Blinking is a voluntary or reflexive rapid closing and opening of the eyelids that lasts for less than a second but may take a few seconds. Tearing is one of the essential functions of the eyes, which aids in distributing tears and clearing the eyes’ surface from any irritants. Blinking is also important in maintaining the moisture and health of the eyes.
The average individual blinks at a rate of between 10 to 20 times per minute and that’s between 7200 to 9600 times a day. It takes only a few hundred milliseconds for each blink. Even though the reflex seems rather straightforward, blinking is governed by several areas of the brain and requires intricate synaptic messages and neural connections between the brain, facial nerves, and muscles of the eyelids. Blinking can be further categorized into two; voluntary blinking which occurs in the absence of any stimulus and defensive blinking which is elicited by a stimulus such as light, smoke, or touch of an object of an object on the eye.
The eyelids contain several muscles whereby the two major muscles are the orbicularis oculi muscle responsible for closing the eye and the levator palpebrae superioris which opens the eye. Several cranial nerves are involved in blinking but the most important ones are cranial nerve VII which is also known as the facial nerve and cranial nerve V also known as the trigeminal nerve. Any injury to these nerves or any disease that affects the nervous system such as a stroke or neurological disorders can interfere with blinking and result in facial paralysis or Bell’s palsy.
A blink goes through three phases for a single blink. The first phase is the closing phase of the eyelid and this action is brought by the contraction of the orbicularis muscle. The second phase is longer and occurs when the eyelid is completely shut and lasts for a brief moment. The third phase is marked by the relaxation of the orbicularis muscle and the contraction of the levator palpebrae superioris thus reopening the eyelid. This entire blink from the time the lid is closed to the time it is opened again takes only 100 to 400 milliseconds. It is also useful to compare it with the camera that shoots 1000 frames per second; it can capture only 2 to 8 frames during a blink.
The primary purpose of blinks is to distribute tears over the ocular surface, ensuring adequate lubrication of the eye. Lacrimal glands are situated above the outer corner of each eye and release tears whenever the eyelids shut. Tears consist of proteins, antibodies, and antimicrobial compounds that are useful in protecting the eyes. Blinking thus plays a crucial role in enabling clear vision since it helps in rubbing off the tear film uniformly across the cornea and conjunctiva. If the eyes do not blink sufficiently, for example in a short period, the tear film may break up and the eyes will become drier and there is more friction between the eyelid and the eye. Eye tear helps reduce the haziness of the eyes.
It also aids in washing the eye’s ‘window’ so to speak, by blinking out irritants on the surface of the eye, like dust and pollen. Small droplets that can be inhaled reach the eyes, and during a blink, the eyelids move like a squeegee to sweep them to the corner of the eyes where they are mixed with tears to be drained from the nasolacrimal duct which is part of the nose. This removal mechanism through blinking has the advantage of avoiding further irritation or infection by particles that may deposit themselves on the delicate eye tissue. A slower blink rate or less frequent blinking can let in dust and germs as well as other irritants.
There are several ways through which the blinking reflex can be elicited. Spontaneous or reflex blinking takes place involuntarily almost every 2-10 seconds when the eye starts to dry to rebalance the tear film. The average interval that is taken by a human being to blink their eyes is about five seconds. Although the rate may be different between two people, all human beings possess an average and stable subconscious blinking frequency. It is well established that reflex blinking in particular provides an important component of the protective and reparative mechanisms of healthy ocular tissues. There is also the involuntary blinking which is caused by an external stimulus; this type of blinking is known as reflexive blinking. This is caused by bright lights, smoke, particles touching the eye surface, or emotions such as anger and tension. This type of blinking is considered exogenous or reflex and is accomplished through the optic and ophthalmic branches of the trigeminal nerve (CN V) and is a rapid response to possible dangers. Excessive reflex blinking may be associated with neurological disorders and can cause blepharospasm.
The blinking rates depend on one or another factor such as gender, age, hormones, certain drugs, and pathologies. It is important to note that women on average blink almost twice as much as men. It has been established that blinking rates are variable and can be influenced by hormonal changes where estrogen is known to impact blinks. Other medications such as antihistamines, antidepressants, antipsychotics, and even medications used in the treatment of Parkinson’s disease also affect normal blinking patterns. Conditions such as dry eye, blepharitis, photophobia, dyskinesias, Parkinsonism, and Tourette’s Syndrome also affect blinking reflexes. Normal activities such as reading, computer use, and concentration can alter blink rates. Excessive blinking that is done consciously has no dangerous ramifications but those that are involuntary may warrant an ophthalmological examination. Applying eye drops to lubricate the eyes can help ease a person’s suffering. Blinking may also be useful in certain situations, such as blinking exercises.
In addition to tear production and eye coating, blinking could also involve brain functions as well as attention, memory, and thinking. Blinking may rise during different situations such as when one feels tired, bored, or stressed. It can also happen more frequently when dealing with issues or when speaking as a sign of mental processes and intelligence. Other researchers speculate that blinking is linked to refocusing or shifting attention from the physical environment to resident concepts. When one is blinking, the eyes are shut momentarily and this may help in focusing, just like how it helps in imagination and recall of events.
In conclusion, the seemingly uncomplicated and automatic response of blinking is connected to many more complex responses of the eyes and the nervous system than one would expect. While blinking is still considered an automatic reflex, scientists’ findings continue to discover the essential functions of blinking to eye health, cognitive functions, and behavioral patterns. Thus, next time when your eyes blink, do not take it lightly because many cells, nerves, glands, muscles, and regions of the brain work together to perform this simple act.
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