The effect of induced visual stress on three dimensional perception.

Previous studies have shown that stress on the vergence and accommodation systems, either artificially induced or naturally occurring, results in small misalignment of the visual axes, reduces binocular visual acuity and produces symptoms of ocular discomfort. This study examines the effect of artificially induced visual stress using ophthalmic prisms on three dimensional perception on 30 optometry students ages ranging from 19 to 29 years old. 6D base-in prisms, equally divided between the eyes (3D base-in each) was used to induce stress on the visual system producing misalignment of visual axes known as fixation disparity. The fixation disparity is quantified using near vision Mallett Unit and an enlarged scaled diagram. Stereoscopic perception was measured with the TNO test, with and without the presence of stress and the results was compared. Wilcoxon's matched pair ranked tests show statistically significant difference in the stereo thresholds of both conditions, p = 0.01 for advancing stereopsis and p = 0.01 for receding stereopsis, respectively. The study concludes that visual stress induced by prisms, produce misalignment of the visual axes and thus reduces three dimensional performance.