The vestibulo-ocular reflex has an important clinical use in the setting of the comatose patient.
As a result of the reflex, when the head is moved from side-to-side, the eyes will deviate to the opposite direction of head movement. This is called a doll's eye reflex, referring to old-fashioned dolls with counterweighted eyes.
Note that in awake subjects, the ability to maintain gaze on a target as the head is moved slowly from side to side (as opposed to the rapid movement of the Head Impulse Test) reflects the combined effect of a number of reflexes on the eys (vestibular, visual and cervical)1.
(vv)Doll.mp4(tt)
The preservation of this reflex suggest an intact medial longitudinal fasciculus, and consequently an intact brainstem. SInce brain death is defined operationally as loss of brainstem function, loss of doll's eyes movements in the appropriate clinical setting, are potentially indicative of brain death.
Note that the usual clinical situations are as follows:
- Normal humans orientate their head and body towards a novel stimulus. That is, normal awake humans do not displays a doll's eye reflex.
- Patients in coma, with preserved brainstem function, have a doll's eye reflex.
- Patients in coma, with absent brainstem function, will not have a doll's eye reflex.The eyes will remain in line with the nose as the head is moved from side to side.
Video shows patient with normal caloric responses indicating preserved vestibular responses, followed by segment of patient with absent caloric responses, indicating brain death.
(vv)caloric.mp4(tt)
From: Wijdicks EFM. The Comatose patient. VC 3-5: Eye Movements in Coma. Oxford Medicine Online.
Retrieved from: https://oxfordmedicine.com/view/10.1093/med/9780199331215.001.0001/med-9780199331215-appendix-6