The phrase "doll's eye reflex" or "doll's eye response" refers to a test for evaluating brain stem function in patients who are unconscious or comatose; more properly, it is a test of the oculocephalic reflex. Anyone who owned a doll with movable eyes as a child knows that the eyeballs in such toys are weighted. No matter how you position the doll, the eyes will move so that they are always fixated in the same direction. Human beings respond to head motions in a similar fashion. The doll's eye response is generally used as a preliminary diagnostic in cases of head injury or suspected brain damage.

Testing the doll's eye response involves elevating the patient's head by 30 degrees and then rapidly rotating the head from side to side while observing the patient's open eyes. For obvious reasons, this test should not be performed if there is suspected cervical (neck) injury. A positive or normal response occurs when the eyes automatically move in the direction opposite the rotation (for example, when the head is turned left, the eyes move to the right). A negative response occurs when the eyes move in the same direction as the head rotation. A negative doll's eye response may indicate severe brain damage or brain death.

The oculocephalic response is a manifestation of the vestibulo-ocular reflex (sometimes called the oculovestibular reflex), which stabilizes an image on the retina by producing counter-movements of the eye in response to movements of the head. In humans, this reflex develops within the first week of life and is necessary for normal vision. A person's head is almost constantly moving, however minutely, and the vestibulo-ocular reflex allows one to fixate on a particular object or point in space despite these movements. If such a reflex did not exist, our vision might resemble the blurry images captured by a camera held in shaky hands.

The oculocephalic response and vestibulo-ocular reflex are controlled by the brain stem, which receives signals related to head movement from the vestibular nerve and responds by sending signals to the oculomotor nerve, which controls eye movement. Although the vestibulo-ocular reflex is always active when one visually fixates on a target, the oculocephalic response is only apparent in unconscious patients. Conscious, alert people usually suppress the doll's eye response without realizing it; otherwise, one would have trouble turning one's head to look at something located outside the current field of vision.

A negative doll's eye response is great cause for concern. However, by itself, the test does not provide conclusive evidence of damage to the brain stem or brain death. Such evidence is obtained by further testing, including cold calorics (a more potent test of the vestibulo-ocular reflex), tests of various other reflexes, observing the patient's response to noxious or painful stimuli, an electroencephalogram, a cerebral blood flow study, and perhaps the use of magnetic resonance imaging. However, this process is time-consuming and often requires specialized equipment and testing techniques. The doll's eye response represents a quick and easy diagnostic that helps indicate whether further testing is necessary.

Sources:

• Ashe, Allison and Mason, Jon. "Assessing and Managing Head Injury." Emergency Medicine. http://mdchoice.com/emed/drugs.asp?template=423&page=detail&type=8&id=948
• Blumenfeld, Hal. "Extraocular Movements." Neuroanatomy through Clinical Cases. http://www.neuroexam.com/20.html
• Grant, Jim. "Evaluation of the Dizzy Patient." http://www.utmb.edu/otoref/Grnds/dizzy.htm
• Olson, Leslie. "How Brain Death Works." http://health.howstuffworks.com/brain-death.htm
• "Vestibulo-ocular reflex." http://en.wikipedia.org/wiki/Vestibulo-ocular_reflex