A Multi-Site Study of an Electrophysiological Test for Rapid and Objective Assessment of Glaucomatous Damage

Abstract

Purpose: : To assess the classification accuracy of an electrophysiological test designed to measure the functional integrity of a large-cell pathway involved in early-stage glaucoma.

Methods: : Based on previous work that demonstrated glaucomatous deficits in the ON magnocellular pathway, an isolated-check visual evoked potential (icVEP) test was evaluated in a multi-site clinical study. This subsystem was assessed in fellow monocular pathways of 50 patients with open-angle glaucoma, 51 controls, and 52 ocular hypertensives/glaucoma suspects, ages 40-75 yrs, who had visual acuities of 20/30 or higher. An isolated-check pattern (11x11 deg, 24x24 bright checks), was presented with the luminance of the checks modulated at 10 Hz (15% peak contrast) against a background (50 nits). Each test yielded eight 1-s epochs of EEG. Fourier analysis extracted the response at the stimulus frequency. A signal-to-noise ratio (SNR) was derived from the amplitude and phase data. Responses were considered significant (.05 level) when SNR exceeded 1, and fellow monocular responses were required to exceed an SNR of 1 to pass the test. Automated perimetry and frequency-doubling technology (FDT) data were also obtained. Classification accuracy was measured by estimating the area under the receiver-operating-characteristic (ROC) curve.

Results: : Glaucoma cases yielded significant deficits in SNR relative to other participants (p < .01). ROC curve analysis of icVEP data yielded an overall accuracy estimate (glaucoma cases vs. controls) of 89.2% (sensitivity = 84%, specificity = 80.4%). The icVEP measure was only weakly correlated with perimetry and FDT data, which had much lower sensitivities but higher specificities.

Conclusions: : The icVEP, a quick and objective measure of central visual function, yielded high classification accuracy, even given glaucoma cases with high acuities. The icVEP measure provides complementary information to that obtained with automated perimetry and FDT, which assess mainly peripheral visual function.

Keywords: electrophysiology: clinical • visual cortex