AskDefine | Define sclera

Dictionary Definition

sclera n : whitish fibrous membrane (albuginea) that with the cornea forms the outer covering of the eyeball [syn: sclerotic coat]

User Contributed Dictionary

English

Pronunciation

Noun

sclera (plural scleras or sclerae)
  1. The white of the eye. It is the tough outer coat of the eye that covers the eyeball except for the cornea.

Derived terms

Translations

Extensive Definition

The sclera, called the white or white of the eye, is the opaque (usually white, though certain animals, such as horses and lizards, can have black sclera), fibrous, protective, outer layer of the eye containing collagen and elastic fibers. It is derived from the neural crest. In children, it is thinner and shows some of the underlying pigment, appearing slightly blue. In the elderly, however, fatty deposits on the sclera can make it appear slightly yellow.
The sclera forms the posterior five sixths of the connective tissue coat of the globe. It is continuous with the dura mater, and maintains the shape of the globe, offering resistance to internal and external forces, and provides an attachment for the extraocular muscle insertions. The thickness of the sclera varies from 1mm at the posterior pole to 0.3 mm just behind the rectus muscle insertions. The main parts of the eye also include the conjunctiva. This is a thin layer covering the sclera.
It borders with the cornea by the corneal limbus.

Histology

From outer to innermost, the three layers of the sclera are:
  • Episclera
  • Stroma
  • Lamina fusca
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To avoid confusion, the cornea, which is an outer continuation from the sclera, has 5 layers. The middle, thickest layer is also called the stroma. Lazic surgery to correct vision is usually done in this region of the cornea. THE CORNEA IS LOCANTED INSIDE THE EYEBALL.

Additional images

References

External links

  • - "Sagittal Section Through the Eyeball"
sclera in Bengali: স্‌ক্লেরা
sclera in Catalan: Escleròtica
sclera in German: Sclera
sclera in Spanish: Esclerótica
sclera in Basque: Esklerotika
sclera in French: Sclère
sclera in Italian: Sclera
sclera in Lithuanian: Odena
sclera in Dutch: Sclera
sclera in Norwegian: Sklera
sclera in Polish: Twardówka
sclera in Portuguese: Esclera
sclera in Russian: Склера
sclera in Slovak: Očné bielko
sclera in Finnish: Kovakalvo
sclera in Urdu: صُلبہ
sclera in Chinese: 巩膜
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