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Oliver Bergamin, David S. Zee, Dale C. Roberts, Klara Landau, Adrian G. Lasker, Dominik Straumann; Three-Dimensional Hess Screen Test with Binocular Dual Search Coils in a Three-Field Magnetic System. Invest. Ophthalmol. Vis. Sci. 2001;42(3):660-667.
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purpose. To establish an objective Hess screen test that allows a simultaneous
and binocular analysis of all three axes of eye rotation.
methods. In orthotropic and strabismic human subjects, both eyes were recorded
with dual scleral search coils in a three-field magnetic system. Before
mounting the search coil annuli on the eyes, the voltage offsets of
each channel and the relative magnitudes of the three magnetic fields
were determined. For calibration, subjects were only required to fix
monocularly on a single reference target. During fixation of targets on
the Hess screen by the uncovered eye, the three-dimensional eye
position of both the occluded and the viewing eye was simultaneously
results. For clinical interpretation, an easy to understand graphical
description of the three-dimensional Hess screen test was developed.
Positions of orthotropic and strabismic eyes tended to follow
Listing’s law, which in both eyes allowed the determination of the
primary position, that is, the position of gaze from which pure
horizontal and pure vertical movements do not lead to an ocular
rotation about the line-of-sight. To a first approximation, the
location of primary position is a result of the summation of the
individual rotation axes of the six extraocular muscles and thus can be
used to infer which muscle is paretic.
conclusions. The three-dimensional Hess screen test with binocular dual search coils
in a three-field magnetic system is an objective method to assess the
ocular alignment in three dimensions with high precision. From these
recordings, the clinician can relate deviations of primary position to
specific eye muscle palsies.
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