Electrophysiological and pupillometric measures of inner retina function in nonproliferative diabetic retinopathy

To evaluate three measures of inner retina function, the pattern electroretinogram (pERG), the photopic negative response (PhNR), and the post-illumination pupil response (PIPR) in diabetics with and without nonproliferative diabetic retinopathy (NPDR).

Fifteen non-diabetic control subjects and 45 type 2 diabetic subjects participated (15 have no clinically apparent retinopathy [NDR], 15 have mild NPDR, and 15 have moderate/severe NPDR). The pERG was elicited by a contrast-reversing checkerboard pattern, and the PhNR was measured in response to a full-field, long-wavelength flash presented against a short-wavelength adapting field. The PIPR was elicited by a full-field, 450 cd/m², short-wavelength flash. All responses were recorded and analyzed using conventional techniques. One-way ANOVAs were performed to compare the pERG, PhNR, and PIPR among the control and diabetic groups.

ANOVA indicated statistically significant differences among the control and diabetic subjects for all three measures. Holm-Sidak post hoc comparisons indicated small, nonsignificant reductions in the pERG (8%), PhNR (8%), and PIPR (10%) for the NDR group compared to the controls (all p > 0.25). In contrast, there were significant reductions in the pERG (35), PhNR (34%), and PIPR (30%) for the mild NPDR group compared to the controls (all p < 0.01). Likewise, there were significant reductions in the pERG (40%), PhNR (32%), and PIPR (32%) for the moderate/severe NPDR group compared to the controls (all p < 0.01).

Abnormalities of the pERG, PhNR, and PIPR suggest inner retina neural dysfunction in diabetics who have clinically apparent vascular abnormalities. Taken together, these measures provide a noninvasive, objective approach to study neural dysfunction in these individuals.