Foveal cone function in nonproliferative diabetic retinopathy and macular edema

Purpose. To study results of foveal cone electroretinography (ERG) in patients with nonproliferative diabetic retinopathy (NPDR), with and without clinically significant macular edema (CSME). Methods. Electroretinograms of foveal cones were elicited, with a dual-beam stimulator-ophthalmoscope, from 18 consecutive patients with bilateral NPDR and unilateral CSME. Results. Analysis of resulting data revealed that mean amplitude was significantly lower in eyes with CSME and in eyes without CSME, compared with that in normal eyes. Mean implicit time was significantly longer in eyes with CSME compared with that in normal eyes, but in eyes of diabetic patients without CSME, mean implicit time was the same as that in normal eyes. Amplitudes were directly correlated and implicit times were inversely correlated with best- corrected Snellen visual activity in eyes with and without CSME. Eyes with CSME and significantly lower amplitudes and longer implicit times than their fellow eyes without CSME. In addition, eyes with NPDR, with or without CSME, did not exhibit the normal size in amplitude with increasing duration of light exposure. Conclusions. Electroretinographic findings showed abnormalities in foveal cone responses in eyes with NPDR, particularly in the presence of CSME. These results may support a functional role for outer retinal dysfunction in patients with diabetic retinopathy and loss of central vision.