Corneal ulcer pathophysiology: Difference between revisions
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{{CMG}} | {{CMG}} | ||
{{Corneal ulcer}} | {{Corneal ulcer}} | ||
==Pathophysiology== | ==Pathophysiology== | ||
=== | ===Cornea=== | ||
The cornea is a transparent structure that is part of the outer layer of the [[eye]]. It [[refraction|refract]]s light and protects the contents of the eye. The corneal thickness ranges from 450 to 610 micrometres and on an average 550 µm. thick in caucasian eyes. In Indian eyes, the average thickness is slightly less at 510 µm. The[[trigeminal nerve]] supplies the cornea via the [[long ciliary nerve]]s. There are [[nociceptor|pain receptor]]s in the outer layers and [[mechanoreceptor|pressure receptor]]s are deeper. | The cornea is a transparent structure that is part of the outer layer of the [[eye]]. It [[refraction|refract]]s light and protects the contents of the eye. The corneal thickness ranges from 450 to 610 micrometres and on an average 550 µm. thick in caucasian eyes. In Indian eyes, the average thickness is slightly less at 510 µm. The [[trigeminal nerve]] supplies the cornea via the [[long ciliary nerve]]s. There are [[nociceptor|pain receptor]]s in the outer layers and [[mechanoreceptor|pressure receptor]]s are deeper. | ||
Transparency is achieved through a lack of blood vessels, pigmentation, and [[keratin]], and through tight layered organization of the [[collagen]] fibers. The collagen fibers cross the full diameter of the cornea in a strictly parallel fashion and allow 99 percent of the light to pass through without scattering. | Transparency is achieved through a lack of blood vessels, pigmentation, and [[keratin]], and through tight layered organization of the [[collagen]] fibers. The collagen fibers cross the full diameter of the cornea in a strictly parallel fashion and allow 99 percent of the light to pass through without scattering. | ||
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The outer layer is the [[epithelium]], which is 25 to 40 µm micrometers and five to seven [[cell (biology)|cell]] layers thick. The epithelium holds the tear film in place and also prevents water from invading the cornea and disrupting the collagen fibers. This prevents corneal [[edema]], which gives it a cloudy appearance. It is also a barrier to infectious agents. The epithelium sticks to the [[basal lamina|basement membrane]], which also separates the epithelium from the [[stroma]]. The corneal stroma comprises 90 percent of the thickness of the cornea. It contains the collagen fibers organized into [[lamella]]e. The lamellae are in sheets which separate easily. Posterior to the stroma is [[Descemet's membrane]], which is a basement membrane for the [[corneal endothelium]]. The endothelium is a single cell layer that separates the cornea from the [[aqueous humor]]. | The outer layer is the [[epithelium]], which is 25 to 40 µm micrometers and five to seven [[cell (biology)|cell]] layers thick. The epithelium holds the tear film in place and also prevents water from invading the cornea and disrupting the collagen fibers. This prevents corneal [[edema]], which gives it a cloudy appearance. It is also a barrier to infectious agents. The epithelium sticks to the [[basal lamina|basement membrane]], which also separates the epithelium from the [[stroma]]. The corneal stroma comprises 90 percent of the thickness of the cornea. It contains the collagen fibers organized into [[lamella]]e. The lamellae are in sheets which separate easily. Posterior to the stroma is [[Descemet's membrane]], which is a basement membrane for the [[corneal endothelium]]. The endothelium is a single cell layer that separates the cornea from the [[aqueous humor]]. | ||
===Corneal Ulcer Healing=== | ===Corneal Ulcer Healing=== | ||
An ulcer of the cornea heals by two methods, migration of surrounding epithelial cells followed by [[mitosis]] (dividing) of the cells, and introduction of blood vessels from the [[conjunctiva]]. Superficial small ulcers heal rapidly by the first method. However, larger or deeper ulcers often require the presence of blood vessels to supply inflammatory cells. [[White blood cell]]s and [[fibroblast]]s produce [[granulation tissue]] and then scar tissue, effectively healing the cornea. | An ulcer of the cornea heals by two methods, migration of surrounding epithelial cells followed by [[mitosis]] (dividing) of the cells, and introduction of blood vessels from the [[conjunctiva]]. Superficial small ulcers heal rapidly by the first method. However, larger or deeper ulcers often require the presence of blood vessels to supply inflammatory cells. [[White blood cell]]s and [[fibroblast]]s produce [[granulation tissue]] and then scar tissue, effectively healing the cornea. | ||
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==References== | ==References== | ||
{{reflist|2}} | {{reflist|2}} | ||
{{WH}} | |||
{{WS}} | |||
[[Category:Needs overview]] | [[Category:Needs overview]] | ||
[[Category:Disease]] | [[Category:Disease]] | ||
[[Category:Ophthalmology]] | [[Category:Ophthalmology]] | ||
Latest revision as of 21:09, 29 July 2020
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
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Pathophysiology
Cornea
The cornea is a transparent structure that is part of the outer layer of the eye. It refracts light and protects the contents of the eye. The corneal thickness ranges from 450 to 610 micrometres and on an average 550 µm. thick in caucasian eyes. In Indian eyes, the average thickness is slightly less at 510 µm. The trigeminal nerve supplies the cornea via the long ciliary nerves. There are pain receptors in the outer layers and pressure receptors are deeper.
Transparency is achieved through a lack of blood vessels, pigmentation, and keratin, and through tight layered organization of the collagen fibers. The collagen fibers cross the full diameter of the cornea in a strictly parallel fashion and allow 99 percent of the light to pass through without scattering.
There are five layers in the human cornea, from outer to inner:
The outer layer is the epithelium, which is 25 to 40 µm micrometers and five to seven cell layers thick. The epithelium holds the tear film in place and also prevents water from invading the cornea and disrupting the collagen fibers. This prevents corneal edema, which gives it a cloudy appearance. It is also a barrier to infectious agents. The epithelium sticks to the basement membrane, which also separates the epithelium from the stroma. The corneal stroma comprises 90 percent of the thickness of the cornea. It contains the collagen fibers organized into lamellae. The lamellae are in sheets which separate easily. Posterior to the stroma is Descemet's membrane, which is a basement membrane for the corneal endothelium. The endothelium is a single cell layer that separates the cornea from the aqueous humor.
Corneal Ulcer Healing
An ulcer of the cornea heals by two methods, migration of surrounding epithelial cells followed by mitosis (dividing) of the cells, and introduction of blood vessels from the conjunctiva. Superficial small ulcers heal rapidly by the first method. However, larger or deeper ulcers often require the presence of blood vessels to supply inflammatory cells. White blood cells and fibroblasts produce granulation tissue and then scar tissue, effectively healing the cornea.