Purpose: To answer the following questions regarding the effect of intensive diabetes management on retinopathy in insulin-dependent diabetes mellitus (IDDM): (1) Does intensive therapy completely prevent the development of retinopathy? (2) Are some states of retinopathy too advanced to benefit from intensive therapy? (3) Are the retinopathy endpoints in the Diabetes Control and Complications Trial (DCCT) clinically important? and (4) What other factors influence the effectiveness of therapy?
Methods: A total of 1441 patients, ranging in age from 13 and 39 years and with IDDM of 1 to 5 years' duration and no retinopathy at baseline (primary prevention cohort) or with 1 to 15 years' duration and minimal to moderate nonproliferative retinopathy (secondary intervention cohort), were assigned randomly to either intensive or conventional diabetes therapy. Intensive therapy, aimed at achieving glycemic levels as close to the normal range as possible, included three or more daily insulin injections or a continuous subcutaneous insulin infusion, guided by four or more glucose tests daily. Conventional therapy included one or two daily injections. Seven-field stereo-scopic fundus photography was performed every 6 months, for a mean follow-up of 6.5 years (range, 4-9 years).
Results: Intensive therapy reduced the risk of any retinopathy (> or = 1 microaneurysm) developing in the primary prevention cohort (70% of intensive versus 90% of conventional treatment group; P = 0.002) by 27%. It reduced the risk of retinopathy developing or progressing to clinically significant degrees by 34% to 76%. Intensive therapy was most effective when initiated early in the course of IDDM. It had a substantial beneficial effect over the entire spectrum of retinopathy studied in the DCCT and, with rare exceptions, in all patient subgroups.
Conclusion: Although intensive therapy does not prevent retinopathy completely, it has a beneficial effect that begins after 3 years of therapy on all levels of retinopathy studied in the DCCT. The reduction in risk observed in the study is translatable directly into reduced need for laser treatment and saved sight. Intensive therapy should form the backbone of any healthcare strategy aimed at reducing the risk of visual loss from diabetic retinopathy.