Ranibizumab (rhuFab V2) and Scatter Laser Photocoagulation in Treatment of Patients With Clinically-significant Diabetic Macular Edema With Peripheral Retinal Nonperfusion (RaScaL)

Diabetic retinopathy is a leading cause of moderate and severe visual loss in developed countries. It is of paramount socioeconomic impact as the prevalence of diabetes is sharply increasing, diabetic macular edema is the leading cause of vision loss in working age patients, it is a significant cause of vision loss in patients older than 65 years of age, it frequently affects patients bilaterally, and the costs of therapy are increasing.

Diabetic macular edema (DME) is the most common cause of vision loss in diabetic retinopathy. The pathophysiology of DME is complex and multifactorial. Chronic hyperglycemia, protein kinase C (PKC) formation, free radical accumulation, advanced glycation end-product (AGE) proteins, and ischemia-driven release of vascular endothelial growth factor (VEGF) are some of the better understood factors that contribute to chronic retinal arterial and capillary damage and increased permeability.

The RIDE and RISE Studies demonstrated the superiority of anti-VEGF monotherapy with ranibizumab over sham therapy, when all groups were allowed to receive macular laser therapy after month 3 based on predefined criteria. Furthermore, other studies have demonstrated VEGF inhibitors to be beneficial for DME, either as monotherapy or in combination with macular laser.

The benefit of VEGF antagonists in treating DME validates that the VEGF pathway is a key target. The need for repeated anti-VEGF injections to maintain the benefit of treatment begs the question whether persistent peripheral retinal ischemia may be driving VEGF production in at least a subset of patients with DME. Fluorescein angiographic studies of the mid- and far-periphery of diabetic patients by Shimizu in the 1980's demonstrated areas of peripheral retinal nonperfusion in diabetic patients. These findings have been reproduced and substantiated more recently utilizing a novel, commercially-available imaging system for ultrawide-field angiography (UWFA) that employs a scanning laser ophthalmoscope and an ellipsoidal mirror.

We investigated whether patients with diabetic macular edema associated with peripheral nonperfusion on UWFA would have improved visual acuity, resolution of retinal thickening on OCT, and durability of therapy using a novel strategy of a single intravitreal injection of Ranibizumab, a VEGF-A inhibitor + UWFA-guided peripheral Scatter Laser, or RaScaL. A second goal of the study was to guide DME treatment by the imaging signature of UWFA and OCT.