Objective: The study was designed to estimate the incidence and factors of diabetic retinopathy among Bangladeshi type 2 diabetic subjects.
Methods: A random sample of 977 diabetic patients were recruited in 2008 from amongst those who were first time diagnosed in 1993 in the outpatient department of the Bangladesh Institute of Research and Rehabilitation in Diabetes, Endocrine & Metabolic Disorders (BIRDEM). From Patient Guide Books baseline data on clinical, anthropometric and biochemical parameters were collected and, at the time of the study, ie at the end of 15 year follow up blood glucose, lipid profile, HbA1c and serum creatinine were measured in addition to clinical and anthropometric features. A structured questionnaire was administered to collect dietary history and socio-demographic information. Diabetes was diagnosed following the WHO diagnostic criteria. Diabetic Retinopathy (DR) was diagnosed by retinal color photography and classified according to the Early Treatment Diabetic Retinopathy Study (ETDRS). All patients were examined by an Ophthalmologist and were reconfirmed by a senior Ophthalmologist. Data were first compiled through a custom made software and imported into SPSS version 12.0. Appropriate formula was used to estimate stratified incidence rate per 1000 person-years and 95% confidence intervals. To reduce time the formula was put into SPSS 16.0 using syntax to perform the calculation. Student’s t test was performed to compare between Diabetic Retinopathy and No Diabetic Retinopathy. Univariate and multivariate generalized linear models were used to assess the associations of clinical, biochemical and anthropometric variables with retinopathy. The associations were presented in the form of relative risks (RRs) and 95% Confidence Intervals (CIs). When the univariate analyses showed significant relationship (p < 0.25) between exposure variables and retinopathy, then these exposure variables (risk factors) were further included into the multivariate analysis. A p-value less than 0.05 was considered to be statistically significant. All p-values presented are two tailed. The data were analyzed using a computer program Statistical Package for Social Science (SPSS) (Windows version 16.0).
Results: The incidence rates of DR (95% CI) were 23.54 (19.61-28.26), 17.52 (14.93-20.55) and 21.47 (18.86-24.44) per 1000 person-years at 5, 10 and 15 years respectively. The study showed a high incidence of DR at 5 years and relatively lower incidence at 10 years and an increased incidence at 15 years after diagnosis. Incidence of DR increased with increasing age, but this was more prominent in female subjects. Most of the moderate to severe NPDR cases were identified at 15 years after diagnosis.
Patients with retinopathy had worse glycemic control during three different time periods than patients without retinopathy (HbA1c 9.6±2.6 vs 7.7±2.3%, 9.9±2.1 vs 8.0±2.3% and 10.38±2.1 vs 7.27±1.5%, respectively; P<0.05). Glycaemic control, measured either by FBG or OGTT and HbA1C, was found to be the strongest risk factors for 5, 10 and 15 years of incidental cases of diabetic retinopathy controlling for potential confounding factors. It was also noted that age, area of residence, occupation, total cholesterol, triglycerides, the serum creatinine level and hypertension were significantly associated with the development of retinopathy in this study. Nevertheless multivariate model showed increasing age, FBG, 2 hr BG, A1C, TG and SBP were important independent risk factors for the development of DR. Measures of obesity like BMI and intake of nutrients were not found to be associated with the incidental cases of DR.
Conclusion: Bangladeshi type 2 diabetic subjects show a fairly high rate of DR and NPDR. The incidence increases with age with predominance in female and the severity of the condition increases with the duration of diabetes. Along with duration of diabetes glycemic control was the prime significant risk factor for the development of retinopathy in 15 year follow-ups. Other potential risk factors include elevated blood pressure, TG and the presence of nephropathy. A closer cooperation between the diabetologists and ophthalmologists is required to reduce the risk of complications and improve the quality of care.
Key words- Type 2 diabetes, Incidence, Diabetic retinopathy, Risk Factors.