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Matthew J. Taylor, Dale C. Roberts, David S. Zee; Effect of Sustained Cyclovergence on Eye Alignment: Rapid Torsional Phoria Adaptation. Invest. Ophthalmol. Vis. Sci. 2000;41(5):1076-1083. doi: https://doi.org/.
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purpose. To describe adaptive changes in torsional alignment that follow
sustained cyclovergence in healthy humans.
methods. Eye movements were recorded binocularly from four healthy subjects
using dual-coil scleral annuli. Cyclovergence movements were evoked
over periods of 30 to 150 seconds using a stereoscopic display,
presenting gratings of lines arranged horizontally, vertically, or at
45°, subtending angles of up to 48°. In- and excyclodisparities of
5° were introduced and removed in a single-step fashion. After
stimulation, the time course and magnitude of the decay in
cyclovergence was compared with the subject either in darkness or
viewing a baseline stimulus of zero cyclodisparity.
results. As reported previously, the cyclovergence response to
incyclodisparities was greater than to excyclodisparities. After
sustained excyclovergence, however, in all subjects and in response to
all orientations of the gratings, the decay in darkness was incomplete,
implying an adaptive change in torsional alignment. In response to the
horizontal gratings, for incyclovergence there was also an incomplete
decay in darkness but to a lesser degree than in response to
excyclovergence, and in only three of four subjects. The
incyclovergence evoked by the oblique and vertical gratings was of
small magnitude, and its decay was unaffected by the presence or
absence of a visual stimulus.
conclusions. After sustained cyclovergence, its decay in the absence of a visual
stimulus may be incomplete. The residual component may be interpreted,
by analogy with horizontal and vertical vergence, as reflecting
so-called phoria adaptation for torsional
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