Limbal ring
{{Short description|Dark ring around the iris of the eye}}
{{Distinguish|Kayser–Fleischer ring|}}
File:Human eye with limbal ring, anterior view.jpg
A limbal ring is a dark ring around the iris of the eye, where the sclera meets the cornea.{{cite patent |country=United States |number=US7246903B2 |assign=Johnson and Johnson Vision Care Inc. |title=Tinted contact lenses with combined limbal ring and iris patterns |pubdate=24 July 2007 |url=http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&p=1&u=/netahtml/PTO/srchnum.html&r=1&f=G&l=50&d=PALL&s1=7246903.PN }} It is a dark-colored manifestation of the corneal limbus resulting from optical properties of the region.{{cite journal |last1=Shyu |first1=Betsy P. |last2=Wyatt |first2=Harry J. |year=2009 |title=Appearance of the human eye: Optical contributions to the 'limbal ring' |journal=Optometry and Vision Science |volume=86 |issue=9 |pages=E1069–E1077 |doi=10.1097/OPX.0b013e3181b4f010 |pmid=19648842 |s2cid=39174174 }} The appearance and visibility of the limbal ring can be negatively affected by a variety of medical conditions concerning the peripheral cornea.{{cite journal |vauthors=Peshek D, Semmaknejad N, Hoffman D, Foley P |year=2011 |title=Preliminary evidence that the limbal ring influences facial attractiveness |journal=Evolutionary Psychology |volume=9 |issue=2 |pages=137–146 |doi=10.1177/147470491100900201 |doi-access=free |pmid=22947961 |url=https://escholarship.org/content/qt0964610k/qt0964610k.pdf?t=nfa9wu }} It has been suggested that limbal ring thickness may correlate with health or youthfulness and may contribute to facial attractiveness. The thickness of the limbal ring varies by pupil dilation: When the pupil is larger, the limbal ring narrows.{{cite journal |last=Shyu |first=Betsy P. |last2=Wyatt |first2=Harry J. |date=September 2009 |title=Appearance of the human eye: Optical contributions to the "limbal ring" |journal=Optometry and Vision Science |volume=86 |issue=9 |pages=E1069–E1077 |doi=10.1097/OPX.0b013e3181b4f010 |issn=1040-5488 |lang=en |url=https://journals.lww.com/00006324-200909000-00007 }} Some contact lenses are colored to simulate limbal rings.
Youth, health, and attractiveness
File:Eye Central Heterochromia crop and lighter.jpg
Both health and youth are positively correlated with a prominent limbal ring.{{cite journal |vauthors=Peshek D, Semmaknejad N, Hoffman D, Foley P |year=2011 |title=Preliminary evidence that the limbal ring influences facial attractiveness |journal=Evolutionary Psychology |volume=9 |issue=2 |pages=137–146 |doi=10.1177/147470491100900201 |doi-access=free |pmid=22947961 |url=https://escholarship.org/content/qt0964610k/qt0964610k.pdf?t=nfa9wu }} For instance, a darker limbal ring tends to be found more attractive than the absence of a limbal ring, suggesting that both sexes "use the limbal ring as a probabilistic indicator of reproductive fitness". Furthermore, limbal rings appear to be most noticeable "for individuals relatively free from chronic health issues".{{cite journal |vauthors=Brown M, Sacco DF | year=2018 |title=Put a (limbal) ring on it: Women perceive men's limbal rings as a health cue in short-term mating domains |journal=Personality and Social Psychology Bulletin |volume=44 |issue=1 |pages=80–91 |doi=10.1177/0146167217733072 |doi-access= |pmid=28978250 }}
The limbal ring is thought to contain corneal epithelium stem cells.{{cite journal |last1=Li |first1=De-Quan |last2=Chen |first2=Zhuo |last3=Song |first3=Xiu Jun |last4=de Paiva |first4=Cintia S. |last5=Kim |first5=Hyun-Seung |last6=Pflugfelder |first6=Stephen C. |date=April 2005 |title=Partial enrichment of a population of human limbal epithelial cells with putative stem cell properties based on collagen type IV adhesiveness |journal=Experimental Eye Research |volume=80 |issue=4 |pages=581–590 |doi=10.1016/j.exer.2004.11.011 |issn=0014-4835 |pmc=2906384 |pmid=15781286 }} Diseases involving a limbal stem cell deficiency are associated with blindness, as those with such deficiencies are "unable to maintain a stable corneal surface".{{Cite journal |last1=James |first1=S. Elizabeth |last2=Rowe |first2=Andrea |last3=Ilari |first3=Luca |last4=Daya |first4=Sheraz |last5=Martin |first5=Robin |date=July 2001 |title=The potential for eye bank limbal rings to generate cultured corneal epithelial allografts |journal=Cornea |volume=20 |issue=5 |pages=488–494 |issn=0277-3740 |doi=10.1097/00003226-200107000-00010 |pmid=11413404 |s2cid=21296292 |lang=en-US }} Transplantation of limbal stem cells is a promising therapy for limbal stem cell deficiency.{{cite journal |last1=Utheim |first1=O.A. |last2=Pasovic |first2=L. |last3=Raeder |first3=S. |last4=Eidet |first4=J.R. |last5=Fostad |first5=I.–G. |last6=Sehic |first6=A. |last7=Roald |first7=B. |last8=de la Paz |first8=M.F. |last9=Lyberg |first9=T. |last10=Dartt |first10=D. A. |last11=Utheim |first11=T.P. |date=2019-03-12 |title=Effects of explant size on epithelial outgrowth, thickness, stratification, ultrastructure, and phenotype of cultured limbal epithelial cells |journal=PLoS One |volume=14 |issue=3 |page=e0212524 |doi=10.1371/journal.pone.0212524 |doi-access=free |issn=1932-6203 |pmc=6413940 |pmid=30861002 |bibcode=2019PLoSO..1412524U |lang=en }}
See also
References
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