The role of vitrectomy in the treatment of diabetic macular edema.

incidence of diabetic macular edema among individuals with diabetes was between 13.9% and 25.4%.2 It has been predicted that 42% of individuals with type I diabetes will develop macular edema in their lifetime,3 so diabetic macular edema is an important public health problem and a major cause of suffering, disability, and lost productivity. Causes of diabetic macular edema include increased vasopermeability and damage to the retinal capillaries and the barrier provided by the retinal pigment epithelium. Our understanding of the mechanisms responsible for the breakdown of the blood-retinal barrier and the development of macular edema in diabetics has increased in recent years. Aiello and colleagues demonstrated that vascular endothelial growth factor induces retinal vascular permeability and that this effect is mediated primarily by the activation of the beta-isoform of protein kinase C.4 The loss of the barrier function of the blood-retinal barrier can be explained by damage in the structure of the retinal endothelial junction. Antonetti and colleagues showed that increased levels of vascular endothelial growth factor in the vitreous decrease levels of occludin, a membranespanning tight junction protein, which could account for the increased vasopermeability in patients with diabetic macular edema.5 Histamine can also increase the permeability of the blood–retinal barrier by reducing the expression of the tight junction/adherens junction protein, ZO1.6 Although diabetic macular edema can spontaneously resolve,7–8 the Early Treatment Diabetic Retinopathy Study demonstrated that most eyes with diabetic macular edema, whether treated by photocoagulation or not, develop progressive loss of vision.8 The treatment for diabetic macular edema includes medical control of metabolic abnormalities. Patients should achieve excellent glycemic control, normalize blood pressure, improve cardiac and renal status, and reduce serum lipids; photocoagulation therapy also is beneficial. The Early Treatment Diabetic Retinopathy Study showed that focal macular photocoagulation for clinically significant diabetic macular edema reduced the incidence of moderate vision loss by 50%; however, only 3% of patients in the study had improvement of 3 or more lines of visions.8 As a result, focal laser treatment is likely to reduce the rate of vision loss only, not to improve vision, and patients are frequently disappointed with the results of treatment. The high and increasing prevalence of diabetic macular edema and the absence of a fully successful treatment have resulted in the search for alternative therapies. Since our publication in 1992 (Ophthalmology 99:753– 759, ● 2000), which described a subset of patients with diabetic macular traction and edema associated with posterior hyaloidal thickening, there has been an interest in vitreous surgery as a potential treatment for diabetic macular edema.9 What evidence exists that the vitreous plays a role in the development or exacerbation of macular edema in diabetic patients and that removing it is beneficial? The prevalence of posterior vitreous detachment in patients with diabetic macular edema is significantly higher than in diabetic patients without macular edema.10 Moreover, a small prospective study by Hikichi and colleagues strongly suggested that vitreomacular separation may cause spontaneous resolution of diabetic macular edema.7 Several groups have confirmed our initial observation that vitrectomy seems to be beneficial for patients with Accepted for publication Jul 14, 2000. From the Cole Eye Institute, The Cleveland Clinic Foundation, Cleveland, Ohio Reprint requests to Hilel Lewis, MD, Cole Eye Institute and the Division of Ophthalmology (i30), The Cleveland Clinic Foundation, 9500 Euclid Ave, Cleveland, OH 44195; fax: (216) 445-7654; e-mail: lewish@ccf.org