Editing Tapetum lucidum

{{short description|Layer of eye tissue which aids in night vision}}
{{Redirect|Eyeshine|the Edge Rock band|Eyeshine (band)}}
{{title language|la}}
[[File:Bovine Tapetum Lucidum.jpg|thumb|The  dark blue, teal, and gold tapetum lucidum from the eye of a [[Cattle|cow]]]]
[[File:Sonny09b.png|thumb|Retina of a [[mongrel dog]] with strong tapetal reflex]]

The {{langnf|la| '''tapetum lucidum'''|bright tapestry, coverlet|paren=left}}; {{IPAc-en|t|ə|ˈ|p|iː|t|əm|_|'|l|uː|s|ɪ|d|əm}} {{respell|tə|PEE|təm|_|LOO|sih|dəm}}; {{plural form}}: '''tapeta lucida''')<ref>{{cite web |url=http://www.archives.nd.edu/cgi-bin/lookup.pl?stem=tapet&ending=um |title=Latin Word Lookup |publisher=Archives.nd.edu |access-date=2014-03-20}}</ref> is a layer of tissue in the [[eye]] of many [[vertebrate]]s and some other animals. Lying immediately behind the [[retina]], it is a [[retroreflector]]. It [[Reflection (physics)|reflects]] visible [[light]] back through the retina, increasing the light available to the [[Photoreceptor cell|photoreceptors]] (although slightly blurring the image).

The tapetum lucidum contributes to the superior [[night vision]] of some animals. Many of these animals are [[nocturnality|nocturnal]], especially [[carnivore]]s, while others are [[Deep-sea community|deep-sea animals]]. Similar adaptations occur in some species of [[spider]]s.<ref name="RFB2004Spiders">{{cite book |last1=Ruppert|first1=E. E. |last2=Fox|first2=R. S. |last3=Barnes|first3=R. D. |title=Invertebrate Zoology |publisher=[[Cengage|Brooks/Cole]] |edition=7th |isbn=978-0-03-025982-1 |year=2004 |pages=[https://archive.org/details/isbn_9780030259821/page/578 578–81] |chapter=Chelicerata: Araneae |url=https://archive.org/details/isbn_9780030259821 |chapter-url=https://archive.org/details/isbn_9780030259821/page/571}}</ref> [[Haplorhini|Haplorhine primates]], including humans, are [[Diurnality|diurnal]] and lack a tapetum lucidum.{{refn|group=Note|The one exception to this generalization is the neotropical night monkey genus ''[[Aotus (monkey)|Aotus]]''; they are sometimes described as having a tapetum lucidum of [[collagen]] fibrils, but lack the reflective [[riboflavin]] crystals present in the eyes of nocturnal [[Strepsirrhini|strepsirrhine]] primates.<ref name="Ollivier+2004"/>}}

==Function and mechanism==
[[Image:Calf-Eye-Posterior-With-Retina-Detached-2005-Oct-13.jpg|thumb|Choroid dissected from a calf's eye, tapetum lucidum appearing iridescent blue]]

The presence of a tapetum lucidum enables animals to see in dimmer light than would otherwise be possible. The tapetum lucidum, which is [[iridescent]], reflects light roughly on the [[Interference (wave propagation)|interference]] principles of [[thin-film optics]], as seen in other iridescent tissues. However, the tapetum lucidum cells are [[Chromatophore#Iridophores and leucophores|leucophore]]s, not [[Chromatophore#Iridophores and leucophores|iridophore]]s.{{dubious|date=January 2021|reason=Then why is the tapetum lucidum colored?}}

The tapetum functions as a [[retroreflector]] which reflects light directly back along the light path. This serves to match the original and reflected light, thus maintaining the sharpness and contrast of the image on the retina. The tapetum lucidum reflects with [[Interference (wave propagation)|constructive interference]],<ref name="Locket1974"/> thus increasing the quantity of light passing through the retina. In the cat, the tapetum lucidum increases the sensitivity of vision by 44%, allowing the cat to see light that is imperceptible to human eyes.<ref>{{cite journal |vauthors=Gunter R, Harding HG, Stiles WS |title=Spectral reflexion factor of the cat's tapetum |journal=Nature |volume=168 |issue=4268 |pages=293–4 |date=August 1951 |pmid=14875072 |doi= 10.1038/168293a0|bibcode=1951Natur.168..293G |s2cid=4166491 }}</ref> When a tapetum lucidum is present, its location on the eyeball varies with the placement of the eyeball in the head.<ref name="Lee1886">{{cite journal |last=Lee |first=Henry |year=1886 |title=On the ''Tapetum Lucidum'' |journal=Med Chir Trans |volume=69 |pages=239–245 |doi=10.1177/095952878606900113 |pmc=2121549 |pmid=20896672}}</ref>

