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P. Satgunam, N. Fogt; The Influence Of Voluntary Vergence On Vergence Adaptation . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3142.
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© ARVO (1962-2015); The Authors (2016-present)
Controversy remains concerning the influence of accommodative vergence on vergence adaptation. This study reports on an individual who demonstrated vergence adaptation after a 15 minute period in which voluntary (accommodative) vergence was used to visually superimpose non–fusible contours.
Computer generated anaglyphic targets (0.9 degrees) were displayed at a distance of 93 cm. The entire testing procedure occurred in a dark room to avoid fusional artifacts. The edges of the computer screen were masked using a black screen in the dark room. First, a binocular fixation line was viewed for one second. Then a monocular target (green circle) was presented for 30 seconds to assess the phoria (pre–adaptation). This was followed by the presentation of a non–fusible target (red circle for the right eye and green cross for the left eye) for 15 minutes. The target had a crossed disparity of 5 degrees. The subject was instructed to overlap the non–fusible images. The phoria was assessed again after the adaptation period (post–adaptation) by displaying the same monocular target used in the pre–adaptation period for thirty seconds. Head movements were minimized using a chin rest and eye movements were recorded using the ISCAN infrared eye tracking system with red (right eye) and green filters attached. Three trials on 3 different days were recorded. A control trial with fusible targets (red and green circles) was also performed.
Comparison of the phoria values between the pre–adapted and post–adapted vergence conditions with the non–fusible target showed a mean increase in esophoria of 2.3±0.7 degrees after adaptation. The adapted phoria value was sustained over the 30 second measurement period. This was comparable to the control trial with the fusible target where a sustained increase in esophoria of 2 degrees was found after adaptation.
For this subject, voluntary convergence was able to drive vergence adaptation. Fusible stimuli were not necessary to produce vergence adaptation. Thus, voluntary vergence has an influence on the vergence adaptive controller along with fast fusional vergence.
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