cornea


cornea
corneal, adj.
/kawr"nee euh/, n. Anat.
the transparent anterior part of the external coat of the eye covering the iris and the pupil and continuous with the sclera. See diag. under eye.
[1350-1400; ME < ML cornea (tela, later tunica) horny (web or tunic), fem. of corneus CORNEOUS]

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 dome-shaped transparent membrane about 12 mm (0.5 inch) in diameter that covers the front part of the eye (eye, human). Except at its margins, the cornea contains no blood vessels (blood vessel), but it does contain many nerves and is very sensitive to pain or touch. It is nourished and provided with oxygen anteriorly by tears (tear duct and glands) and is bathed posteriorly by aqueous humour. It protects the pupil, the iris, and the inside of the eye from penetration by foreign bodies and is the first and most powerful element in the eye's focusing system. As light passes through the cornea, it is partially refracted before reaching the lens. The curvature of the cornea, which is spherical in infancy but changes with age, gives it its focusing power; when the curve becomes irregular, it causes a focusing defect called astigmatism, in which images appear elongated or distorted.

      The cornea itself is composed of multiple layers, including a surface epithelium, a central, thicker stroma, and an inner endothelium. The epithelium (outer surface covering) of the cornea is an important barrier to infection. A corneal abrasion, or scratch, most often causes a sensation of something being on the eye and is accompanied by intense tearing, pain, and light sensitivity. Fortunately, the corneal epithelium is able to heal quickly in most situations.

      The collagen fibres (collagen) that make up the corneal stroma (middle layer) are arranged in a strictly regular, geometric fashion. This arrangement has been shown to be the essential factor resulting in the cornea's transparency. When the cornea is damaged by infection or trauma, the collagen laid down in the repair processes is not regularly arranged, with the result that an opaque patch or scar may occur. If the clouded cornea is removed and replaced by a healthy one (i.e., by means of corneal transplant), usually taken from a deceased donor, normal vision can result.

      The innermost layer of the cornea, the endothelium, plays a critical role in keeping the cornea from becoming swollen with excess fluid. As endothelial cells are lost, new cells are not produced; rather, existing cells expand to fill in the space left behind. Once loss of a critical number of endothelial cells has occurred, however, the cornea can swell, causing decreased vision and, in severe cases, surface changes and pain. Endothelial cell loss can be accelerated via mechanical trauma or abnormal age-related endothelial cell death (called Fuchs endothelial dystrophy). Treatment may ultimately require corneal transplant.

Daniel M. Albert David M. Gamm
 

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Universalium. 2010.

Look at other dictionaries:

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  • Cornea — ist der Familienname folgender Personen: Doina Cornea (* 1929), rumänische Dissidentin und Menschenrechtlerin Carol Cornea, Pseudonym von Kurt E. Koch (1913–1987), evangelischer Theologe und Publizist Cornea ist die lateinische Bezeichnung für… …   Deutsch Wikipedia

  • cornea — late 14c., from M.L. cornea tela horny web or sheath, from L. cornu (gen. cornus) horn (see HORN (Cf. horn)). So called for its consistency. Related: Corneal …   Etymology dictionary

  • córnea — s. f. 1. Túnica espessa e transparente do olho. 2. córnea opaca: esclerótica …   Dicionário da Língua Portuguesa

  • córnea — sustantivo femenino 1. Área: anatomía Membrana dura y transparente del ojo, encajada en la esclerótica, a través de la cual se ve el iris: Vengo asustado del oculista, porque me ha dicho que tengo una lesión en la córnea …   Diccionario Salamanca de la Lengua Española

  • cornea — ► NOUN ▪ the transparent layer forming the front of the eye. DERIVATIVES corneal adjective. ORIGIN from Latin cornea tela horny tissue …   English terms dictionary

  • cornea — [kôr′nē ə] n. [ME < ML < L cornea (tela), horny (web, tissue), fem. sing. of corneus < cornu,HORN] the transparent tissue over the front of the eyeball, covering the iris and pupil: see EYE corneal adj …   English World dictionary

  • Cornea — Cor ne*a (k?r n? ?), n.; pl. {Corneas} ( ?z). [Fem. sing., fr. L. corneus horny, fr. cornu a horn. See {Horn}.] (Anat.) The transparent part of the coat of the eyeball which covers the iris and pupil and admits light to the interior. See {Eye}.… …   The Collaborative International Dictionary of English

  • Cornĕa [1] — Cornĕa, Dorf im Kreise Temes des österreichischen Verwaltungsgebietes Temesvar. (Ungarn). Hier am 4. Juli 1738 Überfall der Österreicher durch die Türken. Die Türken kamen bis ans Zelt des Großherzogs von Toscana, wurden aber geworfen …   Pierer's Universal-Lexikon

  • Cornĕa [2] — Cornĕa (lat.), die Hornhaut, s. u. Auge …   Pierer's Universal-Lexikon

  • Cornĕa — (lat.), die Hornhaut des Auges; s. Tafel »Auge II« (mit Text) …   Meyers Großes Konversations-Lexikon


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