Three dimensional vestibular ocular reflex testing using a six degrees of freedom motion platform

Area of Science:

• Neuroscience
• Ophthalmology
• Biomechanics

Background:

• The vestibular organ is crucial for equilibrium, sensing motion in six degrees of freedom.
• Defects in the vestibular organ cause balance issues like vertigo and dizziness.
• Gaze stabilization, quantified by VOR gain, is vital for visual stability during head movement.

Purpose of the Study:

• To present a method for measuring the three-dimensional vestibulo-ocular reflex (3D VOR) using whole-body rotation on a 6DF motion platform.
• To analyze 3D VOR gain and alignment in response to sinusoidal and impulse stimulation in healthy subjects.
• To investigate how stimulus axis orientation affects 3D VOR responses in light and darkness.

Main Methods:

• Utilized a 6DF motion platform for whole-body sinusoidal and impulse rotational stimulation.
• Measured eye movements using the scleral search coil technique at a 1 kHz sampling frequency.
• Calculated 3D VOR gain and alignment from eye coil signals in response to various stimulus axis orientations.

Main Results:

• 3D VOR gain and alignment were dependent on the orientation of the stimulus axis.
• Systematic deviations in eye rotation axis alignment were observed during horizontal axis stimulation, particularly at intermediate azimuth angles.
• In darkness, VOR gain decreased, altering misalignment patterns compared to light conditions.

Conclusions:

• The described method effectively measures 3D VOR responses, revealing stimulus-dependent variations in gain and alignment.
• Deviations in eye rotation axis can be explained by differential gains for torsional and vertical eye movements.
• Vestibular function assessment requires considering the multi-axis nature of head movements and resulting eye compensatory responses.