sclera

sclera:

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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Sclera

the external tough fibrous tunic of the eye, which performs a supportive and protective function. In most vertebrates the sclera contains cartilaginous tissue and bony laminae that form a sclerotic ring. (Chondrichthians and modern amphibians and mammals do not have sclerotic rings.)

In humans the sclera consists of a dense fibrous tissue in which intermixed collagenous and elastic fibers are arranged predominantly in meridional and equatorial directions. Connective tissue cells are located between the fibers, and pigment cells (melanocytes) are found where the optic nerve leaves the eye. The external layer of the sclera contains a highly motile system of slender collagenous fibers and laminae separated from one another by slitlike cavities (Tenon’s capsule); the fibers and laminae facilitate rotation of the eyeball in various directions. The external surface of the sclera is attached to the tendons of the oculomotor muscles.

In humans the thickness of the sclera at the posterior pole of the eyeball is approximately 1 mm, at the equator approximately 0.3–0.4 mm, and at the anterior pole of the eyeball at the site of the transition into the cornea approximately 0.6 mm. Small branching cavities are found at the junction of the sclera and cornea; the cavities join to form Schlemm’s canal, which drains fluid from the anterior chamber of the eye.

O. G. STROEVA

sclera

[′skler·ə] (anatomy) The hard outer coat of the eye, continuous with the cornea in front and with the sheath of the optic nerve behind.

sclera

the firm white fibrous membrane that forms the outer covering of the eyeball

sclera

[skle´rah] (L.) the tough, white outer coat of the eyeball, covering approximately the posterior five-sixths of its surface, continuous anteriorly with the cornea and posteriorly with the external sheath of the optic nerve. adj., adj scle´ral.

The sclera and other eye structures. From Lammon et al., 1995.blue sclera abnormal blueness of the sclera; it is a prominent feature of osteogenesis imperfecta and is also seen in certain other conditions. (See Atlas 1, Part B.)

scle·ra

, pl.

scle·ras

scler·ae

(sklē'ră, -ăz, -ē), [TA] A portion of the fibrous layer forming the outer envelope of the eyeball, except for its anterior sixth, which is the cornea. Synonym(s): sclerotic coat, sclerotica, tunica albuginea oculi, tunica sclerotica [Mod. L. fr. G. sklēros, hard]

sclera

(sklîr′ə)n. The tough white fibrous outer envelope of tissue covering all of the eyeball except the cornea. Also called sclerotic, sclerotic coat.

scle′ral adj.

scle·ra

, pl. scleras, pl. sclerae (skleră, -ăz, -ē) [TA] A portion of the fibrous tunic forming the outer envelope of the eye, except for its anterior one sixth, which is the cornea.
Synonym(s): sclerotica. [Mod. L. fr. G. sklēros, hard]

sclera

The white of the eye. The tough outer coating of dense, interwoven collagen fibrils visible through the transparent overlying CONJUNCTIVA.

sclera

sclerotic

the outer coat of the vertebrate eye to which are attached extrinsic muscles for moving the eyeball. The sclera is lined by a vascular layer, the CHOROID, except for the forward-facing part which is called the CORNEA and is transparent, with no underlying choroid.

Sclera

The tough, fibrous, white outer protective covering that surrounds the eye.Mentioned in: Eye Examination, Eye Muscle Surgery, Glaucoma, Osteogenesis Imperfecta, Trabeculectomy

sclera

The tough, white, opaque, fibrous outer tunic of the eyeball covering most of its surface (the cornea contributes 7% of, and completes, the outer tunic). Its anterior portion is visible and constitutes the 'white' of the eye. In childhood (or in pathological conditions) when the sclera is thin, it appears bluish, while in old age it may become yellowish, due to a deposition of fat. The sclera is thickest posteriorly (about 1 mm) and gradually becomes thinner towards the front of the eyeball. It is a sieve-like membrane at the lamina cribrosa. The sclera is pierced by three sets of apertures: (1) the posterior apertures round the optic nerve and through which pass the long and short posterior ciliary vessels and nerves; (2) the middle apertures, 4 mm behind the equator which give exit to the vortex veins; and (3) the anterior apertures through which pass the anterior ciliary vessels. The tendons of insertion of the extraocular muscles run into the sclera as parallel fibres and then spread out in a fan-shaped manner. The sclera is commonly considered to be divided into three layers from without inward: (1) the episclera, (2) the scleral stroma and (3) the suprachoroid (lamina fusca) which is interposed between choroid and sclera. Syn. sclerotic. Note: some authors consider the suprachoroid as belonging to the choroid. However, when choroid and sclera are separated part of the suprachoroid adheres to the choroid and part to the sclera. See cribriform plate; evisceration.
blue sclera A hereditary defect in which the sclera has a bluish appearance. The sclera is thinner than normal and is susceptible to rupture if the person engages in contact sports. It is often associated with fragility of the bones and deafness as part of a condition called osteogenesis imperfecta (fragilitas ossium, van der Hoeve's syndrome), with keratoconus or with acquired scleral thinning (e. g. necrotizing scleritis). Syn. blue sclerotic (Fig. S3). See Ehlers-Danlos syndrome; Marfan's syndrome.

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Fig. S3 Blue sclera

scle·ra

, pl. scleras, pl. sclerae (skleră, -ăz, -ē) [TA] Portion of fibrous layer forming outer envelope of eyeball, except for its anterior sixth, which is the cornea. [Mod. L. fr. G. sklēros, hard]

Patient discussion about sclera

Q. My 11 y/o son eyes appear to have a slight yellow in the whites toward the corners. I am assuming he will need blood work, but does anyone have any idea what may be the cause?A. If it's not a spot, but rather a diffuse color, it may be jaundice - high levels in the blood of a substance called bilirubin (http://en.wikipedia.org/wiki/Jaundice).
If your child is generally healthy, and this change appeared without any overt problem (e.g. liver disease or blood problem), or your child had fever or fasted recently, this jaundice may represents Gilbert syndrome. It's a syndrome of slightly elevated levels of bilirubin, and considered not dangerous.
You may read more here:http://www.nlm.nih.gov/medlineplus/ency/article/000301.htm

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Synonyms for sclera

noun the whitish fibrous membrane (albuginea) that with the cornea forms the outer covering and protection of the eyeball

Synonyms

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