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==Overview==
==Overview==
A '''corneal ulcer''', or '''ulcerative keratitis''', is an inflammatory or more seriously, infective condition of the [[cornea]] involving disruption of its epithelial layer with involvement of the corneal stroma. It is a common condition in humans particularly in the tropics and the agrarian societies. In developing countries, as well as in Florida, corneal ulcer is frequently the cause of great morbidity as well as economic loss to the person and family. Children afflicted by Vitamin A deficiency are at high risk for corneal ulcer and may become blind in both eyes, which may persist lifelong, causing tremendous & avoidable loss to the person and the society.
A '''corneal ulcer''', or '''ulcerative keratitis''', is an inflammatory or more seriously, infective condition of the [[cornea]] involving disruption of its epithelial layer with involvement of the corneal stroma. It is a common condition in humans particularly in the tropics and the agrarian societies. In developing countries, as well as in Florida, corneal ulcer is frequently the cause of great morbidity as well as economic loss to the person and family. Children afflicted by Vitamin A deficiency are at high risk for corneal ulcer and may become blind in both eyes, which may persist lifelong, causing tremendous & avoidable loss to the person and the society.


==Corneal anatomy of the humans==
==Causes==
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.
Corneal ulcers are a common human eye disease. They are caused by trauma, particularly with vegetable matter, chemical injury, contact lenses, and infections. Other eye conditions can cause corneal ulcers, such as [[entropion]], [[distichia]]e, [[corneal dystrophy]], and [[keratoconjunctivitis sicca]] (dry eye).


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.
==Risk Factors==
People with poor eye [[hygiene]] and [[contact lens]] abusers (e.g. those who wear [[contact lens|contact lenses]] overnight) are at an increased risk of developing corneal ulcers. Corneal ulcers are a common condition in humans, particularly those living in the tropics and in agrarian societies. In developing countries, children afflicted by[[vitamin A]] deficiency are at a high risk for corneal ulcer and may become [[blind]] in both eyes, which may persist lifelong if not treated.


There are five layers in the human cornea, from outer to inner:
==History and Symptoms==
* [[Epithelium]]
Corneal ulcers are painful due to nerve exposure, and can cause tearing, squinting, and vision loss of the eye.  There may also be signs of anterior [[uveitis]], such as [[miosis]] (small pupil), aqueous flare (protein in the [[aqueous humour]]), and redness of the eye.  An axon reflex may be responsible for uveitis formation — stimulation of pain receptors in the cornea results in release inflammatory mediators such as [[prostaglandin]]s, [[histamine]], and [[acetylcholine]].
* [[Bowman's membrane]]
* [[Stroma]]
* [[Descemet's membrane]]
* [[Endothelium ]]


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]].
==Laboratory Findings==
Diagnosis is done by direct observation under magnified view of [[slit lamp]] revealing the ulcer on the cornea. The use of [[fluorescein]] stain, which is taken up by exposed corneal [[stroma]] and appears green, helps in defining the margins of the corneal ulcer, and can reveal additional details of the surrounding epithelium. Herpes simplex ulcers show a typical dendritic pattern of staining. Rose-Bengal dye is also used for supra-vital staining purposes, but it may be very irritating to the eyes. In descemetoceles, the Descemet's membrane will bulge forward and after staining will appear as a dark circle with a green boundary, because it does not absorb the stain. Doing a corneal scraping and examining under the microscope with stains like Gram's and KOH preparation may reveal the bacteria and fungi respectively. Microbiological culture tests may be necessary to isolate the causative organisms for some cases. Other tests that may be necessary include a [[Schirmer's test]] for keratoconjunctivitis sicca and an analysis of [[facial nerve]] function for facial nerve paralysis.


==Refractory corneal ulcers==
==Prevention==
{{main|Recurrent corneal erosion}}
Contact lens wearers must be sure to wash their hands and pay very close attention to cleanliness while handling their [[contact lenses|lenses]] to prevent corneal ulcers. Also,[[contact lenses]] should not be worn overnight or when swimming, and eye lubricants should be used prior to [[contact lens|lens]] removal to avoid scratches due to dryness. Prompt, early attention by an [[ophthalmologist]] or [[optometrist]] for an eye [[infection]] may prevent ulcers from forming.
Refractory corneal ulcers are superficial ulcers that heal poorly and tend to recur. They are also known as '''indolent ulcers''' or '''Boxer ulcers'''.  They are believed to be caused by a defect in the basement membrane and a lack of [[hemidesmosome|hemidesmosomal]] attachments. They are recognized by undermined epithelium that surrounds the ulcer and easily peels back. Refractory corneal ulcers are most commonly seen in diabetics and often occur in the other eye later.  They are similar to Cogan's cystic dystrophy.


