Detection of glaucomatous visual field loss using multifocal visual evoked potential

purpose: To evaluate a new multifocal visual evoked potential (VEP) system for its ability to detect glaucomatous visual field loss in a clinical setting. Methods: Multifocal VEPs were recorded in both eyes of 36 patients with glaucoma and 35 control subjects using the AccuMap system (ObjectiVision Pty, Ltd, Sydney). Glaucoma diagnosis was based upon optic disc appearance (glaucomatous optic neuropathy in at least one eye) and visual field loss measured by standard automated perimetry (SAP; p < 0.05 for mean defect (MD) or pattern standard deviation (PSD); or glaucoma hemifield test (GHT) outside normal limits) confirmed in at least one eye. Controls had normal visual fields (by above criteria) and normal optic disc appearance in both eyes. Sensitivity and specificity levels were determined for various criteria using the AccuMap internal normative database. Results: SAP visual field MD ranged from 1.8 to -28.6 dB (mean, -8.4 SD 7.4). At a fixed specificity level of 90%, sensitivity for detection of an abnormal SAP visual field was 75 and 82%, based on the number of abnormal VEP points (max 58 possible per eye) below the p = 0.02 and p = 0.01 level, respectively. Using the AccuMap 'severity index' (a proprietary algorithm that uses weighted combinations of above, interocular asymmetry, and clustering factors), sensitivity was 78 at 90% specificity. Adding the requirement of a cluster of at least three abnormal sectors on the interocular asymmetry plot (p < 0.1% level) to the monocular amplitude criteria improved sensitivity to 92% for all glaucoma eyes and 97% for glaucoma subjects, with 90% specificity. Conclusions: The AccuMap multifocal VEP (mfVEP) system can be used to detect glaucomatous visual field loss with reasonably high sensitivity and specificity. Although control subjects commonly have isolated 'defects' for mfVEPs obtained using the AccuMap system, these defects are rarely clustered.