Pupil

The pupil is a hole located in the center of the iris of the eye that allows light to strike the retina.[1] It appears black because light rays entering the pupil are either absorbed by the tissues inside the eye directly, or absorbed after diffuse reflections within the eye that mostly miss exiting the narrow pupil.[2] The size of the pupil is controlled by the iris, and varies depending on many factors, the most significant being the amount of light in the environment. The term "pupil" was coined by Gerard of Cremona.[3]

In humans, the pupil is circular, but its shape varies between species; some cats, reptiles, and foxes have vertical slit pupils, goats and sheep have horizontally oriented pupils, and some catfish have annular types.[4] In optical terms, the anatomical pupil is the eye's aperture and the iris is the aperture stop. The image of the pupil as seen from outside the eye is the entrance pupil, which does not exactly correspond to the location and size of the physical pupil because it is magnified by the cornea. On the inner edge lies a prominent structure, the collarette, marking the junction of the embryonic pupillary membrane covering the embryonic pupil.

## Contents

* 1 Function
* 1.1 Effect of light
* 2 Clinical significance
* 2.1 Effect of drugs
* 2.2 Diseases
* 2.3 Size
* 3 Animals
* 3.1 Evolution and adaptation
* 3.2 Activity pattern and behavior
* 4 Society and culture
* 5 See also
* 6 References
* 7 External links

## Function

See also: Medicine:Iris (anatomy)

The iris is a contractile structure, consisting mainly of smooth muscle, surrounding the pupil. Light enters the eye through the pupil, and the iris regulates the amount of light by controlling the size of the pupil. This is known as the pupillary light reflex.

The iris contains two groups of smooth muscles; a circular group called the sphincter pupillae, and a radial group called the dilator pupillae. When the sphincter pupillae contract, the iris decreases or constricts the size of the pupil. The dilator pupillae, innervated by sympathetic nerves from the superior cervical ganglion, cause the pupil to dilate when they contract. These muscles are sometimes referred to as intrinsic eye muscles.

The sensory pathway (rod or cone, bipolar, ganglion) is linked with its counterpart in the other eye by a partial crossover of each eye's fibers. This causes the effect in one eye to carry over to the other.

### Effect of light

The pupil diameter can vary greatly due to various factors (primarily the pupillary light reflex), from constriction to as small as 2 mm, to dilation larger than 8 mm in some individuals, though the maximal dilation also varies substantially by individual and decreases with age

The pupil gets wider in the dark and narrower in light. When narrow, the diameter be 1.5 to 4 millimeters.[5] In the dark it will be the same at first, but will approach the maximum distance for a wide pupil 3 to 8 mm.[5] However, in any human age group there is considerable variation in maximal pupil size. For example, at the peak age of 15, the dark-adapted pupil can vary from 4 mm to 9 mm with different individuals. After 25 years of age, the average pupil size decreases, though not at a steady rate.[6][7] At this stage the pupils do not remain completely still, therefore may lead to oscillation, which may intensify and become known as hippus. The constriction of the pupil and near vision are closely tied. In bright light, the pupils constrict to prevent aberrations of light rays and thus attain their expected acuity; in the dark, this is not necessary, so it is chiefly concerned with admitting sufficient light into the eye.[8]

## Clinical significance

### Effect of drugs

If the drug pilocarpine is administered, the pupils will constrict and accommodation is increased due to the parasympathetic action on the circular muscle fibers, conversely, atropine will cause paralysis of accommodation (cycloplegia) and dilation of the pupil.

Certain drugs cause constriction of the pupils, such as opioids.[9] Other drugs, such as atropine, LSD, MDMA, mescaline, psilocybin mushrooms, cocaine and amphetamines may cause pupil dilation.[10][11]

The sphincter muscle has a parasympathetic innervation, and the dilator has a sympathetic innervation. In pupillary constriction induced by pilocarpine, not only is the sphincter nerve supply activated but that of the dilator is inhibited. The reverse is true, so control of pupil size is controlled by differences in contraction intensity of each muscle.

Another term for the constriction of the pupil is miosis. Substances that cause miosis are described as miotic. Dilation of the pupil is mydriasis. Dilation can be caused by mydriatic substances such as an eye drop solution containing tropicamide.

### Diseases

A condition called bene dilitatism occurs when the optic nerves are partially damaged. This condition is typified by chronically widened pupils due to the decreased ability of the optic nerves to respond to light. In normal lighting, people affected by this condition normally have dilated pupils, and bright lighting can cause pain. At the other end of the spectrum, people with this condition have trouble seeing in darkness. It is necessary for these people to be especially careful when driving at night due to their inability to see objects in their full perspective. This condition is not otherwise dangerous.

