cornea

enUK

cornea:

see eyeeye,
organ of vision and light perception. In humans the eye is of the camera type, with an iris diaphragm and variable focusing, or accommodation. Other types of eye are the simple eye, found in many invertebrates, and the compound eye, found in insects and many other
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Cornea

the anterior transparent part of the outer tunic of the eye that is part of the eye’s light-refracting apparatus and protects the eye from injury and dust.

There are five layers in the cornea: the anterior epithelium, the anterior limiting membrane (Bowman’s membrane), the substantia propria (connective-tissue stroma), the posterior, or Descemet’s, membrane, and the endothelium of the anterior chamber. Corneal epithelium is multilayered—in man it is composed of eight to ten layers with a total thickness reaching 50 micrometers. It is lined with Bowman’s membrane, which is an acellular part of the postepithelial stroma consisting of a network of collagenous fibers that run in various directions parallel to the surface of the cornea.

A membrane without a distinct boundary becomes the substantia propria of the cornea. In man the substantia propria occupies as much as 90 percent of the entire thickness of the cornea. It is solidly packed with collagenous fibers that are produced by fibroblasts; the intercellular matter of this layer contains mucopolysaccharides, chondroitin sulfate, chondroitin, and keratosulfate. The transparency of the cornea depends on the degree of dehydration and orderliness of the molecules of the acellular portion of the cornea’s basic matter.

Descemet’s membrane lines the basic matter of the cornea and is tough and elastic; its posterior surface is covered by the single-layered endothelium of the anterior chamber of the eye.

There are no blood vessels in corneal tissues. In man the cornea is innervated by 70–80 radial nerve trunks that originate in the optical branch of the fifth pair of cranial nerves; the branching of the trunks penetrates the entire thickness of the cornea, except Descemet’s membrane and the endothelium.

The most common diseases of the cornea include traumas, blennorrhea, keratitis, and staphyloma.

O. G. STROEVA

cornea

[′kȯr·nē·ə] (anatomy) The transparent anterior portion of the outer coat of the vertebrate eye covering the iris and the pupil. (invertebrate zoology) The outer transparent portion of each ommatidium of a compound eye.

cornea

the convex transparent membrane that forms the anterior covering of the eyeball and is continuous with the sclera

See cornea

Cornea

enUK

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

(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.

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.Mentioned in: Cataract Surgery, Corneal Abrasion, Corneal Transplantation, Exophthalmos, Eye Cancer, Eye Examination, Eye Glasses and Contact Lenses, Foreign Objects, Glaucoma, Hyperopia, Inclusion Conjunctivitis, Laser Surgery, Myopia, Photorefractive Keratectomy and Laser-Assisted In-Situ Keratomileusis, Pinguecula and Pterygium, Radial Keratotomy, Sjögren's Syndrome, Starvation, Tarsorrhaphy, Tissue Typing, Trabeculectomy, Trachoma, Uveitis, Visual Impairment, Vitamin A Deficiency

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.

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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]

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 :)

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noun the transparent dome-shaped anterior portion of the outer covering of the eye

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