conjunctiva

The conjunctiva is typically divided into three parts:

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.{{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 }}

Sensory innervation of the conjunctiva is divided into four parts:{{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 }}

The conjunctiva consists of unkeratinized, both stratified squamous and stratified columnar epithelium, with interspersed goblet cells.{{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}} The epithelial layer contains blood vessels, fibrous tissue, and lymphatic channels. Accessory lacrimal glands in the conjunctiva constantly produce the aqueous portion of tears. Additional cells present in the conjunctival epithelium include melanocytes, T and B cell lymphocytes.

The conjunctiva helps lubricate the eye by producing mucus and tears, although a smaller volume of tears than the lacrimal gland.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.

It also contributes to immune surveillance and helps to prevent the entrance of microbes into the eye.

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 trauma, infections, chemical irritation, allergic reactions, and dryness.

• The conjunctival microvascular hemodynamics are affected by diabetic retinopathy (DR), hence can be useful for DR diagnosis and monitoring,{{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 }} and discriminating stages of DR.{{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 }}
• Type II diabetes is associated with conjunctival hypoxia,{{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 }} increased average blood vessel diameter, and capillary loss.{{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 }}{{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 }}{{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 }}
• Sickle-cell anemia is associated with blood vessel sludging, altered blood flow and blood vessel diameter, and capillary micro-haemorrhages.{{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 }}{{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 }}{{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 }}
• Hypertension is associated with an increase in the tortuosity of bulbar conjunctival blood vessels and capillary and arteriole loss.{{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 }}{{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 }}
• Carotid artery occlusion is associated with slower conjunctival blood flow and apparent capillary loss.
• With age, the conjunctiva can stretch and loosen from the underlying sclera, leading to the formation of conjunctival folds, a condition known as conjunctivochalasis.{{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}}{{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 }}
• The conjunctiva can be affected by tumors which can be benign, pre-malignant or malignant.{{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 }}
• Leptospirosis, an infection with Leptospira, can cause conjunctival suffusion, which is characterized by chemosis, and redness without exudates.

The bulbar conjunctival microvasculature contains arterioles, meta-arterioles, venules, 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.{{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 }} 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.{{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 }}

The bulbar conjunctival microvasculature is in close proximity to ambient air, thus oxygen diffusion from ambient air strongly influences their blood oxygen saturation. Because of oxygen diffusion, 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.{{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 }}

The bulbar conjunctival microvessels are typically imaged with a high-magnification slit lamp with green filters.{{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 }}{{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 }}{{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 }} With such high-magnification imaging systems, it is possible to see groups of individual red blood cells flowing in vivo. 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 {{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 }} and to measure blood oxygen saturation. Fluorescein angiography has been used to study the blood flow of the bulbar conjunctiva and to differentiate the bulbar conjunctival and episcleral microcirculation.{{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 }}{{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 }}{{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 = }}

The bulbar conjunctival microvasculature is known to dilate in response to several stimuli and external conditions, including allergens (e.g. pollen),{{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 }} temperature,{{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 }} time-of-day, contact-lens wear, and acute mild hypoxia. Bulbar conjunctival vasodilation has also been shown to correlate changes in emotional state.{{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}}

Type 2 diabetes is associated with an increase in average bulbar conjunctival vessel diameter and capillary loss. Sickle-cell anemia is associated with altered average vessel diameter.

• Conjunctivitis (pink-eye)
• Conjunctivochalasis
• Dry eye
• Pinguecula
• Pterygium
• Rougine
• Subconjunctival hemorrhage
• Diabetes
• Sickle-cell disease
• Slit lamp

Image:Gray893.png|Sagittal section through the upper eyelid

File:Slide2www.JPG|Extrinsic eye muscle. Nerves of orbita. Deep dissection.

{{Reflist}}

• {{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}}

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Category:Human eye anatomy