Effect of simulated octant visual field defects on the visual evoked potential (VEP)

Several previous clinical research studies1–6 have found the pattern visual-evoked potential (VEP) to be useful in detecting a wide range of visual-field defects objectively. In a previous study completed in our laboratory,6 circular, annular, hemi-field, and quadrant absolute visual-field defects were simulated and assessed objectively for detection and discrimination using the pattern VEP method. The results were clear and consistent, and thus encouraging. The group mean VEP amplitude exhibited a linear increase (y = 0.805x + 2; R = 0.986) with increase in central circular field diameter. In comparison, the group mean amplitude decreased linearly (y = −0.769x + 16.22; R = 0.987) with increase in central blank field diameter for the annular stimuli. Lastly, VEP responses were able to differentiate between hemi- and quad-defects. No significant change in latency was found with any stimulus configuration. All of the aforementioned categories of simulated visual-field defects were detected with excellent repeatability. Thus, these findings suggested that the VEP could be used as an objective technique to detect different types of visual field defects rapidly and reliably. However, none of the previous studies further simulated and tested visual-field defects smaller than quadrants.1–6 Therefore, in the current study, our checkerboard pattern test field was further divided into eight horizontally oriented, rectangular stimulus regions (i.e., octants). Thus, the purpose of the present study was to assess quantitatively the effect of simulated octant, absolute visual field defects on VEP responsivity in a visually normal adult population. This avenue was pursued to assess potential detectability of even smaller, simulated absolute visual-field defects than in previous investigations.