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Mark Nawrot, Megan Frankl, Chad Stockert; Elevated motion parallax thresholds are related to eye movement anomalies in strabismus. Journal of Vision 2004;4(8):202. doi: 10.1167/4.8.202.
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A link between eye movements and the perception of depth from motion parallax was investigated in strabismus. Elevated motion parallax thresholds have been found in strabismic observers (Thompson & Nawrot, 1999) and observers having poor binocular stereopsis (Rogers, 1984). Strabismic observers have also shown horizontal pursuit and optokinetic eye movement deficits, especially for nasal-temporal eye movements (Tychsen & Lisberger, 1986; Demer & von Noorden, 1988; Westall et al, 1998). Are elevated thresholds for the perception of depth from motion parallax a result of the strabismic eye movement anomalies? If so, the two anomalies should be concordant. Ten eyes were tested in five strabismic observers. For each eye, an interleaved staircase was used to determine separate motion parallax thresholds for observer head movements to the left and right. Slow eye movements were measured during pursuit and during lateral head translations in both the light and dark. Five eyes in four strabismic observers showed a marked motion parallax asymmetry: thresholds were different for opposing directions of head movements, often going to the floor for one direction while reaching ceiling in the opposite direction. Three of these eyes showed a marked eye movement asymmetry with much lower gain values found with eye movements in the same direction as the elevated motion parallax thresholds. Three eyes in two observers had symmetrical and normal motion parallax thresholds and normal pursuit gains. Two eyes in two observers had elevated motion parallax thresholds for both direction of head movement and low eye movement gain values. Eye movement anomalies in strabismus are related to elevated motion parallax thresholds. This result underscores the role of eye movements in the perception of depth from motion parallax, provides an alternative explanation for previous results, and suggests that motion parallax be included as part of the constellation of interrelated strabismic anomalies.
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