Apart from its eyeshine, the tapetum lucidum itself has a color. It is often described as iridescent. In [[tiger]]s, it is greenish.<ref>Fayrer, Sir Joseph (1889) ''The deadly wild beasts of India'', pp. 218–240 in James Knowls (ed) ''The Nineteenth Century'', Henry S. King & Co., v. 26; p. 219. [https://books.google.com/books?id=kTMAAAAAYAAJ via Google Books]</ref> In [[ruminant]]s, it may be golden green with a blue periphery,<ref name="Charnock1896" /> or whitish or pale blue with a lavender periphery. In [[dog]]s, it may be whitish with a blue periphery.<ref name="Charnock1896" /> The color in [[reindeer]] changes seasonally, allowing the animals to better avoid predators in low-light winter at the price of blurrier vision.<ref>{{cite journal |doi=10.1098/rspb.2013.2451 |title=Shifting mirrors: adaptive changes in retinal reflections to winter darkness in Arctic reindeer |author1=Karl-Arne Stokkan |author2=Lars Folkow |author3=Juliet Dukes |author4=Magella Neveu |author5=Chris Hogg |author6= Sandra Siefken |author7=Steven C. Dakin |author8=Glen Jeffery |date=22 December 2013 |journal=Proceedings of the Royal Society B|volume=280 |issue=1773 |pmid=24174115 |pmc=3826237 }}</ref>

==Classification==
A [[Biological classification|classification]] of anatomical variants of tapeta lucida<ref name="Ollivier+2004"/><!-- classification is not Ollivier's; dates from 1967 or before --> defines four types:
# ''Retinal tapetum'', as seen in [[teleost]]s (with a variety of reflecting materials from [[Lipid|lipids]] to [[phenols]]), [[crocodile]]s (with [[guanine]]), [[marsupial]]s (with lipid spheres), and [[fruit bat]]s (with [[Phospholipid|phospholipids]]).<ref name="Ollivier+2004"/>{{rp|16}} The tapetum lucidum is within the [[retinal pigment epithelium]]; in the other three types the tapetum is within the [[choroid]] behind the retina. Two anatomical classes can be distinguished: occlusible and non-occlusible.
#* The [[brownsnout spookfish]] has an extraordinary focusing mirror derived from a retinal tapetum.<ref name="pmid19110427">{{cite journal 
|vauthors=Wagner HJ, Douglas RH, Frank TM, Roberts NW, Partridge JC
| title = A novel vertebrate eye using both refractive and reflective optics | journal = Curr. Biol.
| volume = 19
| issue = 2
| pages = 108–114
|date=January 2009
| pmid = 19110427
| doi = 10.1016/j.cub.2008.11.061
| doi-access = free
| bibcode = 2009CBio...19..108W }}</ref>
# ''[[Choroid]]al guainine tapetum'', as seen in [[chondrichthyes|cartilaginous fish]].<ref name="DentonandNichol1964">{{cite journal |author1=Denton, EJ |author-link=Eric James Denton |author2=Nichol, JAC |title=The chorioidal tapeta of some cartilaginous fishes (Chondrichthyes) |journal=J. Mar. Biol. Assoc. U. K. |volume=44 |pages=219–258 |year=1964 |issue=1 |doi=10.1017/S0025315400024760 |bibcode=1964JMBUK..44..219D |s2cid=84527918 |url=http://sabella.mba.ac.uk/2257/01/The_chorioidal_tapeta_of_some_cartilaginous_fishes_(Chondrichthyes).pdf |access-date=2011-09-12 |archive-url=https://web.archive.org/web/20120322163635/http://sabella.mba.ac.uk/2257/01/The_chorioidal_tapeta_of_some_cartilaginous_fishes_(Chondrichthyes).pdf |archive-date=2012-03-22 }}</ref> The tapetum is a palisade of cells containing stacks of flat hexagonal crystals of [[guanine]].<ref name="Locket1974">{{cite journal |author=Locket NA |title=The choroidal tapetum lucidum of ''Latimeria chalumnae'' |journal=Proceedings of the Royal Society B |volume=186 |issue=84 |pages=281–290 |date=July 1974 |pmid=4153107 |doi= 10.1098/rspb.1974.0049|bibcode=1974RSPSB.186..281L |s2cid=38419473 }}</ref>
# ''Choroidal tapetum cellulosum'', as seen in [[carnivore]]s, [[rodent]]s, and [[cetacea]]. The tapetum consists of layers of cells containing organized, highly refractive crystals. These crystals are diverse in shape and makeup: dogs and ferrets use [[zinc]], cats use [[riboflavin]] and zinc, and lemurs use only riboflavin.<ref name="Ollivier+2004"/>{{rp|17}}
# ''Choroidal tapetum fibrosum'', as seen in [[cow]]s, [[sheep]], [[goat]]s, and [[horse]]s. The tapetum is an array of extracellular fibers, most commonly [[collagen]].<ref name="Ollivier+2004"/>{{rp|17}}

