Smooth Pursuit Substitution: A Hidden Gem for Treating Vestibular Hypofunction

Photo by Yevhenii Aihubov on Unsplash

Imagine a patient whose world blurs and spins with every turn of their head. They struggle to read street signs while walking, or find navigating a grocery store overwhelming. This often happens because the vestibulo-ocular reflex (VOR) – the rapid, automatic reflex that stabilizes our gaze during head movement – is compromised or absent. While traditional vestibular rehabilitation often focuses on adapting a diminished VOR, for individuals with bilateral or profound unilateral vestibular hypofunction, this cornerstone technique may fall short. This is precisely where Smooth Pursuit Substitution (SPS) shines as a hidden gem in the physical therapist's toolkit, offering a powerful and active compensatory strategy.

The Power of SPS: Beyond Traditional Smooth Pursuit

At FYZICAL, we understand the importance of a diverse toolkit to address complex vestibular challenges. While standard smooth pursuit exercises involve tracking a moving target with the eyes, SPS takes this foundational movement further. It strategically incorporates a deliberate head movement at the end of the smooth pursuit, effectively mimicking the VOR's compensatory eye movement. This seamless combination of smooth pursuit and coordinated head movement provides a robust substitute for lost or diminished VOR function, actively engaging the patient in their recovery and empowering them to regain control.

Who Can Benefit from SPS?

SPS offers significant clinical utility across a range of vestibular pathologies:

• Bilateral Vestibular Hypofunction (BVH): SPS is particularly beneficial for individuals with BVH, where both inner ear balance organs are impaired and VOR function is severely limited or absent. By actively substituting for the missing VOR, SPS significantly reduces oscillopsia (the illusion of objects jumping or blurring) and dramatically improves gaze stability during head movement, empowering patients to navigate their environment with greater clarity.

• Unilateral Vestibular Hypofunction (UVH): Even those with UVH, where only one inner ear is affected, can benefit from SPS. SPS can enhance visual stability and reduce dizziness by strengthening the coordination between smooth pursuit and head movement, facilitating compensation.

• Broader Applicability: SPS offers broad applicability beyond chronic hypofunction. It can also be a valuable tool for individuals in the recovery phase after acute vestibular events, such as vestibular neuritis and labyrinthitis, or for those experiencing vestibular symptoms from other neurological disorders. This versatility underscores its effectiveness and potential in a wide range of cases where the VOR is not fully functional.

The Intricate Dance of the Visual and Vestibular Systems

At its core, SPS cleverly exploits the inherent interplay between the visual and vestibular systems, building a learned, active compensation. Unlike the automatic, reflexive nature of a fully functioning VOR, SPS is a learned, compensatory strategy that actively substitutes for its absence or impairment:

• Intact Smooth Pursuit: BVH primarily affects the vestibular organs responsible for detecting head motion and generating the VOR. However, the smooth pursuit system, which enables the eyes to track moving objects smoothly, often remains largely intact.

• Capitalizing on Smooth Pursuit: SPS harnesses this preserved smooth pursuit ability by having the patient visually track a moving target. This actively engages the neural pathways responsible for smooth eye movements, priming the system for coordinated action.

• The Head Movement ‘Hack’: The crucial innovation of SPS lies in the deliberate, coordinated head movement towards the target after the smooth pursuit phase. This conscious, active head movement initiates a profound cascade of physiological consequences:

  • Retinal Slip Reduction: The rapid, precisely timed head movement minimizes the discrepancy between the target's position on the retina and the fovea (the central part of the retina responsible for the sharpest vision). This significant reduction in retinal slip signals to the brain that the gaze is stable, even though the head is in motion.

  • Proprioceptive Feedback: The head movement also powerfully activates proprioceptors in the neck muscles and joints, providing crucial additional sensory information about head position and movement. This rich proprioceptive feedback further reinforces the brain's perception of a stable gaze and helps to drive the adaptive process.

  • Neural Integration: The brain actively integrates visual information from smooth pursuit and robust proprioceptive input from head movement. This complex integration creates a unified sensory experience that effectively mimics the VOR's compensatory eye movement, even though the primary vestibular signals are absent or severely diminished.

• The Result: A Virtual VOR: Through this orchestrated symphony of active visual tracking, deliberate head movement, retinal slip reduction, proprioceptive feedback, and dynamic neural integration, SPS effectively constructs a "virtual VOR" that compensates for the loss of the original reflex.

