Benefit of Prior Intensive Diabetes Therapy on Retinopathy Risk Wanes Over Time

The persistent difference in retinopathy complications between former intensive and conventional therapy for type 1 diabetes continues for years, but begins to decline within a decade, according to new data from the Epidemiology of Diabetes Interventions and Complications (EDIC) study.

Dr. David M. Nathan at Massachusetts General Hospital, Boston, and colleagues note in their report in the Archives of Ophthalmology for December that in the original Diabetes Control and Complications Trial (DCCT), “intensive therapy aimed at near-normal glycemia reduced the risk of microvascular complications of type 1 diabetes mellitus compared with conventional therapy.”

At the end of the 6.5-year DCCT, mean HbA1c levels were 7.3% in the intensive therapy group and 9.0% in the conventional therapy group. At that point, patients returned to their usual health care providers and most were enrolled in the observational EDIC study.

By the end of the first year following the close of the DCCT, HbA1c values had begun to converge, and after 4 years they were no longer significantly different.

Nonetheless, among the 1211 subjects with complete follow-up, the adjusted odds of retinopathy progression were reduced by 74% at EDIC year 4; however, this fell to 57% at year 10.

The authors observed similar patterns for severe nonproliferative and proliferative diabetic retinopathy, and clinically significant macular edema.

According to the authors’ calculations, “the likelihood of further progression of retinopathy in both groups was strongly associated with the mean HbA1c value during the DCCT and EDIC combined, with a stronger effect of the mean HbA1c value during the DCCT.”

They stress that the persistence of benefit does not mean that intensive therapy need only be applied for a limited period. “Rather,” they conclude, “the results support the implementation of intensive treatment as early in the course of the disease as possible.” If aggressive glycemic control is not maintained, however, the advantages are likely to diminish.

Arch Ophthalmol 2008;126:1707-1715.