Motion–in–Depth Perception of Strabismus Patients

Abstract

Abstract: : Purpose: In strabismus clinics, stereoscopic depth perception is usually examined with static stimuli. However, ability of perceiving motion in depth cannot be assessed with the method. We developed a technique to assess dynamic aspect of stereopsis and compared it between patients with esotropia and exotropia. Methods: We investigate stereo acuity or disparity threshold to see motion in depth of patients with esotropia or exotropia. Four types of computer–generated visual stimuli were used. Three of the conditions used random dot stereograms that represented a plate that was rotating or moving in depth. The upper and lower parts of the plate moved in different direction in depth and the patients were asked direction of motion. The last condition used random dot stereograms that represented a rotating cylinder. The upper and lower parts of the cylinder rotated in the opposite directions from each other and the patients were asked the location of the border between the two parts. Threshold disparity (between the nearest and farthest points of the cylinder, or the motion path of the plate) was defined as the disparity which gave a critical level of performance with the method of limit as a conventional stereo test with static stimuli. Titmus stereo test was also used for comparison. Twenty nine patients with esotropia or exotropia were examined after obtained informed consent from either the patients or their parents. Results: This study performed in the Department of Ophthalmology, Tokyo Medical University Hospital between January 2003 and July 2004. Fourteen esotropic, ten exophoria and six exotropia patients were studied. There was a high correlation between the result of the stereo motion condition and velocity condition, whereas little correlation between the result of the stereo motion test and Titmus stereo test Ability to perceive motion in depth was revealed (disparity threshold < 500 sec of arc) for three of the patients who was not able to detect depth in static stimuli (0/9 for Titmus circle). Patients with ocular alignment within 20 prism diopters showed sensitivity to motion in depth independently of the alignment direction (esotropia or exotropia) or of ability to see static depth. Conclusions: The present results showed the importance of testing the ability for motion in depth perception to assess the ability to perceive depth of strabismic patients and to investigate the effect of the degree and direction of ocular alignment.

Keywords: binocular vision/stereopsis • strabismus • motion-3D