Sclera
1. sclera (sclera)
2. choroid ( choroid )
3. Schlemm's canal ( sinus venosus sclerae / venous plexus sclera )
4. orris root ( Radix iris )
5. cornea ( cornea )
6. iris ( Iris )
7. Pupil ( Pupilla )
8. Anterior chamber of the eye ( Camera anterior bulbi )
9. Posterior chamber of the eye ( Camera posterior bulbi )
10. Ciliary body ( Corpus ciliare )
11. Lens ( Lens )
12. Vitreous body ( Corpus vitreum )
13. Retina ( Retina )
14. Optic nerve ( Nervus opticus )
15. Zonula fibers ( Fibrae zonulares )
Outer eye skin ( Tunica externa bulbi ): 1. + 5.
Middle eye skin ( Tunica media bulbi / uvea ): 2. + 6. + 10.
Inner eye skin ( Tunica interna bulbi ): 13.
Sclera and the sclera ( Greek σκληρός skleros , German , hard ' ) is the medical term for the sclera of the eye . Because of its whitish color, it is also called white eye skin . It almost completely encloses the eyeball and protects it from external influences. Together with the cornea (cornea) it belongs to the outer skin of the eye, tunica externa bulbi . The sclera extends from the point of entry of the optic nerve to the cornea of the eye and is enclosed by the Tenon's capsule , an elastic membrane.
The visible part of the sclera in humans is around three times that of the more than 200 species of non-human primates. This means that the eye movement and thus the direction in which the person is looking can be seen much better. The sclera is thus part of human non-verbal communication .
construction
The sclera consists of a collagen connective tissue and vascular-poor layer of its own ( substantia propria ), which is stretched by the intraocular pressure. The vascular lamina episcleralis lies on the outside . In the transition area to the cornea, the sclera is covered on the outside by the tunica conjunctiva bulbi , a section of the conjunctiva (conjunctiva).
In the border area between the cornea and sclera, the so-called limbus (hem), the sclera roofs the cornea like a roof tile ( corneoscleral fold ). At this point, the sclera is thickened by an internal connective tissue ring ( annulus sclerae ) to form a scleral bulge , where the ciliary muscle is also anchored.
At the posterior pole of the eye, the sclera has an opening about 3.5 mm in size in humans for the optic nerve to pass into the eye. In humans, this hole lies around 3 mm inward and 1 mm below the central fovea . It is covered by a sieve plate ( Lamina cribrosa sclerae ) with numerous openings . Here the dermis merges with the hard meninges of the optic nerve.
Blood vessels
The blood supply to the sclera is mainly via the lamina episcleralis . In the scleral bulge there is a venous plexus ( plexus venosus sclerae , Schlemm's canal ), which serves to drain the aqueous humor .
The terminal branches of the blood vessels in the conjunctiva of the seam area are called the peripheral loop network. This plays a role in supplying the cornea, which is actually vascular. In the case of corneal inflammation, blood vessels can sprout into the cornea from this marginal loop network.
Diseases
Diseases of the sclera are primarily inflammations , which are seldom caused by local infection, but by systemic autoimmune diseases (e.g. rheumatism ) or gout , and more rarely by infectious diseases ( syphilis , borreliosis , herpes zoster ). This is especially true for deep scleritis (as opposed to episcleritis).
In jaundice ( jaundice ), scleric terus (yellowing of the sclera) occurs first when the total bilirubin in the serum rises> 2 mg / dl (or> 34 µmol / l), after which the skin and mucous membrane also turn yellow.
In addition, injuries to the sclera play an important role in ophthalmology.
Diagnosis
A look at the sclera, i.e. the white part of the eye, can indicate various diseases not only in the eye:
- It is reddened when it is infected. The conjunctivitis is superficial and therefore displaceable. The episcleritis is often circumscribed, lens-shaped and tender on pressure, the scleritis diffuse and spontaneously painful, especially at night.
- A bluish color suggests inflammation has passed (or osteogenesis imperfecta ) but is normal in infants or very thin sclera.
- Yellowing occurs due to increased bilirubin due to liver disease or the like.
- A blackish sclera indicates alkaptonuria .
literature
- Theodor Axenfeld (founder), Hans Pau (ed.): Textbook and atlas of ophthalmology. With the collaboration of Rudolf Sachsenweger and others 12th, completely revised edition. Gustav Fischer, Stuttgart et al. 1980, ISBN 3-437-00255-4 .
- Pschyrembel clinical dictionary. With clinical syndromes and nouns anatomica. = Clinical Dictionary. Edited by the publisher's dictionary editor under the direction of Christoph Zink. 256th, revised edition. de Gruyter, Berlin et al. 1990, ISBN 3-11-010881-X .
Individual evidence
- ↑ Duden: Sclera .
- ↑ Michael Tomasello : Why we cooperate. Suhrkamp Verlag Berlin 2010, ISBN 978-3-518-26036-4 , (Original title: Why We Cooperate), p. 65
- ↑ Walther Graumann, Dieter Sasse: Compact textbook anatomy . tape 4 . Schattauer, 2005, ISBN 978-3-7945-2064-0 , pp. 20 .