Cornea


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cornea

 [kor´ne-ah]
the clear, transparent anterior covering of the eye (see also color plates). The cornea is subject to injury by foreign bodies in the eye, bacterial infection, and viral infection, especially by the herpesvirus that causes herpes simplex. The herpesvirus that causes herpes zoster (shingles) can also infect the cornea. Prompt treatment of any corneal injury or infection is essential to avoid ulceration and loss of vision.
Cornea. From Dorland's, 2000.

cor·ne·a

(kōr'nē-ă), [TA]
The transparent tissue constituting the anterior sixth of the outer wall of the eye, with a 7.7-mm radius of curvature as contrasted with the 13.5 mm of the sclera; it consists of stratified squamous epithelium continuous with that of the conjunctiva, a substantia propria, substantially regularly arranged collagen imbedded in mucopolysaccharide, and an inner layer of endothelium. It is the chief refractory structure of the eye.
[L. fem. of corneus, horny]

cornea

/cor·nea/ (kor´ne-ah) the transparent anterior part of the eye. cor´neal
conical cornea  keratoconus.

cornea

(kôr′nē-ə)
n.
The transparent convex anterior portion of the outer fibrous coat of the eyeball that covers the iris and the pupil and is continuous with the sclera.

cor′ne·al (-əl) adj.

cornea

[kôr′nē·ə]
Etymology: L, corneus, horny
the convex, transparent anterior part of the eye, comprising one sixth of the outermost tunic of the eye bulb. It allows light to pass through it to the lens. The cornea is a fibrous structure with five layers: the anterior corneal epithelium, continuous with that of the conjunctiva; the anterior limiting layer (Bowman's membrane); the substantia propria; the posterior limiting layer (Descemet's membrane); and the endothelium of the anterior chamber (keratoderma). It is dense, uniform in thickness, and nonvascular, and it projects like a dome beyond the sclera, which forms the other five sixths of the eye's outermost tunic. The degree of corneal curvature varies among different individuals and in the same person at different ages; the curvature is more pronounced in youth than in advanced age. corneal, adj.

cor·ne·a

(kōr'nē-ă) [TA]
The transparent tissue constituting the anterior sixth of the outer wall of the eye, with a 7.7-mm radius of curvature as contrasted with the 13.5-mm radius of the sclera. It consists of stratified squamous epithelium continuous with that of the conjunctiva, a substantia propria, regularly arranged collagen imbedded in mucopolysaccharide, and an inner layer of endothelium. It is the chief refractory structure of the eye.
[L. fem. of corneus, horny]

cornea

The outer, and principle, lens of the eye through which the coloured iris with its central hole (the pupil) can be seen. The cornea performs most of the focusing of the eye. Fine adjustment (ACCOMMODATION) is done by the internal crystalline lens.

cornea

that part of the SCLERA at the front of the eye of vertebrates overlaying the iris and lens. It is a transparent layer of EPITHELIUM and CONNECTIVE TISSUE through which light enters the eye and is refracted so that the lens can then focus it on the retina. The cornea contains no blood vessels, oxygen coming directly from air dissolved in tear secretions, and is therefore easy to transplant as no tissue-typing is required.

Cornea

Clear, bowl-shaped structure at the front of the eye. It is located in front of the colored part of the eye (iris). The cornea lets light into the eye and partially focuses it.

