Blinking

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Blinking Eye opening and closing.gif
Blinking

Blinking is a bodily function; it is a semi-autonomic rapid closing of the eyelid. [1] 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.[ citation needed ] It is an essential function of the eye that helps spread tears across and remove irritants from the surface of the cornea and conjunctiva.

Contents

Blinking may have other functions since it occurs more often than necessary just to keep the eye lubricated. Researchers think blinking may help with disengagement of attention; following blink onset, cortical activity decreases in the dorsal network and increases in the default-mode network, associated with internal processing. [2] Blink speed can be affected by elements such as fatigue, eye injury, medication, and disease. The blinking rate is determined by the "blinking center", but it can also be affected by external stimulus.

Some animals, such as tortoises and hamsters, blink their eyes independently of each other. Humans use winking, the blinking of only one eye, as a form of body language.

Function and anatomy

Birds, reptiles and sharks blink with a nictitating membrane from one side of the eye to the other. Bird blink-edit.jpg
Birds, reptiles and sharks blink with a nictitating membrane from one side of the eye to the other.

Blinking provides moisture to the eye by irrigation using tears and a lubricant the eyes secrete. The eyelid provides suction across the eye from the tear duct to the entire eyeball to keep it from drying out.

Closed eye of a human, displaying eyelashes which function to catch irritants when the eye is blinked. Closed human eye, superior view.jpg
Closed eye of a human, displaying eyelashes which 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 that create a line of defense against dust and other elements to the eye. The eyelashes catch most of these irritants before they reach the eyeball.

There are 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 3 eyelid are responsible for widening the eyes. These muscles are not only imperative in blinking, but they are also 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.

The correlation between human eyelid blink behavior and psychological stress was also demonstrated by means of a laboratory study. [3] [4] Lying may affect the rate of blinking. [5]

Central nervous system's control

Though one may think that the stimulus triggering blinking is dry or irritated eyes, it is most likely that it is controlled by a "blinking center" of the globus pallidus of the lenticular nucleus—a body of nerve cells between the base and outer surface of the brain. Nevertheless, external stimuli can contribute. The orbicularis oculi is a facial muscle; therefore its actions are translated 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 according to UCL researcher [6] and between 100 and 400 ms according to the Harvard Database of Useful Biological Numbers. [7] Closures in excess of 1000 ms were defined as microsleeps.

Greater activation of dopaminergic pathways dopamine production in the striatum is associated with a higher rate of spontaneous eye blinking. [8] [9] Conditions in which there is reduced dopamine availability such as Parkinson's disease have reduced eye blink rate, [10] while conditions in which it is raised such as schizophrenia have an increased rate. [11] Blink rate is associated with dopamine-related executive function and creativity. [12] [13] [14]

Evolutionary origins

Blinking is present in all major tetrapod crown groups. The soft tissues involved in blinking have not been preserved in the fossil record, but study of mudskippers (a group of amphibious fish species that evolved blinking independently from other tetrapod species, but for similar purposes), suggest that blinking (which involves the eye retracting in mudskippers) may have arose in response to selective pressures upon species shifting from aquatic to terrestrial habitats. For example, compared to an aquatic environment, in a terrestrial environment, the corneal cells must be kept moist such that vital substances like oxygen can more easily diffuse into them, detritus may adhere to the eye in dry conditions, and objects may move towards the eye at faster and more dangerous speeds in air than in water. Additionally, when at their fully aquatic juvenile stage of development, their eyes are not in the positioning with which they blink, but as adults, their eyes elevate to a position that can blink, which they do when they are not submerged or bump into a surface, suggesting blinking emerged as an adaptation to terrestrial life as opposed to aquatic life. [15]

Early tetrapods in the transition to land, which would later yield all non-mudskipper blinking species, possessed similar characteristics regarding eye positioning that suggest blinking arose in response to aerial vision and terrestrial lifestyle. [15]

Types of blinking

There are three types of blinking.

Spontaneous blinking is done without external stimuli and internal effort. This type of blinking 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 either; however it does happen faster than a spontaneous blink. [1] Reflex blink may occur in response to tactile stimuli (e.g., corneal, eyelash, skin of eyelid, contact with eyebrow), optical stimuli (e.g. dazzle reflex, [16] or menace reflex) or auditory stimuli (e.g., menace reflex).

