Eye
movements can be assessed by activating them through reflexes. The
oculocephalic reflex, or "doll's eyes reflex," is tested by turning
the patient's head from side to side (show figure 1). If there is any
chance that there has been a traumatic injury to the cervical spine, plain
films of the cervical spine must be obtained before testing this reflex. When
the oculocephalic reflex is present (positive doll's eyes), the eyes do not
turn with the head; it is as if the patient is maintaining fixation on a single
point in space. The eyes thus appear to be moving relative to the head in the
direction opposite to the head movement. This reflex is usually suppressed (and
therefore not usually tested) in conscious patients, but it is a normal finding
in comatose patients. Absence or asymmetry of this reflex in a comatose patient
indicates dysfunction somewhere in the reflex pathway: in the afferent limb
(from the labyrinth and vestibular nerve, and also from neck proprioceptors),
the efferent limb (cranial nerves III and VI and the muscles they innervate),
or the pathways connecting them in the pons and medulla.
Another reflex that activates eye movements
even more strongly is the vestibuloocular reflex (cold calorics). The patient
is supine, with the head or upper body tilted forward so that the neck forms an
angle of 30 degrees with the horizontal (show figure 1). A syringe is filled
with 50 to 100 mL of ice cold water with a small catheter attached. The water
is injected against the tympanic membrane (checking with an otoscope first to
be sure the membrane is intact). In this position, this stimulus has the same
effect on the horizontal semicircular canal as sustained turning of the head in
the opposite direction; this results in sustained deviation of both eyes toward
the ear being stimulated. Absence of this reflex indicates dysfunction of the
pons, medulla, or (less commonly) cranial nerves. Five minutes should intervene
before testing the other side.
