PATTERN EVOKED RETINAL AND CORTICAL POTENTIALS IN DIABETIC-PATIENTS

1. Diabetic patients frequently exhibit mild forms of visual loss; in some cases preceding the development of detectable retinopathy. The physiologic basis of the neural damage, and the subsequent visual impairment, associated with diabetes has not been delineated fully. 2. To more completely characterize the neurophysiological basis of the visual deficits observed in diabetes, simultaneous pattern reversal retinal (PERG) and cortical (PVEP) evoked potentials were recorded in diabetic patients (n = 70) with little or no retinopathy as well as in visually normal controls of similar age (n = 35). Transient (4 reversals per second, rps) and steady-state (16 rps) responses were examined using two check sizes (15 and 60 min). 3. For the controls PERG amplitude was maximum for the 60 min checks reversing at 16 rps, while the implicit time of the transient PERGs was greater for the 15 min checks than for the 60 min checks. PVEP amplitude was greater for the lower temporal frequency with little change in amplitude evident when check size was varied. However, PVEP implicit time was greater for the 15 min checks than for the 60 min checks. 4. Among the patients with diabetes significant reductions in amplitude, but not implicit time, were detected for both the PERG and the PVEP. Furthermore, in the diabetic patients the amplitude of both biopotentials varied with temporal frequency and check size and the trend was similar to the pattern observed for the controls. 5. PERG and PVEP amplitudes generally were lower in diabetic patients with background retinopathy than in patients with diabetes and no retinopathy. However, this difference was not significant statistically. 6. The PERG and PVEP changes observed in the diabetic patients were not associated with the either the duration of diabetes or the HBA1c level. These changes also appeared to be unrelated to the insulin-dependence of the patients. 7. For the controls and the patients with diabetes both PERG and PVEP amplitude varied with test condition, however, the PVEP amplitude changes did not parallel the PERG amplitude changes. This observation supports the suggestion that the PVEP is not a direct reflection of the PERG.