Gaze stabilization during head movements is provided by the vestibulo-ocular reflex (VOR). Clinical assessment of this reflex is performed using the video Head Impulse Test (vHIT). To date, the influence of different fixation distances on VOR gain using the vHIT has not been explored. We assessed the effect of target proximity on the horizontal VOR using the vHIT. Firstly, we assessed the VOR gain in 18 healthy subjects with 5 viewing target distances (150, 40, 30, 20, and 10 cm). The gain increased significantly as the viewing target distance decreased. A second experiment on 10 subjects was performed in darkness whilst the subjects were imagining targets at different distances. There were significant inverse relationships between gain and distance for both the real and the imaginary targets. There was a statistically significant difference between light and dark gains for the 20- and 40-cm distances, but not for the 150-cm distance. Theoretical VOR gains for different target distances were calculated and compared with those found in light and darkness. The increase in gain observed for near targets was lower than predicted by geometrical calculations, implying a physiological ceiling effect on the VOR. The VOR gain in the dark, as assessed with the vHIT, demonstrates an enhancement associated with a reduced target distance.

Keywords:
Video Head Impulse Test, Convergence, Vestibulo-ocular reflex
1.
Chim D, Lasker DM, Migliaccio AA: Visual contribution to the high-frequency human an­gular vestibulo-ocular reflex. Exp Brain Res 2013; 230: 127–135.
2.
Clément G, Maciel F: Adjustment of the vestibulo-ocular reflex gain as a function of perceived target distance in humans. Neurosci Lett 2004; 366: 115–119.
3.
Collewijn H, Smeets JBJ: Early components of the human vestibulo-ocular response to head rotation: latency and gain. J Neurophysiol 2000; 84: 376–389.
4.
Crane BT, Demer JL: Human horizontal vestibulo-ocular reflex initiation: effects of acceleration, target distance, and unilateral deafferentation. J Neurophysiol 1998; 80: 1151–1166.
5.
Crane BT, Viirre ES, Demer JL: The human horizontal vestibulo-ocular reflex during combined linear and angular acceleration. Exp Brain Res 1997; 114: 304–320.
6.
Drake RL, Vogl W, Mitchell AWM, Tibbitts R, Richardson P, Horn A: Gray’s Basic Anatomy. Philadelphia, Elsevier/Churchill Livingstone, 2012.
7.
Fernandez C, Goldberg JM: Physiology of peripheral neurons innervating semicircular canals of the squirrel monkey. II. Response to sinusoidal stimulation and dynamics of peripheral vestibular system. J Neurophysiol 1971; 34: 661–675.
8.
Goldberg JM, Fernandez C: Physiology of peripheral neurons innervating semicircular canals of the squirrel monkey. I. Resting discharge and response to constant angular accelerations. J Neurophysiol 1971; 34: 635–660.
9.
Gresty MA, Bronstein AM: Otolith stimulation evokes compensatory reflex eye movements of high velocity when linear motion of the head is combined with concurrent angular motion. Neurosci Lett 1986; 65: 149–154.
10.
Gresty MA, Bronstein AM, Barratt H: Eye movement responses to combined linear and angular head movement. Exp Brain Res 1987; 65: 377–384.
11.
Hine T, Thorn F: Compensatory eye movements during active head rotation for near targets: effects of imagination, rapid head oscillation and vergence. Vision Res 1987; 27: 1639–1657.
12.
Leigh RJ, Zee DS: The Neurology of Eye Movements, ed 5. Oxford/New York, Oxford University Press, 2015.
13.
MacDougall HG, Weber KP, McGarvie LA, Halmagyi GM, Curthoys IS: The video head impulse test: diagnostic accuracy in peripheral vestibulopathy. Neurology 2009; 73: 1134–1141.
14.
Paige GD: The influence of target distance on eye movement responses during vertical linear motion. Exp Brain Res 1989; 77: 585–593.
15.
Schwarz U, Busettini C, Miles FA: Ocular responses to linear motion are inversely proportional to viewing distance. Science 1989; 245: 1394–1396.
16.
Viirre E, Tweed D, Milner K, Vilis T: A reexamination of the gain of the vestibuloocular reflex. J Neurophysiol 1986; 56: 439–450.
© 2018 S. Karger AG, Basel
2018
Copyright / Drug Dosage / Disclaimer
Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher.
Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug.
Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.
You do not currently have access to this content.