The multifocal pattern visual evoked potential (VEP) has been adapted to detect visual field loss as a form of objective perimetry, with specific application to glaucoma. Multifocal pattern stimuli are cortically scaled and presented using a standard system. In order to effectively record the visual field responses, a unique array of bipolar occipital straddle electrode positions are employed, overlying the occipital visual cortex. Multi-channel VEP recording is then performed using these electrode positions. The responses are combined from the channels to produce a representation of the visual up to 25 DEG of eccentricity. Analysis of results to detect early field defects is enhanced by asymmetry analysis between fellow eyes, and by a scaling algorithm to compensate for inter-individual variations. VEP objective perimetry corresponds well with subjective Humphrey visual field defects, showing loss of signal in the areas of visual field loss. Further, it shows reductions in areas of the visual field in glaucoma suspects where subjective testing is still within normal limits. This technique represents the first practical application of the multifocal pattern VEP to objective detection of visual field defects in glaucoma, and may have the potential for detecting disease at an earlier stage than conventional testing.
ELECTROPHYSIOLOGICAL VISUAL FIELD MEASUREMENT