Editing Compound eye

{{Short description|Visual organ found in arthropods such as insects and crustaceans}}
[[Image:Krilleyekils.jpg|thumb|Compound eye of [[Antarctic krill]] as imaged by an [[electron microscope]]]]

A '''compound eye''' is a [[Eye|visual organ]] found in [[arthropod]]s such as [[insect]]s and [[crustacean]]s. It may consist of thousands of [[ommatidium|ommatidia]],<ref>{{cite book |title=Insects and Spiders of the World. Volume 8: Scorpion fly - Stinkbug |chapter-url=https://archive.org/details/insectsspidersof0011unse/page/459 |chapter-url-access=registration |date=2003 |publisher=Marshall Cavendish |location=New York |isbn=978-0761473428 |page=[https://archive.org/details/insectsspidersof0011unse/page/459 459] |chapter=Senses. Insect eyes }}</ref> which are tiny independent photoreception units that consist of a [[cornea]], [[lens (anatomy)|lens]], and [[photoreceptor cell]]s which distinguish brightness and color. The image perceived by this [[arthropod eye]] is a combination of inputs from the numerous ommatidia, which are oriented to point in slightly different directions. Compared with single-aperture [[eye]]s, compound eyes have poor [[image resolution]]; however, they possess a very large view angle and the ability to detect fast movement and, in some cases, the [[Polarization (waves)|polarization]] of light.<ref>{{cite journal |last1=Völkel |first1=R. |last2=Eisner |first2=M. |last3=Weible |first3=K.J. |title=Miniaturized imaging systems |journal=Microelectronic Engineering |date=June 2003 |volume=67-68 |issue=8 |pages=461–472 |doi=10.1016/S0167-9317(03)00102-3|url=http://www.suss-microoptics.com/downloads/Publications/Miniaturized_Imaging_Systems.pdf|url-status=usurped |archive-url=https://web.archive.org/web/20081001225326/http://www.suss-microoptics.com/downloads/Publications/Miniaturized_Imaging_Systems.pdf |archive-date=2008-10-01 }}</ref> Because a compound eye is made up of a collection of ommatidia, each with its own lens, light will enter each ommatidium instead of using a single entrance point. The individual light receptors behind each lens are then turned on and off due to a series of changes in the light intensity during movement or when an object is moving, creating a flicker-effect known as the flicker frequency, which is the rate at which the ommatidia are turned on and off– this facilitates faster reaction to movement; [[honey bee]]s respond in 0.01s compared with 0.05s for humans.<ref>[https://books.google.com/books?id=kISACgAAQBAJ&dq=compound+eyes+elementary+motion+detectors+%28EMDs%29&pg=PA117 Biologically Inspired Computer Vision: Fundamentals and Applications]</ref>

==Types==
Compound eyes are typically classified as either apposition eyes, which form multiple inverted images, or superposition eyes, which form a single erect image.<ref name="Gaten">{{cite journal |last1=Gaten |first1=Edward |title=Optics and phylogeny: is there an insight? The evolution of superposition eyes in the Decapoda (Crustacea) |journal=Contributions to Zoology |date=1998 |volume=67 |issue=4 |pages=223–236 |doi=10.1163/18759866-06704001 |doi-access=free }}</ref>

===Apposition eyes===
[[File:Mantis Fly - Genus Plega.jpg|thumb|Head of a [[mantisfly]] showing a compound eye]]
'''Apposition eyes''' can be divided into two groups. The typical apposition eye has a lens focusing light from one direction on the [[rhabdom]], while light from other directions is absorbed by the dark wall of the [[ommatidium]]. The [[mantis shrimp]] is the most advanced example of an animal with this type of eye. In the other kind of apposition eye, found in the [[Strepsiptera]], each lens forms an image, and the images are combined in the brain.<ref>{{cite journal |last1=Buschbeck |first1=Elke K. |title=The compound lens eye of Strepsiptera: morphological development of larvae and pupae |journal=Arthropod Structure & Development |date=1 July 2005 |volume=34 |issue=3 |pages=315–326 |doi=10.1016/j.asd.2005.04.002 |bibcode=2005ArtSD..34..315B |url=https://www.sciencedirect.com/science/article/pii/S1467803905000411 |access-date=3 July 2022 |language=en |issn=1467-8039|url-access=subscription }}</ref> This is called the schizochroal compound eye or the neural superposition eye (which, despite its name, is a form of the apposition eye).

===Superposition eyes===
The '''superposition eye''' is divided into three subtypes; the ''refracting'', the ''reflecting'', and the ''parabolic'' superposition eye. The '''refracting superposition eye''' has a gap between the lens and the rhabdom, and no side wall. Each lens takes light at an angle to its axis and reflects it to the same angle on the other side. The result is an image at half the radius of the eye, which is where the tips of the rhabdoms are. This kind is used mostly by nocturnal insects. In the '''parabolic superposition eye''', seen in arthropods such as [[mayfly|mayflies]], the parabolic surfaces of the inside of each facet focus light from a reflector to a [[sensor array]]. Long-bodied decapod crustaceans such as [[shrimp]], [[prawn]]s, [[crayfish]] and [[lobster]]s are alone in having '''reflecting superposition eyes''', which also have a transparent gap but use [[corner mirror]]s instead of lenses.