Why It Matters for Vestibular Patients

Implementing SPS can lead to profound functional improvements:

• Improved Gaze Stability: The coordinated eye and head movement drastically reduces retinal slip, leading to a stable gaze even during head motion.

• Enhanced Visual Clarity: By stabilizing the gaze, SPS minimizes the common and distressing blurring and jumping of objects (oscillopsia), significantly improving visual clarity and comfort.

• Reduced Dizziness: SPS helps resolve the often disorienting sensory conflict between the impaired vestibular system and visual input, actively decreasing dizziness and improving overall balance confidence.

Practical Implementation: How to Perform SPS

Integrating SPS exercises into vestibular rehabilitation programs is straightforward and highly adaptable. They can be performed in various planes of movement (horizontal, vertical, diagonal) and with different target speeds and complexities, making their implementation flexible and empowering for both therapist and patient.

Core Movement:

1. Target Tracking: The patient focuses intently on a moving target (e.g., a penlight, a therapist's finger, or a laser pointer) and smoothly tracks it with their eyes only through a prescribed range.

2. Head Movement: As the target reaches the end of its path, the patient quickly and precisely moves their head in the same direction as the target is moving. This head movement should be smooth and controlled, ideally matching the target's speed and ensuring the target remains clearly in focus.

Key Points for Progression and Adaptation:

• Gaze Stabilization Focus: The primary aim of head movement is to maintain the target's image on the fovea actively (the center of the retina) even as the head moves. This minimizes blurring and the sensation of objects jumping (oscillopsia).

• Progression: Start with slow target speeds and simple movements (e.g., horizontal tracking with a limited range). As the patient improves, incrementally increase target speed, vary directions (vertical, diagonal), expand the range of motion, and introduce more complex target paths or environmental challenges.

• Adaptation: SPS helps the brain actively adapt to the loss of VOR, so consistency is key. Encourage regular, diligent practice at home between therapy sessions, emphasizing precision and symptom tolerance.

Additional Clinical Considerations:

• Target Distance: Start with a comfortable distance (approximately 1-2 feet) and adjust it based on the patient's visual acuity and comfort level.

• Head Movement Range: The head movement should be sufficient to challenge the system but not so significant as to cause discomfort, pain, or cervical strain. Continually assess cervical range of motion and pain before implementing head movements. Start gently with patients experiencing acute vertigo or significant neck pathology.

• Patient Feedback & Monitoring: Pay close attention to the patient's experience. If they report dizziness, nausea, or headache, modify the exercise (reduce speed, range, or complexity) or take a break. Progress should be gradual and symptom-limited.

• Cognitive Load: For some patients, the initial cognitive load of coordinating eyes and head can be high. Start in a quiet, uncluttered environment and gradually increase distractions as tolerance improves.

Patient Education: Explaining the ‘Virtual VOR’

When introducing SPS to patients, framing it effectively can significantly enhance understanding and adherence. You can explain:

Your inner ear's natural 'camera stabilizer' isn't functioning properly, causing objects to blur when you move your head. We're going to teach your brain a new, active way to 'stabilize the camera' by coordinating your eyes and head, creating a 'virtual VOR. ‘This new strategy will help you keep things clear and feel steadier.

Conclusion

Smooth pursuit substitution (SPS) is a versatile and highly effective therapeutic tool for individuals with vestibular disorders, particularly when VOR function is compromised. By understanding its unique mechanism, leveraging active smooth pursuit and deliberate head movements to create a ‘virtual VOR’, and by expertly incorporating its implementation into your practice, you can empower your patients to regain crucial visual stability, significantly reduce distressing dizziness, and dramatically improve their quality of life.

---

Brian K. Werner, PT, MPT, National Director of Vestibular Education & Training at FYZICAL. Brian Werner has been a dedicated physical therapist specializing in vestibular and balance disorders for over 25 years. His expertise in advanced rehabilitation techniques makes him a leading voice in the field.

Additional Articles to Read

Lacour M, Yavo Dosso N, Heuschen S, Thiry A, Van Nechel C, Toupet M, et al. How Eye Movements Stabilize Posture in Patients With Bilateral Vestibular Hypofunction. Front Neurol. 2018;9:744. doi: 10.3389/fneur.2018.00744

McCall, A. A., & Shepard, N. T. (2016). The effect of gaze stabilization exercise on visual acuity during head movement in patients with vestibular hypofunction. Journal of Vestibular Research, 26(2), 119-127.