### Size

Main articles: Medicine:Mydriasis, Miosis, and Pupillary response

The size of the pupil (often measured as diameter) can vary between 8 and 1.5 mm.[5] Pupil size can be a symptom of an underlying disease. Dilation of the pupil is known as mydriasis and contraction as miosis.

A human adult exhibiting voluntary control over his iris muscles, which grants him the ability to dilate and constrict his pupils on commandPupil dilated naturally to 9 mm due to dim light. The subject is an extreme case, as most individuals are not able to naturally dilate their pupils to that extent Pupil constriction can be in response to negative emotional states

Not all variations in size are indicative of disease however. In addition to dilation and contraction caused by light and darkness, it has been shown that solving simple multiplication problems affects the size of the pupil.[12] The simple act of recollection can dilate the size of the pupil,[13] however when the brain is required to process at a rate above its maximum capacity, the pupils contract.[14] There is also evidence that pupil size is related to the extent of positive or negative emotional arousal experienced by a person.[15]

Myopic individuals have larger resting and dark dilated pupils than hyperopic and emmetropic individuals, likely due to requiring less accommodation (which results in pupil constriction).[16]

Some humans are able to exert direct control over their iris muscles, giving them the ability to manipulate the size of their pupils (i.e. dilating and constricting them) on command, without any changes in lighting condition or eye accommodation state.[17] However, this ability is likely very rare and its purpose or advantages over those without it are unclear.

## Animals

File:Sepia eyelid shape.theora.ogv Not all animals have circular pupils. Some have slits or ovals which may be oriented vertically, as in crocodiles, vipers, cats and foxes, or horizontally as in some rays, flying frogs, mongooses and artiodactyls such as elk, red deer, reindeer and hippopotamus, as well as the domestic horse. Goats, sheep, toads and octopus pupils tend to be horizontal and rectangular with rounded corners. Gecko pupils are generally of the shape of a slit with multiple notches, such that when it is closed, the pupil becomes a series of pinholes, and when it is open, the pupil is roughly circular.[18] When a pupil has a slit form, it is sometimes called stenopaic.[19] The cuttlefish pupil is a smoothly curving W shape.

Bony fishes generally have circular pupils with a nearly spherical lens behind it. But in some, especially nocturnal ones, the pupil is elongated in the rostral end to create a lensless (aphakic) gap.[20][21]

Amphibian pupils can be circular (urodeles and aquatic anurans), horizontal oval (most anurans), horizontal diamond (Hyperolius horstockii), vertical diamond (Corythomantis greeningi), heart-shaped (Bombinator pachypus), vertically pear-shaped (Pelobates fuscus) or diagonally pear-shaped (Caloptochephalus quoyi).[22][23]Template:Pg The king penguin's pupil when contracting in bright light becomes square-shaped.[24] The pupil of some sharks is a diagonal slit, as in nurse shark, tassled wobbegong, and angel shark, though it is more commonly a vertical oval slit. It is a square diamond in the tiger shark. A certain Scyliorhinidae sp. is reported to have diagonal slit pupil with multiple openings, similar to that of a gecko.[25] Most seals have vertical slit pupils, but Phoca barbata has diagonal slit pupils. Most prosimians have vertical slit pupils, except the tarsiers with their circular pupils with an enormous dynamic range.[23]Template:Pg

Only one bird, black skimmer, is known to have slit pupils.[23]Template:Pg

Llamas and camels have horizontal rectangular pupils with a pair of serrated edges, such that when the pupil shrinks, the edges mesh together like two rows of fangs. This structure is the umbraculum. In horses, gazelles, and goats, the umbraculum is much smaller, and in these species, the umbraculum is usually called the corpora nigra[26] or sometimes the granula iridica.[27] Newborn horses have round pupils, but at around 5 years old, the pupil reaches its final form. The horse has 3 or 4 large ones on the top edge, and 5 or 6 small ones on the bottom edge. The sheep has up to 20, the highest recorded.[23]Template:Pg Many artiodactyls have a similar pupil.[28] The rock hyrax has a circular pupil with a spade-shaped umbraculum, attached to the upper edge of the pupil, and it contains muscles that can extend or contract independently of the pupil. Under a strong light, the pupil would contract, and the umbraculum would extend, shielding the pupil.[29] This allows them to look into the sun, leading to a Zulu legend that they are blind.[30] Similar structures appear in some Loricariids,[31] flatfishes,[23]Template:Pg the bottlenose dolphin,[32] the beluga whale.[33] In these species, it is usually called the operculum or the operculum pupillare.[34] In the bottlenose dolphin, it has the function of allowing equivalent visual acuity both in air and in water.[35] The operculum of skates (such as the clearnose skate or the thornback skate) is particularly complex, as it is a spade with frills on its edges. Thus, at maximal extension, the pupil becomes a series of pinholes arranged in a U-shape.[25][28][23]Template:Pg In a few amphibians, the tadpole has a similarly shaped structure named the elygium, although it is disputed on whether it differs from the umbraculum.[36][37]

Although human pupils are normally circular, abnormalities like colobomas can result in unusual pupil shapes, such as teardrop, keyhole or oval pupil shapes.

