Purchase this article with an account.
Agnes M. F. Wong, Douglas Tweed, James A. Sharpe; Adaptations and Deficits in the Vestibulo-Ocular Reflex after Sixth Nerve Palsy. Invest. Ophthalmol. Vis. Sci. 2002;43(1):99-111.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
purpose. The effects of paralytic strabismus on the vestibulo-ocular reflex
(VOR) have not been systematically investigated in humans. The purpose
of this study was to analyze the VOR in patients with unilateral
peripheral sixth nerve palsy.
methods. Twenty-one patients with unilateral peripheral sixth nerve palsy (6
severe, 7 moderate, 8 mild) and 15 normal subjects were studied.
Subjects made sinusoidal ±10° head-on-body rotations in yaw and
pitch at approximately 0.5 and 2 Hz, and in roll at approximately 0.5,
1, and 2 Hz. Eye movement recordings were obtained using magnetic
scleral search coils in each eye in darkness and during monocular
viewing in light. Static torsional VOR gains, defined as change in
torsional eye position divided by change in head position during
sustained head roll, were also measured.
results. In all patients, horizontal VOR gains in darkness were decreased in the
paretic eye in both abduction and adduction, but remained normal in the
nonparetic eye in both directions. In light, horizontal visually
enhanced VOR (VVOR) gains were normal in both eyes in moderate and mild
palsy. In severe palsy, horizontal VVOR gains remained low in the
paretic eye during viewing with either eye, whereas those in the
nonparetic eye were higher than normal when the paretic eye viewed.
Vertical VOR and VVOR were normal, but dynamic and static torsional VOR
and VVOR gains were reduced in both eyes in all patients.
conclusions. In darkness, horizontal VOR gains were reduced during abduction of the
paretic eye in all patients, as anticipated in sixth nerve palsy. Gains
were also reduced during adduction of the paretic eye, suggesting that
innervation to the medial rectus has changed. After severe palsy,
vision did not increase abducting or adducting horizontal VVOR gains to
normal in the paretic eye, but caused secondary increase in VVOR gains
to values above unity in the nonparetic eye, when the paretic eye
fixated. In mild and moderate palsy, vision enhanced the VOR in the
paretic eye but caused no change in the nonparetic eye, suggesting a
monocular readjustment of innervation selectively to the paretic eye.
Vertical VOR and VVOR gains were normal, indicating that the lateral
rectus did not have significant vertical actions through the excursions
that we tested (±10°). Reduced torsional VOR gains in the paretic
eye can be explained by the esotropia in sixth nerve palsy. Torsional
VOR gain normally varies with vergence. We attribute the reduced
torsional gains in the paretic eye to the mechanism that normally
lowers it during convergence. The low torsional gains in the nonparetic
eye may be an adaptation to reduce torsional disparity between the two
This PDF is available to Subscribers Only