THE EFFECT OF GLYCEMIC CONTROL AND THE INTRODUCTION OF INSULIN THERAPY ON RETINOPATHY IN NON-INSULIN-DEPENDENT DIABETES-MELLITUS

To study the progression of diabetic retinopathy in relation to diabet es treatment and glycaemic control in patients with non-insulin depend ent (Type 2) diabetes mellitus (NIDDM), we performed a prospective stu dy in a cohort of 1378 diabetic patients, aged greater than or equal t o 40 years at diagnosis, of whom 333 were treated with insulin, and 10 45 with oral antihyperglycaemic agents or diet atone. In the latter gr oup 174 patients changed to insulin therapy during follow-up. We used the Wisconsin scale to grade retinopathy, recorded blindness (visual a cuity less than or equal to 0.1) and visual impairment (visual acuity 0.2-0.4), and measured the average HbA(1c) for each patient during a m ean 3.1-year study period. In a multivariate analysis, patients who ch anged treatment from oral agents or diet alone to insulin therapy had a relative risk of 2.0 (95% confidence interval 1.7-2.3) for progressi on of retinopathy greater than or equal to 3 levels compared with all other patients in the study. The increase in risk remained even after controlling for mean HbA(1c) (relative risk 1.6; 95% confidence interv al 1.3-1.9). progression greater than or equal to 3 levels was signifi cantly associated with a higher incidence of macular oedema and deteri oration of visual acuity (p < 0.001). The relative risk for blindness/ visual impairment due to retinopathy was 2.7 (95% confidence interval 1.8-4.0) in the group with changed treatment compared with all the oth er patients in the study. Poor glycaemic control (HbA(1c)%) before the start of insulin therapy and any retinopathy at baseline were signifi cant risk factors for progression in the group with changed treatment (both p < 0.01). In the whole study group, poor glycaemic control was significantly associated with retinopathy progression greater than or equal to 3 levels; the relative risk for those having mean HbA(1c) abo ve the median being 1.7 (95% confidence interval 1.4-2.1), compared to those with a HbA(1c) value below the median. Moderate non-proliferati ve diabetic retinopathy at baseline was also associated with progressi on (relative risk 2.5; 95% confidence interval 1.4-4.5). In contrast, insulin treatment at baseline was not associated with an increased ris k of retinopathy progression. In conclusion, while hyperglycaemia was a risk factor for the progression of retinopathy in all patients, chan ge of treatment from oral drugs to insulin was associated with a 100% increased risk of retinopathy progression and a 3-fold increased risk of blindness/visual impairment.