The corneal reflex, also known as the blink reflex or eyelid reflex, is an involuntary blinking of the

eyelid An eyelid is a thin fold of skin that covers and protects an eye. The levator palpebrae superioris muscle retracts the eyelid, exposing the cornea to the outside, giving vision. This can be either voluntarily or involuntarily. The human eyel ...

s elicited by stimulation of the

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

(such as by touching or by a foreign body), though it could result from any peripheral stimulus. Stimulation should elicit both a direct and consensual response (response of the opposite eye). The reflex occurs at a rapid rate of 0.1 seconds. The purpose of this reflex is to protect the

eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and conv ...

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 are made. The reflex is mediated by: * the

nasociliary The nasociliary nerve is a branch of the ophthalmic nerve, itself a branch of the trigeminal nerve (CN V). It is intermediate in size between the other two branches of the ophthalmic nerve, the frontal nerve and lacrimal nerve. Structure The naso ...

branch of the ophthalmic branch (V₁) of the

trigeminal nerve In neuroanatomy, the trigeminal nerve (literal translation, lit. ''triplet'' nerve), also known as the fifth cranial nerve, cranial nerve V, or simply CN V, is a cranial nerve responsible for Sense, sensation in the face and motor functions ...

(CN V) sensing the stimulus on the cornea only (afferent fiber). * the temporal and zygomatic branches of the

facial nerve The facial nerve, also known as the seventh cranial nerve, cranial nerve VII, or simply CN VII, is a cranial nerve that emerges from the pons of the brainstem, controls the muscles of facial expression, and functions in the conveyance of ta ...

(CN VII) initiating the motor response (efferent fiber). * the center (

nucleus Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom * Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucl ...

) is located in the

pons The pons (from Latin , "bridge") is part of the brainstem that in humans and other bipeds lies inferior to the midbrain, superior to the medulla oblongata and anterior to the cerebellum. The pons is also called the pons Varolii ("bridge of ...

of the

brainstem The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is ...

. Use of

contact lens Contact lenses, or simply contacts, are thin lenses placed directly on the surface of the eyes. Contact lenses are ocular prosthetic devices used by over 150 million people worldwide, and they can be worn to correct vision or for cosmetic ...

es may diminish or abolish the testing of this reflex. Corneal Reflex Pathway Flowchart

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

visual cortex The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus and ...

, which resides in the

occipital lobe The occipital lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The name derives from its position at the back of the head, from the Latin ''ob'', "behind", and ''caput'', "head". The occipital lobe is the v ...

of the brain. The reflex is absent in infants under nine months. The examination of the corneal reflex is a part of some neurological exams, particularly when evaluating

coma A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to respond normally to painful stimuli, light, or sound, lacks a normal wake-sleep cycle and does not initiate voluntary actions. Coma patients exhi ...

, such as FOUR score. Damage to the ophthalmic branch (V₁) of the trigeminal 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.

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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). However, blinking is not only dependent on dryness and/or irritation. A brain area, the

globus pallidus The globus pallidus (GP), also known as paleostriatum or dorsal pallidum, is a subcortical structure of the brain. It consists of two adjacent segments, one external, known in rodents simply as the globus pallidus, and one internal, known in rode ...

of the

basal ganglia The basal ganglia (BG), or basal nuclei, are a group of subcortical nuclei, of varied origin, in the brains of vertebrates. In humans, and some primates, there are some differences, mainly in the division of the globus pallidus into an extern ...

, 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.

References

{{Reflex Reflexes

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References