Electroretinogram Changes With Scotopic Stimuli in Retinas of Diabetic Patients With and Without Retinopathy

Abstract

Purpose: : Using electroretinograms (ERGs) with dim flash stimuli, we have detected early dysfunction of rod-driven pathways in STZ-induced diabetic rodents with diabetic retinopathy (DR). Here, we examined the retinal function of diabetic patients with and without DR, to assess if similar dysfunction can be observed in human subjects.

Methods: : Patients with diabetes mellitus between the ages of 25 and 65 were divided in groups with (DR; n=4) or without (DM; n=7) clinically diagnosed retinopathy. Non-diabetic subjects between the ages of 30 and 64 were pooled to serve as controls (CTRL; n=9). Scotopic (white flash; 9.4x10^-3,3.7x10^-2, 1.5x10^-1, 2.4 cd s/m²) recordings and photopic (white flash; 2.4 cd s/m²) recordings followed 20 minutes of dark- and 8 minutes of light-adaptation, respectively. An LKC system was used for all recordings and results from only one eye were analyzed. Amplitudes and implicit times of a- and b-waves, and oscillatory potentials (OP) were measured.

Results: : In response to lower flash intensities (9.4x10^-3 to 1.5x10^-1 cd s/m² ), latencies of OP1, OP2, and OP3 were increased compared to controls in all subjects with diabetes (Two Way RM ANOVA: OP1, p=0.009; OP2, p=0.004; OP3, p<0.001). In response to bright flash (2.4 cd s/m²) stimuli under scotopic conditions, OP1 amplitude was significantly smaller (p≤0.021) in both groups of diabetic patients when compared to non-diabetic subjects while OP3 amplitude was smaller in the DR group compared to the DM group (p=0.017). Under photopic conditions, OP2 implicit time was significantly delayed in DR patients (p=0.023) compared to CTRL while there were no differences in amplitudes. Functional delays in OPs of DM patients were detected more consistently at a dim flash intensity (3.7x10^-2 cd s/m²). No significant a- and b-wave measurement differences were observed in response to any of the flash intensities across groups.

Conclusions: : Our clinical findings suggest inner retinal neuronal changes in patients with diabetes mellitus. Although these changes were more evident in patients with diagnosed retinopathy, dim flash stimuli were able to detect subtle delays in inner retinal neuron function in diabetic patients who weren’t clinically diagnosed with retinopathy. These results suggest that rod pathway transmission that is not apparent with current clinical methods may be disrupted in early diabetic retinopathy.

Keywords: diabetic retinopathy • electroretinography: clinical • retina