Oculocephalic and oculovestibular reflexes

OVERVIEW

Oculocephalic and oculovestibular reflexes are primarily used to determine whether a patient’s brainstem is intact (e.g. coma or brain death assessment)

OCULOCEPHALIC REFLEX

Oculocephalic reflex:

• ensure the C-spine is cleared.
• the patient’s eyes are held open.
• the head is briskly turned from side to side with the head held briefly at the end of each turn.
• a positive response occurs when the eyes rotate to the opposite side to the direction of head rotation, thus indicating that the brainstem (CN3,6,8) is intact.
• a similar result is seen when the head is flexed and extended — a positive result is downward deviation of the eyes during extension, and upward deviation during flexion (the eyelids, if closed, may also open as part of the ‘doll’s head phenomenon’). These vertical responses indicates that the brainstem (CN3,4,8) is intact.
• The eyes should gradually return to the mid-position in a smooth, conjugate movement if the brainstem is intact.

Patients with metabolic coma (e.g. hepatic failure) may have exaggerated, brisk oculocephalic reflexes.

OCULOVESTIBULAR REFLEX

Oculovestibular reflex (caloric stimulation):

• the head is elevated to 30 degrees above horizontal so that the lateral semicircular canal is vertical, and so that stimulation with generate a maximal response.
• check that the tympanum is intact and that the external ear canal is clear — C-spine clearance is not necessary.
• introduce iced water into the external ear canal through a small catheter until one of the following occurs:
  • nystagmus (in the intact brainstem the slow phase is towards the irrigated ear)
  • ocular deviation
  • 200mL of iced water has been instilled.
• allow 5 minutes between testing ears to allow re-equilibration of the oculovestibular system.
• as consciousness is lost, the fast component (towards the non-irrigated ear) is lost and the slow component deviates the eye in the direction of the irrigated ear.

Vertical oculovestibular eye responses can be assessed by irrigating both ears simultaneously.

• If the brainstem is intact, cold water causes the eyes to deviate downwards and warm water causes the eyes to deviate upwards.

The positive brainstem responses described above are those seen in a comatose patient with an intact brainstem.

TYPICAL FINDINGS

Typical findings for various lesions are shown in this graphic from Posner et al (2008):

References and Links

• Posner JB, Saper CB, Schiff N, Plum F. Plum and Posner’s Diagnosis of Stupor and Coma 4e Oxford university Press, 2009.