Blinking, a bodily function, and is a semi-autonomic rapid closing of the eyelid.
A single blink is determined by the forceful closing of the eyelid or inactivation of the levator palpebrae superioris and the activation of the palpebral portion of the orbicularis oculi, not the full open and close.
A blink is an essential function of the eye that helps spread tears across and remove irritants from the surface of the cornea and conjunctiva.
Blinking provides moisture to the eye by irrigation using tears and a lubricant the eyes secrete.
Blinking may have other functions since it occurs more often than necessary just to keep the eye lubricated.
Blinking may help with disengagement of attention; following blink onset, cortical activity decreases in the dorsal network and increases in the default network, associated with internal processing.
Blink speed can be affected by fatigue, eye injury, medication, and disease.
The blinking rate is determined by a blinking center, but it can also be affected by external stimuli.
Normally, eyes instinctively blink at around 20 times per minute, but looking at a person the viewer finds attractive can make this rate faster.
Humans use winking, the blinking of only one eye, as a form of body language.
Birds, reptiles and sharks blink with a nictitating membrane from one side of the eye to the other.
The eyelid provides suction across the eye from the tear duct to the entire eyeball to keep it from drying out.
Eyelashes function to catch irritants when the eye is blinked.
Blinking also protects the eye from irritants.
Eyelashes are hairs which grow from the edges of the upper and lower eyelids.
Eyelashes create a line of defense against dust and other elements to the eye, catching most of these irritants before they reach the eyeball.
Multiple muscles that control reflexes of blinking: The main muscles, in the upper eyelid, that control the opening and closing are the orbicularis oculi and levator palpebrae superioris muscle.
The orbicularis oculi closes the eye, while the contraction of the levator palpebrae muscle opens the eye.
The Müller’s muscle, or the superior tarsal muscle, in the upper eyelid and the inferior palpebral muscle in the lower eyelid are responsible for widening the eyes.
These muscles are imperative in blinking, and important in many other functions such as squinting and winking.
The inferior palpebral muscle is coordinated with the inferior rectus to pull down the lower lid when one looks down.
Lying may affect the rate of blinking.
Blinking is used for communication in humans.
Central nervous system’s control blinking.
Blinking is controlled by a blinking center of the globus pallidus of the lenticular nucleus in the CNS, but external stimuli can contribute.
The orbicularis oculi is a facial muscle; innervated by the facial nerve root.
The levator palpebrae superioris’ action is sent through the oculomotor nerve.
The duration of a blink is on average 100–150 milliseconds, and up 400 ms.
Greater activation of dopaminergic pathways in the striatum is associated with a higher rate of spontaneous eye blinking.
Conditions in which there is reduced dopamine availability such as Parkinson’s disease have reduced eye blink rate, while conditions in which it is raised such as schizophrenia have an increased rate.
Blink rate is associated with dopamine-related executive function and creativity.
There are three types of blinking:spontaneous, reflex blink, voluntary blink
Spontaneous blinking is done without external stimuli and internal effort, and is conducted in the pre-motor brain stem and happens without conscious effort, like breathing and digestion.
A reflex blink occurs in response to an external stimulus, such as contact with the cornea or objects that appear rapidly in front of the eye.
A reflex blink is not necessarily a conscious blink bit it does happen faster than a spontaneous blink.
Reflex blink may occur in response to tactile stimuli- corneal, eyelash, skin of eyelid, contact with eyebrow), optical stimuli , or menace reflex or auditory stimuli.
A voluntary blink is a conscious blink, with the use of all 3 divisions of the orbicularis oculi muscle.
Infants do not blink at the same rate of adults.
Infants only blink at an average rate of one or two times in a minute:infants do not require the same amount of eye lubrication that adults do because their eyelid opening is smaller in relation to adults.
Infants do not produce tears during their first month of life. Infants also get a significant amount more sleep than adults do and, fatigued eyes blink more.
Throughout childhood the blink rate increases, and by adolescence, it is usually equivalent to that of adults.
Women using oral contraceptives blink 32% more often than other women on average for unknown reasons.
Generally, between each blink is an interval of 2–10 seconds.
Rates vary by individual, averaging around 17 blinks per minute in a laboratory setting.
When the eyes are focused on an object for an extended period of time (reading) the rate of blinking decreases to about 4 to 5 times per minute.
This is the major reason that eyes dry out and become fatigued when reading.
When the eyes dry out or become fatigued due to reading on a computer screen, it can lead to computer vision syndrome.
Computer vision syndrome can be prevented by taking regular breaks, focusing on objects far from the screen, having a well-lit workplace, or using a blink reminder application.
Studies suggest that adults can learn to maintain a healthy blinking rate while reading or looking at a computer screen using biofeedback.
Excessive blinking may help to indicate the onset of Tourette syndrome, strokes or disorders of the nervous system.
A reduced rate of blinking is associated with Parkinson’s disease.