The corneal reflex is an involuntary closing of the eyelids when the cornea is touched by a foreign object. The function of this reflex is to protect the eye from damage. Absence of a corneal reflex may indicate damage to the fifth and seventh cranial nerves, which mediate the reflex.
Also known as the blink reflex, the corneal reflex occurs when the eye is touched by a finger, a cotton swab or even by bright light. It is a quick reflex, occurring in approximately 0.1 second in healthy patients. People who wear contact lenses may show a diminished blink reflex, since they have adapted to touching the surfaces of their eyes.
Physicians often evaluate the corneal reflex when neurological damage is suspected. When a patient is in a coma, a physician can attempt to stimulate the corneal reflex in order to determine whether the cranial nerves have been damaged. In healthy patients, touching one cornea should cause both eyes to blink at the same time.
The corneal reflex is one of many involuntary muscle reactions that humans display as a response to specific stimuli. Other well-known reflexes include the patellar reflex, which causes the leg to kick when the tendon below the knee cap is struck, as well as sneezing, which occurs as a reflex when the nasal passages are irritated by foreign bodies.