Conjunctiva

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Conjunctiva
The upper half of a sagittal section through the front of the eyeball. (Label for 'Conjunctiva' visible at center-left.)
Horizontal section of the eyeball. (Conjunctiva labeled at upper left.)
Details
Arterylacrimal artery, anterior ciliary arteries
Nervesupratrochlear nerve
Identifiers
Latintunica conjunctiva
MeSHD003228
TA98A15.2.07.047
TA26836
FMA59011
Anatomical terminology
Image of a human eye showing the blood vessels of the bulbar conjunctiva.
Hyperaemia of the superficial bulbar conjunctiva blood vessels.

The conjunctiva lines the inside of the eyelids and covers the sclera (the white of the eye). It is composed of non-keratinized, stratified columnar epithelium with goblet cells, and also stratified columnar epithelium. The conjunctiva is highly vascularised, with many microvessels easily accessible for imaging studies.

Function

The conjunctiva helps lubricate the eye by producing mucus and tears, although a smaller volume of tears than the lacrimal gland.[1] It also contributes to immune surveillance and helps to prevent the entrance of microbes into the eye.

Anatomy

The conjunctiva is typically divided into three parts:

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 conjuntival membrane is 33 microns.[2]
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.[3]

Sensory innervation

Sensory innervation of the conjunctiva is divided into four parts:[4]

Area Nerve
Superior
Inferior Infraorbital nerve
Lateral Lacrimal nerve (with contribution from zygomaticofacial nerve)
Circumcorneal Long ciliary nerves

Histology

The conjunctiva consists of non-keratinized, both stratified squamous and stratified columnar epithelium, with interspersed goblet cells.[5] The epithelial layer contains blood vessels, fibrous tissue, and lymphatic channels.[5] Accessory lacrimal glands in the conjunctiva constantly produce the aqueous portion of tears.[5] Additional cells present in the conjunctival epithelium include melanocytes, T and B cell lymphocytes.[5]

Diseases and disorders

Main article: List of eye diseases and disorders

Disorders of the conjunctiva and cornea are a common source 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.

Blood supply of the conjunctiva

Blood to the bulbar conjunctiva is primarily derived from the ophthalmic artery. The blood supply to the palperbral conjunctiva (the eyelid) is derived from the external corotid artery. However, the circulation of the bulbar conjunctiva and palpebral conjunctiva are linked, so both bulbar conjunctival and palpebral conjunctival vessels will be supplied by both the ophthalmic artery and the external carotid artery, to varying extents.[15]

Bulbar conjunctival microvasculature

Vessel morphology

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.[19] 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 nano meters in diameter.[20]

Blood oxygen dynamics

The bulbar conjunctival microvasculature is in close proximity to ambient air, thus oxygen diffusion from ambient air strongly influences their blood oxygen saturation. It has been shown that because of oxygen diffusion, hypoxic bulbar conjunctival vessels will rapidly re-oxygenate (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.[21]

Blood vessel imaging methods

The bulbar conjunctival microvessels are typically imaged with a high-magnification slit-lamp with green filters.[22] With such high-magnification imaging systems, it is possible to see groups of individual red blood cells flowing in vivo.[22] 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[23] and to measure blood oxygen saturation.[21] Fluorescein angiography has been used to study the blood flow of the bulbar conjunctiva and to differentiate the bulbar conjunctival and episcleral microcirculation.[24][25][26]

Vasodilation

The bulbar conjunctival microvasculature is known to dilate in response to several stimuli and external conditions, including allergens (e.g. pollen),[27] temperature,[28] time-of-day,[28] contact-lens wear,[9] and acute mild hypoxia.[21] Bulbar conjunctival vasodilation has also been shown to correlate changes in emotional state.[29]

Type II diabetes is associated with an increase in average bulbar conjunctival vessel diameter and capillary loss.[7][8] Sickle-cell anemia is associated with altered average vessel diameter.[10]

See also

Additional images

  • Sagittal section through the upper eyelid.
    Sagittal section through the upper eyelid.
  • Extrinsic eye muscle. Nerves of orbita. Deep dissection.
    Extrinsic eye muscle. Nerves of orbita. Deep dissection.

