Pupil

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For other uses, see Pupil (disambiguation). Pupil_sentence_0

Pupil_table_infobox_0

PupilPupil_header_cell_0_0_0
DetailsPupil_header_cell_0_1_0
Part ofPupil_header_cell_0_2_0 EyePupil_cell_0_2_1
SystemPupil_header_cell_0_3_0 Visual systemPupil_cell_0_3_1
IdentifiersPupil_header_cell_0_4_0
LatinPupil_header_cell_0_5_0 Pupilla. (Plural: Pupillae)Pupil_cell_0_5_1
MeSHPupil_header_cell_0_6_0 Pupil_cell_0_6_1
TA98Pupil_header_cell_0_7_0 Pupil_cell_0_7_1
TA2Pupil_header_cell_0_8_0 Pupil_cell_0_8_1
FMAPupil_header_cell_0_9_0 Pupil_cell_0_9_1

The pupil is a black hole located in the center of the iris of the eye that allows light to strike the retina. Pupil_sentence_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. Pupil_sentence_2

The term “pupil” was created by Gerard of Cremona. Pupil_sentence_3

In humans, the pupil is round, but its shape varies between species; some cats, reptiles, and foxes have vertical slit pupils, goats have horizontally oriented pupils, and some catfish have annular types. Pupil_sentence_4

In optical terms, the anatomical pupil is the eye's aperture and the iris is the aperture stop. Pupil_sentence_5

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. Pupil_sentence_6

On the inner edge lies a prominent structure, the collarette, marking the junction of the embryonic pupillary membrane covering the embryonic pupil. Pupil_sentence_7

Structure Pupil_section_0

The pupil is a hole located in the center of the iris of the eye that allows light to strike the retina. Pupil_sentence_8

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. Pupil_sentence_9

Function Pupil_section_1

See also: Iris (anatomy) Pupil_sentence_10

The iris is a contractile structure, consisting mainly of smooth muscle, surrounding the pupil. Pupil_sentence_11

Light enters the eye through the pupil, and the iris regulates the amount of light by controlling the size of the pupil. Pupil_sentence_12

This is known as the pupillary light reflex. Pupil_sentence_13

The iris contains two groups of smooth muscles; a circular group called the sphincter pupillae, and a radial group called the dilator pupillae. Pupil_sentence_14

When the sphincter pupillae contract, the iris decreases or constricts the size of the pupil. Pupil_sentence_15

The dilator pupillae, innervated by sympathetic nerves from the superior cervical ganglion, cause the pupil to dilate when they contract. Pupil_sentence_16

These muscles are sometimes referred to as intrinsic eye muscles. Pupil_sentence_17

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. Pupil_sentence_18

This causes the effect in one eye to carry over to the other. Pupil_sentence_19

Effect of light Pupil_section_2

The pupil gets wider in the dark and narrower in light. Pupil_sentence_20

When narrow, the diameter is 2 to 4 millimeters. Pupil_sentence_21

In the dark it will be the same at first, but will approach the maximum distance for a wide pupil 3 to 8 mm. Pupil_sentence_22

However, in any human age group there is considerable variation in maximal pupil size. Pupil_sentence_23

For example, at the peak age of 15, the dark-adapted pupil can vary from 4 mm to 9 mm with different individuals. Pupil_sentence_24

After 25 years of age, the average pupil size decreases, though not at a steady rate. Pupil_sentence_25

At this stage the pupils do not remain completely still, therefore may lead to oscillation, which may intensify and become known as hippus. Pupil_sentence_26

The constriction of the pupil and near vision are closely tied. Pupil_sentence_27

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. Pupil_sentence_28

When bright light is shone on the eye, light-sensitive cells in the retina, including rod and cone photoreceptors and melanopsin ganglion cells, will send signals to the oculomotor nerve, specifically the parasympathetic part coming from the Edinger-Westphal nucleus, which terminates on the circular iris sphincter muscle. Pupil_sentence_29

When this muscle contracts, it reduces the size of the pupil. Pupil_sentence_30

This is the pupillary light reflex, which is an important test of brainstem function. Pupil_sentence_31

Furthermore, the pupil will dilate if a person sees an object of interest. Pupil_sentence_32

Clinical significance Pupil_section_3

Further information: Pupillary response Pupil_sentence_33

Effect of drugs Pupil_section_4

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. Pupil_sentence_34

Certain drugs cause constriction of the pupils, such as opioids. Pupil_sentence_35

Other drugs, such as atropine, LSD, MDMA, mescaline, psilocybin mushrooms, cocaine and amphetamines may cause pupil dilation. Pupil_sentence_36

The sphincter muscle has a parasympathetic innervation, and the dilator has a sympathetic innervation. Pupil_sentence_37

In pupillary constriction induced by pilocarpine, not only is the sphincter nerve supply activated but that of the dilator is inhibited. Pupil_sentence_38