A voluntary blink is a conscious blink, with the use of all 3 divisions of the orbicularis oculi muscle.

Blinking in everyday life

Children

Infants do not blink at the same rate of adults; in fact, infants only blink at an average rate of one or two times in a minute. The reason for this difference is unknown, but it is suggested that infants do not require the same amount of eye lubrication that adults do because their eyelid opening is smaller in relation to adults. Additionally, infants do not produce tears during their first month of life. Infants also get a significant amount more sleep than adults do and, as discussed earlier, fatigued eyes blink more. However, throughout childhood the blink rate increases, and by adolescence, it is usually equivalent to that of adults. [17]

Adults

There have been mixed results when studying gender-dependent[ dubious – discuss ] differences in blinking rates, with results varying from the women's rate nearly doubling the men's to no significant difference between them. [18] [19] In addition, women using oral contraceptives blink 32% more often than other women on average for unknown reasons. [20] Generally, between each blink is an interval of 2–10 seconds; actual rates vary by individual averaging around 10 blinks per minute in a laboratory setting. However, when the eyes are focused on an object for an extended period of time, such as when reading, the rate of blinking decreases to about 3 to 4 times per minute. [21] 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 be an indication of 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 [22] that adults can learn to maintain a healthy blinking rate while reading or looking at a computer screen using biofeedback.

Eye blinking can be a criterion for diagnosing medical conditions. For example, 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.

See also

Related Research Articles

<span class="mw-page-title-main">Oculomotor nerve</span> Cranial nerve III, for eye movements

The oculomotor nerve, also known as the third cranial nerve, cranial nerve III, or simply CN III, is a cranial nerve that enters the orbit through the superior orbital fissure and innervates extraocular muscles that enable most movements of the eye and that raise the eyelid. The nerve also contains fibers that innervate the intrinsic eye muscles that enable pupillary constriction and accommodation. The oculomotor nerve is derived from the basal plate of the embryonic midbrain. Cranial nerves IV and VI also participate in control of eye movement.

<span class="mw-page-title-main">Eyelid</span> Thin fold of skin that covers and protects the eye

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. "Palpebral" means relating to the eyelids. Its key function is to regularly spread the tears and other secretions on the eye surface to keep it moist, since the cornea must be continuously moist. They keep the eyes from drying out when asleep. Moreover, the blink reflex protects the eye from foreign bodies. A set of specialized hairs known as lashes grow from the upper and lower eyelid margins to further protect the eye from dust and debris.

<span class="mw-page-title-main">Human eye</span> Sensory organ of vision

The human eye is an organ of the sensory nervous system that reacts to visible light and allows the use of visual information for various purposes including seeing things, keeping balance, and maintaining circadian rhythm.

<span class="mw-page-title-main">Levator palpebrae superioris muscle</span> Muscle in orbit that elevates upper eyelid

The levator palpebrae superioris is the muscle in the orbit that elevates the upper eyelid.

<span class="mw-page-title-main">Extraocular muscles</span> Seven extrinsic muscles of the eye

The extraocular muscles, or extrinsic ocular muscles, are the seven extrinsic muscles of the eye in humans and other animals. Six of the extraocular muscles, the four recti muscles, and the superior and inferior oblique muscles, control movement of the eye. The other muscle, the levator palpebrae superioris, controls eyelid elevation. The actions of the six muscles responsible for eye movement depend on the position of the eye at the time of muscle contraction.

<span class="mw-page-title-main">Bell's phenomenon</span> Reflex of the eye

Bell's phenomenon is a medical sign that allows observers to notice an upward and outward movement of the eye, when an attempt is made to close the eyes. The upward movement of the eye is present in the majority of the population, and is a defensive mechanism. The phenomenon is named after the Scottish anatomist, surgeon, and physiologist Charles Bell. Bell's phenomenon is a normal defense reflex present in about 75% of the population, resulting in elevation of the globes when blinking or when threatened. It becomes noticeable only when the orbicularis oculi muscle becomes weak as in, for example, bilateral facial palsy associated with Guillain–Barré syndrome. It is, however, present behind forcibly closed eyelids in most healthy people and should not be regarded as a pathognomonic sign.

