Editing Eye (section)

==Overview==
[[File:Bison bonasus right eye close-up.jpg|thumb|upright|left|Eye of a [[European bison]]]]
[[File:Голубой глаз.jpg|thumb|[[Human eye]]]]
Complex eyes distinguish shapes and [[colour]]s. The [[Visual perception|visual]] fields of many organisms, especially predators, involve large areas of [[binocular vision]] for [[depth perception]]. In other organisms, particularly prey animals, eyes are located to maximise the field of view, such as in [[rabbit]]s and [[horse]]s, which have [[monocular vision]].

The first proto-eyes evolved among animals {{Ma|600}} about the time of the [[Cambrian explosion]].<ref>{{cite book |last=Breitmeyer|first=Bruno |title=Blindspots: The Many Ways We Cannot See |url=https://archive.org/details/blindspotsmanywa0000brei|url-access=registration|publisher=Oxford University Press |location=New York |year=2010 |page=[https://archive.org/details/blindspotsmanywa0000brei/page/4 4] |isbn=978-0-19-539426-9}}</ref> The last common ancestor of animals possessed the biochemical toolkit necessary for vision, and more advanced eyes have evolved in 96% of animal species in six of the ~35{{efn|There is no universal consensus on the precise total number of phyla Animalia; the stated figure varies slightly from author to author.}} main [[Phylum|phyla]].<ref name=Land1992/> In most [[vertebrate]]s and some [[mollusc]]s, the eye allows light to enter and project onto a light-sensitive layer of [[cell (biology)|cells]] known as the [[retina]]. The [[cone cell]]s (for colour) and the [[rod cell]]s (for low-light contrasts) in the retina detect and convert light into neural signals which are transmitted to the [[brain]] via the [[optic nerve]] to produce vision. Such eyes are typically spheroid, filled with the [[transparency (optics)|transparent]] gel-like [[vitreous humour]], possess a focusing [[lens (anatomy)|lens]], and often an [[iris (anatomy)|iris]]. Muscles around the iris change the size of the [[pupil]], regulating the amount of light that enters the eye<ref>{{cite book | last=Nairne | first=James | title=Psychology | publisher=Wadsworth Publishing | location=Belmont | year=2005 | isbn=978-0-495-03150-5 | url=https://books.google.com/books?id=6MqkLT-Q0oUC&pg=PA146 | oclc=61361417 | access-date=2020-10-19 | archive-date=2023-01-17 | archive-url=https://web.archive.org/web/20230117104216/https://books.google.com/books?id=6MqkLT-Q0oUC&pg=PA146 | url-status=live }}</ref> and reducing aberrations when there is enough light.<ref>{{cite book | title=Visual Perception: Physiology, Psychology and Ecology | author1=Bruce, Vicki | author2=Green, Patrick R. | author3=Georgeson, Mark A. | publisher=Psychology Press | year=1996 | isbn=978-0-86377-450-8 | page=20 | url=https://books.google.com/books?id=ukvei0wge_8C&pg=PA20 | access-date=2020-10-19 | archive-date=2023-01-17 | archive-url=https://web.archive.org/web/20230117104216/https://books.google.com/books?id=ukvei0wge_8C&pg=PA20 | url-status=live }}</ref> The eyes of most [[cephalopod]]s, [[fish]], [[amphibian]]s and [[snake]]s have fixed lens shapes, and focusing is achieved by telescoping the lens in a similar manner to that of a [[camera]].<ref>{{cite web|last1=Kirk|first1=Molly|first2=David|last2=Denning|publisher=BioMedia Associates|date=2001|url=http://ebiomedia.com/gall/eyes/octopus-insect.html|title=What animal has a more sophisticated eye, Octopus or Insect?|archive-url=https://web.archive.org/web/20170226060919/http://www.ebiomedia.com/what-animal-has-a-more-sophisticated-eye-octopus-or-insect.html|archive-date=26 February 2017}}</ref>

The compound eyes of the [[arthropod]]s are composed of many simple facets which, depending on anatomical detail, may give either a single pixelated image or multiple images per eye. Each sensor has its own lens and photosensitive cell(s). Some eyes have up to 28,000 such sensors arranged hexagonally, which can give a full 360° field of vision. Compound eyes are very sensitive to motion. Some arthropods, including many [[Strepsiptera]], have compound eyes of only a few facets, each with a retina capable of creating an image. With each eye producing a different image, a fused, high-resolution image is produced in the brain.

[[Image:Odontodactylus scyllarus eyes.jpg|thumb|upright=1.1|The eyes of a mantis shrimp (here ''[[Odontodactylus scyllarus]]'') are considered the most complex in the whole animal kingdom.]]

The [[mantis shrimp]] has the world's most complex colour vision system. It has detailed [[hyperspectral]] colour vision.<ref>{{cite web|url=http://www.nwf.org/news-and-magazines/national-wildlife/animals/archives/2005/who-you-callin-shrimp.aspx|title=Who You Callin' "Shrimp"?|work=National Wildlife Magazine|publisher=[[National Wildlife Federation]]|date=1 October 2010|access-date=3 April 2014|archive-date=9 August 2010|archive-url=https://web.archive.org/web/20100809032945/http://www.nwf.org/News-and-Magazines/National-Wildlife/Animals/Archives/2005/Who-You-Callin-Shrimp.aspx|url-status=live}}</ref>

[[Trilobite]]s, now extinct, had unique compound eyes. Clear [[calcite]] crystals formed the lenses of their eyes. They differ in this from most other arthropods, which have soft eyes. The number of lenses in such an eye varied widely; some trilobites had only one while others had thousands of lenses per eye.

In contrast to compound eyes, simple eyes have a single lens. [[Jumping spider]]s have one pair of large simple eyes with a narrow [[field of view]], augmented by an array of smaller eyes for [[peripheral vision]]. Some insect [[larva]]e, like [[caterpillar]]s, have a type of simple eye ([[stemmata]]) which usually provides only a rough image, but (as in [[sawfly]] larvae) can possess resolving powers of 4 degrees of arc, be polarization-sensitive, and capable of increasing its absolute sensitivity at night by a factor of 1,000 or more.<ref name="Meyer-Rochow 1974">{{cite journal|last=Meyer-Rochow|first=V.B.|title=Structure and function of the larval eye of the sawfly larva ''Perga''|doi=10.1016/0022-1910(74)90087-0|pmid=4854430|journal=Journal of Insect Physiology|date=1974|volume=20|issue=8|pages=1565–1591}}</ref> [[ocellus|Ocelli]], some of the simplest eyes, are found in animals such as some of the [[snail]]s. They have [[photosensitive]] cells but no lens or other means of projecting an image onto those cells. They can distinguish between light and dark but no more, enabling them to avoid direct [[sunlight]]. In organisms dwelling near [[Hydrothermal vent|deep-sea vents]], compound eyes are adapted to see the [[Infrared|infra-red light]] produced by the hot vents, allowing the creatures to avoid being boiled alive.<ref name=Cronin2008/>