Incidence of and risk factors for diabetic retinopathy in Isfahan, Iran.

BACKGROUND: Evidence on the incidence of and risk factors for diabetic retinopathy is mainly derived from studies in developed countries. Locally derived evidence is required for planning a well-coordinated approach to this public health problem in developing countries.

OBJECTIVE: The objectives of the present study were to estimate the incidence of and risk factors for the development of diabetic retinopathy using routinely collected data from a clinical information system at the Isfahan Endocrinology and Metabolism Research Center, Iran, for non-insulin-dependent (insulin-treated and non-insulin-treated) diabetes.

METHOD: During the mean (standard deviation (SD)) follow-up period of 5.1 (2.1) (range 1-9) years, 549 diabetic patients (161 male and 388 female) from the Isfahan Endocrinology and Metabolism Research Center outpatient clinics at Amin University Hospital, Iran, were examined. The mean (SD) age of the participants was 45.7 (9.3) years with a mean (SD) duration of diabetes of 6.9 (5.7) years at initial registration.

RESULTS: Among the 549 patients free of retinopathy at initial registration with at least one follow-up visit between 1992 and 2001, the incidence of any retinopathy was 89.4 (95% confidence interval (CI): 79.0, 101.0) [96.1 (95% CI: 76.7, 118.0) in males and 86.6 (95% CI: 74.5, 99.9) in females] per 1000 person-years based on 2786 person-years of follow-up. The incidence rate of retinopathy was 60% greater among insulin-treated than non-insulin-treated non-insulin-dependent diabetes mellitus (NIDDM) clinic attenders. The incidence of any retinopathy was greater with older age, longer duration of diabetes, higher diastolic blood pressure and poor metabolic control. Using a Cox's Proportional Hazards Model for insulin-treated and non-insulin-treated NIDDM diabetes separately, poor metabolic control was a significant independent predictor of retinopathy for insulin-treated and non-insulin-treated NIDDM patients. When all variables were entered in the model, age, poor metabolic control and fasting blood glucose were significant predictors of retinopathy. In the insulin-treated group, fasting blood glucose was also a significant predictor of retinopathy. Systolic and diastolic blood pressure, gender, smoking, proteinuria, body mass index and creatinine had no significant independent association with retinopathy when other covariates were considered.

CONCLUSION: These data suggest that diabetic retinopathy in this population of Iranian non-insulin-dependent diabetic patients is common, being found in almost half of the patients after a mean 5-year follow-up. Poor metabolic control is the major risk factor.