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 conjunctival 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]
Blood supplyedit
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.[4]
Nerve supplyedit
Sensory innervation of the conjunctiva is divided into four parts:[5]
The conjunctiva consists of unkeratinized, both stratified squamous and stratified columnar epithelium, with interspersed goblet cells.[6] The epithelial layer contains blood vessels, fibrous tissue, and lymphatic channels.[6]Accessory lacrimal glands in the conjunctiva constantly produce the aqueous portion of tears.[6] Additional cells present in the conjunctival epithelium include melanocytes, T and B cell lymphocytes.[6]
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,[8] and discriminating stages of DR.[9]
Hypertension is associated with an increase in the tortuosity of bulbar conjunctival blood vessels and capillary and arteriole loss.[17][18]
Carotid artery occlusion is associated with slower conjunctival blood flow and apparent capillary loss.[4]
With age, the conjunctiva can stretch and loosen from the underlying sclera, leading to the formation of conjunctival folds, a condition known as conjunctivochalasis.[19][20]
The conjunctiva can be affected by tumors which can be benign, pre-malignant or malignant.[21]
Leptospirosis, an infection with Leptospira, can cause conjunctival suffusion, which is characterized by chemosis, and redness without exudates.
Bulbar conjunctival microvasculatureedit
Vessel morphologyedit
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.[22] 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.[23]
Blood oxygen dynamicsedit
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.[24]
Blood vessel imaging methodsedit
The bulbar conjunctival microvessels are typically imaged with a high-magnification slit lamp with green filters.[25][26][27] With such high-magnification imaging systems, it is possible to see groups of individual red blood cells flowing in vivo.[25] 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 [28] and to measure blood oxygen saturation.[24]Fluorescein angiography has been used to study the blood flow of the bulbar conjunctiva and to differentiate the bulbar conjunctival and episcleral microcirculation.[29][30][31]
Vasodilationedit
The bulbar conjunctival microvasculature is known to dilate in response to several stimuli and external conditions, including allergens (e.g. pollen),[32] temperature,[33] time-of-day,[33]contact-lens wear,[13] and acute mild hypoxia.[24] Bulbar conjunctival vasodilation has also been shown to correlate changes in emotional state.[34]
Type 2 diabetes is associated with an increase in average bulbar conjunctival vessel diameter and capillary loss.[11][12]Sickle-cell anemia is associated with altered average vessel diameter.[14]
Extrinsic eye muscle. Nerves of orbita. Deep dissection.
Referencesedit
^"Conjunctiva". www.sciencedirect.com. Retrieved 4 August 2022.
^Efron N, Al-Dossari M, Pritchard N (May 2009). "In vivo confocal microscopy of the bulbar conjunctiva". Clinical & Experimental Ophthalmology. 37 (4): 335–44. doi:10.1111/j.1442-9071.2009.02065.x. PMID 19594558. S2CID 35398240.
^ abPavlou AT, Wolff HG (July 1959). "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. PMID 13660526.
^"Table 1: Summary of sensory nerve supply". Archived from the original on February 14, 2013. Retrieved July 31, 2016.
^ abcdGoldman L (2012). Goldman's Cecil Medicine (24th ed.). Philadelphia: Elsevier Saunders. p. 2426. ISBN 978-1437727883.
^London Place Eye Center (2003). Conjunctivitis Archived 2004-08-08 at the Wayback Machine. Retrieved July 25, 2004.
^Khansari MM, Wanek J, Tan M, Joslin CE, Kresovich JK, Camardo N, et al. (April 2017). "Assessment of Conjunctival Microvascular Hemodynamics in Stages of Diabetic Microvasculopathy". Scientific Reports. 7: 45916. Bibcode:2017NatSR...745916K. doi:10.1038/srep45916. PMC5384077. PMID 28387229.
^Khansari MM, O'Neill W, Penn R, Chau F, Blair NP, Shahidi M (July 2016). "Automated fine structure image analysis method for discrimination of diabetic retinopathy stage using conjunctival microvasculature images". Biomedical Optics Express. 7 (7): 2597–606. doi:10.1364/BOE.7.002597. PMC4948616. PMID 27446692.
^ abDitzel J (1967-01-12). "The in vivo reactions of the small blood vessels to diabetes mellitus". Acta Medica Scandinavica. Supplementum. 476 (S476): 123–34. doi:10.1111/j.0954-6820.1967.tb12691.x. PMID 5236035.
^ abCheung AT, Ramanujam S, Greer DA, Kumagai LF, Aoki TT (2001-10-01). "Microvascular abnormalities in the bulbar conjunctiva of patients with type 2 diabetes mellitus". Endocrine Practice. 7 (5): 358–63. doi:10.4158/EP.7.5.358. PMID 11585371.
^ abFink AI (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. PMC1310317. PMID 5720854.
^Isenberg SJ, McRee WE, Jedrzynski MS, Gange SN, Gange SL (January 1987). "Effects of sickle cell anemia on conjunctival oxygen tension and temperature". Archives of Internal Medicine. 147 (1): 67–9. doi:10.1001/archinte.147.1.67. PMID 3800533.
