Detection of early diabetic retinopathy using visual electrophysiological tests

Detection of functional impairment of vision in pre-clinical stages helps early identification of diabetic retinopathy. We aimed to determine the functional integrity of retina and post retinal pathways using electro-oculography (EOG), pattern electroretinography (PERG) and pattern-reversal visual evoked potentials (PR-VEP) in newly diagnosed diabetic patients who have not developed fundoscopic features of diabetic retinopathy. Twenty-five adults with newly diagnosed diabetes mellitus without fundoscopic evidence of retinopathy and a control group of healthy adults were subjected to visual electrophysiological assessment. Retinal pigment epithelium (RPE)-photoreceptor interaction, photoreceptors and ganglion cells of the macula and post retinal pathways were assessed by EOG, PERG and PR-VEP, respectively. Fourteen of the 25 diabetic patients, i.e. 56% (95% confidence intervals 34.9%, 75.6%), had LP:DT (light peak to dark trough) ratio less than 1.7, to the cut-off defined by the International Society for Clinical Electrophysiology of Vision (ISCEV). All control group subjects had LP:DT ratios above 1.7. The median LP:DT ratio in diabetic group (1.62 ± IQR 0.27) was significantly lower than that of the controls (1.8 ± IQR 0.21). Four patients had prolonged PR-VEP P100 latencies, and seven had prolonged PERG P50 latencies as per the ISCEV cut-offs, whereas none of the control group had abnormal PERG or PR-VEP measures. With a limited sample, we found that 56% of newly diagnosed diabetic patients with normal fundoscopy had defective RPE-photoreceptor interaction. Further studies are needed to obtain more precise point estimates of these EOG abnormalities, and to determine the conversion rates into more advanced stages of diabetic retinopathy.