===Other===
[[File:DragonFly macrogiants E.jpg|thumb|Compound eye of a [[dragonfly]]]]
Good fliers like flies or honey bees, or prey-catching insects like [[praying mantis]]es or [[dragonfly|dragonflies]], have specialized zones of [[ommatidium|ommatidia]] organized into a fovea area which gives acute vision. In the acute zone the eye is flattened and the facets larger. The flattening allows more ommatidia to receive light from a spot and therefore higher resolution.

There are some exceptions from the types mentioned above. Some insects have a so-called single lens compound eye, a transitional type which is something between a superposition type of the multi-lens compound eye and the single lens eye found in animals with simple eyes. Then there is the [[mysid]] shrimp, ''Dioptromysis paucispinosa''. The shrimp has an eye of the refracting superposition type, in the rear behind this in each eye there is a single large facet that is three times in diameter the others in the eye and behind this is an enlarged crystalline cone. This projects an upright image on a specialized retina. The resulting eye is a mixture of a simple eye within a compound eye.

Another version is the pseudofaceted eye, as seen in [[Scutigera]]. This type of eye consists of a cluster of numerous [[ocelli]] on each side of the head, organized in a way that resembles a true compound eye.

Asymmetries in compound eyes may be associated with asymmetries in behaviour. For example, ''[[Temnothorax albipennis]]'' ant scouts show behavioural lateralization when exploring unknown nest sites, showing a population-level bias to prefer left turns. One possible reason for this is that its environment is partly maze-like and consistently turning in one direction is a good way to search and exit mazes without getting lost.<ref>{{cite journal |vauthors=Hunt ER, etal | year=2014 |title=Ants show a leftward turning bias when exploring unknown nest sites|journal=[[Biology Letters]] |volume=10 |issue=12 |pmid=25540159 |doi=10.1098/rsbl.2014.0945 |pmc=4298197 |page=20140945}}</ref> This turning bias is correlated with slight asymmetries in the ants' compound eyes (differential ommatidia count).<ref>{{cite journal |vauthors=Hunt ER, etal |title=Asymmetric ommatidia count and behavioural lateralization in the ant ''Temnothorax albipennis'' |journal=[[Scientific Reports]] |date=11 April 2018 |volume=8 |issue=1 |page=5825 |doi=10.1038/s41598-018-23652-4 |pmid=29643429 |pmc=5895843|bibcode=2018NatSR...8.5825H }}</ref>

The body of ''[[Ophiomastix wendtii]]'', a type of [[brittle star]], was previously thought to be covered with ommatidia, turning its whole skin into a compound eye, but this has since been found to be erroneous; the system does not rely on lenses or image formation.<ref>{{cite journal | vauthors = Sumner-Rooney L, Rahman IA, Sigwart JD, Ullrich-Lüter E | title = Whole-body photoreceptor networks are independent of 'lenses' in brittle stars | journal = Proceedings. Biological Sciences | volume = 285 | issue = 1871 | pages = 20172590 | date = January 2018 | pmid = 29367398 | pmc = 5805950 | doi = 10.1098/rspb.2017.2590 }}</ref>

==Cultural references==
"Dragonfly eyes" (Chinese: 蜻蜓眼 ''qingting yan'') is a term for knobbly multi-coloured glass beads made in Western and Eastern Asia 2000–2500 years ago.<ref>https://www.cambridge.org/core/journals/microscopy-and-microanalysis/article/abs/nondestructive-analysis-of-dragonfly-eye-beads-from-the-warring-states-period-excavated-from-a-chu-tomb-at-the-shenmingpu-site-henan-province-china/E2FCF854D5324115F503E1643C33BDBD DOI: https://doi.org/10.1017/S1431927612014201</ref>
Owing to the multiple views and stimuli, compound eyes or dragonfly eyes have become a feature in art, film and literature, particularly in the 2010s. For example:
* ''[[The Man with the Compound Eyes]]'', novel (2011) by [[Wu Ming-yi]], English translation (2013) by [[Darryl Sterk]]
* [https://www.imdb.com/title/tt6576482/ ''Dragonfly Eyes''], movie (2017) by [[Xu Bing]]
* [https://www.worldcat.org/oclc/1127096979 ''Dragonfly Eyes''], novel (2016) by [[Cao Wenxuan]], English translation (2021) by [[Helen Wang]]

==See also==
*[[Arthropod eye]]
*[[Eye]]
*[[Pseudopupil]]

==References==
{{Reflist}}

==External links==
{{Commons category|Compound eye}}
*''[http://www.biology-pages.info/C/CompoundEye.html The Compound Eye]''
*[http://www.uky.edu/Agriculture/Entomology/ythfacts/bugfun/cmpdeye.htm ''Make Your Own Compound Eye'' by Stephanie Bailey]
*[https://web.archive.org/web/20050204192908/http://www.le.ac.uk/biology/gat/eyeblink.html  ''Did you know that shrimps blink?'']
{{Vision in animals}}
{{Authority control}}

[[Category:Arthropod anatomy]]
[[Category:Entomology]]
[[Category:Eye]]