^Wanek J, Gaynes B, Lim JI, Molokie R, Shahidi M (August 2013). "Human bulbar conjunctival hemodynamics in hemoglobin SS and SC disease". American Journal of Hematology. 88 (8): 661–4. doi:10.1002/ajh.23475. PMC4040222. PMID 23657867.
^Harper RN, Moore MA, Marr MC, Watts LE, Hutchins PM (November 1978). "Arteriolar rarefaction in the conjunctiva of human essential hypertensives". Microvascular Research. 16 (3): 369–72. doi:10.1016/0026-2862(78)90070-5. PMID 748720.
^Lee RE (August 1955). "Anatomical and physiological aspects of the capillary bed in the bulbar conjunctiva of man in health and disease". Angiology. 6 (4): 369–82. doi:10.1177/000331975500600408. PMID 13275744. S2CID 11589129.
^"Conjunctivochalasis - Medical Definition". Medilexicon.com. Archived from the original on 2016-03-03. Retrieved 2012-11-13.
^Hughes WL (January 1942). "Conjunctivochalasis". American Journal of Ophthalmology. 25 (1): 48–51. doi:10.1016/S0002-9394(42)93297-5.
^Varde MA, Biswas J (January 2009). "Ocular surface tumors". Oman Journal of Ophthalmology. 2 (1): 1–2. doi:10.4103/0974-620X.48414. PMC3018098. PMID 21234216.
^Meighan SS (September 1956). "Blood vessels of the bulbar conjunctiva in man". The British Journal of Ophthalmology. 40 (9): 513–26. doi:10.1136/bjo.40.9.513. PMC1324675. PMID 13364178.
^Shahidi M, Wanek J, Gaynes B, Wu T (March 2010). "Quantitative assessment of conjunctival microvascular circulation of the human eye". Microvascular Research. 79 (2): 109–13. doi:10.1016/j.mvr.2009.12.003. PMC3253734. PMID 20053367.
^ abcMacKenzie LE, Choudhary TR, McNaught AI, Harvey AR (August 2016). "In vivo oximetry of human bulbar conjunctival and episcleral microvasculature using snapshot multispectral imaging" (PDF). Experimental Eye Research. 149: 48–58. doi:10.1016/j.exer.2016.06.008. PMID 27317046. S2CID 25038785.
^ abvan Zijderveld R, Ince C, Schlingemann RO (May 2014). "Orthogonal polarization spectral imaging of conjunctival microcirculation". Graefe's Archive for Clinical and Experimental Ophthalmology. 252 (5): 773–9. doi:10.1007/s00417-014-2603-9. PMID 24627137. S2CID 1595902.
^Khansari MM, O'Neill W, Penn R, Chau F, Blair NP, Shahidi M (July 2016). "Automated fine structure image analysis method for discrimination of diabetic retinopathy stage using conjunctival microvasculature images". Biomedical Optics Express. 7 (7): 2597–606. doi:10.1364/BOE.7.002597. PMC4948616. PMID 27446692.
^Khansari MM, Wanek J, Felder AE, Camardo N, Shahidi M (February 2016). "Automated Assessment of Hemodynamics in the Conjunctival Microvasculature Network". IEEE Transactions on Medical Imaging. 35 (2): 605–11. doi:10.1109/TMI.2015.2486619. PMC4821773. PMID 26452274.
^Jiang H, Ye Y, DeBuc DC, Lam BL, Rundek T, Tao A, et al. (January 2013). "Human conjunctival microvasculature assessed with a retinal function imager (RFI)". Microvascular Research. 85: 134–7. doi:10.1016/j.mvr.2012.10.003. PMC3534915. PMID 23084966.
^Meyer PA (1988-01-01). "Patterns of blood flow in episcleral vessels studied by low-dose fluorescein videoangiography". Eye. 2 ( Pt 5) (5): 533–46. doi:10.1038/eye.1988.104. PMID 3256492.
^Ormerod LD, Fariza E, Webb RH (1995-01-01). "Dynamics of external ocular blood flow studied by scanning angiographic microscopy". Eye. 9 ( Pt 5) (5): 605–14. doi:10.1038/eye.1995.148. PMID 8543081.
^Meyer PA, Watson PG (January 1987). "Low dose fluorescein angiography of the conjunctiva and episclera". The British Journal of Ophthalmology. 71 (1): 2–10. doi:10.1136/bjo.71.1.2. PMC1041073. PMID 3814565.
^Horak F, Berger U, Menapace R, Schuster N (September 1996). "Quantification of conjunctival vascular reaction by digital imaging". The Journal of Allergy and Clinical Immunology. 98 (3): 495–500. doi:10.1016/S0091-6749(96)70081-7. PMID 8828525.
^ abDuench S, Simpson T, Jones LW, Flanagan JG, Fonn D (June 2007). "Assessment of variation in bulbar conjunctival redness, temperature, and blood flow". Optometry and Vision Science. 84 (6): 511–6. doi:10.1097/OPX.0b013e318073c304. PMID 17568321. S2CID 943038.
^Provine RR, Nave-Blodgett J, Cabrera MO (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 linksedit
"Conjunctiva". Medicinenet.com. 1999. Archived from the original on 7 June 2014. Retrieved 25 July 2004.