References

  1. ^ London Place Eye Center (2003). Conjunctivitis. Retrieved July 25, 2004.
  2. ^ Efron, Nathan; Al-Dossari, Munira; Pritchard, Nicola (2009-05-01). "In vivo confocal microscopy of the bulbar conjunctiva". Clinical & Experimental Ophthalmology. 37 (4): 335–344. doi:10.1111/j.1442-9071.2009.02065.x. ISSN 1442-9071. PMID 19594558.
  3. ^ Eye, human Encyclopaedia Britannica
  4. ^ "Table 1: Summary of sensory nerve supply". Archived from the original on February 14, 2013. Retrieved July 31, 2016. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  5. ^ a b c d Goldman, Lee. Goldman's Cecil Medicine (24th ed.). Philadelphia: Elsevier Saunders. p. 2426. ISBN 1437727883.
  6. ^ Isenberg, S. J.; McRee, W. E.; Jedrzynski, M. S. (1986-10-01). "Conjunctival hypoxia in diabetes mellitus". Investigative Ophthalmology & Visual Science. 27 (10): 1512–1515. ISSN 0146-0404. PMID 3759367.
  7. ^ a b Fenton, B. M.; Zweifach, B. W.; Worthen, D. M. (1979-09-01). "Quantitative morphometry of conjunctival microcirculation in diabetes mellitus". Microvascular Research. 18 (2): 153–166. ISSN 0026-2862. PMID 491983.
  8. ^ a b Ditzel, Jørn (1967-01-12). "The in Vivo Reactions of the Small Blood Vessels to Diabetes Mellitus". Acta Medica Scandinavica. 182 (S476): 123–134. doi:10.1111/j.0954-6820.1967.tb12691.x. ISSN 0954-6820.
  9. ^ a b Cheung, A. T.; Ramanujam, S.; Greer, D. A.; Kumagai, L. F.; Aoki, T. T. (2001-10-01). "Microvascular abnormalities in the bulbar conjunctiva of patients with type 2 diabetes mellitus". Endocrine Practice: Official Journal of the American College of Endocrinology and the American Association of Clinical Endocrinologists. 7 (5): 358–363. doi:10.4158/EP.7.5.358. ISSN 1530-891X. PMID 11585371.
  10. ^ a b Fink, A I (1968-01-01). "Vascular changes in the bulbar conjunctiva associated with sickle-cell disease: some observations on fine structure". Transactions of the American Ophthalmological Society. 66: 788–826. ISSN 0065-9533. PMC 1310317. PMID 5720854.
  11. ^ Isenberg, S. J.; McRee, W. E.; Jedrzynski, M. S.; Gange, S. N.; Gange, S. L. (1987-01-01). "Effects of sickle cell anemia on conjunctival oxygen tension and temperature". Archives of Internal Medicine. 147 (1): 67–69. ISSN 0003-9926. PMID 3800533.
  12. ^ Wanek, Justin; Gaynes, Bruce; Lim, Jennifer I.; Molokie, Robert; Shahidi, Mahnaz (2013-08-01). "Human bulbar conjunctival hemodynamics in hemoglobin SS and SC disease". American Journal of Hematology. 88 (8): 661–664. doi:10.1002/ajh.23475. ISSN 1096-8652. PMC 4040222. PMID 23657867.
  13. ^ Harper, Robert N.; Moore, Michael A.; Marr, Melissa C.; Watts, L. Earl; Hutchins, Phillip M. (1978-11-01). "Arteriolar rarefaction in the conjunctiva of human essential hypertensives". Microvascular Research. 16 (3): 369–372. doi:10.1016/0026-2862(78)90070-5.
  14. ^ Lee, R. E. (1955-08-01). "Anatomical and physiological aspects of the capillary bed in the bulbar conjunctiva of man in health and disease". Angiology. 6 (4): 369–382. ISSN 0003-3197. PMID 13275744.
  15. ^ a b PAVLOU AT; WOLFF HG (1959-07-01). "THe bulbar conjunctival vessels in occlusion of the internal carotid artery". A.M.A. Archives of Internal Medicine. 104 (1): 53–60. doi:10.1001/archinte.1959.00270070055007. ISSN 0888-2479.
  16. ^ "Conjunctivochalasis - Medical Definition". Medilexicon.com. Retrieved 2012-11-13.
