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The Vestibulo-ocular Reflex During Active Head Motion in Chiari II Malformation

Published online by Cambridge University Press:  02 December 2014

Michael S. Salman ,
James A. Sharpe ,
Linda Lillakas ,
Maureen Dennis  and
Martin J. Steinbach
Michael S. Salman*
Affiliation:
Section of Pediatric Neurology, Children’s Hospital, University of Manitoba, Winnipeg, Manitoba
James A. Sharpe
Affiliation:
Division of Neurology, University Health Network Vision Science Research Program, University Health Network The Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada
Linda Lillakas
Affiliation:
Vision Science Research Program, University Health Network
Maureen Dennis
Affiliation:
Division of Psychology, University of Toronto, Toronto, Ontario, Canada The Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada
Martin J. Steinbach
Affiliation:
Vision Science Research Program, University Health Network The Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada
*
Section of Pediatric Neurology, AE 308, Children’s Hospital, 820 Sherbrook St., Winnipeg, Manitoba, R3A 1R9, Canada.
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Abstract

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Background:

Chiari type II malformation (CII) is a developmental anomaly of the cerebellum and brainstem, which are important structures for processing the vestibulo-ocular reflex (VOR). We investigated the effects of the deformity of CII on the angular VOR during active head motion.

Methods:

Eye and head movements were recorded using an infrared eye tracker and magnetic head tracker in 20 participants with CII [11 males, age range 8-19 years, mean (SD) 14.4 (3.2) years]. Thirty-eight age-matched healthy children and adolescents (21 males) constituted the control group. Participants were instructed to ‘look’ in darkness at the position of their thumb, placed 25 cm away, while they made horizontal and vertical sinusoidal head rotations at frequencies of about 0.5 Hz and 2 Hz. Parametric and non-parametric tests were used to compare the two groups.

Results:

The VOR gains, the ratio of eye to head velocities, were abnormally low in two participants with CII and abnormally high in one participant with CII.

Conclusion:

The majority of participants with CII had normal VOR performance in this investigation. However, the deformity of CII can impair the active angular VOR in some patients with CII. Low gain is attributed to brainstem damage and high gain to cerebellar dysfunction.

Résumé:

RÉSUMÉ:Contexte:

La malformation de Chiari de type II (CII) est une anomalie du développement du cervelet et du tronc cérébral, deux structures importantes pour l’intégrité du réflexe vestibulo–oculaire (RVO). Nous avons étudié les effets de la malformation CII sur le RVO angulaire pendant les mouvements actifs de la tête.

Méthodes:

Les mouvements des yeux et de la tête ont êtê enregistrés au moyen d’ un ecartometre infra rouge et d’un écartomètre magnétique de la tête chez 20 participants atteints de CII, 11 garçons et 9 filles âgés de 8 á 19 ans (âge moyen 14,4 ans ; ÉT 3,2 ans). Le groupe t émoin était compos é de trente–huit enfants et adolescents en bonne santé, appariés pour l’âge (21 garçons et 17 filles). Les participants devaient fixer la position de leur pouce dans l’obscurité à une distance de 25 cm, pendant qu’ils faisaient des rotations sinusoidales horizontales et verticales de la tête à des fréquencies d’ à peu près 0,5 Hz et 2 Hz. Des tests paramétriques et non paramétriques ont été utilisés pour comparer les deux groupes.

Résultats:

Les gains du RVO, le rapport de la vitesse des yeux à la vitesse de la tête, étaient anormalement bas chez deux sujets atteints de CII et anormalement élev és chez un sujet atteint de CII.

Conclusion:

La majorité des participants atteints de CII avaient un fonctionnement normal du ROV dans cette étude. Cependant, la malformation de CII peut altérer le ROV angulaire actif chez certains patients. Un gain bas est attribué à l’atteinte du tronc cérébral et un gain élevé à la dysfonction cérebélleuse.

Type
Original Articles
Information
Canadian Journal of Neurological Sciences , Volume 35 , Issue 4 , September 2008 , pp. 495 - 500
Copyright
Copyright © The Canadian Journal of Neurological 2008

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