Affiliations: [a] School of Medicine, Case Western Reserve University School of Medicine and Louis Stokes Cleveland Department of Veterans Affairs Medical Center, Cleveland, OH, USA
| [b] Current address: Department of Neurology, University of California, San Francisco, CA, USA
| [c] Department of Neurology, Case Western Reserve University and Louis Stokes Cleveland Department of Veterans Affairs Medical Center, Cleveland, OH, USA
Correspondence:
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Corresponding author: Mark Walker, M.D., Department of Neurology, Case Western Reserve University, Louis Stokes Cleveland VAMC, 10701 East Blvd., 127W, Cleveland, OH 44106, USA. Tel.: +1 216 421 3224; Fax: +1 216 231 3461; E-mail: mark.walker@case.edu.
Abstract: Dynamic visual acuity is an important clinical tool for assessment of the rotational vestibulo-ocular reflex (rVOR). It is based on the fact that the normal rVOR stabilizes vision and maintains visual acuity during head rotation. The translational VOR (tVOR) generates eye movements during linear head motion. Studies in humans have shown that gaze stabilization during translation is incomplete and that there is a strong effect of the visual environment: eye velocity is much greater in the light than in the dark. In this study, we measured visual acuity during vertical translation in 11 subjects and asked whether a more complex visual background would enhance the response and improve acuity. During 2 Hz whole-body translation, tumbling-E optotypes (0.0–0.9 logMAR in steps of 0.1 logMAR, six trials of each size randomly ordered) were flashed on a screen that was 30 cm in front of the subject’s eyes. The subject reported the optotype’s orientation with a joystick. Based on a threshold of 75% trials correctly identified, the group dynamic acuity was 0.72 logMAR, compared to a static acuity of 0.0 logMAR. When the background was enhanced with a stationary dot pattern, dynamic acuity improved to 0.42 logMAR. Our findings show that vertical head translation degrades vision more than head rotation. This may limit the use of dynamic acuity as a clinical measure of otolith function.