  17. ^ WL Hughes Conjunctivochalasis. American Journal of Ophthalmology 1942
  18. ^ Biswas, J.; Varde, M. (2009). "Ocular surface tumors". Oman Journal of Ophthalmology. 2: 1–2. doi:10.4103/0974-620X.48414. PMC 3018098. PMID 21234216.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  19. ^ Meighan, S. Spence (1956-09-01). "Blood Vessels of the Bulbar Conjunctiva". The British Journal of Ophthalmology. 40 (9): 513–526. ISSN 0007-1161. PMC 1324675. PMID 13364178.
  20. ^ Shahidi, M.; Wanek, J.; Gaynes, B.; Wu, T. (2010-03-01). "Quantitative Assessment of Conjunctival Microvascular Circulation of the Human Eye". Microvascular Research. 79 (2): 109–113. doi:10.1016/j.mvr.2009.12.003. ISSN 0026-2862. PMC 3253734. PMID 20053367.
  21. ^ a b c MacKenzie, L. E.; Choudhary, T. R.; McNaught, A. I.; Harvey, A. R. (2016-06-15). "In vivo oximetry of human bulbar conjunctival and episcleral microvasculature using snapshot multispectral imaging". Experimental Eye Research. 149: 48–58. doi:10.1016/j.exer.2016.06.008. ISSN 1096-0007. PMID 27317046.
  22. ^ a b van Zijderveld, Rogier; Ince, Can; Schlingemann, Reinier O. (2014-05-01). "Orthogonal polarization spectral imaging of conjunctival microcirculation". Graefe's Archive for Clinical and Experimental Ophthalmology = Albrecht Von Graefes Archiv Für Klinische Und Experimentelle Ophthalmologie. 252 (5): 773–779. doi:10.1007/s00417-014-2603-9. ISSN 1435-702X. PMID 24627137.
  23. ^ Jiang, Hong; Ye, Yufeng; DeBuc, Delia Cabrera; Lam, Byron L; Rundek, Tatjana; Tao, Aizhu; Shao, Yilei; Wang, Jianhua (2013-01-01). "Human conjunctival microvasculature assessed with a retinal function imager (RFI)". Microvascular research. 85: 134–137. doi:10.1016/j.mvr.2012.10.003. ISSN 0026-2862. PMC 3534915. PMID 23084966.
  24. ^ Meyer, P. A. (1988-01-01). "Patterns of blood flow in episcleral vessels studied by low-dose fluorescein videoangiography". Eye (London, England). 2 ( Pt 5): 533–546. doi:10.1038/eye.1988.104. ISSN 0950-222X. PMID 3256492.
  25. ^ Ormerod, L. D.; Fariza, E.; Webb, R. H. (1995-01-01). "Dynamics of external ocular blood flow studied by scanning angiographic microscopy". Eye (London, England). 9 ( Pt 5): 605–614. doi:10.1038/eye.1995.148. ISSN 0950-222X. PMID 8543081.
  26. ^ Meyer, P. A.; Watson, P. G. (1987-01-01). "Low dose fluorescein angiography of the conjunctiva and episclera". British Journal of Ophthalmology. 71 (1): 2–10. doi:10.1136/bjo.71.1.2. ISSN 1468-2079. PMID 3814565.
  27. ^ Hvoarak, Friedrich; Berger, Uwe; Menapace, Reinhard; Schuster, Norbert (1996). "Quantification of conjunctival vascular reaction by digital imaging". Journal of Allergy and Clinical Immunology. 98 (3). doi:10.1016/S0091-6749(96)70081-7. Retrieved July 31, 2016 – via Elsevier Science Direct.
  28. ^ a b Duench, Stephanie; Simpson, Trefford; Jones, Lyndon W.; Flanagan, John G.; Fonn, Desmond (2007-06-01). "Assessment of variation in bulbar conjunctival redness, temperature, and blood flow". Optometry and Vision Science: Official Publication of the American Academy of Optometry. 84 (6): 511–516. doi:10.1097/OPX.0b013e318073c304. ISSN 1040-5488. PMID 17568321.
  29. ^ Provine, Robert R.; Nave-Blodgett, Jessica; Cabrera, Marcello O. (2013-11-01). "The Emotional Eye: Red Sclera as a Uniquely Human Cue of Emotion". Ethology. 119 (11): 993–998. doi:10.1111/eth.12144. ISSN 1439-0310.

External links

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