Abdhish R Bhavsar, MD
Good metabolic control is essential to properly manage diabetic macular edema (DME). The foundation of that control is having good control of hyperglycemia. Everyone knows that the Diabetes Control and Complications Trial (DCCT) was the landmark study of patients with type 1 diabetes that proved that reducing hyperglycemia reduces the incidence of diabetic retinopathy (DR), but few people recall that the evidence of benefit for intensive control obtained from this trial was so compelling that the DCCT was terminated early.
The follow-on study to the DCCT, the Epidemiology of Diabetes Interventions and Complications (EDIC) trial, has shown that even a limited period of good glycemic control is beneficial. If intensive control is maintained for 6.5 years, that effect will last 7-10 years later, even if the degree of glycemic control is not as tight then. The United Kingdom Prospective Diabetes Study (UKPDS) confirmed similar results for patients with type 2 diabetes.
Other important systemic issues in DR management are pregnancy, lipid control, hypertension, renal function (fluid balance), and plasma vascular endothelial growth factor (VEGF).
Focal laser photocoagulation is the standard treatment for DME, with a retreatment interval of 4 months for as long as the DME persists. It must be emphasized that the 4-month retreatment interval is just a convention inherited from the Early Treatment Diabetic Retinopathy Study; there is no evidence to support it.
Pars plana vitrectomy (PPV) is another treatment option for persistent DME. PPV is the obvious choice for DME complicated by vitreomacular traction, but it is a less certain choice for refractory DME. PPV surgical technique includes posterior hyaloid separation, epiretinal membrane or inner limiting membrane peeling, and sometimes intravitreal injection of triamcinolone. To date, only noncomparative, retrospective case series of PPV for refractory DME have been published, but the results are encouraging. PPV appears to be effective in reducing edema to some degree 70%-100% of the time. Visual benefits are more variable, with 40%-90% of patients reporting at least some improvement in vision. The Diabetes Clinical Research network is currently conducting a large prospective, nonrandomized study of PPV for refractory DME. Outcomes to be reported include change in visual acuity, change in retinal thickening on optical coherence tomography, resolution of traction, and complications. Data analyses will be performed 6 months and 36 months post-PPV to assess short- and long-term results respectively.
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