In contrast, vHIT and VEMP are both so new that researchers are still working to establish normal vs. abnormal, and to correlate vHIT and VEMP results with clinical conditions. Because the new tests assess the vestibular system in ways that were previously impossible, however, healthcare providers are beginning to incorporate them into clinical practice.
Explore this issue:January 2015
Video Head Impulse Testing (vHIT)
“In a lot of ways, video head impulse testing has revolutionized our ability to test the function of the canals in a rigorous, quantitative way,” said Yuri Agrawal, MD, assistant professor of otolaryngology-head and neck surgery at Johns Hopkins University School of Medicine in Baltimore.
The FDA approved vHIT in 2013. The test utilizes a pair of video-equipped goggles to record eye movements in response to head movement. The testing equipment records and compares both the direction and velocity of head movement and the direction and velocity of eye movement. Well tolerated by most patients, vHIT measures the function of all six semicircular canals in each ear in about 10 minutes. (Caloric testing, in contrast, takes approximately 30 minutes and cannot be tolerated by some patients.)
Clinicians can use vHIT testing to detect saccades they might otherwise miss. “The camera can detect saccade whether it’s happening overtly or covertly,” Dr. Adams said. “It also gives an objective gain measure, a number that compares the amount of eye movement to the amount of head movement.”
The vHIT equipment also provides feedback regarding head thrust technique; there’s “more real-time feedback to make sure you’re doing it correctly,” Dr. Adams said.
Because vHIT is fast, well-tolerated and objective, it has “opened our eyes to a lot of things we didn’t even know were happening,” said Devin
McCaslin, PhD, associate professor in the department of hearing and speech sciences at Vanderbilt University in Nashville. “It allows us to track impairment, to learn how the vestibular system heals itself.”
The difference between bedside head impulse testing and vHIT is so stark that Dr. McCaslin likens bedside testing to a telescope and vHIT to the Hubble Space Telescope. For the first time, researchers can get a large-scale, intricately detailed look at vestibular function. “We’ve never really had population norms,” Dr. Agrawal said. “Now we’re able to get that because we can survey a lot of people. We’re gaining a better understanding of what normal function should look like and how it should change, so when we see patients, we can interpret their findings in the context of those population norms.”