What is the Vestibulo-Ocular Reflex (VOR)?
The Vestibulo-Ocular Reflex (VOR) is a reflex that produces compensatory eye movements in response to head movement. These eye movements match the amplitude and speed of the head movements but occur in the opposite direction. The purpose of this reflex is to maintain a stable gaze during head movements, minimizing the blurring of visual targets in our environment.
Individuals with reduced VOR function, often due to vestibular disorders, may struggle to produce adequate compensatory eye movements in response to head movements. This can lead to a common complaint known as oscillopsia, where visual blurring occurs during motion (please refer to the video below, though caution is advised as it may provoke symptoms).
Since our heads and bodies are constantly in motion, having a clear image while moving is essential. Even when walking straight and looking ahead, our heads naturally bob up and down and move side to side (see the image below). If we couldn't keep our vision stable while moving, it would lead to dizziness and nausea—it's no surprise that these symptoms frequently arise after a concussion or with vestibular disorders!
BEWARE: Watching this video can be symptom-provoking!
Dang, Duc & Dang, Khanh & Chee, Young & Suh, Young. (2017). Neck Flexion Angle Estimation during Walking. Journal of Sensors. 2017. 1-9. 10.1155/2017/2936041.
VOR Testing
VOR Testing is an essential part of a comprehensive vestibular assessment. Some physical tests specifically designed to evaluate VOR function include:
Head Impulse Test (or Head Thrust Test):
This common bedside test involves abruptly turning the patient’s head while observing whether they can maintain a steady gaze on a target during the movement. An abnormal result occurs when the patient struggles to keep a steady gaze, indicating a possible unilateral or bilateral loss of VOR function.
Dynamic Visual Acuity Test:
This bedside test involves passively turning the patient’s head at a specific speed while they read lines on an eye chart. An abnormal result is noted when the patient's ability to read the lines significantly differs between head movements and when their head is still.
Head-Shaking Nystagmus Test (with Infrared Video Goggles):
In this test, the patient's head is oscillated for a set number of repetitions, followed by an observation of their eyes for nystagmus (a type of involuntary eye movement). This test is usually conducted with infrared video goggles to clearly capture the eye movements. Since these movements can be subtle and difficult to perceive, it is crucial that a trained vestibular therapist conducts the assessment.
The vestibular system is capable of detecting and responding to a wide range of head velocities, making it essential to train at various speeds. Daily activities, such as walking, typically involve lower head velocities, while running requires higher velocities. Therefore, training across this spectrum is crucial for a complete return to daily life. The primary goal of improving vestibulo-ocular reflex (VOR) function is to normalize gaze stability and postural control by reprogramming eye movements and postural responses to movement.
As a vestibular therapist, when I prescribe exercises to enhance VOR function, I take into account whether the patient’s symptoms are triggered by specific movements, positions, or environmental situations. This ensures that the treatment is tailored to the symptoms reported by the patient rather than focusing solely on their diagnosis. It's essential that the exercises are closely supervised and progressed appropriately, as it is easy to overdo them, causing significant aggravation of symptoms, or to perform them insufficiently, rendering them ineffective.
If you want to learn more about the VOR (Vestibular Ocular Reflex), check out my educational series, "The Dizzy Brain: Demystifying Vestibular Exercises." Whether you've already been prescribed VOR exercises and want to understand their purpose better or you're unsure if you need them and want to find out more, take a look at the "VOR/Gaze Stabilization Exercises."
You will learn about vestibulo-ocular reflex (VOR) and gaze stabilization exercises, which are used to enhance eye control during head and body movements. VOR and gaze stabilization exercises are prescribed to address blurred vision that occurs while moving around. We will review how it’s typically tested, the purpose of this exercise, and how the exercise can be modified.
