What are the Fundamental Rules When Performing a vHIT?

Question

Answer

Here are some simple but fundamental rules to perform a vHIT:

Environmental Setup

• Darkness is not mandatory
• Small target is easily visible
• Use a room with LED or fluorescent lighting
• No direct sunlight
• Use a solid chair without wheels and with a sufficiently high back but does not prevent the examiner's maneuvers

• Place the target on the wall so that the patient eye – target distance is > 150/200 cm (only for patient eye – target distances > 150/200 cm, eye rotations are equal (right = left) and equal to head rotation); the gain calculation can be wrong (hyper gain) for shorter distance

Patient Instructions

• Look carefully at the target on the wall 
• Always keep the eyes wide open, especially while performing the movement (partial closure should also be avoided)
• If at the end of the movement, the patient realizes that the gaze is no longer on the target, they must move their eyes to regain immediately
• Keep the neck as soft as possible and do not oppose and/or contribute to the movement
• Keep the back straight and in contact with the seatback (frequent tendency to anteropulsion of the head and trunk during the examination)

Execution of The Test

• Before starting the test, check conjugation and amplitude of eye movements
• Initially, move the patient's head slowly in the examination field to make the patient understand the direction and amplitude of the movements
• Perform high acceleration maneuvers but with limited amplitude (ideal <10-15°).
• Avoid the head bounce: you must stop at the end of the movement and do not immediately return to the initial position
• During the movement the pupil must not go beyond the region of interest (ROI); otherwise that impulse will not be valid
• Prevent hair from being present in the examination field
• Wearing latex gloves can improve the grip of the patient's head

Warning

• Mascara (usually does not interfere too much, but it is better to avoid it)
• Crystalline prosthesis (parasitic reflexes)
• Tear films on the free edge of the lower eyelid (parasitic reflexes)
• Patient distraction can lead to tests burdened with heavy artifacts

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