There may be differences in pupil shape even between closely related animals. In felids, there are differences between small- and large eyed species. The domestic cat (Felis sylvestris domesticus) has vertical slit pupils,[19] its large relative the Siberian tiger (Panthera tigris altaica) has circular pupils and the Eurasian lynx (Lynx lynx) is intermediate between those of the domestic cat and the Siberian tiger. A similar difference between small and large species may be present in canines. The small red fox (Vulpes vulpes) has vertical slit pupils whereas their large relatives, the gray wolf (Canis lupus lupus) and domestic dogs (Canis lupus familiaris) have round pupils.[38]

### Evolution and adaptation

One explanation for the evolution of slit pupils is that they can exclude light more effectively than a circular pupil.[39][40] This would explain why slit pupils tend to be found in the eyes of animals with a crepuscular or nocturnal lifestyle that need to protect their eyes during daylight. Constriction of a circular pupil (by a ring-shaped muscle) is less complete than closure of a slit pupil, which uses two additional muscles that laterally compress the pupil.[41] For example, the cat's slit pupil can change the light intensity on the retina 135-fold compared to 10-fold in humans.[42] However, this explanation does not account for circular pupils that can be closed to a very small size (e.g., 0.5 mm in the tarsier) and the rectangular pupils of many ungulates which do not close to a narrow slit in bright light.[43] An alternative explanation is that a partially constricted circular pupil shades the peripheral zones of the lens which would lead to poorly focused images at relevant wavelengths. The vertical slit pupil allows for use of all wavelengths across the full diameter of the lens, even in bright light.[4] It has also been suggested that in ambush predators such as some snakes, vertical slit pupils may aid in camouflage, breaking up the circular outline of the eye.[44]

The W-shape of the cuttlefish reduces light from the dorsal visual field significantly more than it reduces light from the horizontal band. This is hypothesized to benefit cuttlefish in its natural habitat, where the scene is brighter near the sea surface. Also, it preserves more of the frontal and caudal visual acuity compared to a circular pupil.[45]

Many pupils, at maximal constriction, would become two or more pinholes. The pinholes are vertically aligned in some geckos and the cat.[18] In the geckos, there are usually 4 diamond pinholes. The pinholes are horizontally aligned in many species with prominently horizontal rectangular pupils, such as the goat, the horse, and many artiodactyls.[28] The pinholes are U-shaped in some skates.[28][23]Template:Pg Similarly, in species with a roughly horizontal pupil and an operculum, when the operculum is maximally extended, it would bisect the pupil into two vertical slits.[33][35] This is usually assumed to have certain optical advantages. For example, it is shown that by dividing the pupil in the middle by an operculum, a nocturnal animal may have a slit pupil that protects the retina, and yet still pass high spatial frequencies.[46] One hypothesis for the gecko's multi-pinhole eye is that it allows the eye to use defocus blur to estimate distance, similar to Scheiner's disc used in clinical eye examination.[47] Generally, animals that form multiple pinholes under bright light have rod-rich retinas, have no fovea, and are neither strictly nocturnal nor strictly diurnal.[28]

### Activity pattern and behavior

In a study of Australian snakes, pupil shapes correlated both with diel activity times and with foraging behavior. Most snake species with vertical pupils were nocturnal and also ambush foragers, and most snakes with circular pupils were diurnal and active foragers. Overall, foraging behaviour predicted pupil shape accurately in more cases than did diel time of activity, because many active-foraging snakes with circular pupils were not diurnal. It has been suggested that there may be a similar link between foraging behaviour and pupil shape amongst the felidae and canidae discussed above.[44]

A 2015 study[48] confirmed the hypothesis that elongated pupils have increased dynamic range, and furthered the correlations with diel activity. However it noted that other hypotheses could not explain the orientation of the pupils. They showed that vertical pupils enable ambush predators to optimise their depth perception, and horizontal pupils to optimise the field of view and image quality of horizontal contours. They further explained why elongated pupils are correlated with the animal's height.

