[Effect of vertical prism induced stress on binocular visual evoked potential]

To evaluate the effect of vertical prism induced stress on binocular visual evoked potentials. Using checkerboard stimulus patterns in two spatial frequencies [SFs] of 0.48 cpd as a low SF and 2.18 cpd as a moderate SF reversing with temporal frequency of 4 Hz, the effect of increasing visual stress using vertical prisms of 0, 1, 2 and 3 prism diopters on binocular visual evoked potentials was investigated. The project was performed on 23 participants [11 male and 12 female] with normal binocular visual function, i.e., vertical prism vergences and stereo acuities were within normal limits. The amplitude and latency of N75, P100 and N135 components were measured during different vertical prism induced stresses in all cases. To compare mean amplitude and latency with different vertical prism induced stresses, the repeated measure ANOVA statistical method was used. The amplitude of N75, P100 and N135 components showed reduction as a function of vertical prism induced stress at both low and moderate SFs [P<0.001]. This reducing trend was more severe with increasing intensity of prism stress, while the latency of these components showed an increase as a function of vertical prism induced stress at both low and moderate SFs [P<0.001]. Based on clinical findings, ocular symptoms are caused by the vertical prism induced stress; in visual evoked potential as a paraclinical test, amplitude and latency of all components of the VEP wave, are affected by this stress