The reverse is true, so control of pupil size is controlled by differences in contraction intensity of each muscle. Pupil_sentence_39

Another term for the constriction of the pupil is miosis. Pupil_sentence_40

Substances that cause miosis are described as miotic. Pupil_sentence_41

Dilation of the pupil is mydriasis. Pupil_sentence_42

Dilation can be caused by mydriatic substances such as an eye drop solution containing tropicamide. Pupil_sentence_43

Diseases Pupil_section_5

A condition called bene dilitatism occurs when the optic nerves are partially damaged. Pupil_sentence_44

This condition is typified by chronically widened pupils due to the decreased ability of the optic nerves to respond to light. Pupil_sentence_45

In normal lighting, people afflicted with this condition normally have dilated pupils, and bright lighting can cause pain. Pupil_sentence_46

At the other end of the spectrum, people with this condition have trouble seeing in darkness. Pupil_sentence_47

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. Pupil_sentence_48

This condition is not otherwise dangerous. Pupil_sentence_49

Size Pupil_section_6

Main articles: Mydriasis and Miosis Pupil_sentence_50

The size of the pupil (often measured as diameter) can be a symptom of an underlying disease. Pupil_sentence_51

Dilation of the pupil is known as mydriasis and contraction as miosis. Pupil_sentence_52

Not all variations in size are indicative of disease however. Pupil_sentence_53

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. Pupil_sentence_54

The simple act of recollection can dilate the size of the pupil, however when the brain is required to process at a rate above its maximum capacity, the pupils contract. Pupil_sentence_55

There is also evidence that pupil size is related to the extent of positive or negative emotional arousal experienced by a person. Pupil_sentence_56

Other animals Pupil_section_7

Not all animals have circular pupils. Pupil_sentence_57

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 sheep, elk, red deer, reindeer and hippopotamus, as well as the domestic horse. Pupil_sentence_58

Goats, toads and octopus pupils tend to be horizontal and rectangular with rounded corners. Pupil_sentence_59

Some skates and rays have crescent shaped pupils, gecko pupils range from circular, to a slit, to a series of pinholes, and the cuttlefish pupil is a smoothly curving W shape. Pupil_sentence_60

Although human pupils are normally circular, abnormalities like colobomas can result in unusual pupil shapes, such as teardrop, keyhole or oval pupil shapes. Pupil_sentence_61

There may be differences in pupil shape even between closely related animals. Pupil_sentence_62

In felids, there are differences between small- and large eyed species. Pupil_sentence_63

The domestic cat (Felis sylvestris domesticus) has vertical slit pupils, 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. Pupil_sentence_64

A similar difference between small and large species may be present in canines. Pupil_sentence_65

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. Pupil_sentence_66

One explanation for the evolution of slit pupils is that they can exclude light more effectively than a circular pupil. Pupil_sentence_67

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. Pupil_sentence_68

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. Pupil_sentence_69

For example, the cat's slit pupil can change the light intensity on the retina 135-fold compared to 10-fold in humans. Pupil_sentence_70

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. Pupil_sentence_71

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. Pupil_sentence_72

The vertical slit pupil allows for use of all wavelengths across the full diameter of the lens, even in bright light. Pupil_sentence_73

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. Pupil_sentence_74

In a study of Australian snakes, pupil shapes correlated both with diel activity times and with foraging behaviour. Pupil_sentence_75

Most snake species with vertical pupils were nocturnal and also ambush foragers, and most snakes with circular pupils were diurnal and active foragers. Pupil_sentence_76

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. Pupil_sentence_77

It has been suggested that there may be a similar link between foraging behaviour and pupil shape amongst the felidae and canidae discussed above. Pupil_sentence_78

A 2015 study confirmed the hypothesis that elongated pupils have increased dynamic range, and furthered the correlations with diel activity. Pupil_sentence_79

However it noted that other hypotheses could not explain the orientation of the pupils. Pupil_sentence_80

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. Pupil_sentence_81

They further explained why elongated pupils are correlated with the animal's height. Pupil_sentence_82

Pupil_unordered_list_0

  • Animals with non-circular pupilsPupil_item_0_0
  • Pupil_item_0_1
  • Pupil_item_0_2
  • Pupil_item_0_3
  • Pupil_item_0_4
  • Pupil_item_0_5
  • Pupil_item_0_6

Society and culture Pupil_section_8

In a surprising number of unrelated languages, the etymological meaning of the term for pupil is "little person". Pupil_sentence_83

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". Pupil_sentence_84

(The double meaning in Latin is preserved in English, where pupil means both "schoolchild" and "dark central portion of the eye within the iris".) Pupil_sentence_85

This may be because the reflection of one's image in the pupil is a minuscule version of one's self. Pupil_sentence_86

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. Pupil_sentence_87

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. Pupil_sentence_88

See also Pupil_section_9

Pupil_unordered_list_1


Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Pupil.