* Animals with non-circular pupils
* A goat with horizontal rectangular pupils

* A stingray with crescent pupils

* A crocodile with thin vertical slit pupils

* A cuttlefish with W-shaped pupils

* A gecko with 'thin string of pearls' pupils

* A cat with thick vertical slit pupils

* Horse, ass, gazelle, goat, hyrax, camel, llama.

## Society and culture

The pupil plays a role in eye contact and nonverbal communication. The voluntary or involuntary enlargement or dilation of the pupils indicates cognitive arousal, interest in the subject of attention, and/or sexual arousal. On the other hand, when the pupil is voluntarily or involuntarily contracted, it could indicate the opposite - disinterest or disgust. Exceptionally large or dilated pupils are also perceived to be an attractive feature in body language.[49]

In a surprising number of unrelated languages, the etymological meaning of the term for pupil is "little person".[50][51] This is true, for example, of the word pupil itself: this comes into English from Latin pūpilla, which means "doll, girl", and is a diminutive form of pupa, "girl". (The double meaning in Latin is preserved in English, where pupil means both "schoolchild" and "dark central portion of the eye within the iris".)[52] This may be because the reflection of one's image in the pupil is a minuscule version of one's self.[50] In the Old Babylonian period (c. 1800-1600 BC) in ancient Mesopotamia, the expression "protective spirit of the eye" is attested, perhaps arising from the same phenomenon.

The English phrase apple of my eye arises from an Old English usage, in which the word apple meant not only the fruit but also the pupil or eyeball.[53]

## See also

* Pupillary response
* Pupil function
* Dilated fundus examination
* Eye contact
* Horner's syndrome
* Mydriasis
* Synechia (eye)
* Anisocoria
* Adie's pupil
* Argyll Robertson pupil
* Light-near dissociation
* Marcus Gunn Pupil
* Pupillary distance

