The effect of stereoscopic display viewing upon sensory and motor aspects of binocular function

• Main Author: Sweeney, Laura E.
• Published: Glasgow Caledonian University 2015
• Subjects: 617.7
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.687411

Stereoscopic displays provide an unnatural visual environment requiring the accommodation and vergence systems to respond unequally. In natural visual environments accommodation and vergence systems alter simultaneously with changes in viewing distance, through signals generated via the cross-link interactions between the systems. These interactions are quantified by the AC/A and CA/C ratios. This thesis aims to provide a comprehensive evaluation of the effect of stereoscopic displays on oculomotor function and clinical measures of binocular vision. Previous work has studied the AC/A ratio widely, whereas the CA/C ratio is under reported. One study in the thesis examined stimulus and response ACfA and CAfC ratios in a larger population than investigated previously. A significant linear relationship existed between the stimulus and response cNe ratios, although the correlation between the two measures was weaker than the linear relationship found between stimulus and response AC/A ratios. The study demonstrated that further work is needed to refine the methodology for the clinical measurement of the CA/C ratio. Previous work suggests that adaptive vergence changes cause alterations in the cross-link interactions. Another experiment in the thesis measured adaptive vergence output before, during and after viewing stereoscopic targets with varying levels of disparity stimulus. Adaptive vergence has not been investigated previously following stereoscopic viewing. The effect of stereoscopic viewing upon adaptive vergence showed wide inter-subject variability however, changes in adaptive vergence were found to be dependent on the magnitude and direction of the stimulus disparity. In a further experiment both cross-link interactions were measured before and after stereoscopic viewing using the stimulus identified in the previous experiment as producing the most significant change in adaptive vergence. Previous studies have only investigated the AC/ A ratio following stereoscopic viewing. A novel finding was the AC/ A ratio was found to be predictable such that at low AC/A ratio values the ratio increased, and at high ratio values the ratio decreased after stereoscopic viewing. The CA/C ratio showed substantial changes in individual subjects, the changes within the group were not predictable. Changes in the adaptive vergence component were not related to changes in the AC/A ratio following stereoscopic viewing. This work provides evidence that stereoscopic displays cause vergence adaptation and modification of the cross-link interactions. Previous studies have found stereothresholds to be elevated significantly during stereoscopic viewing. However following stereoscopic viewing studies have only examined stereoacuity using clinical methods and these tests cannot measure stereopsis to threshold levels. The experiment in the thesis found no change in stereothresholds after stereoscopic viewing suggesting that the oculomotor changes identified in other experiments do not affect sensory binocular vision. In the final experiment, clinical measures of binocular function were investigated before and after stereoscopic viewing, using the stimulus which had been shown to cause changes in laboratory measures of oculomotor function in previous experiments. A significant increase was found in the stimulus AC/A ratio while the positive fusional reserves were found to decrease significantly, suggesting that these measures may be the most helpful in identifying the effects of stereoscopic viewing In the clinical domain.