Nonlinear characteristics of visual evoked potential in glaucoma patients and their correlation with the visual responses on magnocellular and parvocellular pathways.

Purpose was to investigate the linear and nonlinear characteristics of VEPs, and their correlation with the visual parvocellular and magnocellular systems. The VEPs were elicited by pseudorandom luminance modulated stimulation from patients with primary open angle glaucoma and compared with normal subjects. VEPs were recorded from 26 eyes with primary open angle glaucoma (POAG) and 10 eyes of age-matched normal volunteers. To acquire the VEPs, the eye was stimulated with a pseudorandom binary sequence (PRBS) stimulus of 40 sec duration. The first (linear) and second-order (nonlinear) binary kernels were determined by a cross-correlation function between PRBS and VEP. The amplitudes of the first- and second-order kernels decreased with the advancement of POAG. Positive peak latencies around 120 ms of first slice of second-order kernels increased with the advancement of POAG, while the second slice amplitudes were not different in normal, early POAG and moderate POAG patients. These results support the observations in previous studies that the first and second slice response functions reflect the response of the M- and P-pathways, respectively.