## References

1. ↑ Cassin, B. and Solomon, S. (1990) Dictionary of Eye Terminology. Gainesville, Florida: Triad Publishing Company.
2. ↑ Manion, Garrett N.; Stokkermans, Thomas J. (2025), "The Effect of Pupil Size on Visual Resolution", StatPearls (Treasure Island (FL): StatPearls Publishing), PMID 38753941, http://www.ncbi.nlm.nih.gov/books/NBK603732/, retrieved 2025-08-10
3. ↑ Arráez-Aybar, Luis-A (2015). "Toledo School of Translators and their influence on anatomical terminology". Annals of Anatomy - Anatomischer Anzeiger 198: 21–33. doi:10.1016/j.aanat.2014.12.003. PMID 25667112.
4. ↑ 4.0 4.1 "Pupil shapes and lens optics in the eyes of terrestrial vertebrates". J. Exp. Biol. 209 (Pt 1): 18–25. January 2006. doi:10.1242/jeb.01959. PMID 16354774. Bibcode: 2006JExpB.209...18M.
5. ↑ 5.0 5.1 5.2 McDougal, David H.; Gamlin, Paul D. (2015). "Autonomic Control of the Eye". Comprehensive Physiology 5 (1): 439–473. doi:10.1002/cphy.c140014. ISBN 978-0-470-65071-4. PMID 25589275.
6. ↑ "Aging Eyes and Pupil Size". Amateurastronomy.org. http://amateurastronomy.org/Events/EH361.html.
7. ↑ Winn, B.; Whitaker, D.; Elliott, D. B.; Phillips, N. J. (March 1994). "Factors Affecting Light-Adapted Pupil Size in Normal Human Subjects". Investigative Ophthalmology & Visual Science 35 (3): 1132–1137. PMID 8125724. http://www.iovs.org/content/35/3/1132.full.pdf. Retrieved 2013-08-28.
8. ↑ "Sensory Reception: Human Vision: Structure and Function of the Eye" Encyclopædia Brtiannicam Chicago, 1987
9. ↑ Larson, Merlin D. (2008-06-01). "Mechanism of opioid-induced pupillary effects". Clinical Neurophysiology 119 (6): 1358–64. doi:10.1016/j.clinph.2008.01.106. PMID 18397839.
10. ↑ Johnson, Michael D. (October 1, 1999). "How to spot illicit drug abuse in your patients". Postgraduate Medicine 106 (4): 199–200, 203–6, 211–4 passim. doi:10.3810/pgm.1999.10.1.721. PMID 10533519. https://www.csam-asam.org/sites/default/files/pdf/misc/Howtospot.pdf. Retrieved March 22, 2018.
11. ↑ Alderman, Elizabeth M.; Schwartz, Brian (1997-06-01). "Substances of Abuse". Pediatrics in Review 18 (6): 204–215. doi:10.1542/pir.18-6-204. https://pedsinreview.aappublications.org/content/18/6/204.
12. ↑ Hess, Eckhard H.; Polt, James M. (1964-03-13). "Pupil Size in Relation to Mental Activity during Simple Problem-Solving". Science 143 (3611): 1190–2. doi:10.1126/science.143.3611.1190. PMID 17833905. Bibcode: 1964Sci...143.1190H.
13. ↑ L. Andreassi, John (2006). Psychophysiology: Human Behavior and Physiological Response (Psychophysiology: Human Behavior & Physiological Response) (5th ed.). Psychology Press. ISBN 978-0-8058-4951-6.
14. ↑ "My Brain is Overloaded". https://prezi.com/e00bcswh1fhp/my-brain-is-overloaded/.
15. ↑ Partala, T.; Surakka, V. (2003). "Pupil size variation as an indication of affective processing". International Journal of Human-Computer Studies 59 (1–2): 185–198. doi:10.1016/S1071-5819(03)00017-X.
16. ↑ Cakmak, Hasan Basri; Cagil, Nurullah; Simavlı, Hüseyin; Duzen, Betul; Simsek, Saban (February 2010). "Refractive Error May Influence Mesopic Pupil Size" (in en). Current Eye Research 35 (2): 130–136. doi:10.3109/02713680903447892. ISSN 0271-3683. PMID 20136423. http://www.tandfonline.com/doi/full/10.3109/02713680903447892.
17. ↑ Eberhardt, Lisa V.; Grön, Georg; Ulrich, Martin; Huckauf, Anke; Strauch, Christoph (2021-10-01). "Direct voluntary control of pupil constriction and dilation: Exploratory evidence from pupillometry, optometry, skin conductance, perception, and functional MRI". International Journal of Psychophysiology 168: 33–42. doi:10.1016/j.ijpsycho.2021.08.001. ISSN 0167-8760. PMID 34391820. https://www.sciencedirect.com/science/article/pii/S0167876021008448.
18. ↑ 18.0 18.1 Roth, Lina S. V.; Lundström, Linda; Kelber, Almut; Kröger, Ronald H. H.; Unsbo, Peter (2009-03-01). "The pupils and optical systems of gecko eyes". Journal of Vision 9 (3): 27.1–11. doi:10.1167/9.3.27. PMID 19757966.
19. ↑ 19.0 19.1 Smythe, R. H. (1975), Smythe, R. H., ed., "The Eye of the Cat" (in en), Vision in the Animal World (London: Palgrave Macmillan UK): pp. 75–79, doi:10.1007/978-1-349-02533-6_5, ISBN 978-1-349-02533-6
20. ↑ Schmitz, Lars; Wainwright, Peter C (2011). "Nocturnality constrains morphological and functional diversity in the eyes of reef fishes" (in en). BMC Evolutionary Biology 11 (1): 338. doi:10.1186/1471-2148-11-338. ISSN 1471-2148. PMID 22098687. Bibcode: 2011BMCEE..11..338S.
