The vestibulo-ocular reflex response to head impulses rarely decreases after cochlear implantation

Measure vestibular function using the head impulse test and assess the change in function due to unilateral cochlear implantation.

Cochlear implantation entails risks to vestibular function in the implanted ear. However, the nature and extent of this risk is not known. The head impulse test uses physiologically relevant stimuli that allow detection of subtle changes in vestibular function of individual semicircular canals.

Sixteen adults (age, 28-65 years) were recruited for prospective study from the Listening Center at Johns Hopkins. Eleven of these subjects were tested 4 to 6 weeks after cochlear implantation.

Three-dimensional eye movement recordings were made using the scleral search coil technique. Stimuli were rapid, passive, transient, head-on-body rotations (acceleration approximately 3000 degrees /s) in the direction excitatory for each of the six semicircular canals.

Of the 16 subjects measured preoperatively, 6 (36%) had low (< 0.74) VOR gains in one or both of the horizontal canals and 8 (50%) had low (< 0.64) vestibulo-ocular reflex (VOR) gains in one or more of the vertical canals. These preoperative gain deficits were bilateral in six subjects. The VOR gain did not significantly change after implantation in 10 out of the 11 subjects tested postoperatively. The remaining subject suffered a partial loss of function in the implanted ear and was the only subject who experienced transient vertigo and oscillopsia after implantation.

Preoperative vestibular deficits were common among this group of candidates for cochlear implantation; however, significant loss of vestibular function due to cochlear implantation was uncommon.