Role of central preprogramming in dynamic visual acuity with vestibular loss.

OBJECTIVE To determine the contribution of central preprogramming of eye movements to dynamic visual acuity (DVA) during head movement in patients with vestibular hypofunction. STUDY DESIGN Prospective, clinical study. SETTING Tertiary care, academic hospitals. PARTICIPANTS Twenty-six healthy subjects and 20 patients with unilateral (UVL) and 7 with bilateral vestibular loss (BVL) (age range, 20-86 years). INTERVENTIONS Diagnostic interventions, including caloric and rotational chair testing. MAIN OUTCOME MEASURE Measurements of DVA during predictable (DVA-predictable) and unpredictable (DVA-unpredictable) head movements using a computerized test. RESULTS There was a difference between DVA-predictable and DVA-unpredictable scores in all groups (P<.02). The difference between DVA-predictable and DVA-unpredictable scores for the BVL group was significantly greater than that for the other groups (P<.005). Age was a significant factor in DVA-unpredictable scores for the healthy subjects (P<.001) and UVL group (P<.02). Comparisons of DVA between groups were significant (P<.03), with the following exceptions: UVL group for head movements toward the unaffected side for DVA-predictable and DVA-unpredictable scores, compared with healthy subjects, and UVL group for head movements toward the affected side for DVA-predictable scores, compared with the BVL group. CONCLUSIONS Unpredictable head movements cause a greater decrement in visual acuity than do predictable head movements. This suggests that central programming of eye movements and/or efference copy contributes to gaze stability during predictable head movements in healthy subjects and patients with vestibular hypofunction. Patients with BVL use central programming of eye movements to maintain gaze stability more than do healthy subjects or patients with UVL.