21. ↑ Sivak, J. G. (March 1978). "The functional significance of the aphakic space of the fish eye". Canadian Journal of Zoology 56 (3): 513–516. doi:10.1139/z78-072. ISSN 0008-4301. Bibcode: 1978CaJZ...56..513S. https://cdnsciencepub.com/doi/abs/10.1139/z78-072.
22. ↑ MAnn, Ida (1931). "Iris Pattern in the Vertebrates" (in en). The Transactions of the Zoological Society of London 21 (4): 355–412. doi:10.1111/j.1096-3642.1931.tb00659.x. ISSN 1469-7998. https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1096-3642.1931.tb00659.x.
23. ↑ 23.0 23.1 23.2 23.3 23.4 23.5 23.6 Walls, Gordon Lynn (1942). The vertebrate eye and its adaptive radiation. Bloomfield Hills, Mich., Cranbrook Institute of Science. http://archive.org/details/vertebrateeyeits00wall.
24. ↑ Martin, Graham R. (1999). "Eye structure and foraging in King Penguins Aptenodytes patagonicus" (in en). Ibis 141 (3): 444–450. doi:10.1111/j.1474-919X.1999.tb04413.x. ISSN 1474-919X. https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1474-919X.1999.tb04413.x.
25. ↑ 25.0 25.1 Williams, David (2022), Montiani-Ferreira, Fabiano; Moore, Bret A.; Ben-Shlomo, Gil, eds., "Ophthalmology of Cartilaginous Fish: Skates, Rays, and Sharks" (in en), Wild and Exotic Animal Ophthalmology: Volume 1: Invertebrates, Fishes, Amphibians, Reptiles, and Birds (Cham: Springer International Publishing): pp. 47–59, doi:10.1007/978-3-030-71302-7_4, ISBN 978-3-030-71302-7
26. ↑ Johnson, George Lindsay; Gadow, Hans Friedrich (January 1997). "I. Contributions to the comparative anatomy of the mammalian eye, chiefly based on ophthalmoscopic examination". Philosophical Transactions of the Royal Society of London. Series B, Containing Papers of a Biological Character 194 (194–206): 1–82. doi:10.1098/rstb.1901.0001. https://royalsocietypublishing.org/doi/abs/10.1098/rstb.1901.0001.
27. ↑ Crispin, Sheila M. (2000). "Developmental anomalies and abnormalities of the equine iris" (in en). Veterinary Ophthalmology 3 (2–3): 93–98. doi:10.1046/j.1463-5224.2000.3230093.x. ISSN 1463-5224. https://onlinelibrary.wiley.com/doi/abs/10.1046/j.1463-5224.2000.3230093.x.
28. ↑ 28.0 28.1 28.2 28.3 28.4 Murphy, C.J.; Howland, H.C. (1990). "The functional significance of crescent-shaped pupils and multiple pupillary apertures". Journal of Experimental Zoology 256 (S5): 22. doi:10.1002/jez.1402560505. Bibcode: 1990JEZ...256S..22M.
29. ↑ Freeman, Katie; Ben-Shlomo, Gil; McMullen, Richard; Moore, Bret A. (2022), Montiani-Ferreira, Fabiano; Moore, Bret A.; Ben-Shlomo, Gil, eds., "Ophthalmology of Afrotheria: Aardvarks, Hyraxes, Elephants, Manatees, and Relatives" (in en), Wild and Exotic Animal Ophthalmology: Volume 2: Mammals (Cham: Springer International Publishing): pp. 49–70, doi:10.1007/978-3-030-81273-7_5, ISBN 978-3-030-81273-7
30. ↑ Roberts, Austin (1951). The mammals of South Africa. South Africa: Trustees of "The Mammals of South Africa" Book Fund. p. 254.
31. ↑ Roth, Willi (1920) (in de). Die Iris der Loricariiden. https://archive.org/details/die-iris-der-loricariiden.
32. ↑ Mass, Alla M.; Supin, Alexander YA. (2007). "Adaptive features of aquatic mammals' eye" (in en). The Anatomical Record 290 (6): 701–715. doi:10.1002/ar.20529. ISSN 1932-8494. PMID 17516421. https://onlinelibrary.wiley.com/doi/abs/10.1002/ar.20529.
33. ↑ 33.0 33.1 Mass, A. M. (2001-11-01). "Visual Field Organization and Retinal Resolution in the Beluga Whale Delphinapterus leucas (Pallas)" (in en). Doklady Biological Sciences 381 (1): 555–558. doi:10.1023/A:1013326521559. ISSN 1608-3105. PMID 12918432.
34. ↑ Millar, R. P. (August 1973). "An unusual light-shielding structure in the eye of the dassie, Procavia capensis Pallas (Mammalia: Hydracoidea)". Annals of the Transvaal Museum 28 (11): 203–205. https://journals.co.za/doi/abs/10.10520/AJA00411752_258.
35. ↑ 35.0 35.1 Herman, Louis M.; Peacock, Michael F.; Yunker, Michael P.; Madsen, Carolyn J. (1975-08-22). "Bottle-Nosed Dolphin: Double-Slit Pupil Yields Equivalent Aerial and Underwater Diurnal Acuity". Science 189 (4203): 650–652. doi:10.1126/science.1162351. Bibcode: 1975Sci...189..650H. https://www.science.org/doi/abs/10.1126/science.1162351.
