Surgical Treatment for Diabetic Macular Edema

Abstract

Diabetic macular edema (DME) is defined as excess fluid accumulation within the retina in the macular area, and when it is centered on the fovea it is the most common cause of decreased visual acuity in patients with diabetic retinopathy. The development of diabetic macular edema is closely related to the duration of diabetes, poor glycemic control, and type 2 diabetes on insulin therapy. The first-line therapy in diabetic macular edema has been the intravitreal injection of anti-vascular endothelial growth factors (VEGF). Other treatment modalities are intravitreal corticosteroid injection and focal laser photocoagulation. However, the efficacy of intravitreal therapy may decrease significantly over time, especially in the presence of vitreomacular traction, tight posterior hyaloid, or epiretinal membrane (ERM). At this stage, pars plana vitrectomy (PPV) is preferred as an alternative treatment method in eyes with chronic DME resistant to intravitreal injections. The vitreous of diabetic patients contains high amounts of VEGF and Angiotensin 2, which cause DME, and cytokines such as interleukin-6 and ICAM-1. In addition, due to the enzymes, it contains, the vitreous causes cross-linking and thickening of the collagen fibers in its structure, causing tight adhesion and traction on the macula. The mechanism of action of pars plana vitrectomy in macular edema can be explained by removing the vitreous and vitreomacular tractions. Vitrectomy may also increase retinal oxygenation. Selection of the appropriate case is important. The undisturbed integrity of the outer retinal layers including the external limiting membrane(ELM) and the ellipsoid zone, no preoperative foveal ischemia, and performing surgery early before ELM is damaged, have been found to be related to better postoperative visual acuity gain. Further, prospective, randomized, controlled studies with large series including detailed parameters and long follow-up evaluating the efficacy of surgical treatment in diabetic macular edema are warranted.