Retinal potentials in patients with primary open-angle glaucoma: physiological evidence for temporal frequency tuning deficits.

The pattern-reversal retinal potential is a bio-electrical signal which can be recorded from the cornea of the human eye when a phase-alternating (contrast-reversing) pattern is viewed. The PRRP is correlated with activity of the retinal ganglion cells and visual diseases which affect the proximal retinal layers (such as optic atrophy and optic neuritis) and cause significant alterations in the waveform of the human PRRP. This study examined the PRRP in 32 patients with primary open-angle glaucoma (POAG) and 32 age-matched visual normals (AMVNs). Counterphasing (2, 4, 8 and 16 reversals/sec) checkerboard patterns (15', 30', 60', and 120' checks) were used as visual stimuli. PRRP amplitude was significantly reduced in patients with POAG. When temporal frequency was held constant, the magnitude of the observed PRRP amplitude reductions was identical for all check sizes. However, the magnitude of the observed amplitude reductions increased as temporal frequency increased. Therefore, in patients with POAG, the shape of the PRRP spatial tuning function was normal (although uniformly reduced for all check sizes), while the temporal tuning function was attenuated for high frequencies. Statistically significant increases in PRRP latency were also observed in the POAG patients, but these increases were quite small (mean = 3.6 ms).