This reflex is brainstem mediated and keeps the eyes looking straight ahead when the head is turned, in an unconscious patient. It’s a test to use on the unconscious patient to see if the brainstem is intact.
The best way to remember this is by thinking of doll’s eyes. It is in fact called the doll’s eye reflex. The old dolls used to have the eyes painted on, so that when you turned the head, the eyes moved with the head. This would indicate that the brainstem was not intact. The more modern dolls have eyes that move back towards the centre, when the head is turned.
The reflex is mediated by three cranial nerves VIII, III and VI.
When the head is turned to one side, the semicircular canals pick up this movement and send a signal via CN VIII to the medial vestibular nucleus, which then sends a signal via the ipsilateral CNIII to the medial rectus muscle and via the contralateral CNVI to the lateral rectus muscle. So when the head is turned to one side, the eyes move in the opposite direction to face the centre.
The way to perform this test in the unconscious patient, is to hold the head(assuming no cervical injury), with eyes held open. The head is turned rapidly to one side. The eyes will move in a smooth motion to the centre, i.e.., looking forward. If they do not and continue to look sideways; it indicates that the brainstem is not intact ie., a possible poor outcome.