<span class="mw-page-title-main">Corrugator supercilii muscle</span> Muscle near the eye

The corrugator supercilii muscle is a small, narrow, pyramidal muscle of the face. It arises from the medial end of the superciliary arch; it inserts into the deep surface of the skin of the eyebrow.

<span class="mw-page-title-main">Orbicularis oculi muscle</span> Facial muscle that closes the eyelids

The orbicularis oculi is a muscle in the face that closes the eyelids. It arises from the nasal part of the frontal bone, from the frontal process of the maxilla in front of the lacrimal groove, and from the anterior surface and borders of a short fibrous band, the medial palpebral ligament.

Blepharospasm is any abnormal contraction of the orbicularis oculi muscle. The condition should be distinguished from the more common, and milder, involuntary quivering of an eyelid, known as myokymia, or fasciculation. In most cases, blepharospasm symptoms last for a few days and then disappear without treatment, but in some cases the twitching is chronic and persistent, causing life-long challenges. In these cases, the symptoms are often severe enough to result in functional blindness. The person's eyelids feel like they are clamping shut and will not open without great effort. People have normal eyes, but for periods of time are effectively blind due to their inability to open their eyelids. In contrast, the reflex blepharospasm is due to any pain in and around the eye.

<span class="mw-page-title-main">Corneal reflex</span> Involuntary blinking of the eyelids

The corneal reflex, also known as the blink reflex or eyelid reflex, is an involuntary blinking of the eyelids elicited by stimulation of the cornea, though it could result from any peripheral stimulus. Stimulation should elicit both a direct and consensual response. The reflex occurs at a rapid rate of 0.1 seconds. The purpose of this reflex is to protect the eyes from foreign bodies and bright lights. The blink reflex also occurs when sounds greater than 40–60 dB are made.

<span class="mw-page-title-main">Tarsus (eyelids)</span>

The tarsi or tarsal plates are two comparatively thick, elongated plates of dense connective tissue, about 10 mm (0.39 in) in length for the upper eyelid and 5 mm for the lower eyelid; one is found in each eyelid, and contributes to its form and support. They are located directly above the lid margins. The tarsus has a lower and upper part making up the palpebrae.

<span class="mw-page-title-main">Medial palpebral ligament</span> Ligament connecting the maxilla and the lacrimal bone to the eyelids

The medial palpebral ligament is a ligament of the face. It attaches to the frontal process of the maxilla, the lacrimal groove, and the tarsus of each eyelid. It has a superficial (anterior) and a deep (posterior) layer, with many surrounding attachments. It connects the medial canthus of each eyelid to the medial part of the orbit. It is a useful point of fixation during eyelid reconstructive surgery.

<span class="mw-page-title-main">Superior tarsal muscle</span>

The superior tarsal muscle is a smooth muscle adjoining the levator palpebrae superioris muscle that helps to raise the upper eyelid.

<span class="mw-page-title-main">Angular artery</span> Artery of the face

The angular artery is an artery of the face. It is the terminal part of the facial artery. It ascends to the medial angle of the eye's orbit. It is accompanied by the angular vein. It ends by anastomosing with the dorsal nasal branch of the ophthalmic artery. It supplies the lacrimal sac, the orbicularis oculi muscle, and the outer side of the nose.

<span class="mw-page-title-main">Orbital septum</span>

In anatomy, the orbital septum is a membranous sheet that acts as the anterior (frontal) boundary of the orbit. It extends from the orbital rims to the eyelids. It forms the fibrous portion of the eyelids.

<span class="mw-page-title-main">Ptosis (eyelid)</span> Drooping of the upper eyelid over the eye

Ptosis, also known as blepharoptosis, is a drooping or falling of the upper eyelid. This condition is sometimes called "lazy eye", but that term normally refers to the condition amblyopia. If severe enough and left untreated, the drooping eyelid can cause other conditions, such as amblyopia or astigmatism, so it is especially important to treat the disorder in children before it can interfere with vision development.

<span class="mw-page-title-main">Marcus Gunn phenomenon</span> Medical condition

Marcus Gunn phenomenon is an autosomal dominant condition with incomplete penetrance, in which nursing infants will have rhythmic upward jerking of their upper eyelid. This condition is characterized as a synkinesis: when two or more muscles that are independently innervated have either simultaneous or coordinated movements.

