Dynamic visual acuity (DVA) assesses a subject’s ability to perceive objects accurately while the head is moved passively.

Patients with vestibular hypofunction will have marked degradation of visual acuity with oscillopsia (an illusory movement of the environment) while the head is moving, but not when the head is still. 
If the VOR is no longer able to stabilize gaze, and if head movements are too fast for the smooth pursuit system to keep the eyes on target, there will be a decrease in visual acuity compared with what the patient is able to read when the head remains still. 
At the testing frequency of 2 Hz, visual tracking systems are too sluggish to contribute much to gaze stability, and therefore the function of the rVOR can be assessed acting alone, almost as if one were testing it in the dark¹. 

The specificity and sensitivity of DVA for detecting unilateral and especially bilateral loss is quite high, and diagnosis can be made with a relatively few number of head rotations if the visual stimuli are adapted to the performance of the patient.

Method
The patient’s best corrected visual acuity can be measured using a distance acuity chart with the head still. With the examiner standing behind the patient's head, the head is rotated passively by about 20⁰ at a frequency of about 2 Hz, in order to prevent visual-following reflexes from helping to stabilise the eyes, and while viewing a distance acuity chart.  The patient must not be allowed to stop at the turn-around point. 

Normal individuals may lose one or two lines of acuity during headshaking; a decline of more than two lines is considered abnormal. 
 -Patients with complete loss of labyrinthine function usually lose about five lines.
 -Although particularly affected in cases of bilateral vestibulopathy, DVA will be abnormal in unilateral vestibulopathy especially as higher head oscillation frequencies.

Note that with myopic lenses, the VOR gain is reduced, and with hyperopic lenses, VOR gain is increased. This does not apply to contact lens wearers as the lenses move with the eyes.

DVA may also be assessed while oscillating the head vertically or in the roll plane (from ear to shoulder).  With unilateral vestibular hypofunction DVA is symmetric during pitch (vertical) and roll (torsion) but not yaw (horizontal) rotation. For roll movements of the head, the fovea (line of sight) is not displaced far from the visual target and so causes smaller decreases in visual acuity, even when labyrinthine function is completely lost.