Using Visual Evoked Potentials for Glaucoma Detection
The present study evaluated the reliability of an electrophysiological technique that assesses early-stage glaucomatous damage. This technique uses visual evoked potentials (VEPs) to measure the activity of specific pathways of the visual system. The stimuli presented were low contrast isolated-check patterns sinusoidally modulated over time. One subpopulation of these ganglion cells, the On-center cells of the magnocellular pathway, is responsible for the perception of low bright contrast and high temporal frequency achromatic patterns. It is this group of cells that is believed to first begin to die when there is loss of vision due to glaucoma. The diagnostic tool used in this study has a 94% accuracy rate when separating glaucoma patients from normal control participants. Ten participants (three males and seven females) with no history of visual disorders were part of this study. Eight 2-second runs of the bright and dark check conditions at 10% and 15% contrast level were displayed for the participants on a computer monitor. Both eyes (left and right) of each participant were tested twice in two separate testing sessions. The isolated-check visual evoked potentials (icVEP) responses were analyzed using the T-square statistic. The appropriate signal-to-noise ratios (SNRs) were calculated from the eight 2-second stimuli. Since previous studies have shown that one condition (15% bright) is most sensitive to glaucomatous damage, two correlations using the SNRs of the first and second session were computed to test its reliability and two strong positive correlations were found (r= 0.89, p< .01 and r= 0.73, p< .01 respectively). These results imply that the signal-to-noise ratios of the 15% bright condition are highly reliable. The diagnostic tool used in this study should be considered to be used by ophthalmologists on a regular basis for screening the population prone to damage of the visual system caused by glaucoma.