Visual vestibular interaction in the dynamic visual acuity test during voluntary head rotation.
BACKGROUND
Although intact vestibular function is indispensable to maintaining spatial orientation, no good screening tests of vestibular function are implemented in the aviation community. High frequency voluntary head rotation was selected as a vestibular stimulus to isolate the vestibulo-ocular reflex (VOR) from visual influence.


METHODS
A dynamic visual acuity test that incorporates voluntary head rotation was evaluated as a potential vestibular function screening tool: 27 normal subjects performed voluntary sinusoidal head rotation at frequencies from 0.7-4 Hz under 3 different visual conditions: visually-enhanced VOR, normal VOR, and visually suppressed VOR. Standardized Bailey-Lovie chart letters were presented on a computer monitor in front of the subject, who then was asked to read the letters while rotating his head horizontally. The electro-oculogram and dynamic visual acuity score were recorded and analyzed.


RESULTS
There was no significant difference in gain or phase shift among 3 visual conditions in the frequency range 2.8-4 Hz. The dynamic visual acuity score shifted less than 0.3 log MAR at frequencies under 2.0 Hz.


CONCLUSIONS
The dynamic visual acuity test at frequencies around 2 Hz can be recommended for evaluating vestibular function.
Lee
M H
MH
Aeromedial Research Institute, ROKAF, Cheungwon-Gun, Chung-Buk, Republic of Korea.
Durnford
S J
SJ
Crowley
J S
JS
Rupert
A H
AH
D000328:Adult; D000337:Aerospace Medicine; D004585:Electrooculography; D005133:Eye Movements; D005240:Feasibility Studies; D006257:Head / Q000502:physiology*; D006801:Humans; D008403:Mass Screening / Q000379:methods*; D011434:Proprioception; D012027:Reflex, Vestibulo-Ocular / Q000502:physiology*; D015203:Reproducibility of Results; D012399:Rotation; D015837:Vestibular Diseases / Q000517:prevention & control; D014724:Vestibular Function Tests / Q000379:methods* / Q000592:standards; D014792:Visual Acuity