The corneal reflex, also known as the blink reflex, is an involuntary blink

Blink

Blinking is the rapid closing and opening of the eyelid. It is an essential function of the eye that helps spread tears across and remove irritants from the surface of the cornea and conjunctiva. Blink speed can be affected by elements such as fatigue, eye injury, medication, and disease...

ing of the eyelid

Eyelid

An eyelid is a thin fold of skin that covers and protects an eye. With the exception of the prepuce and the labia minora, it has the thinnest skin of the whole body. The levator palpebrae superioris muscle retracts the eyelid to "open" the eye. This can be either voluntarily or involuntarily...

s elicited by stimulation of the cornea

Cornea

The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is...

 (such as by touching or by a foreign body), or bright light, though could result from any peripheral stimulus. Stimulation should elicit both a direct and consensual response (response of the opposite eye). The reflex consumes a rapid rate of 0.1 second. The evolution

Evolution

Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...

ary purpose of this reflex is to protect the eye

Human eye

The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...

s from foreign bodies and bright lights (the latter known as the optical reflex). The blink reflex also occurs when sounds greater than 40-60 dB

Decibel

The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...

 are made.

The reflex is mediated by:

• the nasociliary branch of the ophthalmic branch
  Ophthalmic nerve
  The ophthalmic nerve is one of the three branches of the trigeminal nerve, the fifth cranial nerve. The ophthalmic nerve carries only sensory fibers.-Branches:*Nasociliary nerve**sensory root of ciliary ganglion**posterior ethmoidal nerve...
  
   (V₁) of the 5th cranial nerve
  Cranial nerves
  Cranial nerves are nerves that emerge directly from the brain, in contrast to spinal nerves, which emerge from segments of the spinal cord. In humans, there are traditionally twelve pairs of cranial nerves...
  
   (trigeminal nerve
  Trigeminal nerve
  The trigeminal nerve contains both sensory and motor fibres. It is responsible for sensation in the face and certain motor functions such as biting, chewing, and swallowing. Sensory information from the face and body is processed by parallel pathways in the central nervous system...
  
  ) sensing the stimulus on the cornea, lid, or conjunctiva (i.e. it is the afferent).
• the 7th cranial nerve (Facial nerve
  Facial nerve
  The facial nerve is the seventh of twelve paired cranial nerves. It emerges from the brainstem between the pons and the medulla, and controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue and oral cavity...
  
  ) initiating the motor response (i.e. it is the efferent).
• possibly mediated by a medullary center.

Use of contact lens

Contact lens

A contact lens, or simply contact, is a lens placed on the eye. They are considered medical devices and can be worn to correct vision, for cosmetic or therapeutic reasons. In 2004, it was estimated that 125 million people use contact lenses worldwide, including 28 to 38 million in the United...

es may diminish or abolish the testing of this reflex.

The optical reflex, on the other hand, is slower and is mediated by the visual cortex

Visual cortex

The visual cortex of the brain is the part of the cerebral cortex responsible for processing visual information. It is located in the occipital lobe, in the back of the brain....

, which resides in the occipital lobe

Occipital lobe

The occipital lobe is the visual processing center of the mammalian brain containing most of the anatomical region of the visual cortex. The primary visual cortex is Brodmann area 17, commonly called V1...

 of the brain. The reflex is absent in infants under 9 months.

The examination of the corneal reflex is a part of some neurological

Neurology

Neurology is a medical specialty dealing with disorders of the nervous system. Specifically, it deals with the diagnosis and treatment of all categories of disease involving the central, peripheral, and autonomic nervous systems, including their coverings, blood vessels, and all effector tissue,...

 exams, coma

Coma

In medicine, a coma is a state of unconsciousness, lasting more than 6 hours in which a person cannot be awakened, fails to respond normally to painful stimuli, light or sound, lacks a normal sleep-wake cycle and does not initiate voluntary actions. A person in a state of coma is described as...

. Damage to the ophthalmic branch (V₁) of the 5th cranial nerve results in absent corneal reflex when the affected eye is stimulated. Stimulation of one cornea normally has a consensual response, with both eyelids normally closing.

Rates

When awake, the lids spread the tear secretions over the corneal surface, on a typical basis of 2 to 10 seconds (though this may vary individually). But blinking is not only dependent on dryness and/or irritation. A brain area, the globus pallidus of the basal ganglia contains a blinking center that controls blinking. Nonetheless, the external stimuli are still involved. Blinking is linked with the extraocular muscles. Blinking is often concurrent with a shift in gaze, and it is believed that this helps the movement of the eye.