Electrophysiological detection of delayed postretinal neural conduction in human amblyopia.

PURPOSE To evaluate macular function and neural conduction along postretinal visual pathways in amblyopic patients. METHODS Twenty-five anisometropic amblyopic patients (mean age, 7 ± 1.9 years; visual acuity [VA]: 0.44 ± 0.27 logMAR in amblyopic [AM] eyes and 0.023 ± 0.067 logMAR in sound [SE] eyes) and 25 age-similar control subject ([CE] eyes, VA of 0.0 ± 0.0 logMAR in both eyes) were enrolled. In AM, SE, and CE eyes, simultaneous pattern electroretinograms (PERGs) and visual evoked potentials (VEPs) were recorded in response to checks reversed at the rate of two reversals/second stimulating macular or extramacular areas (the check edge subtended 15 minutes and 60 minutes of visual arc, respectively). RESULTS Nonsignificant differences (ANOVA, P > 0.005) were observed in PERG, in VEP responses to the 60-minute stimulus, and in retinocortical time with the 60-minute stimulus (RCT; the difference between VEP P100 and PERG P50 implicit times) between AM, SE, and CE eyes. AM eyes showed a significant (P < 0.005) increase in VEP P100 implicit time and in RCT in response to the 15-minute stimulus, compared with the values observed in SE and CE eyes. In AM patients, the interocular difference in VA was significantly (Pearson's test, P < 0.005) related to the interocular difference VEP P100 latencies and RCT with the 15-minute stimulus. CONCLUSIONS Amblyopic eyes showed abnormal visual cortical responses only when the macular area was stimulated (increase in VEP P100 implicit times with the 15-minute stimulus). This functional impairment, in the presence of normal macular function (PERG responses similar to control eyes) may be attributable to a delay in postretinal neural conduction (increase in RCT).