Proximal vergence and perceived distance



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The purpose of this study was to measure the vergence response to a change in physical distance (proximal vergence) and to evaluate its presumed stimulus, change of perceived distance. Vergence posture was measured haploscopically for a large field of blurred horizontal lines, providing minimal disparity and accommodative stimulation, under binocular and monocular viewing at 40, 67 and 200cm. Perceived distances were calculated from the estimated size of projected after images. For 18 normal observers, the change in vergence (in prism diopters per meter angle change in test distance) averaged 2.59 (S.D.[equals]1.44) binocularly and 2.11 (S.D.[equals]1.22) monocularly. Clinical measures were significantly higher, 4.38 (S.D.[equals]1.20) binocularly and 3.42 (S.D.[equals]1.09) monocularly. Haploscopic and clinical measures of proximal vergence correlated only when a modified clinical technique was used. Taking estimated perceived distance into account only partially reduced differences between proximal vergence measured haploscopically and clinically as well as binocularly and monocularly. Both haploscopic and clinical measures of proximal vergence were sizable, indicating this vergence component can contribute substantially to normal vergence responses.



Eye--Movements, Binocular vision