<span class="mw-page-title-main">Lateral palpebral raphe</span> Ligamentous band at the lateral edge of the eyelids

The lateral palpebral raphe is a ligamentous band near the eye. Its existence is contentious, and many sources describe it as the continuation of nearby muscles. It is formed from the lateral ends of the orbicularis oculi muscle. It connects the orbicularis oculi muscle, the frontosphenoidal process of the zygomatic bone, and the tarsi of the eyelids.

Bienfang's test is a clinical test used in the diagnosis of ocular myasthenia gravis. It is used in conjunction with other examination techniques such as Cogan's lid twitch test or enhancement of blepharoptosis from prolonged upward gaze. It is a simple, quick, and non-invasive test for ocular myasthenia gravis that can be performed not only by ophthalmologists or neurologists, but also by other physicians evaluating patients with ptosis, diplopia, or other symptoms of myasthenia gravis.

In ophthalmology, apraxia of lid opening (ALO) is an inability to initiate voluntary opening of the eyelid following a period of eyelid closure, with normal function at other times. Manual lifting of the eyelid often resolves the problem and the lid is able to stay open.

References

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  2. ↑ Nakano, T.; Kato, M.; Morito, Y.; Itoi, S.; Kitazawa, S. (2012). "Blink-related momentary activation of the default mode network while viewing videos". Proceedings of the National Academy of Sciences . 110 (2): 702–6. Bibcode:2013PNAS..110..702N. doi: 10.1073/pnas.1214804110 . JSTOR   42553853. PMC   3545766 . PMID   23267078.
  3. ↑ N Reßut (2021): Das Lidschlagverhalten als Indikator psychischer Belastung, Wiesbaden: Springer Vieweg, 2021. DOI: https://doi.org/10.1007/978-3-658-36052-8 – ISBN 978-3-658-36051-1
  4. ↑ N Reßut & A Hoppe (2019): Erfassung von individuellem Beanspruchungserleben bei kognitiven Belastungssituationen mittels Mustererkennung im Lidschlagverhalten. In: Zeitschrift für Arbeitswissenschaft 65 (2019), S. 1–13. DOI: https://doi.org/10.1007/s41449-019-00165-y. – ISSN 0340-2444
  5. ↑ Leal, Sharon; Vrij, Aldert (2008). "Blinking During and After Lying". Journal of Nonverbal Behavior. 32 (4): 187–194. doi:10.1007/s10919-008-0051-0. S2CID   43996756.
  6. ↑ "Blink and you miss it". 3 August 2005.
  7. ↑ "Average duration of a single eye blink – Human Homo sapiens – BNID 100706".
  8. ↑ Taylor, JR; Elsworth, JD; Lawrence, MS; Sladek Jr, JR; Roth, RH; Redmond Jr, DE (1999). "Spontaneous blink rates correlate with dopamine levels in the caudate nucleus of MPTP-treated monkeys". Experimental Neurology. 158 (1): 214–20. doi: 10.1006/exnr.1999.7093 . PMID   10448434. S2CID   43504305.
  9. ↑ Colzato, LS; Van Den Wildenberg, WP; Van Wouwe, NC; Pannebakker, MM; Hommel, B (2009). "Dopamine and inhibitory action control: evidence from spontaneous eye blink rates". Experimental Brain Research. Experimentelle Hirnforschung. Experimentation Cerebrale. 196 (3): 467–74. doi:10.1007/s00221-009-1862-x. PMC   2700244 . PMID   19484465.
  10. ↑ Deuschl, G; Goddemeier, C (1998). "Spontaneous and reflex activity of facial muscles in dystonia, Parkinson's disease, and in normal subjects". Journal of Neurology, Neurosurgery, and Psychiatry . 64 (3): 320–4. doi:10.1136/jnnp.64.3.320. PMC   2169979 . PMID   9527141.
