Anti-vascular endothelial growth factor drug treatment of diabetic macular edema: the evolution continues

Diabetic mellitus is the leading cause of blindness in working aged patients in developing nations. Due to the buildup of abnormal metabolites from several overactive biochemical pathways, chronic hyperglycemia causes oxidative stress in the retina which upregulates vascular endothelial growth factor (VEGF). Together with other growth factors and metabolites, VEGF causes endothelial cell proliferation, vasodilation, recruitment of inflammatory cells, and increased vascular permeability, leading to breakdown of the blood-retinal barrier. This allows trans-cellular exudation into the interstitial space resulting in diabetic macular edema (DME). For over 3 decades the standard treatment for DME has been laser photocoagulation. Though laser reduces the incidence of vision loss by 50%, few eyes with diffuse edema experience improved vision. This has led physicians to use the VEGF-binding drugs pegaptanib, ranibizumab, and aflibercept, each of which has been approved for the treatment of exudative macular degeneration, and bevacizumab which is commonly used off-label for a variety of chorioretinal disorders. Intravitreal administration of each drug frequently causes rapid improvement of DME with sustained improvement in vision through 2 years. Though these drugs significantly outperform laser photocoagulation over treatment periods of 1 year of less, the advantages appear to lessen when trials approach 2 years. Further studies to better determine relative efficacies of anti-VEGF drugs and laser photocoagulation are continuing.