Retinal layer location of increased retinal thickness in eyes with subclinical and clinical macular edema in diabetes type 2

PURPOSE: To identify the retinal layer predominantly affected in eyes with subclinical and clinical macular edema in diabetes type 2. METHODS: A cohort of 194 type 2 diabetic eyes/patients with mild nonproliferative diabetic retinopathy (ETDRS levels 20/35) were examined with Cirrus spectral-domain optical coherence tomography (OCT) at the baseline visit (ClinicalTrials.gov identifier: NCT01145599). Automated segmentation of the retinal layers of the eyes with subclinical and clinical macular edema was compared with a sample of 31 eyes from diabetic patients with normal OCT and an age-matched control group of 58 healthy eyes. RESULTS: From the 194 eyes in the study, 62 had subclinical macular edema and 12 had clinical macular edema. The highest increases in retinal thickness (RT) were found in the inner nuclear layer (INL; 33.6% in subclinical macular edema and 81.8% in clinical macular edema). Increases were also found in the neighboring layers. Thinning of the retina was registered in the retinal nerve fiber, ganglion cells and inner plexiform layers in the diabetic eyes without macular edema. CONCLUSIONS: The increase in RT occurring in diabetic eyes with macular edema is predominantly located in the INL but extends to neighboring retinal layers indicating that it may be due to extracellular fluid accumulation.