Multifocal electroretinogram responses of the clinically normal retinal areas in diabetes

Aims: To investigate the degree of implicit time delay in aretinopathic hexagons according to the grading of diabetic retinopathy and factors that affect the mfERG responses of aretinopathic areas. Methods: MfERG was recorded using the RETIscan system (Roland consult, Brandenbrug, Germany) in 40 eyes of 20 nondiabetic controls, 32 eyes of 16 diabetic patients without retinopathy, and 96 eyes of 48 diabetic patients with nonproliferative diabetic retinopathy (NPDR). Hexagons are divided into retinopathic and aretinopathic hexagons, which were selected using fundus photographs and fluorescence angiography. Relative amplitude and implicit time delay were compared between patient groups and controls. Results: The mean implicit time delay in aretinopathic hexagons was significantly different between each subject group and correlated with the retinopathy severity of the whole retina, as well as in retinopathic hexagons. In all three NPDR groups, implicit time was significantly more delayed in retinopathic hexagons compared to aretinopathic hexagons. Relative amplitude was significantly decreased only in the severe NPDR group in both retinopathic and aretinopathic hexagons. The duration of diabetes and glycemic control status did not correlate with the local mfERG responses. Conclusions: Local mfERG showed considerable implicit time delays in clinically normal retinal areas that correlated significantly with the severity of diabetic retinopathy of the whole retina.