Hey colleagues,
When addressing vestibular dysfunction, our strategies often differ based on whether the origin is peripheral or central. Central vestibular disorders, impacting pathways within the brain itself, necessitate specific rehabilitation approaches. Our understanding of the mechanisms behind techniques like Vestibulo-Ocular Reflex (VOR) Suppression and VOR Memory training is not just crucial; it's empowering. It's this understanding that allows us to treat our patients effectively.
The VOR, ensuring stable vision during head movements, follows a pathway from peripheral receptors through the brainstem nuclei (vestibular and oculomotor) to the eye muscles. Higher central nervous system centers like the cerebellum typically exert inhibitory control over this reflex. This inhibition is compromised in many central vestibular diseases, leading to a hyperactive VOR. This often presents clinically as a failure of VOR suppression – the inability to keep the eyes steady when tracking a target that moves in sync with head rotation, resulting in unwanted eye movements like nystagmus due to excessive VOR gain.
To address this VOR hyperfunction directly, we employ VOR suppression training. This precise and effective technique involves having the patient fixate on a target that moves precisely with their head rotation. The exercise aims to retrain the central nervous system's inhibitory pathways, helping to reduce the overactive VOR gain. Patients need adequate peripheral vestibular function and intact visual smooth pursuit for this technique to be effective.
Beyond direct suppression, VOR memory training offers another vital strategy, tapping into the brain's cognitive functions like prediction and internal modeling (efference copy). In these exercises, the patient views a target, closes their eyes, turns their head while keeping their gaze on the target's location, and then opens their eyes to verify accuracy. This method strengthens the central nervous system's capacity to guide eye movements relative to head motion without continuous visual input, enhancing reliance on internal predictive mechanisms within areas like the cortex and cerebellum.
While VOR suppression and memory are key for VOR control issues, it's also worth noting that other exercises, such as anti-saccades and memory-guided saccades, play essential roles in addressing the central fixation dysfunctions that frequently accompany these disorders.
In summary, rehabilitating central vestibular dysfunction requires a targeted approach. Techniques like VOR suppression and VOR memory training are designed to address the specific neural mechanisms affected, whether it's restoring central inhibition or enhancing predictive gaze control. Understanding and applying these strategies allows us to provide more precise and effective care for our patients with these complex conditions.
Keep up the great work helping people Love Their Life! Your dedication and expertise are invaluable in the field of vestibular rehabilitation.
Best,
Brian K. Werner, PT, MPT
PS - Here are some specific, practical treatment examples of VOR Suppression and VOR Memory exercises that therapists can readily implement in daily sessions for patients with relevant central vestibular dysfunction:
1. VOR Suppression (VOR Cancellation) Exercises
Goal: To improve the brain's ability to inhibit the VOR when the head and eyes need to move together to track a target moving with the head. Addresses VOR hyperfunction.
Example 1: Thumb/Target Tracking (Seated/Standing)
Setup: Patient sits or stands comfortably. Instruct them to extend one arm straight out, making a fist with the thumb up (or holding a small target like a business card with a letter).
Execution: The patient intently focuses on their thumbnail (or the target). They then slowly rotate their head and torso together as a unit (or just their head and arm together), side-to-side, keeping the thumb/target directly in front of their face. The key is that the target moves with the head. The patient's eyes should remain fixed on the target without slipping off, needing a corrective saccade, or showing overt nystagmus.
Parameters: Start with slow, small arcs of motion (e.g., +/- 20-30 degrees). Perform for 30-60 seconds, rest, and repeat 3-5 times.
Progression: Increase the speed of rotation.
Increase the arc/range of motion.
Progress from sitting to standing with a broad base of support, then a narrow base, then a tandem stance (use the SOS for safety if needed).
Perform while strolling in place or forward/backward (advanced, requires SOS).
Use a more complex visual target or background.
Example 2: Laser Pointer Tracking
Setup: Patient holds a laser pointer. Project the laser onto a wall about 5-10 feet away.
Execution: The patient focuses visually on the laser dot. They then move their head side-to-side (or up/down) while simultaneously moving the hand holding the laser pointer so the dot stays aligned with their nose. The goal is to keep the visual target (laser dot) stable relative to the head during the head movement. Eyes should remain "locked" on the dot.
Parameters/Progression: Similar to Example 1 – adjust speed, range, and base of support. This can sometimes be easier for patients initially struggling with arm/head coordination.
2. VOR Memory (Memory-Guided VOR) Exercises
Goal: To enhance the brain's ability to use internal prediction and memory to control eye position accurately during head movements when visual feedback is temporarily absent.
Example 1: Target-Eyes Closed Head Turn (Seated/Standing)
Setup: Patient sits or stands facing a distinct visual target on the wall (e.g., a large letter, a colored dot) at eye level.
Execution: The patient stares intently at the target for a few seconds.
The patient closes their eyes.
The patient slowly turns their head to one side (e.g., 30 degrees) while actively imagining that their eyes stay perfectly aligned with the target's remembered location in space.
The patient opens their eyes after reaching the head turn position (or holding briefly).
Patient notes the accuracy – are their eyes still pointed at the target, or did they overshoot/undershoot?
The patient turns their head back to the center (eyes open or closed) and repeats, potentially turning to the other or the same side again.
Parameters: Start with slow head turns and smaller angles. Repeat 5-10 times per side/direction.
Progression: Increase the speed of the head turn.
Increase the angle of the head turn.
Increase the duration of the eyes' closing before opening.
Progress from sitting to standing (use SOS if needed).
Use less predictable head turn angles called out by the therapist.
Example 2: Sequential Target Memory
Setup: Place two distinct targets horizontally on the wall (e.g., Target A and Target B). The patient sits/stands facing midway between them.
Execution: Patient looks at Target A.
The patient closes their eyes.
The patient turns their head towards the remembered location of Target B, imagining their eyes moving accurately to it.
The patient opens their eyes and checks the accuracy of Target B.
(Optional) Close your eyes, turn your head back to Target A, open your eyes, and check accuracy.
Parameters/Progression: Similar to Example 1 – adjust speed, target separation (angle), and base of support. You can add more targets or vertical components.
Monitor patient symptoms (dizziness, nausea, fatigue) closely and adjust parameters accordingly. These exercises directly challenge central processing and can be demanding. Always prioritize safety, using gait belts or the Safety Overhead Support System (SOS) when progressing to standing or more dynamic variations.
Very good and explicative