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a smooth surface (as of a bone or cut gemstone)
any of the numerous small cone-shaped eyes that make up the compound eyes of some arthropods

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(宝石・結晶などのなめらかな)面,切り子面 / (物事の)面(aspect)
片目しかない,単眼の / 単眼用の

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/11/30 15:55:45」(JST)

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Ommatidium: A – cornea, B – crystalline cone, C & D – pigment cells, E – rhabdom, F – photoreceptor cells, G – membrana fenestrata, H – optic nerve

Ommatidium of a krill.

The compound eyes of arthropods like insects, crustaceans and millipedes^[1] are composed of units called ommatidia (singular: ommatidium). An ommatidium contains a cluster of photoreceptor cells surrounded by support cells and pigment cells. The outer part of the ommatidium is overlaid with a transparent cornea. Each ommatidium is innervated by one axon bundle (usually consisting of 6-9 axons, depending on the number of rhabdomeres)^[2] and provides the brain with one picture element. The brain forms an image from these independent picture elements. The number of ommatidia in the eye depends upon the type of insect and ranges from just a handful in the primitive Archaeognatha and Thysanura to around 30 thousand in larger Anisoptera dragonflies and in some Sphingidae moths.^[3]

Ommatidia are typically hexagonal in cross section and approximately ten times longer than wide. The diameter is largest at the surface, tapering toward the inner end. At the outer surface there is a cornea, below which is a pseudocone that acts to further focus the light. The cornea and pseudocone form the outer ten percent of the length of the ommatidium.

The inner 90% of the ommatidium contains 6 to 9 (depending on the species) long and thin photoreceptor cells in the case of some butterflies^[4] often abbreviated "R cells" in literature and often numbered, e.g. R1 through R9.^[4] These "R cells" tightly pack the ommatidium. The portion of the R cells at the central axis of the ommatidium collectively form a light guide, a transparent tube, called the rhabdom.

In true flies, the rhabdom has separated into seven independent rhabdomeres (there are actually eight, but the two central rhabdomeres responsible for color vision sit one atop the other), such that a small inverted 7-pixel image is formed in each ommatidium. Simultaneously, the rhabdomeres in adjacent ommatidia are aligned such that the field of view within an ommatidium is the same as that between ommatidia. The advantage of this arrangement is that the same visual axis is sampled from a larger area of the eye, thereby increasing sensitivity by a factor of seven, without increasing the size of the eye or reducing its acuity. Achieving this has also required the rewiring of the eye such that the axon bundles are twisted through 180 degrees (re-inverted), and each rhabdomere is united with those from the six adjacent ommatidia that share the same visual axis. Thus, at the level of the lamina - the first optical processing center of the insect brain - the signals are input in exactly the same manner as in the case of a normal apposition compound eye, but the image is enhanced. This visual arrangement is known as neural superposition.^[5]

Since an image from the compound eye is created from the independent picture elements produced by ommatidia, it is important for the ommatidia to react only to that part of the scene directly in front of it. To prevent light entering at an angle from being detected by the ommatidium it entered, or by any of the neighboring ommatidia, six pigment cells are present. The pigment cells line the outside of each ommatidium. Each pigment cell is situated at the apex of the hexagons and thus lines the outside of three ommatidia. Light entering at an angle passes through the thin cross-section of the photoreceptor cell, with only a tiny chance of exciting it, and is absorbed by the pigment cell, before it can enter a neighboring ommatidium. In many species, in low-light situations, the pigment is withdrawn, so that light entering the eye might be detected by any of several ommatidia. This enhances light detection but lowers resolution.

The size of the ommatidia varies according to species, but ranges from 5 to 50 micrometres. The rhabdoms within them may cross-section at least as small as 1.x micrometres, the category of "small" being assigned in some cross-species studies to those under 2 micrometers.^[6] Naively, microlens arrays can be seen as a biomimetic analogy of ommatidia.

References

^ Muller, C; Sombke, A; Rosenberg, J (2007). "The fine structure of the eyes of some bristly millipedes (Penicillata, Diplopoda): Additional support for the homology of mandibulate ommatidia". Arthropod Structure & Development 36 (4): 463–76. doi:10.1016/j.asd.2007.09.002.
^ Land, Michael F. and Nilsson, Dan-Eric. Animal Eyes, Second Edition. Oxford University Press, 2012. p. 162. ISBN 978-0-19-958114-6.
^ Common, I. F. B. (1990). Moths of Australia. Brill. p. 15. ISBN 978-90-04-09227-3.
^ ^a ^b Briscoe, A. D. (2008). "Reconstructing the ancestral butterfly eye: Focus on the opsins". Journal of Experimental Biology 211 (11): 1805–13. doi:10.1242/jeb.013045.
^ Land, Michael F. and Nilsson, Dan-Eric. Animal Eyes, Second Edition. Oxford University Press, 2012. pp. 163-164. ISBN 978-0-19-958114-6.
^ Land, Michael F. (1997). "Visual Acuity in Insects". Annual Review of Entomology 42: 147–77. doi:10.1146/annurev.ento.42.1.147. PMID 15012311.

