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M. Schlenker, G. Mirabella, H. Goltz, P. Kessler, A. Blakeman, A. M. F. Wong; Abnormal Head Heave Response in Patients With Skew Deviation. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1801. doi: https://doi.org/.
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The translational vestibulo-ocular reflex (tVOR) is primarily mediated by the otolithic organ in the inner ear. Skew deviation is a vertical strabismus believed to be caused by damage to the otolithic-ocular reflex pathway. We investigated whether patients with skew deviation show abnormal tVOR responses during transient, high-acceleration interaural head-heaves.
Five patients with skew deviation caused by brainstem or cerebellar lesions, and 11 normal controls were studied. All subjects underwent brief sudden interaural translations of the head (i.e., head-heaves) using a head-sled device at an average peak acceleration of 0.62g while continuously viewing an earth-fixed target at 15 cm. Eye rotations were measured with binocular search coils, while head rotation was measured with a search coil attached to a bite bar. Head translation was measured using an accelerometer attached to the bite bar, and with a linear potentiometer attached to the head restraint. Sensitivity gain (ratio of peak eye velocity to peak head velocity) was calculated for the tVOR response within the first 100 msec after onset of head movement (i.e., before visual feedback).
In normal subjects and patients with skew deviation, tVOR responses do not modulate with the amplitude of peak acceleration. All five patients with skew deviation exhibited bilateral decrease in sensitivity gain in both eyes, and in both heave directions. Two of five patients had abnormal vergence.
The abnormal tVOR responses may be caused by damage to the otolith-ocular reflex pathway, or failure of vergence, or both. The decrease in sensitivity gain in three patients who had normal vergence provides support that damage to the otolithic-ocular reflex pathway is a cause of skew deviation.
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