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Introduction Patients with bilateral vestibular dysfunction cannot fully compensate passive head rotations with eye movements, and therefore experience oscillopsia, making everyday activities, such as walking or driving harder to undertake. Their dynamic vision during passive head movements depends on their residual vestibulo-ocular reflex (VOR) function and on re-fixation saccades. The Head Impulse Testing Device – Functional Test (HITD-FT) is a recently proposed and innovative technique for assessing dynamic vision during passive high-acceleration head rotations, mimicking natural everyday movements. Goals To validate the HITD-FT as a tool to assess the performance of the vestibulo-ocular reflex (VOR) and the effect of re-fixation saccades on the overall dynamic visual function in opioid-induced bilateral vestibular dysfunction. Materials and methods The opioid remifentanil was continuously administrated in 14 healthy men (median age 26 years, range 21–31) in order to reversibly induce a bilateral vestibular impairment. Each subject was tested with the HITD-FT before and during opioid administration. In each test, passive, unpredictable, high-acceleration (2000–7000°/s 2 ) and small amplitude (10–20°) the ects-FT score mirrorice comched 300°/srdmic visual function matters. Unctionality, i.e. disturbing oscillopsia lity to com head rotations where applied while subjects fixated a visual stimulus. The visual stimulus consisted of a standard Landolt ring and appeared on a screen 80 ± 2 ms after head acceleration reached 300°/s 2 . Subjects were asked to identify the orientation of the ring and the provided answers were analyzed together with eye and head movements recorded with EyeSeeCam system. Results Before opioid application, VOR and dynamic reading performances were intact (head-impulse gain: 0.87 ± 0.08, mean ± SD; HITD-FT rate of correct answers: 90 ± 9%). The opioid administration induced impairment in the VOR function (head-impulse gain 0.63 ± 0.19) and in dynamic reading (HITD-FT 26 ± 15%) in 12/14 subjects. HITD-FT scores correlated with head-impulse gain impairment ( R = 0.63, p = 0.03) and with gain difference (before/during opioid R = −0.64, p = 0.02). One subject had non-pathological head-impulse gain (0.82 ± 0.03) and high HITD-FT score (92%). One subject could read (93%) despite a low head-impulse gain (0.59 ± 0.03) performing re-fixation saccades. Summary Our study suggests that the recently proposed HITD-FT is an appropriate method to document the combined effect of VOR performance and re-fixation saccades in vestibular dysfunction. Testing dynamic vision with head movement characteristics closely related to subjects’ daily activities makes the HITD-FT a suitable tool for assessing overall dynamic visual performance, e.g., to monitor progress during vestibular rehabilitation. [ABSTRACT FROM AUTHOR]

The article describes the association between abnormal eye movements and unilateral loss of vestibular function. A spontaneous nystagmus that is horizontal and torsional results from an acute unilateral loss of peripheral vestibular function. An imbalance in tonic activity between the two vestibular nerves also causes the nystagmus, which is initially present during visual fixation. The spontaneous nystagmus resolves after a rebalancing of central vestibular tone. The loss of peripheral vestibular function results to abnormal response to the head-thrust test, which is used to assess the vestibulo-ocular reflex.

We examined 420 patients with vestibular diseases of different origin; 273 with peripheral vestibular disease and 147 with both peripheral and central vestibular disease. Recurrent vestibulopathy like Menière's disease, or benign paroxysmal positional vertigo, were not included. Patients were evaluated initially and 6 months after pharmacological and/or rehabilitation therapy. At the initial assessment, the head-shaking test was specific for the side of the lesion in both groups, even if spontaneous nystagmus was no longer present. Thus, head-shaking nystagmus is a physical sign that can be easily evoked and gives useful information about the presence of vestibulo-ocular reflex asymmetry. At the follow-up at 6 months, many changes in the head-shaking nystagmus were noted: in some cases it appeared, in some others it changed direction and more often it disappeared. There is actually no acceptable explanation for the disappearance of the head-shaking nystagmus, despite some evidence that vestibular compensation could play a role. It is definitely proved that sensitivity of the head-shaking test is really poor, especially in the course of time and, therefore, it should not be used alone in the follow-up of patients with vestibular disease. [ABSTRACT FROM AUTHOR]