Relationship Between Corrective Saccades and Measures of Physical Function in Unilateral and Bilateral Vestibular Loss

Objectives: Following the loss of vestibular function, some patients functionally improve and are minimally bothered by their loss of peripheral function while others remain more symptomatic and are unable to return to their activities of daily living. To date, the mechanisms for functional improvement remain poorly understood. The purpose of the present study was to examine the association between corrective saccades and measures of handicap, dynamic visual acuity, gait, and falls. Design: A retrospective chart review was performed to identify patients who were diagnosed with unilateral or bilateral vestibular hypofunction and who also completed a baseline vestibular rehabilitation evaluation. A total of 82 patients with unilateral vestibular hypofunction and 17 patients with bilateral vestibular hypofunction were identified. The video head impulse test results for each patient were grouped based on the type of presenting saccades. Specifically, the saccade grouping included the following: (1) covert, (2) overt, or (3) a combination of both types of saccades. Results: The results show that covert saccades are associated with better performance on measures of dynamic visual acuity, gait, and balance in patients with unilateral vestibular hypofunction. Patients exhibiting overt saccades or combination of both covert and overt saccades were more often found to have an abnormal gait speed and be characterized as being at risk for falls using the Dynamic Gait Index. We observed no differences in physical function for those patients with bilateral vestibular hypofunction as a function of saccade grouping. Conclusions: When comparing saccade groups (covert, overt, or combination of both), patients with unilateral vestibular hypofunction and covert saccades demonstrated better performance on standard baseline physical therapy measures of dynamic visual acuity and gait and balance. We did not observe any significant associations between saccade group and physical function in patients with bilateral vestibular hypofunction; however, additional studies are needed with adequate sample sizes. Our findings may suggest that corrective saccade latency in patients with unilateral vestibular hypofunction is related to measures of physical function. The extent to which saccade latency has the potential to be a useful target for vestibular rehabilitation is still to be determined and may be promising target to improve functional outcomes.