The functional differences between these four structural classes of tapeta lucida are not known.<ref name="Ollivier+2004" />

== Variation across species ==

=== Primates ===
Humans like [[Haplorhini|haplorhine primates]]  lack a tapetum lucidum as they are [[Diurnality|diurnal]].<ref name="Ollivier+2004">{{cite journal |vauthors=Ollivier FJ, Samuelson DA, Brooks DE, Lewis PA, Kallberg ME, Komáromy AM |title=Comparative morphology of the tapetum lucidum (among selected species) |journal=Veterinary Ophthalmology |volume=7 |issue=1 |pages=11–22 |year=2004 |pmid=14738502 |doi=10.1111/j.1463-5224.2004.00318.x }}</ref> [[Strepsirrhini|Strepsirrhine]] primates are mostly nocturnal and, with the exception of several diurnal ''[[Eulemur]]'' species, have a tapetum lucidum of riboflavin crystals.<ref name="Ankel-Simons2007">{{cite book | last = Ankel-Simons | first = Friderun | title= Primate Anatomy | edition = 3rd | publisher = Academic Press | year = 2007 |isbn= 978-0-12-372576-9 | page = 375}}</ref>

=== Dogs ===
In canids, the tapetum lucidum is found in the dorsal half of the eye's fundus. It consists of 9-20 layers of specialized rectangular cells between the choroid and retinal pigment epithelium, thinning towards the periphery. The cells contain zinc-rich rodlets arranged in parallel. The structure appears yellow-green in adults, though blue in puppies until four months of age. Zinc concentration varies among species, with red foxes showing highest levels, followed by Arctic foxes, then domestic dogs. A hereditary zinc-deficiency condition in some beagles results in degenerated tapetal cells with disrupted rodlet arrangement.<ref name="a165">{{cite book |last1=Mowat |first1=Freya M. |title=Wild and Exotic Animal Ophthalmology |last2=Peichl |first2=Leo |publisher=Springer International Publishing |year=2022 |isbn=978-3-030-81272-0 |pages=181–214 |chapter=Ophthalmology of Canidae: Foxes, Wolves, and Relatives |doi=10.1007/978-3-030-81273-7_11}}</ref>

=== Cats ===
The tapetum lucidum in cats is renowned for its brilliance, even inspiring ancient Egyptians to believe it reflected the sun at night. This reflective layer is composed of 15-20 layers of cells arranged in a central pattern. This structure, denser than that of dogs, results in high reflectance, nearly 130 times that of humans. Its color is heterogeneous, varying with age and species due to factors like rodlet spacing, refractive index, and light interactions. Young cats exhibit a blue appearance, which shifts to yellow with age, with adult coloration ranging from light orange to green. While enhancing night vision, increased light scatter within the tapetum slightly compromises visual acuity.<ref name="g085">{{cite book |last1=Corsi |first1=Francesca |title=Wild and Exotic Animal Ophthalmology |last2=Guandalini |first2=Adolfo |last3=Rossi |first3=João Luiz |last4=Ben-Shlomo |first4=Gil |last5=Montiani-Ferreira |first5=Fabiano |last6=Moore |first6=Bret A. |publisher=Springer International Publishing |isbn=978-3-030-81272-0 |pages=155–180 |chapter=Ophthalmology of Felidae: Cats |date=2022 |doi=10.1007/978-3-030-81273-7_10}}</ref>

