Gaze stability as a measure of vestibular function:
Deficits and corrective strategies of 3D gaze stability in singel sided vestibular loss

The vestibular system contributes to body balance, gaze stability and spatial
orientation, both in stationary position and during movement.
Sudden, single sided loss of function leads to vertigo and instability and to
symptom related to reduced gaze stability as oscillopsia and visual lag.
Dizziness and instability may also arise as result of neurological and
cardiological disease. It may be difficult to distinguish between causes.
Single sided vestibular loss will usually be readily compensated for, reducing
symptoms. On clinical examination nystagmus disappears and corrective saccades
develop.
The commonly used clinical tests calculate the ratio of eye versus head
movement, which yields a relative measure, not aimed at setting criteria for
compensatory strategies. Retinal slip velocity, which is is not commonly
calculated, is an absolute measure of the difference between head and eye
movement. increase of retinal slip velocity increases misalignment between head
and eye direction.
Furthermore, only horizontal and vertical eye movements are analysed, due to
methodological limitations. However, torsion is a component of virtually every
eye movement. We will use a new technique to measure eyeball torsion with the
help of a contact lens.

To validate the method of measuring torsional eye movements
To measure 3D eye movements
To assess the age dependency of the responses
To measure the gain of eye- versus headmovement and retinal slip velocity in
clinical diagnosis by comparing patients with single sided vestibular disease
to normal subjects.
To describe the amplitue and timing of corrective saccades as a function of
misalignment, to correlate the ability to correct for loss of vestibular
function to symptoms

Pilot study, with 3 experiments:
1. Validation of the measurement method for torsional eye movements
2. Obtain age dependent normal values for accuracy of gaze stabiisation
3. Assess gaze stability in single sided vestibular loss and in stationairy
retinal dysfunction syndrom

All participants will fill out the dizziness handicap inventory and the
questionnaire from the Rotterdam study. The questionnaire has been slightly
adapted for this experiment. The questionnaires serve to investigate the
correlation between symptoms and compensatory eye movement strategies.

The horizontal, vertical and torsional will be measured by a infrared camera,
mounted on a pair of goggles, held in place by a tight fitting headband.
Torsional eye movement will stand out more clearly when the subject wears a
structured contact lens, approved by METC (MEC*2016*327),

In the validation experiment the head movements are generated by a motion
platform, the head is immobilised by supports and a bite board. This equipment
has been assessed and approved by the METC (METC-2003-82) .

For registering eye movements a contact lens, or a scleral coil (approved by
METC (MEC*2016*327)) will be used

For experiment 2 and 3 a standard clinical protocol will be used. Low frequency
movements are generated by a rotatory chair, high frequency head movements are
generated by head impulses that are manually applied.

The bite board, the lenses, the scleral coils and het video goggles all
generate some discomfort without causing a risk.