Relationships between the vascular structure and neural function of the macula in patients with diabetes mellitus

Purpose To determine the significance of the correlation between the vascular structure and neural function of the macula in patients with diabetes mellitus. Study design Single-center observational study. Patients and methods Ninety eyes of 90 diabetic patients with an average (SD) age of 63.5 (3.8) years were studied. Fifty of the eyes had no clinically apparent diabetic retinopathy (non-DR), and 40 eyes had mild-to-moderate nonproliferative DR (NPDR). Thirty age-matched healthy individuals were also studied in the same way. Swept-source optical coherence tomography angiography (OCTA) was performed to obtain 3 x 3-mm en face images of the posterior pole of the eye. The vascular densities (VDs) of the superficial capillary plexus (SCP) and the deep capillary plexus (DCP) were determined. The focal macular electroretinograms (ERGs) elicited by a 15 degrees circular stimulus centered on the fovea were recorded. The amplitudes of the a- and b-waves, sum of the oscillatory potentials (sigma OPs), photopic negative response (PhNR), and implicit times of the individual OPs (OP1-OP3) were measured. Results The VDs of the SCP and DCP were reduced in eyes with advanced DR (P < .01 for SCP). The implicit times of OP1-OP3 were significantly prolonged in eyes with a lower VD of the SCP and DCP in the non-DR group (P < .05). The amplitudes of the sigma OPs were significantly smaller in eyes with a reduced VD of the SCP and DCP in the NPDR group (P < .05). The correlation coefficients were higher for the OP implicit times than for the sigma OP amplitudes in the non-DR group. Conclusions The OPs of the focal macular ERG are smaller with prolonged implicit times in association with capillary loss in the macula of diabetic patients. The implicit times are the most sensitive functional parameter that reflects the early changes of the microvasculature in the macula caused by diabetes.