Multifocal electroretinogram (mfERG) in patients with diabetes mellitus and an enlarged foveal avascular zone (FAZ)

Purpose To assess the relationship between foveal microcirculation and central retinal function in diabetic patients having both an enlarged foveal avascular zone (FAZ) and a preserved visual acuity (0.6 or better). Methods Twenty-five patients with diabetes type 1 or 2 with an enlarged FAZ (largest diameter > 650 μm) measured in fluorescein angiograms were examined with multifocal ERG (mfERG). The largest FAZ diameter, the FAZ area as well as the adjacent perifoveal intercapillary area (PIA), was calculated from the fluorescein angiogram. The retinopathy level was mild to preproliferative. There was no macular edema and no eye had previously been treated with photocoagulation. Results The mean FAZ diameter was 0.92 ± 0.17 mm and the mean summed area (FAZ and PIA) was 0.74 ± 0.24 mm². There was a significant correlation between increasing FAZ diameter and increasing implicit time of the innermost concentric rings and of the third concentric ring in the first order kernel of the mfERG (P = 0.03 and P = 0.008, respectively). An increasing summed area (FAZ and PIA) was correlated to increasing implicit time in the same areas of the mfERG (P = 0.005 and P = 0.026, respectively). No correlation was seen between the ischemic areas and the mfERG amplitudes. Conclusion A correlation between the ischemic areas and prolonged implicit time in the mfERG indicates that alterations in neuronal macular function due to ischemia might precede the deterioration of visual acuity.