Flicker visual evoked potential differentiation of glaucoma

We have been recording visual evoked potentials (VEP's) produced by a series of increasing rate flicker stimuli to find early neuronal loss in chronic open-angle glaucoma patients and suspects. This technique has demonstrated selective early signal losses in high flicker frequency responses (25 and 31 Hz). This signal loss can precede the characteristic arcuate losses found with automated perimetry. In this retrospective study, 428 visual fields were graded and grouped with their associated cup/disk ratios, peak recorded intraocular pressures (IOP's), and flicker VEP measures in a population of patients either diagnosed with glaucoma or at risk for glaucoma (glaucoma suspects). The correlation of selective high frequency (31 Hz) flicker VEP amplitude loss with visual field damage was confirmed. More severe VEP losses correlate well with optic cup size and visual field grade, but not with peak recorded IOP. Phase angle data did not differentiate between populations separated by visual field losses and VEP amplitude measurements.