OCT-Leakage: A New Method to Identify and Locate Abnormal Fluid Accumulation in Diabetic Retinal Edema

PURPOSE. To identify retinal extracellular fluid changes and their correlation with increased retinal thickness (RT) in eyes with subclinical and clinical macular edema in diabetes type 2. METHODS. A cohort of 48 eyes from 48 type 2 diabetic patients with mild or moderate nonproliferative diabetic retinopathy (Early Treatment Diabetic Retinopathy Study levels 20/35) were classified as having normal RT (10), subclinical macular edema (30), or clinical macular edema (8). They were examined with Cirrus spectral-domain optical coherence tomography (OCT) at baseline visits (ClinicalTrials. gov number, NCT01145599) in the Coimbra center. Results from automated analysis of the retinal extracellular space, using our OCT-Leakage algorithm to identify sites of low optical reflectivity, were compared with those from a control group of 25 healthy eyes. RESULTS. The highest increases in RT in the eyes with subclinical and clinical macular edema were found in the inner nuclear layer (INL). These increases were, on average, 49.9% in subclinical macular edema and 104.7% in clinical macular edema. Extracellular space increases in the INL that were identified with the OCT-Leakage algorithm showed a strong positive correlation with the increases in RT in the central subfield (r = 0.71, P < 0.001). CONCLUSIONS. Increases in number of sites with lower optical reflectivity positively correlate with the increase in RT in the initial stages of macular edema in diabetes type 2. Diabetic macular edema is represented mainly by extracellular fluid accumulation that preferentially involves the INL of the retina.