Objective perimetry in glaucoma

Purpose: Objective perimetry in glaucoma is described using the multifocal pattern visually evoked potential (VEP). A multichannel recording technique was used to improve signal detection in healthy volunteers and assess its ability to detect glaucoma and early changes in patients with suspected gla ucoma. Design: Prospective, case-control study. Participants: Thirty healthy volunteers, 30 patients with suspected glaucom a, and 30 patients with glaucomatous visual field defects were tested, Method: The VEP was recorded using cortically scaled, multifocal, pseudoran domly alternated pattern stimuli with the VERIS system (Electro-Diagnostic Imaging, Inc., San Francisco, GA). An array of four bipolar occipital elect rodes provided four differently oriented channels for simultaneous recordin g. Signals were compared for different locations within the field up to 26 degrees of eccentricity. Healthy volunteers, patients with suspected glauco ma, and glaucoma patients with established visual field defects were tested , and results were compared with Humphrey visual fields (Humphrey Systems, Dublin, CA) performed on the same day. For reproducibility, five healthy Vo lunteers were each tested on four separate days. The patients with suspecte d glaucoma and the established glaucoma patients were analyzed for intereye asymmetry of signals, and these data were compared with the asymmetry valu es of the healthy volunteers. Results: Multiple recording channels significantly enhanced the recording o f signals from parts of the visual field not reliably sampled with a single channel technique in all healthy volunteers, particularly along the horizo ntal meridian (P < 0.001). Signal amplitude did not decline with age in hea lthy volunteers, Recordings showed good reproducibility within individuals. In all 30 glaucoma patients, the Humphrey visual field defects were weil d emonstrated by the VEP, and topographic location was strongly correlated (r (s) = 0.79), Despite large interindividual variations in amplitude, scotoma s were well demonstrated when compared with normal values. In the patients with suspected glaucoma, smaller changes in signal amplitude could be ident ified in parts of the field still normal on perimetry using intereye asymme try analysis. Conclusions: The multifocal, multichannel VEP can objectively detect glauco matous visual field defects. The nasal step region can be more reliably tes ted using multiple channels. Asymmetry analysis has the potential to detect early defects. This technique represents a significant step toward the cli nical application of objective perimetry in glaucoma. (C) 2000 by the Ameri can Academy of Ophthalmology.