Vertical dynamic visual acuity in normal subjects and patients with vestibular hypofunction

Objective: This study was designed to measure visual acuity during active vertical head movement and to examine its relationship to subjective reports of oscillopsia. Study Design: This was a prospective, clinical study. Setting: The study was performed in a tertiary, ambulatory referral center. Patients: Thirty normal subjects, 13 patients with unilateral vestibular hypofunction, 11 patients with bilateral vestibular loss, and 10 patients with nonvestibular dizziness were examined. Vestibular loss was confirmed with caloric or rotary chair testing. Intervention: Diagnostic. Main Outcome Measure: Reliability, sensitivity, and specificity of a computerized test that measures visual acuity during active vertical head movement. Subjective complaint of oscillopsia was measured by use of a visual analog scale. Results: The active vertical head movement test was reliable both for normal subjects (intraclass correlation coefficient, r = 0.89) and for patients with dizziness (intraclass correlation coefficient, r = 0.94). Age contributed significantly to active vertical head movement in normal subjects and in patients with dizziness over the age of 46 years but not in younger subjects. Older subjects had a decrement in active vertical head movement compared with younger subjects. Subjective reports of oscillopsia did not correlate positively with active vertical head movement. Conclusion: The active vertical head movement test is a reliable measure of visual acuity during active vertical head motion. The effect of age on active vertical head movement may reflect the physiologic impact of neuronal loss with aging. The poor correlation between active vertical head movement and reports of oscillopsia may be caused by the predictability of head movements during the active vertical head movement test compared with the unpredictability of head movements during walking.