Editing Conjunctiva

{{Short description|Part of the eye; protective outer layer covering the sclera}}
{{Infobox anatomy
| Name        = Conjunctiva
| Latin       = tunica conjunctiva
| Greek       =
| Image       = Gray883.png
| Caption     = The upper half of a sagittal section through the front of the eyeball (label for 'Conjunctiva' visible at center-left)
| Width       =
| Image2      = Gray869.png
| Caption2    = Horizontal section of the eyeball (conjunctiva labeled at upper left)
| Precursor   =
| part_of     = [[Eye]]
| System      =
| Artery      = [[Lacrimal artery]], [[anterior ciliary arteries]]
| Vein        =
| Nerve       = [[Supratrochlear nerve]]
| Lymph       =
}}
[[File:Beccas Oga.JPG|thumb|Image of a human eye showing the blood vessels of the bulbar conjunctiva]]
[[File:Hyperemia conjunctiva.jpg|thumb|[[Hyperaemia]] of the superficial bulbar conjunctiva blood vessels]]

In the [[anatomy]] of the [[eye]], the '''conjunctiva''' ({{plural form}}: '''conjunctivae''') is a thin [[mucous membrane]] that lines the inside of the [[eyelid]]s and covers the [[sclera]] (the white of the eye).<ref name="SD">{{cite web |title=Conjunctiva |url=https://sciencedirect.com/topics/agricultural-and-biological-sciences/conjunctiva |website=www.sciencedirect.com |access-date=4 August 2022}}</ref> It is composed of non-keratinized, [[stratified squamous epithelium]] with [[goblet cell]]s, [[stratified columnar epithelium]] and [[stratified cuboidal epithelium]] (depending on the zone). The conjunctiva is highly [[Angiogenesis|vascularised]], with many [[microvessel]]s easily accessible for imaging studies.

== Structure ==
The conjunctiva is typically divided into three parts:
{| class="wikitable"
|-
! Part
! Area
|-
| Palpebral or tarsal conjunctiva
| Lines the eyelids
|-
| Bulbar or ocular conjunctiva
| Covers the eyeball, over the anterior [[sclera]]: This region of the conjunctiva is tightly bound to the underlying sclera by [[Tenon's capsule]] and moves with the eyeball movements. The average thickness of the bulbar conjunctival membrane is 33 microns.<ref>{{cite journal | vauthors = Efron N, Al-Dossari M, Pritchard N | title = In vivo confocal microscopy of the bulbar conjunctiva | journal = Clinical & Experimental Ophthalmology | volume = 37 | issue = 4 | pages = 335–44 | date = May 2009 | pmid = 19594558 | doi = 10.1111/j.1442-9071.2009.02065.x | s2cid = 35398240 }}</ref>
|-
| Fornix conjunctiva
| Forms the junction between the bulbar and palpebral conjunctivas:  It is loose and flexible, allowing the free movement of the lids and eyeball.<ref>Eye, human Encyclopædia Britannica</ref>
|}

===Blood supply===
Blood to the bulbar conjunctiva is primarily derived from the ophthalmic artery. The blood supply to the palpebral conjunctiva (the eyelid) is derived from the [[external carotid artery]]. However, the circulations of the bulbar conjunctiva and palpebral conjunctiva are linked, so both bulbar conjunctival and palpebral conjunctival vessels are supplied by both the ophthalmic artery and the external carotid artery, to varying extents.<ref name=":6">{{cite journal | vauthors = Pavlou AT, Wolff HG | title = The bulbar conjunctival vessels in occlusion of the internal carotid artery | journal = A.M.A. Archives of Internal Medicine | volume = 104 | issue = 1 | pages = 53–60 | date = July 1959 | pmid = 13660526 | doi = 10.1001/archinte.1959.00270070055007 }}</ref>

===Nerve supply===
Sensory innervation of the conjunctiva is divided into four parts:<ref>{{cite web|url=http://www.nda.ox.ac.uk/wfsa/html/u06/u06_b06.htm |title=Table 1: Summary of sensory nerve supply |access-date=July 31, 2016 |url-status=dead |archive-url=https://web.archive.org/web/20130214055618/http://www.nda.ox.ac.uk/wfsa/html/u06/u06_b06.htm |archive-date=February 14, 2013 }}</ref>

{| class="wikitable"
|-
! Area
! Nerve
|-
| Superior
|
* [[Supraorbital nerve]]
* [[Supratrochlear nerve]]
* [[Infratrochlear nerve]]
|-
| Inferior
| [[Infraorbital nerve]]
|-
| Lateral
| [[Lacrimal nerve]] (with contribution from [[zygomaticofacial nerve]])
|-
| Circumcorneal
| [[Long ciliary nerves]]
|}