cornea 

The transparent anterior portion of the fibrous coat of the globe of the eye. It has a curvature somewhat greater than the rest of the globe, so a slight furrow marks its junction with the sclera. Looked at from the front the cornea is about 12 mm horizontally and 11 mm vertically. It is the first and most important refracting surface of the eye, having a power of about 42 D. The anterior surface has a radius of curvature of about 7.8 m, the posterior surface 6.5 mm, and the central thickness is about 0.5 mm. It consists of five layers, starting from the outside: (1) the stratified squamous epithelium; (2) Bowman's layer; (3) the stroma (substantia propria); (4) Descemet's membrane; and (5) the endothelium. The cornea is avascular, receiving its nourishment by permeation through spaces between the lamellae. The sources of nourishment are the aqueous humour, the tears and the limbal capillaries. The cornea is innervated by the long ciliary and other nerves of the surrounding conjunctiva, which are all branches of the ophthalmic division of the trigeminal nerve. Innervation is entirely sensory. Within the cornea there are only unmyelinated nerve endings. The density of nerves in the cornea is very high, making it the most sensitive structure in the body. The major structural component of the cornea is collagen, mostly type I, and most of the ground substance between the collagen fibrils in the corneal stroma is proteoglycans whose core proteins bind with keratan sulfate and dermatan sulfate (chondroitin sulfate B). The cornea owes its transparency to the regular arrangement of the collagen fibrils, but any factor that affects this lattice structure (e.g. swelling, pressure) results in a loss of transparency. The cornea contains some 78% water, some 15% collagen and some 5% of other proteins (Fig. C18). See endothelial bedewing; corneal stroma; corneal topography; dellen; deturgescence; dyskeratosis; glycosaminoglycan; keratitis; keratomycosis; Hudson-Stahli line; Bowman's layer; Descemet's membrane; microcornea; specular microscope; optical zone of cornea; pachometer; Maurice's theory; Hurler's syndrome; videokeratoscope.
conical cornea See keratoconus.
cornea farinata A bilateral corneal degeneration characterized by faint dust-like opacities in the deep stroma. They do not impair vision and are usually age-related.
cornea guttata Dystrophy of the endothelial cells of the cornea which may result from corneal trauma, cataract surgery, keratic precipitates, tonography, ageing, continuous contact lens wear, or as part of the early stages of Fuch's endothelial dystrophy (a disease associated with ageing and with females more than males). It is seen clinically by slit-lamp examination as black spherules in the endothelial pattern. The condition is bilateral, although one eye may be affected more than the other. As the condition progresses the cornea becomes oedematous with a consequent loss of vision and eventually turns into bullous keratopathy. If the degenerated cells are located at the periphery of the cornea they are called Hassall-Henle bodies and are of no clinical significance except as an indication of ageing. Syn. corneal guttae; endothelial corneal dystrophy. See specular reflection illumination; keratic precipitates.
optical zone of cornea See optical zone of cornea.
cornea plana A rare, congenital, usually bilateral condition in which the corneal curvature is flatter than normal with a significant decrease in refractive power. The eye is usually hyperopic with a shallow anterior chamber often resulting in angle-closure glaucoma. There is some degree of peripheral scleralization and it is closely associated with sclerocornea.
Fig. C18 Diagram showing the various layers of the cornea (k, keratocytes)enlarge picture
Fig. C18 Diagram showing the various layers of the cornea (k, keratocytes)

cor·ne·a

(kōr'nē-ă) [TA]
Transparent tissue constituting the anterior sixth of the outer wall of the eye, with a 7.7-mm radius of curvature.
[L. fem. of corneus, horny]

cornea (kor´nēə),

n the transparent anterior part of the eye.

cornea

the clear, transparent anterior segment of the fibrous tunic of the eye. The cornea is subject to injury by foreign bodies in the eye, and bacterial and viral infections. See also corneal, keratitis, keratopathy.

cornea nigrum
see corneal sequestrum.
cornea plana
a congenital flattening of the cornea.

Patient discussion about Cornea

Q. Has anyone had experience with a corneal transplant because of keratoconus?

A. my uncle had to do a transplant- it took 5 weeks until he could see anything , another year to get his vision straightened up. but now he is fine! i know that he looked for information in the "National Keratoconus Foundation". they were very helpful (and nice!), they have a website with information on all forms of treatment:
http://www.nkcf.org/

good luck :)

More discussions about Cornea
References in periodicals archive ?
The new layer that has been discovered is located at the back of the cornea between the corneal stroma and Descemet's membrane.
I think the first thing is to increase the [local] procurement of corneas," said Beatrice Senemaud from Agence de la Biomedecine, who is visiting Lebanon to help change its organ donation practices.
Between 2005 and 2009 he collaborated with interdisciplinary teams and private companies to successfully develop an artificial cornea specifically for patients whose cornea had become clouded - a condition that is extremely difficult to treat.
He said: "Her cornea is clear and I hope that it will maintain clarity.
Artificial cornea transplantation - The diseased cornea was removed and replaced with an artificial cornea, known as the Boston KPro.
With further research, said Griffith, this approach could help restore sight to millions of people who are waiting for a donated human cornea for transplantation.
In its appeal to the DCO, PHR warned that preventing the exit of the vision-impaired patients for eye operations this week will necessarily cause them to lose the opportunity for cornea transplants in the near future, if ever, because the corneas designated for the transplants have a very short expiration date.
In February 2008, SKMC obtained the support of Abu Dhabi Health Services Company (SEHA) to officially commence a multi-organ transplantation programme that would cover all major transplant services such as kidney, liver, pancreas and cornea.
The operation, which takes about an hour, involves replacing a patient's diseased or damaged cornea with healthy tissue donated by someone after their death.
SANTA CLARITA -- A Moorpark man who slowly went blind in one eye over the past few years is expected to see again after an artificial cornea was implanted Wednesday afternoon in the first surgery of its kind in the Santa Clarita Valley.
Also, corneal tissue without nerves doesn't heal as quickly as a wounded human cornea does.