==Melting ulcers==
==References==
Melting ulcers are a type of corneal ulcer involving progressive loss of stroma in a dissolving fashion.  This is most commonly seen in ''[[Pseudomonas]]'' infection, but it can be caused by other types of [[bacteria]] or [[fungus|fungi]].  These infectious agents produce [[protease]]s and [[collagenase]]s which break down the corneal stroma.  Complete loss of the stroma can occur within 24 hours. Treatment includes antibiotics and collagenase inhibitors such as [[acetylcysteine]]. Surgery in the form of corneal transplantation (penetrating keratoplasty) is usually necessary to save the eye.
{{reflist|2}}


==References==
[[Category:Needs content]]
{{Reflist|2}}
[[Category:Disease]][[Category:Infectious disease]]
[[Category:Ophthalmology]]{{WH}}
{{WS}}

Revision as of 20:58, 11 December 2012

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

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Overview

A corneal ulcer, or ulcerative keratitis, is an inflammatory or more seriously, infective condition of the cornea involving disruption of its epithelial layer with involvement of the corneal stroma. It is a common condition in humans particularly in the tropics and the agrarian societies. In developing countries, as well as in Florida, corneal ulcer is frequently the cause of great morbidity as well as economic loss to the person and family. Children afflicted by Vitamin A deficiency are at high risk for corneal ulcer and may become blind in both eyes, which may persist lifelong, causing tremendous & avoidable loss to the person and the society.

Causes

Corneal ulcers are a common human eye disease. They are caused by trauma, particularly with vegetable matter, chemical injury, contact lenses, and infections. Other eye conditions can cause corneal ulcers, such as entropion, distichiae, corneal dystrophy, and keratoconjunctivitis sicca (dry eye).

Risk Factors

People with poor eye hygiene and contact lens abusers (e.g. those who wear contact lenses overnight) are at an increased risk of developing corneal ulcers. Corneal ulcers are a common condition in humans, particularly those living in the tropics and in agrarian societies. In developing countries, children afflicted byvitamin A deficiency are at a high risk for corneal ulcer and may become blind in both eyes, which may persist lifelong if not treated.

History and Symptoms

Corneal ulcers are painful due to nerve exposure, and can cause tearing, squinting, and vision loss of the eye. There may also be signs of anterior uveitis, such as miosis (small pupil), aqueous flare (protein in the aqueous humour), and redness of the eye. An axon reflex may be responsible for uveitis formation — stimulation of pain receptors in the cornea results in release inflammatory mediators such as prostaglandins, histamine, and acetylcholine.

Laboratory Findings

Diagnosis is done by direct observation under magnified view of slit lamp revealing the ulcer on the cornea. The use of fluorescein stain, which is taken up by exposed corneal stroma and appears green, helps in defining the margins of the corneal ulcer, and can reveal additional details of the surrounding epithelium. Herpes simplex ulcers show a typical dendritic pattern of staining. Rose-Bengal dye is also used for supra-vital staining purposes, but it may be very irritating to the eyes. In descemetoceles, the Descemet's membrane will bulge forward and after staining will appear as a dark circle with a green boundary, because it does not absorb the stain. Doing a corneal scraping and examining under the microscope with stains like Gram's and KOH preparation may reveal the bacteria and fungi respectively. Microbiological culture tests may be necessary to isolate the causative organisms for some cases. Other tests that may be necessary include a Schirmer's test for keratoconjunctivitis sicca and an analysis of facial nerve function for facial nerve paralysis.

Prevention

Contact lens wearers must be sure to wash their hands and pay very close attention to cleanliness while handling their lenses to prevent corneal ulcers. Also,contact lenses should not be worn overnight or when swimming, and eye lubricants should be used prior to lens removal to avoid scratches due to dryness. Prompt, early attention by an ophthalmologist or optometrist for an eye infection may prevent ulcers from forming.

References

Template:WH

Template:WS