===Microanatomy===
The conjunctiva consists of unkeratinized, both stratified squamous and stratified columnar epithelium, with interspersed [[goblet cells]].<ref name=Cecil>{{cite book| vauthors = Goldman L |title=Goldman's Cecil Medicine|year=2012|url=https://archive.org/details/goldmanscecilmed00mdle|url-access=limited|publisher=Elsevier Saunders|location=Philadelphia|isbn=978-1437727883|page=[https://archive.org/details/goldmanscecilmed00mdle/page/n2974 2426]|edition=24th}}</ref> The epithelial layer contains blood vessels, fibrous tissue, and lymphatic channels.<ref name=Cecil /> [[Accessory lacrimal glands]] in the conjunctiva constantly produce the aqueous portion of [[tears]].<ref name=Cecil /> Additional cells present in the conjunctival epithelium include [[melanocytes]], [[Lymphocyte|T and B cell lymphocytes]].<ref name=Cecil />

== Function ==
The conjunctiva helps lubricate the eye by producing [[mucus]] and [[tears]], although a smaller volume of tears than the [[lacrimal gland]].<ref>London Place Eye Center (2003). [http://www.lasereye.com/conjuc.htm Conjunctivitis] {{Webarchive|url=https://web.archive.org/web/20040808182217/http://lasereye.com/conjuc.htm |date=2004-08-08 }}. Retrieved July 25, 2004.</ref>
It also contributes to [[immune system|immune surveillance]] and helps to prevent the entrance of [[microbes]] into the eye.

