30+/-10 years) were compared with 40 patients who had background and 47 who had proliferative retinopathy (mean durations of disease 16+/-5 and 19+/-5 years respectively). The three groups had had similar mean ages at onset of diabetes. The mean of all postprandial blood glucose measurements at hospital clinics from diagnosis of diabetes to detection of retinopathy, or to the most recent negative eye examination, was 9.9+/-2.1 mmol/l (178+/-38 mg/100 ml) in the group with no retinopathy, 11.8+/-2.1 mmol/l (213+/-38 mg/100 ml) in those with background retinopathy, and 12.4+/-2.1 mmol/l (223+/-38 mg/100 ml) in those with proliferative retinopathy (p <0.0001). This difference was not reflected in present concentrations of haemoglobin A(1C), probably because glycaemic control had been improved after the development of retinopathy. In the groups with background and proliferative retinopathy there were significant negative correlations between mean blood glucose concentrations and the number of years that had elapsed from diagnosis of diabetes to detection of retinopathy, suggesting that the development of both grades of retinopathy depends on the degree and duration of glycaemic exposure.The patients with no retinopathy had attended clinic more frequently (p <0.025), more of them had required emergency hospital treatment for hypoglycaemia (p <0.0025), and they tended to have had a lower prevalence of hyperglycaemic coma than the other groups. Although mean percentage ideal body weight and diastolic blood pressure were lower in the patients with no retinopathy at the time of study, mean body weight, blood pressure, and the prevalence of smoking in the years before the development of retinopathy had been similar in all groups, suggesting that these did not influence the development of retinopathy.