Abstract Details

We sought to investigate the three-axis vestibulo-ocular reflex and compensatory saccades characteristics before and after complete unilateral vestibular deafferentation (UVD).

Forty subjects before and after total UVD for vestibular and facial nerve schwannoma were studied using the video head impulse test (vHIT). Multivariable regression models were used within the framework of generalised estimating equations and linear mixed model. 

Before UVD, the mean VOR-gain towards the affected ear was reduced for all semicircular canals (lateral, anterior, posterior: 0.69,0.72,0.49). One week after UVD the VOR-gains for impulses towards from the affected ear were markedly reduced (0.22,0.27,0.37), while gains towards the intact ear were unchanged (0.84,0.86,0.62). One year after UVD, the VOR-gains of all canals towards the affected ear slightly increased (+0.03–0.11), most from the posterior-canal. The mean dynamic range of the intact ear’s VOR-gain (towards-away difference) was markedly lower (40%) for the posterior (0.23) compared to the lateral and anterior (0.58,0.57) canals. One week after UVD, the frequency and amplitude of the first refixation saccade rose from pre-surgical values of 61–93% to 96–100% and from 1.9–3.0° to 3.0–5.8° then remained unchanged over one year, while the second saccade frequency and amplitude decreased.

After UVD the innate asymmetry of the high-acceleration VOR is less obvious for posterior-canal impulses. Changes in compensatory saccades are almost immediate, near complete, and change only slightly over time.