Efficient gaze stabilization during video Active Gaze Shift Test (vAGST) in bilateral vestibulopathy

Area of Science:

• Neuroscience
• Ophthalmology
• Vestibular System

Background:

• Current vestibular deficit assessments primarily use passive head movements, which don't fully represent daily active head movements.
• Quantifying gaze stabilization during active movements is crucial for understanding functional deficits in patients with vestibular loss.
• Anticipatory mechanisms play a significant role during active gaze shifts, yet their role in vestibular loss is not fully understood.

Purpose of the Study:

• To investigate the compensatory mechanisms employed by patients with bilateral vestibular loss during active gaze shifts.
• To assess gaze stabilization efficiency during active movements in patients with bilateral vestibular deficits.
• To explore the relationship between head movement speed and gaze stabilization in individuals with vestibular loss.

Main Methods:

• Utilized the Video Head Impulse Test (vHIT) to simultaneously record eye and head movements.
• Implemented a video Active Gaze Shift Test (vAGST) to assess active head movements.
• Tested 38 patients with bilateral vestibular deficits and 61 healthy control subjects.

Main Results:

• Despite deficits in passive tests, most patients achieved normal gaze stabilization (gain ≈ 0.92) during active shifts up to a head speed of ~140°/sec.
• Patients with bilateral vestibular loss spontaneously reduced their head speed during active movements, improving gaze stabilization compared to passive conditions.
• Reduced head speed in patients led to a delay in gaze stabilization (413 ms vs. 358 ms in controls), potentially impacting daily tasks.

Conclusions:

• Bilateral vestibular loss patients adapt by limiting head speed during active gaze shifts to maintain gaze stability.
• The 'stall speed' observed correlates with spontaneous head speeds used in daily activities, highlighting an adaptive strategy.
• The increased delay in gaze stabilization may contribute to functional limitations and symptoms like oscillopsia in affected individuals.