36. ↑ Van, Dijk D. Eduard (September 1966). "Systematic and field keys to the families, genera and described species of Southern African Anuran tadpoles". Annals of the Natal Museum 18 (2): 231–286. https://journals.co.za/doi/abs/10.10520/AJA03040798_751.
37. ↑ Kruger, Donnavan J.D.; Weldon, Ché; Minter, Les R.; Du Preez, Louis H. (2013). "Morphology of the elygium and developing umbraculum in the eye of Amietia vertebralis tadpoles" (in en). Journal of Morphology 274 (5): 551–556. doi:10.1002/jmor.20115. ISSN 1097-4687. PMID 23293087. Bibcode: 2013JMorp.274..551K. https://onlinelibrary.wiley.com/doi/abs/10.1002/jmor.20115.
38. ↑ Kaminski, Juliane; Waller, Bridget M.; Diogo, Rui; Hartstone-Rose, Adam; Burrows, Anne M. (2019-07-16). "Evolution of facial muscle anatomy in dogs". Proceedings of the National Academy of Sciences 116 (29): 14677–14681. doi:10.1073/pnas.1820653116. PMID 31209036. PMC 6642381. https://www.pnas.org/doi/10.1073/pnas.1820653116.
39. ↑ Land, Michael F. (2006-03-07). "Visual Optics: The Shapes of Pupils". Current Biology 16 (5): R167–R168. doi:10.1016/j.cub.2006.02.046. ISSN 0960-9822. https://www.sciencedirect.com/science/article/pii/S0960982206011961. "The explanation usually given for the use of a slit pupil is that it can exclude light more effectively than a circular pupil, and so slit pupils tend to be found in the eyes of animals with a crepuscular or nocturnal lifestyle that need to protect their eyes during daylight.".
40. ↑ Walls, G.L. (1942). The Vertebrate Eye and its Adaptive Radiation. Bloomfield Hills, Michigan: The Cranbrook Institute of Science.
41. ↑ Walls, G.L. (1967). The vertebrate eye and its adaptive radiation. Cranbrook Institute of Science Bulletin. 19. Hafner. OCLC 10363617.
42. ↑ Hughes, A. (2013). "The topography of vision in mammals of contrasting life style: comparative optics and retinal organisation". in Crescitelli, F.. The Visual System in Vertebrates. Handbook of Sensory Physiology. 7/5. Springer. pp. 613–756. ISBN 978-3-642-66468-7. https://books.google.com/books?id=qCDqCAAAQBAJ&pg=PA613.
43. ↑ Land, M.F. (2006). "Visual optics: the shapes of pupils". Current Biology 16 (5): R167–8. doi:10.1016/j.cub.2006.02.046. PMID 16527734. Bibcode: 2006CBio...16.R167L.
44. ↑ 44.0 44.1 Brischoux, F., Pizzatto, L. and Shine, R. (2010). "Insights into the adaptive significance of vertical pupil shape in snakes". Journal of Evolutionary Biology 23 (9): 1878–85. doi:10.1111/j.1420-9101.2010.02046.x. PMID 20629855.
45. ↑ Mäthger, Lydia M.; Hanlon, Roger T.; Håkansson, Jonas; Nilsson, Dan-Eric (2013-05-03). "The W-shaped pupil in cuttlefish (Sepia officinalis): Functions for improving horizontal vision". Vision Research 83: 19–24. doi:10.1016/j.visres.2013.02.016. ISSN 0042-6989. PMID 23474299. https://www.sciencedirect.com/science/article/pii/S0042698913000539.
46. ↑ Miller, William H. (1979), Autrum, H., ed., "Ocular Optical Filtering" (in en), Comparative Physiology and Evolution of Vision in Invertebrates, Handbook of Sensory Physiology (Berlin, Heidelberg: Springer Berlin Heidelberg) 7 / 6 / 6 A: pp. 69–143, doi:10.1007/978-3-642-66999-6_3, ISBN 978-3-642-67001-5, http://link.springer.com/10.1007/978-3-642-66999-6_3
47. ↑ Murphy, Christopher J.; Howland, Howard C. (1986-01-01). "On the gekko pupil and scheiner's disc". Vision Research 26 (5): 815–817. doi:10.1016/0042-6989(86)90097-0. ISSN 0042-6989.
48. ↑ Banks, Martin S.; Sprague, William W.; Schmoll, Jürgen; Parnell, Jared A. Q.; Love, Gordon D. (2015). "Why do animal eyes have pupils of different shapes?". Science Advances 1 (7). doi:10.1126/sciadv.1500391. PMID 26601232. Bibcode: 2015SciA....1E0391B.
49. ↑ Tombs, Selina; Silverman, Irwin (2004-07-01). "Pupillometry: A sexual selection approach" (in en). Evolution and Human Behavior 25 (4): 221–228. doi:10.1016/j.evolhumbehav.2004.05.001. ISSN 1090-5138. Bibcode: 2004EHumB..25..221T. https://www.sciencedirect.com/science/article/pii/S1090513804000261.
50. ↑ 50.0 50.1 Brown, Donald E. (2004). "Human Universals, Human Nature & Human Culture". Daedalus 133 (4): 49. doi:10.1162/0011526042365645.
51. ↑ Brown, Cecil H.; Witkowski, Stanley R. (1981). "Figurative Language in a Universalist Perspective". American Ethnologist 8 (3): 596–615. doi:10.1525/ae.1981.8.3.02a00110.
52. ↑ "pupil, n.2.", Oxford English Dictionary Online, 3rd. edn (Oxford University Press, 2007).
53. ↑ apple, n.", Oxford English Dictionary Online, 3rd ed. (Oxford University Press, 2008), § 6 B.