==Clinical significance==

Disorders of the conjunctiva and [[cornea]] are common sources of eye complaints, in particular because the surface of the eye is exposed to various external influences and is especially susceptible to [[Physical trauma|trauma]], [[infections]], chemical irritation, [[allergic reactions]], and [[Keratoconjunctivitis sicca|dryness]].
* The conjunctival microvascular hemodynamics are affected by [[diabetic retinopathy]] (DR), hence can be useful for DR diagnosis and monitoring,<ref>{{cite journal | vauthors = Khansari MM, Wanek J, Tan M, Joslin CE, Kresovich JK, Camardo N, Blair NP, Shahidi M | display-authors = 6 | title = Assessment of Conjunctival Microvascular Hemodynamics in Stages of Diabetic Microvasculopathy | journal = Scientific Reports | volume = 7 | pages = 45916 | date = April 2017 | pmid = 28387229 | pmc = 5384077 | doi = 10.1038/srep45916 | bibcode = 2017NatSR...745916K }}</ref> and discriminating stages of DR.<ref>{{cite journal | vauthors = Khansari MM, O'Neill W, Penn R, Chau F, Blair NP, Shahidi M | title = Automated fine structure image analysis method for discrimination of diabetic retinopathy stage using conjunctival microvasculature images | language = EN | journal = Biomedical Optics Express | volume = 7 | issue = 7 | pages = 2597–606 | date = July 2016 | pmid = 27446692 | pmc = 4948616 | doi = 10.1364/BOE.7.002597 }}</ref>
* [[Diabetes mellitus type 2|Type II diabetes]] is associated with conjunctival [[Hypoxia (medical)|hypoxia]],<ref>{{cite journal | vauthors = Isenberg SJ, McRee WE, Jedrzynski MS | title = Conjunctival hypoxia in diabetes mellitus | journal = Investigative Ophthalmology & Visual Science | volume = 27 | issue = 10 | pages = 1512–5 | date = October 1986 | pmid = 3759367 }}</ref> increased average blood vessel diameter, and capillary loss.<ref name=":2">{{cite journal | vauthors = Fenton BM, Zweifach BW, Worthen DM | title = Quantitative morphometry of conjunctival microcirculation in diabetes mellitus | journal = Microvascular Research | volume = 18 | issue = 2 | pages = 153–66 | date = September 1979 | pmid = 491983 | doi = 10.1016/0026-2862(79)90025-6 }}</ref><ref name=":3">{{cite journal | vauthors = Ditzel J | title = The in vivo reactions of the small blood vessels to diabetes mellitus | journal = Acta Medica Scandinavica. Supplementum | volume = 476 | issue = S476 | pages = 123–34 | date = 1967-01-12 | pmid = 5236035 | doi = 10.1111/j.0954-6820.1967.tb12691.x }}</ref><ref name=":4">{{cite journal | vauthors = Cheung AT, Ramanujam S, Greer DA, Kumagai LF, Aoki TT | title = Microvascular abnormalities in the bulbar conjunctiva of patients with type 2 diabetes mellitus | journal = Endocrine Practice | volume = 7 | issue = 5 | pages = 358–63 | date = 2001-10-01 | pmid = 11585371 | doi = 10.4158/EP.7.5.358 }}</ref>
* [[Sickle-cell disease|Sickle-cell anemia]] is associated with blood vessel sludging, altered blood flow and blood vessel diameter, and capillary [[Haemorrhages|micro-haemorrhages]].<ref name=":5">{{cite journal | vauthors = Fink AI | title = Vascular changes in the bulbar conjunctiva associated with sickle-cell disease: some observations on fine structure | journal = Transactions of the American Ophthalmological Society | volume = 66 | pages = 788–826 | date = 1968-01-01 | pmid = 5720854 | pmc = 1310317 }}</ref><ref>{{cite journal | vauthors = Isenberg SJ, McRee WE, Jedrzynski MS, Gange SN, Gange SL | title = Effects of sickle cell anemia on conjunctival oxygen tension and temperature | journal = Archives of Internal Medicine | volume = 147 | issue = 1 | pages = 67–9 | date = January 1987 | pmid = 3800533 | doi = 10.1001/archinte.147.1.67 }}</ref><ref>{{cite journal | vauthors = Wanek J, Gaynes B, Lim JI, Molokie R, Shahidi M | title = Human bulbar conjunctival hemodynamics in hemoglobin SS and SC disease | journal = American Journal of Hematology | volume = 88 | issue = 8 | pages = 661–4 | date = August 2013 | pmid = 23657867 | pmc = 4040222 | doi = 10.1002/ajh.23475 }}</ref>
* [[Hypertension]] is associated with an increase in the [[Tortuosity|tortuosity of]] bulbar conjunctival blood vessels and capillary and arteriole loss.<ref>{{cite journal | vauthors = Harper RN, Moore MA, Marr MC, Watts LE, Hutchins PM | title = Arteriolar rarefaction in the conjunctiva of human essential hypertensives | journal = Microvascular Research | volume = 16 | issue = 3 | pages = 369–72 | date = November 1978 | pmid = 748720 | doi = 10.1016/0026-2862(78)90070-5 }}</ref><ref>{{cite journal | vauthors = Lee RE | title = Anatomical and physiological aspects of the capillary bed in the bulbar conjunctiva of man in health and disease | journal = Angiology | volume = 6 | issue = 4 | pages = 369–82 | date = August 1955 | pmid = 13275744 | doi = 10.1177/000331975500600408 | s2cid = 11589129 }}</ref>
* [[Carotid artery stenosis|Carotid artery]] occlusion is associated with slower conjunctival blood flow and apparent capillary loss.<ref name=":6" />
* With age, the conjunctiva can stretch and loosen from the underlying sclera, leading to the formation of conjunctival folds, a condition known as [[conjunctivochalasis]].<ref>{{cite web|url=http://www.medilexicon.com/medicaldictionary.php?t=19916|title=Conjunctivochalasis - Medical Definition|publisher=Medilexicon.com|access-date=2012-11-13|archive-url=https://web.archive.org/web/20160303185940/http://www.medilexicon.com/medicaldictionary.php?t=19916|archive-date=2016-03-03|url-status=dead}}</ref><ref>{{cite journal | vauthors = Hughes WL | title = Conjunctivochalasis | journal = American Journal of Ophthalmology | date = January 1942 | volume = 25 | issue = 1 | pages = 48–51 | doi = 10.1016/S0002-9394(42)93297-5 }}</ref>
* The conjunctiva can be affected by [[Neoplasm|tumors]] which can be benign, pre-malignant or malignant.<ref>{{cite journal | vauthors = Varde MA, Biswas J | title = Ocular surface tumors | journal = Oman Journal of Ophthalmology | volume = 2 | issue = 1 | pages = 1–2 | date = January 2009 | pmid = 21234216 | pmc = 3018098 | doi = 10.4103/0974-620X.48414 | doi-access = free }}</ref>
* [[Leptospirosis]], an infection with Leptospira, can cause [[conjunctival suffusion]], which is characterized by chemosis, and redness without exudates.

