Editing Conjunctiva (section)

== 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" />