Sensory adaptation in exophoria and exotropia

To investigate the effect of exodeviation in spatial visual attention using the illusory line motion paradigm.

The perception of visual illusion (i.e., illusory line motion) in the dominant and nondominant eyes was examined in 12 control subjects (under 5(Δ)), 12 exophoria patients (over 10(Δ)), and 12 exotropia patients. This paradigm presents two cues followed by an instantaneously presented horizontal bar, which the subjects perceive as bars that emanate from the two priming cues. These bars appear to grow toward the center of the visual field and continue to move inward until they collide with each other. In these experiments, the priming cues were asynchronously and simultaneously presented.

In the dominant eye, there was no correlation between the collision point shift and the ocular deviation, regardless of the stimulus patterns. However, a correlation was noted between the collision point shift and the ocular deviation in the nondominant eye when the second cue was presented in the nasal hemi-retina (P < 0.01). The shift of the collision point in exophoria and exotropia was greater than that seen in the control subjects (P < 0.01). When there was simultaneous presentation of the two cues in the nasal and temporal hemi-retina, there was a difference in the shift of the collision point in the exotropia patients, as compared to both the control subjects and exophoria patients (P < 0.05).

Current findings strongly suggest that sensory adaptation in the nondominant eye compensates for visual stress with ocular deviation.