English Journal

Characteristics of corneal lens chitin in dragonfly compound eyes.

Kaya M1, Sargin I2, Al-Jaf I3, Erdogan S4, Arslan G5.
International journal of biological macromolecules.Int J Biol Macromol.2016 Apr 21. pii: S0141-8130(16)30364-6. doi: 10.1016/j.ijbiomac.2016.04.056. [Epub ahead of print]
Chitin in the compound eyes of arthropods serves as a part of the visual system. The quality of chitin in such highly specialised body parts deserves more detailed examination. Chitin in the corneal (ommatidial) lenses of dragonfly (Sympetrum fonscolombii) compound eyes was isolated by using the cla
PMID 27109757

Quantitative Assessment of Eye Phenotypes for Functional Genetic Studies Using Drosophila melanogaster.

Iyer J1, Wang Q1, Le T1, Pizzo L1, Grönke S2, Ambegaokar S3, Imai Y4, Srivastava A1, Llamusí Troisí B5, Mardon G6, Artero R7, Jackson GR6, Isaacs AM8, Partridge L2, Kumar JP9, Girirajan S10.
G3 (Bethesda, Md.).G3 (Bethesda).2016 Mar 18. pii: g3.116.027060. doi: 10.1534/g3.116.027060. [Epub ahead of print]
About two-thirds of the vital genes in the Drosophila genome are involved in eye development, making the fly eye an excellent genetic system to study cellular function and development, neurodevelopment/degeneration, and complex diseases such as cancer and diabetes. We developed a novel computational
PMID 26994292

Knockdown of the Drosophila FIG4 induces deficient locomotive behavior, shortening of motor neuron, axonal targeting aberration, reduction of life span and defects in eye development.

Kyotani A1, Azuma Y2, Yamamoto I1, Yoshida H1, Mizuta I2, Mizuno T2, Nakagawa M3, Tokuda T4, Yamaguchi M5.
Experimental neurology.Exp Neurol.2016 Mar;277:86-95. doi: 10.1016/j.expneurol.2015.12.011. Epub 2015 Dec 19.
Mutations in Factor-Induced-Gene 4 (FIG4) gene have been identified in Charcot-Marie-Tooth disease type 4J (CMT4J), Yunis-Varon syndrome and epilepsy with polymicrogyria. FIG4 protein regulates a cellular abundance of phosphatidylinositol 3,5-bisphosphate (PI(3,5)P2), a signaling lipid on the cytoso
PMID 26708557

Japanese Journal

チャバネアオカメムシPlautia crossota stali の複眼における構造的部域差

山濱由美,弘中満太郎,針山孝彦
日本応用動物昆虫学会誌 58(4), 319-327, 2014
… Towards the frontal end of the eye's equatorial line, we found some special structural features: smaller inter-ommatidial angles, indicating high acuity; … In the dorsal region of the eye, there is another special ommatidial structure: untwisted, orthogonally oriented microvilli, which suggests e-vector discrimination ability. …
NAID 130004783559

長崎市内のオビトラップ,浄化槽,およびアパートで採集した,イヌ糸条虫媒介蚊のチカイエカCulex pipiens molestus Forskalと判定した雌成虫の個眼数の変異

黒川憲次,飯田国洋,三根真理子 [他],吉井学,内田桂吉,江下優樹,小田力
家屋害虫 32(1), 1-8, 2010-07-25
長崎市内において,屋外オビトラップで採集した卵舟由来の雌成虫,浄化槽で採集した未成熟幼虫由来の雌,およびアパートの2階1室で採集した吸血雌の個眼数の変異を調べた.実験室の小瓶内で狭所交尾性と無吸血産卵性を確認したチカイエカ成虫,および個々のF1世代の同様な習性を確かめてチカイエカと判定した吸血雌の複眼4,5,6列目の個眼数を計測した.オビトラップ由来の多くの雌成虫は,複眼4列目の個眼数が8個からな …
NAID 110008723233

都市域における疾病媒介蚊の発生状況調査 : ドライアイストラップを用いた2年間の調査結果

津田良夫,比嘉由紀子,倉橋弘 [他],林利彦,星野啓太,駒形修,伊澤晴彦,葛西真治,佐々木年則,冨田隆史,澤邉京子,二瓶直子,小林陸生
衞生動物 57(2), 75-82, 2006-06-15
… pipiens pipiens, the ommatidial number of the collected females was examined, and autogenous Cx. …
NAID 110004799586