===Birds===
[[Kiwi (bird)|Kiwi]]s, [[stone-curlew]]s, the [[boat-billed heron]], the flightless [[kākāpō]], and many [[nightjar]]s, [[owl]]s, and other night birds such as the [[swallow-tailed gull]] possess a tapetum lucidum.<ref>Gill, Frank, B (2007) "Ornithology", Freeman, New York</ref> Nightjars use a retinal tapetum lucidum composed of lipids.<ref>{{cite journal |title=Tapeta lucida in the eyes of goatsuckers (Caprimulgidae) |journal=Proceedings of the Royal Society of London. Series B. Biological Sciences |date=5 November 1974 |volume=187 |issue=1088 |pages=349–352 |doi=10.1098/rspb.1974.0079|pmid=4154455 |last1=Nicol |first1=J. A. |last2=Arnott |first2=H. J. |bibcode=1974RSPSB.187..349N |s2cid=43626885 }}</ref>

===In spiders===
Most species of spider also have a tapetum, which is located only in their smaller, lateral eyes; the larger central eyes have no such structure. This consists of reflective crystalline deposits and is thought to have a similar function to the structure of the same name in vertebrates. Four general patterns can be distinguished in spiders:<ref name="BoS">{{cite book |author=Rainer F. Foelix |url=https://archive.org/details/biologyofspiders00foel_0/page/84 |title=Biology of Spiders, 2nd ed. |publisher=Oxford University Press |year=1996 |isbn=978-0-19-509594-4 |pages=[https://archive.org/details/biologyofspiders00foel_0/page/84 84–85]}}</ref>
# Primitive type (e.g. [[Mesothelae]], [[Orthognatha]]){{Snd}}a simple sheet behind the retina
# Canoe-shape type (e.g. [[Araneidae]], [[Theridiidae]]){{Snd}}two lateral walls separated by a gap for the nerve fibres
# Grated type (e.g. [[Lycosidae]], [[Pisauridae]]){{Snd}}a relatively complex, grill-shaped structure
# No tapetum (e.g. [[Salticidae]])

=== Animals lacking a tapetum lucidum ===
Animals without tapetum lucidum include haplorhine primates, squirrels, some birds, [[red kangaroo]], and pigs.<ref name="Charnock1896">Orlando Charnock Bradley, 1896, ''Outlines of Veterinary Anatomy. Part I. The Anterior and Posterior Limbs,'' Baillière, Tindall & Cox, p. 224. [https://books.google.com/books?id=ZQOq9yYDK1AC Free full text on Google Books]</ref>

==Eyeshine==
[[Image:TapetumLucidum.JPG|thumb|right|Reflection of camera flash from the tapetum lucidum]]

'''Eyeshine''' is a visible effect of the tapetum lucidum. When light shines into the eye of an animal having a tapetum lucidum, the [[pupil]] appears to glow. Eyeshine can be seen in many animals, in nature, and in [[Flash (photography)|flash]] [[photograph]]s. In low light, a hand-held flashlight is sufficient to produce eyeshine that is visible to humans (despite their inferior [[night vision]]). Eyeshine occurs in a wide variety of [[color]]s including [[white]], [[blue]], [[green]], [[yellow]], [[pink]], and [[red]]. However, since eyeshine is a type of [[iridescence]], the color varies with the angle at which it is seen and the minerals which make up the reflective tapetum lucidum crystals. Individuals with [[heterochromia]] may display red eyeshine in the blue eye and other-colored eyeshine in the other eye. These include [[odd-eyed cat]]s and [[Heterochromia iridum|bi-eyed dogs]].

[[File:Black-Lab-3-months-old-puppy.jpg|thumb|A three-month-old black Labrador puppy with apparent eyeshine]]

Although human eyes lack a tapetum lucidum, they still exhibit a weak reflection from the [[choroid]], as can be seen in photography<!-- Insert an illustrative image of this? --> with the [[red-eye effect]] and with [[Infrared photography|near-infrared]] eyeshine.<ref>{{cite journal|url=https://makezine.com/projects/make-35/how-to-make-and-use-retroreflectors/ |title=How to Make and Use Retroreflectors |journal=Make |date=2013-10-03 |author=Forrest M. Mims III| access-date=2017-10-21}}</ref><ref>{{cite journal |first1=Jann|last1=van de Kraats |first2=Dirk|last2=van Norren |title=Directional and nondirectional spectral reflection from the human fovea |journal=[[Journal of Biomedical Optics]] |volume=13 |issue=2 |page=024010| year=2008 |doi=10.1117/1.2899151 |doi-access=free |pmid=18465973|bibcode=2008JBO....13b4010V }}</ref> Another effect in humans and other animals that may resemble eyeshine is [[leukocoria]], which is a white shine indicative of abnormalities such as [[cataract]]s and [[cancer]]s.

