Age-Related Changes in Vestibular Evoked Myogenic Potentials and Dynamic Visual Acuity at Near and Far Distances

Abstract

Morphological changes in the vestibular system associated with aging are well documented, but the ability to measure these changes clinically has been limited. Two such tests that have been useful for this purpose are Dynamic Visual Acuity (DVA) and Vestibular Evoked Myogenic Potentials (VEMP). DVA is reportedly sub served by the angular vestibulo-ocular reflex (aVOR) for "far" distances (>2 m) and the linear VOR (lVOR) at "near" distances (2 m) and the linear VOR (lVOR) at "near" distances (<1 m). The VEMP also has been shown to be sub served by the linear otolith system. The current study characterized age-related changes in DVA (distance, speed & neck condition) and VEMP in three groups of adults (20-30 yrs, 65-74 yrs, & 75-85 yrs) and analyzed the relationship between the VEMP and DVA. Strength of muscle contraction was monitored by having patients press their heads against a stabilized blood pressure cuff. A significant age-related decline was seen in VEMP amplitude and threshold in the older groups when compared to the younger group, while latency and interamplitude ratios of VEMP components remained consistent across age groups. No gender or ear-related differences were detected in the VEMP responses. There was a significant decline in DVA with speed (0.75 m/s & 1.5 m/s) during "near" (0.5 m) and "far" (3 m) DVA while an interaction between speed and age was seen only in the "near" conditions. There was also a significant decline in DVA with fixed neck condition in the "near" DVA trials. A significant negative correlation between DVA and VEMP was seen in the "near" condition which is consistent with postulated underlying effectors for the VEMP and "near" DVA. Results of this study provide preliminary normative data across age ranges for DVA and VEMP along with evidence that both of these measures can be used to assess age-related changes in vestibular function.