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U. Sverkersten, T. Pansell, J. Ygge; Adaptation of Visual and Vestibular Induced Ocular Torsion Indicate a Similar Gaze Holding Mechanism. Invest. Ophthalmol. Vis. Sci. 2008;49(13):757.
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Ocular torsion in response to a static tilted visual stimulus was recently demonstrated. The present study aims to quantify if visually induced torsion remains stable (i.e. position) over time or undergo changes similar to the vestibular induced ocular torsion during a sustained head roll (presented elsewhere). A similar drift would indicate a common neural "gaze holding" mechanism for ocular torsion, independent of which sensory system inducing the torsional response.
Eye movements (3-D) were recorded in nineteen healthy individuals using a head mounted video oculography system (SMI, Germany). The visual stimuli displayed a photo over a city scene containing visual clues relevant for spatial orientation. The same stimuli were tilted from 0º to 15 (test 1), from 0 to 30º (test 2), from 0 to 45 (test 3) in CCW direction around the fixation point. The tilted stimuli were held static for 4 minutes and 40 seconds in all three test conditions.
The tilted stimuli induced a compensatory response (~0.08 deg/s) of the torsional position in all subjects and test conditions. The 45-degree stimulus tilt induced a slightly larger response (1.5±0.7 deg, p<.001) compared to the 30-degree (1.4±0.6 deg, p<.001) and the 15-degree (1.3±0.6 deg, p<.001) stimulus tilt. The torsional response settled after 15-21s and started to drift back towards the zero-position. The average drift velocity was approximately 0.02 deg/s independent of test condition and the torsional amplitude induced.
Compared to the vestibular induced torsional response presented elsewhere, this visually induced response differed in several aspects. The visual stimulus induced less torsion and the position started to drift back earlier. However, the velocity of the drift movement back towards the zero position is the same as the torsional drift during a head roll paradigm. This result supports the idea of a common torsional gaze holding mechanism with a similar leakage independent of which sensory system inducing the torsional response.
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