  11. ↑ Freed, WJ; Kleinman, JE; Karson, CN; Potkin, SG; Murphy, DL; Wyatt, RJ (1980). "Eye-blink rates and platelet monoamine oxidase activity in chronic schizophrenic patients". Biological Psychiatry . 15 (2): 329–32. PMID   7417620.
  12. ↑ Jongkees, Bryant J.; Colzato, Lorenza S. (December 2016). "Spontaneous eye blink rate as predictor of dopamine-related cognitive function—A review". Neuroscience & Biobehavioral Reviews. 71: 58–82. doi:10.1016/j.neubiorev.2016.08.020. PMID   27555290. S2CID   25094074.
  13. ↑ Chermahini, Soghra Akbari; Hommel, Bernhard (1 June 2010). "The (b)link between creativity and dopamine: Spontaneous eye blink rates predict and dissociate divergent and convergent thinking". Cognition. 115 (3): 458–465. doi:10.1016/j.cognition.2010.03.007. ISSN   0010-0277. PMID   20334856. S2CID   14791691.
  14. ↑ Kuwamizu, Ryuta; Suwabe, Kazuya; Damrongthai, Chorphaka; Fukuie, Takemune; Ochi, Genta; Hyodo, Kazuki; Hiraga, Taichi; Nagano-Saito, Atsuko; Soya, Hideaki (July 2021). "Spontaneous Eye Blink Rate Connects Missing Link between Aerobic Fitness and Cognition". Medicine & Science in Sports & Exercise. 53 (7): 1425–1433. doi:10.1249/MSS.0000000000002590. ISSN   1530-0315. PMID   33433152. S2CID   231585782.
  15. 1 2 Aiello, Brett R.; Bhamla, M. Saad; Gau, Jeff; Morris, John G. L.; Bomar, Kenji; da Cunha, Shashwati; Fu, Harrison; Laws, Julia; Minoguchi, Hajime; Sripathi, Manognya; Washington, Kendra; Wong, Gabriella; Shubin, Neil H.; Sponberg, Simon; Stewart, Thomas A. (24 April 2023). "The origin of blinking in both mudskippers and tetrapods is linked to life on land". PNAS . 120 (18): e2220404120. doi: 10.1073/pnas.2220404120 . PMC   10160996 . PMID   37094121.
  16. ↑ Plainis, S.; Murray, I. J.; Carden, D. (2006). "The dazzle reflex: Electrophysiological signals from ocular muscles reveal strong binocular summation effects". Ophthalmic and Physiological Optics. 26 (3): 318–25. doi:10.1111/j.1475-1313.2006.00350.x. PMID   16684158. S2CID   27075991.
  17. ↑ Juan, Stephen (30 June 2006). "Why do babies blink less often than adults?". The Register .
  18. ↑ Doughty, M. J. (2002). "Further assessment of gender- and blink pattern-related differences in the spontaneous eyeblink activity in primary gaze in young adult humans". Optometry and Vision Science . 79 (7). American Academy of Optometry: 439–47. doi:10.1097/00006324-200207000-00013. PMID   12137399. S2CID   24140202.
  19. ↑ Sforza, Chiarella; Rango, Mario; Galante, Domenico; Bresolin, Nereo; Ferrario, Virgilio F. (2008). "Spontaneous blinking in healthy persons: An optoelectronic study of eyelid motion". Ophthalmic and Physiological Optics. 28 (4): 345–53. doi:10.1111/j.1475-1313.2008.00577.x. PMID   18565090. S2CID   542559.
  20. ↑ Yolton, D. P.; Yolton, R. L.; López, R.; Bogner, B.; Stevens, R.; Rao, D. (1994). "The effects of gender and birth control pill use on spontaneous blink rates". Journal of the American Optometric Association . 65 (11): 763–70. PMID   7822673.
  21. ↑ Bentivoglio, A. R.; Bressman, S. B.; Cassetta, E.; Carretta, D.; Tonali, P.; Albanese, A. (November 1997). "Analysis of blink rate patterns in normal subjects". Movement Disorders. 12 (6): 1028–1034. doi:10.1002/mds.870120629. ISSN   0885-3185. PMID   9399231. S2CID   12607655.
  22. ↑ 修, 福島; 正男, 斎藤 (31 March 1998). "バイオフィードバック法による瞬目の訓練". バイオフィードバック研究 (in Japanese). 25. doi:10.20595/jjbf.25.0_17. ISSN   0386-1856.
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