Pattern Reversal Visual Evoked Potential From Glaucomatous Patients

Abstract

Purpose: : To evaluate pattern reversal visual evoked cortical potentials (PVECPs) along the spatial frequencies and contrast domains in glaucoma patients.

Methods: : Fourteen open-angle glaucomatous patients were recorded using gold-cup surface electrodes in Fpz, Fz and Oz points. PVECPs were elicited by horizontal black and white sinusoidal gratings at 0.4, 0.8, 2, 4, 8, and 10 cpd modulated by square wave function of 1Hz. Eight to ten contrast levels ranged between 2-100% were presented at each spatial frequency. The stimuli had mean luminance of 40 cd/m². P100 component peak-to-baseline amplitude was used as indicator of visibility from the patient along the contrasts and spatial frequencies.

Results: : All glaucomatous patients showed reliable responses in the most all of the contrast ranges at 0.4 and 0.8 cpd. PVECP was reliable at 2-4 cpd at only medium to high contrast; however, when the stimulus had 8-10 cpd, responses were either observed only at high contrast or not at all for most of the patients. The PVECP amplitude versus contrast function for low and intermediate spatial frequencies had saturation at high contrast. The contrast sensitivity was higher at low spatial frequencies than intermediate or high spatial frequencies.

Conclusions: : Glaucomatous patients had a selective decrease or absence of reliable PVECPs at medium to high spatial frequencies. The results could be explained by selective impairment of ganglion cells responding to high spatial frequencies within the retina.

Keywords: contrast sensitivity • visual impairment: neuro-ophthalmological disease • electrophysiology: clinical