Introduction

The Video Head Impulse Test (VHIT) is a key diagnostic tool used to assess the function of the vestibulo-ocular reflex (VOR). It measures the gain of the VOR during rapid, passive head rotations. However, age is an important factor that influences VHIT results and their interpretation. This article examines the effect of age on VHIT outcomes, incorporating the keywords: vestibulo-ocular reflex, gain, semicircular canals, refixation saccades, age-related decline, diagnostic accuracy, and normative data.

Normal Age-Related Changes in the Vestibular System

As people age, many physiological systems undergo degenerative changes, including the vestibular system. The vestibulo-ocular reflex, which stabilizes gaze during head movements, relies on the function of the semicircular canals and central neural pathways. Multiple studies have documented a progressive age-related decline in VOR gain, particularly for high-frequency head impulses used in VHIT.

For example, the VOR gain for the horizontal semicircular canal tends to be stable until around 60 years of age, after which a gradual reduction becomes apparent. This decline is attributed to the loss of hair cells and afferent neurons within the vestibular end organs, as well as central processing changes.

Effect on VHIT Gain

In clinical VHIT, the primary metric is gain—the ratio of eye velocity to head velocity during the head impulse. Normal gain values are typically above 0.8 in young adults. With advancing age, the mean gain can drop to 0.7–0.85 even in healthy older adults without otologic disease. This age-related decline in gain is modest but statistically significant, and it affects all three pairs of semicircular canals to varying degrees.

Importantly, the presence of refixation saccades—corrective eye movements that occur when the VOR is insufficient—can also increase with age. Older adults may show a higher prevalence of covert saccades (occurring during the head movement) even when gain is within normal limits, potentially complicating the interpretation of the test.

Impact on Diagnostic Accuracy

Age-related changes in VHIT parameters can reduce diagnostic accuracy if age-specific normative data are not used. For instance, using young adult norms may incorrectly label an older person as having vestibular hypofunction when the changes are simply due to aging. Similarly, relying solely on gain without considering refixation saccades may lead to missed diagnoses in younger patients or false positives in older ones.

To maintain high diagnostic accuracy, VHIT results must be interpreted with age-stratified reference ranges. Many modern VHIT systems provide built-in normative databases that account for age, allowing clinicians to better distinguish between physiological aging and pathology.

Clinical Recommendations

• Use age-matched normative data: Always compare VHIT results against reference values derived from healthy individuals of the same age group.
• Evaluate refixation saccades carefully: In older patients, a moderate increase in saccades may be normal; however, a high number or large amplitude saccades should raise suspicion for vestibular loss.
• Combine with other tests: VHIT should be part of a comprehensive vestibular assessment including caloric testing and posturography, especially in older adults with dizziness.
• Consider serial testing: For elderly patients, monitoring changes over time is more informative than a single measurement.

Conclusion

Age is a significant modifier of VHIT outcomes. Recognizing the effect of aging on the vestibulo-ocular reflex, gain, and refixation saccades is essential for accurate diagnosis of vestibular disorders. Clinicians must rely on normative data adjusted for age to avoid misinterpretation and to maintain high diagnostic accuracy. Understanding the interplay between age-related decline and semicircular canals function helps ensure that VHIT remains a reliable tool across the lifespan.