## External links

* Atlas image: eye_1 at the University of Michigan Health System — "Sagittal Section Through the Eyeball"
* Atlas image: eye_2 at the University of Michigan Health System — "Sagittal Section Through the Eyeball"
* A pupil examination simulator, demonstrating the changes in pupil reactions for various nerve lesions.

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Anatomy of the globe of the human eye

Fibrous tunic (outer)|

| Sclera|

* Episcleral layer
* Schlemm's canal
* Trabecular meshwork

|

Cornea|

* Limbus
* layers
* Epithelium
* Bowman's
* Stroma
* Dua's layer
* Descemet's
* Endothelium

1:posterior segment 2:ora serrata 3:ciliary muscle 4:ciliary zonules 5:Schlemm's canal 6:pupil 7:anterior chamber 8:cornea 9:iris 10:lens cortex 11:lens nucleus 12:ciliary process 13:conjunctiva 14:inferior oblique muscule 15:inferior rectus muscule 16:medial rectus muscle 17:retinal arteries and veins 18:optic disc 19:dura mater 20:central retinal artery 21:central retinal vein 22:optic nerve 23:vorticose vein 24:bulbar sheath 25:macula 26:fovea 27:sclera 28:choroid 29:superior rectus muscle 30:retina

Uvea/vascular tunic (middle)|

| Choroid|

* Capillary lamina of choroid
* Bruch's membrane
* Sattler's layer

|

Ciliary body|

* Ciliary processes
* Ciliary muscle
* Pars plicata
* Pars plana

Iris|

* Stroma
* Pupil
* Iris dilator muscle
* Iris sphincter muscle

Retina (inner)|

| Layers|

* Inner limiting membrane
* Nerve fiber layer
* Ganglion cell layer
* Inner plexiform layer
* Inner nuclear layer

* Outer plexiform layer
* Outer nuclear layer

* External limiting membrane
* Layer of rods and cones
* Retinal pigment epithelium

|

Cells|

* Photoreceptor cells (Cone cell, Rod cell) → (Horizontal cell) → Bipolar cell → (Amacrine cell) → Retina ganglion cell (Midget cell, [[Biology:Parasol cParasol cell, [[Bistratified cell]], Giant retina ganglion cells, Photosensitive ganglion cell) → Diencephalon: P cell, M cell, K cell, Muller glia

Other|

* Macula
* Perifoveal area
* Parafoveal area
* Fovea
* Foveal avascular zone
* Foveola
* Optic disc
* Optic cup
* Ora serrata

Anatomical regions of the eye|

| Anterior segment|

* Adnexa
* Fibrous tunic
* Anterior chamber
* Aqueous humour
* Iris
* Posterior chamber
* Ciliary body
* Lens
* Capsule of lens
* Zonule of Zinn

|

Posterior segment|

* Vitreous chamber
* Vitreous body
* Retina
* Choroid

Other|

* Keratocytes
* Ocular immune system
* Optical coherence tomography
* Eye care professional
* Eye disease
* Refractive error
* Accommodation
* Physiological Optics
* Visual perception

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Optical illusions (list)

Illusions|

* Afterimage
* Ambiguous image
* Ames room
* Barberpole
* Bezold
* Café wall
* Checker shadow
* Chubb
* Cornsweet
* Delboeuf
* Ebbinghaus
* Ehrenstein
* Flash lag
* Fraser spiral
* Gravity hill
* Grid
* Hering
* Impossible trident
* Jastrow
* Lilac chaser
* Mach bands
* McCollough
* Müller-Lyer
* Necker cube
* Orbison
* Penrose stairs
* Penrose triangle
* Peripheral drift
* Poggendorff
* Ponzo
* Rubin vase
* Sander
* Schroeder stairs
* Shepard tables
* Spinning Dancer
* Ternus
* Vertical–horizontal
* White's
* Wundt
* Zöllner

Popular culture|

* Op art
* Trompe-l'œil
* Spectropia (1864 book)
* Ascending and Descending (1960 drawing)
* Waterfall (1961 drawing)
* The dress (2015 photograph)

Related|

* Auditory illusions
* Tactile illusions
* Temporal illusion

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