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