Associations between local retinal thickness and function in early diabetes.

PURPOSE To investigate, using multifocal electroretinography (mfERG) and optical coherence tomography (OCT), potential spatial associations between local neuroretinal function and local retinal thickness in patients with diabetes. METHODS Forty-five patients without retinopathy (10 with Type 1 diabetes; 35 with Type 2 diabetes; 49.9 ± 10.9 years old) and 29 age-similar controls (47.0 ± 12.8 years old) were studied. N1-P1 amplitude (AMP) and P1 implicit time (IT) of mfERGs within the central approximately 20° diameter were compared to spatially corresponding full retinal thickness measurements acquired by Stratus OCT3. AMP and IT were converted to Z-scores and retinal thickness was converted to percentile values. Local abnormalities were defined as P ≤ 0.023. Subject group differences were examined using t-tests. Retinal thickness was compared to mfERGs to determine spatial associations. RESULTS Average retinal thicknesses were similar for all subject groups. The Type 1 group and controls had similar IT and AMP. The Type 2 group had reduced AMP and longer IT than the controls and the Type 1 group (P < 0.001). Local associations between retinal thickness and mfERGs were not significant within any subject group or individuals, even for abnormal locations (P ≥ 0.09). Abnormalities in most measures were greater in the patient groups than in the controls (P < 0.008) except retinal thinning in the Type 1 group. CONCLUSIONS Local neuroretinal function is not associated with full retinal thickness measured locally in patients with diabetes and no retinopathy, even in abnormal locations. Full retinal thickness measured locally by OCT is not a surrogate for mfERGs in early diabetes. Neuroretinal function in Type 2 diabetes is worse than in Type 1 diabetes and controls. Fewer subjects in the Type 1 group could be a potential limitation.