=== Usage ===
Humans can scan for eyeshine to detect and identify the species of animals in the dark and deploy [[search dog]]s and [[search and rescue horse|search horse]]s at night. The color corresponds approximately to the type of tapetum lucidum, with some variation between species.{{Citation needed paragraph|date=August 2024}}

It has been speculated that some [[Anomalopidae|flashlight fish]] may use eyeshine both to detect and to communicate with other flashlight fish.<ref name="pmid1413559">{{cite journal |vauthors=Howland HC, Murphy CJ, McCosker JE |date=April 1992 |title=Detection of eyeshine by flashlight fishes of the family Anomalopidae |journal=Vision Res. |volume=32 |issue=4 |pages=765–9 |doi=10.1016/0042-6989(92)90191-K |pmid=1413559 |s2cid=28099872}}</ref> American scientist [[Nathan H. Lents]] has proposed that the tapetum lucidum evolved in vertebrates, but not in [[Cephalopod|cephalopods]], which have a very similar eye because of the backwards-facing nature of vertebrate photoreceptors. The tapetum boosts photosensitivity under conditions of low illumination, thus compensating for the [[Argument from poor design|suboptimal design]] of the vertebrate retina.<ref>{{Cite journal |last1=Vee |first1=Samantha |last2=Barclay |first2=Gerald |last3=Lents |first3=Nathan H. |year=2022 |title=The glow of the night: The tapetum lucidum as a co-adaptation for the inverted retina. |url=https://onlinelibrary.wiley.com/doi/abs/10.1002/bies.202200003 |journal=BioEssays |volume=44 |issue=10 |pages=e2200003 |doi=10.1002/bies.202200003 |pmid=36028472 |s2cid=251864970 |via=Wiley|url-access=subscription }}</ref>

=== In photography ===
[[File:House-cat reflective eyes.jpg|thumb|305x305px|Reflective eyes of a cat visible from a [[Flash (photography)|camera flash]]]]
Traditionally, it has been difficult to take retinal images of animals with a tapetum lucidum because [[Ophthalmoscopy|ophthalmoscopy devices]] designed for humans rely on a high level of on-axis illumination.<ref>{{cite book |last1=Maggs |first1=David |title=Slatter's Fundamentals of Veterinary Ophthalmology |last2=Miller |first2=Paul |last3=Ofri |first3=Ron |pages=94}}</ref> This kind of illumination causes [[backscatter]] when it interacts with the tapetum. New devices with variable illumination can make this possible, however.

==Pathology==
In dogs, certain drugs are known to disturb the precise organization of the crystals of the tapetum lucidum, thus compromising the dog's ability to see in low light. These drugs include [[ethambutol]], [[macrolide]] antibiotics, [[dithizone]], [[antimalarial medication]]s, some receptor [[H2 receptor antagonist|H<sub>2</sub>-antagonists]], and [[cardiovascular agents]]. The disturbance "is attributed to the [[chelation|chelating]] action which removes zinc from the ''tapetal'' cells."<ref>{{cite book |last=Cohen |first=Gerald D. |title=Target organ toxicity |publisher=CRC Press |location=Boca Raton |year=1986 |pages=121–122 |isbn=978-0-8493-5776-3}}</ref>

==See also==
* [[Defense mechanism (biology)]]
* [[Emission theory (vision)]]
* [[Nocturnal bottleneck]]
* [[Walleye]]

==Notes==
{{reflist|group=Note}}

==References==
{{Reflist}}

== External links ==
* {{Commons category-inline|Eyeshine}}

{{Eye}}
{{Vision in animals}}

[[Category:Vertebrate anatomy]]
[[Category:Animal communication]]
[[Category:Science of photography]]
[[Category:Eye anatomy]]