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Three methods for determining the tonic vergence position of rest (TPR)

1 April 1986


The tonic vergence position of rest (TPR) is important to any discussion involving a fusion free posture. This posture is assumed whenever the eyes attempt to fixate in an empty field. Therefore, aircraft pilot's visual performance, for example, could be significantly influenced by an individual TPR which was not set to infinity. Furthermore, abnormal TPR's could be either a cause or an indicator of poor visual motor skills. The purpose of this study was to determine the feasibility of three new, clinically available techniques for calculating TPR. Also included in this study was a new method for determining the accommodative posture of rest using a ciliometer. Two of the three TPR techniques proved to be highly correlated (r=.79), reliable, and easy to perform. One of these two techniques involved measuring a head position which caused the greatest stabilization of the autokinetic movement illusion. This was called the AKM technique. A second technique involved stabilizing the head and identifying a stimulus which was monocularly perceived as oculocentric. This was called the oculocentric technique. On the 38 subjects tested, the mean TPR was slightly convergent, between one and two meters, with large intersubject variations. This was consistent with earlier studies of TPR. Though a slightly convergent posture during fusion free situations may not ·be significant to most people, such a posture could be detrimental to pilots, particularly to those who fly at night. Also, abnormal TPR 1s were found on the ·few subjects who had high phorias indicating that TPR may prove a diagnostic measure for visual training.


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