== Bulbar conjunctival microvasculature ==
=== Vessel morphology ===
The bulbar conjunctival [[Microvessel|microvasculature]] contains [[arteriole]]s, [[Metarteriole|meta-arterioles]], [[venule]]s, [[Capillary|capillaries]], and communicating vessels. Vessel morphology varies greatly between subjects and even between regions of the individual eyes. In some subjects, arterioles and venules can be seen to run parallel with each other. Paired arterioles are generally smaller than corresponding venules.<ref>{{cite journal | vauthors = Meighan SS | title = Blood vessels of the bulbar conjunctiva in man | journal = The British Journal of Ophthalmology | volume = 40 | issue = 9 | pages = 513–26 | date = September 1956 | pmid = 13364178 | pmc = 1324675 | doi = 10.1136/bjo.40.9.513 }}</ref> The average bulbar conjunctival vessel has been reported to be 15.1 microns, which reflects the high number of small capillaries, which are typically <10  microns in diameter.<ref>{{cite journal | vauthors = Shahidi M, Wanek J, Gaynes B, Wu T | title = Quantitative assessment of conjunctival microvascular circulation of the human eye | journal = Microvascular Research | volume = 79 | issue = 2 | pages = 109–13 | date = March 2010 | pmid = 20053367 | pmc = 3253734 | doi = 10.1016/j.mvr.2009.12.003 }}</ref>

=== Blood oxygen dynamics ===
The bulbar conjunctival microvasculature is in close proximity to ambient air, thus [[Diffusion|oxygen diffusion]] from ambient air strongly influences their [[Oxygen saturation (medicine)|blood oxygen saturation]]. Because of oxygen diffusion, [[Hypoxia (medical)|hypoxic]] bulbar conjunctival vessels will rapidly reoxygenate (in under 10 seconds) when exposed to ambient air (i.e. when the eyelid is open). Closing the eyelid stops this oxygen diffusion by placing a barrier between the bulbar conjunctival microvessels and ambient air.<ref name=":0">{{cite journal | vauthors = MacKenzie LE, Choudhary TR, McNaught AI, Harvey AR | title = In vivo oximetry of human bulbar conjunctival and episcleral microvasculature using snapshot multispectral imaging | journal = Experimental Eye Research | volume = 149 | pages = 48–58 | date = August 2016 | pmid = 27317046 | doi = 10.1016/j.exer.2016.06.008 | s2cid = 25038785 | url = http://dro.dur.ac.uk/25017/1/25017.pdf }}</ref>

=== Blood vessel imaging methods ===
The bulbar conjunctival microvessels are typically imaged with a high-magnification [[slit lamp]] with green filters.<ref name=":1">{{cite journal | vauthors = van Zijderveld R, Ince C, Schlingemann RO | title = Orthogonal polarization spectral imaging of conjunctival microcirculation | journal = Graefe's Archive for Clinical and Experimental Ophthalmology| volume = 252 | issue = 5 | pages = 773–9 | date = May 2014 | pmid = 24627137 | doi = 10.1007/s00417-014-2603-9 | s2cid = 1595902 }}</ref><ref>{{cite journal | vauthors = Khansari MM, O'Neill W, Penn R, Chau F, Blair NP, Shahidi M | title = Automated fine structure image analysis method for discrimination of diabetic retinopathy stage using conjunctival microvasculature images | journal = Biomedical Optics Express | volume = 7 | issue = 7 | pages = 2597–606 | date = July 2016 | pmid = 27446692 | doi = 10.1364/BOE.7.002597 | pmc = 4948616 | url = https://www.osapublishing.org/boe/abstract.cfm?uri=boe-7-7-2597 }}</ref><ref>{{cite journal | vauthors = Khansari MM, Wanek J, Felder AE, Camardo N, Shahidi M | title = Automated Assessment of Hemodynamics in the Conjunctival Microvasculature Network | journal = IEEE Transactions on Medical Imaging | volume = 35 | issue = 2 | pages = 605–11 | date = February 2016 | pmid = 26452274 | pmc = 4821773 | doi = 10.1109/TMI.2015.2486619 }}</ref> With such high-magnification imaging systems, it is possible to see groups of individual red blood cells flowing in vivo.<ref name=":1" /> Fundus cameras may also be used for low-magnification wide field-of-view imaging of the bulbar conjunctival microvasculature. Modified fundus cameras have been used to measure conjunctival blood flow <ref>{{cite journal | vauthors = Jiang H, Ye Y, DeBuc DC, Lam BL, Rundek T, Tao A, Shao Y, Wang J | display-authors = 6 | title = Human conjunctival microvasculature assessed with a retinal function imager (RFI) | journal = Microvascular Research | volume = 85 | pages = 134–7 | date = January 2013 | pmid = 23084966 | pmc = 3534915 | doi = 10.1016/j.mvr.2012.10.003 }}</ref> and to measure [[Oxygen saturation|blood oxygen saturation]].<ref name=":0" /> [[Fluorescein angiography]] has been used to study the blood flow of the bulbar conjunctiva and to differentiate the bulbar conjunctival and [[Episcleral layer|episcleral]] microcirculation.<ref>{{cite journal | vauthors = Meyer PA | title = Patterns of blood flow in episcleral vessels studied by low-dose fluorescein videoangiography | journal = Eye | volume = 2 ( Pt 5) | issue = 5 | pages = 533–46 | date = 1988-01-01 | pmid = 3256492 | doi = 10.1038/eye.1988.104 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Ormerod LD, Fariza E, Webb RH | title = Dynamics of external ocular blood flow studied by scanning angiographic microscopy | journal = Eye | volume = 9 ( Pt 5) | issue = 5 | pages = 605–14 | date = 1995-01-01 | pmid = 8543081 | doi = 10.1038/eye.1995.148 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Meyer PA, Watson PG | title = Low dose fluorescein angiography of the conjunctiva and episclera | journal = The British Journal of Ophthalmology | volume = 71 | issue = 1 | pages = 2–10 | date = January 1987 | pmid = 3814565 | pmc = 1041073 | doi = 10.1136/bjo.71.1.2 | url = }}</ref>

