Role of central preprogramming in dynamic visual acuity with vestibular loss

Objective: To determine the contribution of central preprogramming of eye m ovements to dynamic visual acuity (DVA) during head movement in patients wi th 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 c hair testing. Main Outcome Measure: Measurements of DVA during predictable (DVA-predictab le) and unpredictable (DVA-unpredictable) head movements using a computeriz ed test. Results: There was a difference between DVA-predictable and DVA-unpredictab le 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-unp redictable scores for the healthy subjects (P<.001) and UVL group (P<.02). Comparisons of DVA between groups were significant (P<.03), with the follow ing exceptions: UVL group for head movements toward the unaffected side for DVA-predictable and DVA-unpredictable scores, compared with healthy subjec ts, and UVL group for head movements toward the affected side for DVA-predi ctable scores, compared with the BVL group. Conclusions: Unpredictable head movements cause a greater decrement in visu al acuity than do predictable head movements. This suggests that central pr ogramming of eye movements and/or efference copy contributes to gaze stabil ity 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 patie nts with UVL.