Optimal Parameters for the Clinical Test of Dynamic Visual Acuity in Patients with a Unilateral Vestibular Deficit

Abstract

To determine the influence of frequency and direction of head movement and type of vision chart on the score of a clinical test of dynamic visual acuity (DVA). The subjects were 31 healthy individuals (22 to 79 years old) and 10 patients (19 to 70 years old) with a unilateral vestibular deficit owing to surgical resection of an acoustic neuroma. They read a Snellen or an E-chart while their head was passively moved +/- 20 degrees back and forth in the horizontal or vertical direction at one of four frequencies (0.5, 1.0, 1.5, and 2.0 Hz). The DVA score was the difference in the number of lines on the vision chart that could be read with the head passively moved versus with the head immobile. Four healthy subjects had a low DVA score during horizontal head movements at the fastest frequency (2.0 Hz) with the Snellen chart. In patients, DVA scores significantly decreased as head movement frequency increased from 0.5 to 1.0 Hz and from 1.0 to 1.5 Hz, during horizontal and vertical movements, and with both vision charts (p < .001). The DVA scores of healthy subjects were more consistent across three trials with the E-chart than with the Snellen chart at 1.0 and 0.5 Hz (horizontal movements, p < .01) and at 1.5 and 1.0 Hz (vertical movements, p < .01). This study provides new indications on the optimal parameters for the clinical test of DVA. From the results, it is recommended that DVA be tested during horizontal and vertical head movements at a frequency of 1.5 Hz with the E-chart.