=== Vasodilation ===
The bulbar conjunctival microvasculature is known to dilate in response to several stimuli and external conditions, including allergens (e.g. pollen),<ref>{{cite journal | vauthors = Horak F, Berger U, Menapace R, Schuster N | title = Quantification of conjunctival vascular reaction by digital imaging | journal = The Journal of Allergy and Clinical Immunology | volume = 98 | issue = 3 | pages = 495–500 | date = September 1996 | pmid = 8828525 | doi = 10.1016/S0091-6749(96)70081-7 }}</ref> temperature,<ref name=":7">{{cite journal | vauthors = Duench S, Simpson T, Jones LW, Flanagan JG, Fonn D | title = Assessment of variation in bulbar conjunctival redness, temperature, and blood flow | journal = Optometry and Vision Science | volume = 84 | issue = 6 | pages = 511–6 | date = June 2007 | pmid = 17568321 | doi = 10.1097/OPX.0b013e318073c304 | s2cid = 943038 }}</ref> time-of-day,<ref name=":7" /> [[Contact lens|contact-lens]] wear,<ref name=":4" /> and acute mild hypoxia.<ref name=":0" /> Bulbar conjunctival vasodilation has also been shown to correlate changes in emotional state.<ref>{{Cite journal| vauthors = Provine RR, Nave-Blodgett J, Cabrera MO |date=2013-11-01|title=The Emotional Eye: Red Sclera as a Uniquely Human Cue of Emotion|journal=Ethology|language=en|volume=119|issue=11|pages=993–998|doi=10.1111/eth.12144|bibcode=2013Ethol.119..993P |issn=1439-0310}}</ref>

Type 2 diabetes is associated with an increase in average bulbar conjunctival vessel diameter and capillary loss.<ref name=":2" /><ref name=":3" /> [[Sickle-cell disease|Sickle-cell anemia]] is associated with altered average vessel diameter.<ref name=":5" />

== See also ==
* [[Conjunctivitis]] (pink-eye)
* [[Conjunctivochalasis]]
* [[Dry eye]]
* [[Pinguecula]]
* [[Pterygium (conjunctiva)|Pterygium]]
* [[Rougine]]
* [[Subconjunctival hemorrhage]]
* [[Diabetes mellitus|Diabetes]]
* [[Sickle-cell disease]]
* [[Slit lamp]]

==Additional images==
<gallery>
 Image:Gray893.png|Sagittal section through the upper eyelid
 File:Slide2www.JPG|Extrinsic eye muscle. Nerves of orbita. Deep dissection.
</gallery>

== References ==
{{Reflist}}

== External links ==
* {{cite web | work = Medicinenet.com | date = 1999 | url = http://www.medterms.com/script/main/art.asp?articlekey=9893 | title = Conjunctiva | access-date = 25 July 2004 | archive-date = 7 June 2014 | archive-url = https://web.archive.org/web/20140607005000/http://www.medterms.com/script/main/art.asp?articlekey=9893 | url-status = dead }}

{{Accessory organs of the eye}}
{{Authority control}}

[[Category:Human eye anatomy]]