Sclera

Sclera (Greek σκληρός skleros "hard" ) is the medical term for the sclera of the eye. Because of their whitish color it is also called " sclera ". It surrounds the eyeball almost completely and protects the eye. Together with the cornea ( cornea) it belongs to the sclera, tunica externa bulbi. The sclera extends from the entry point of the optic nerve to the cornea of ​​the eye and is surrounded by the Tenon's capsule, an elastic membrane.

The visible part of the sclera in humans is approximately three times larger than that of the more than 200 species of non-human primates. Thus, the eye movement, and thus the gaze direction of the person is significantly easier to see. The sclera is thus part of the nonverbal communication of humans.

Construction

The sclera consists of a kollagenbindegewebigen and poorly vascularized own layer ( substantia propria ), which is stressed by the intraocular pressure. Your lies outside the highly vascular lamina episcleralis. In the transition region to the cornea, the sclera is outside of the tunica conjunctiva bulbi, one section of the conjunctiva (conjunctiva ), covered.

In the boundary region between the cornea and sclera, called the limbus ( hem ), the sclera covered the cornea imbricate ( Korneoskleralfalz ). The sclera is ( scleral annulus ) at this point by an inner connective tissue ring adjacent to the scleral thickening, where the musculus ciliaris is anchored.

Blood vessels

The blood supply of the sclera takes place predominantly via the lamina episcleralis. In scleral there is a venous plexus ( plexus venosus sclerae, Schlemm's canal ), pertaining to the outflow of aqueous humor.

The terminal branches of the blood vessels in the conjunctiva of the skirt portion are called edge loop network. This plays a role in supplying the avascular cornea itself. In corneal inflammation can one sprout into the cornea from this edge loop network of blood vessels.

Diseases

Diseases of the sclera are mainly inflammation, but here rarely by local infection, but by systemic autoimmune diseases (eg rheumatoid ) or gout, rarely by infectious diseases ( syphilis, Lyme disease, herpes zoster) come about. This is especially true for deep scleritis (in contrast to episcleritis ).

When jaundice ( jaundice ), there is first a scleral icterus (yellowing of the sclera ) when the Serum total bilirubin > 2 mg / dl ( or > 34 micromol / L ) increases, then the skin and mucosa is also yellow.

In addition, violations of the sclera play an important role in the field of ophthalmology.

Diagnostics

The view of the sclera, which is the white part of the eye, may indicate various diseases not only on the eye:

• If there is inflammation, it is flushed. The conjunctivitis is superficial and therefore displaced. The episcleritis is often paraphrased lenticular and painful to pressure, the diffuse scleritis and already spontaneously painful, especially at night.
• A bluish color indicates an expired inflammation down ( or osteogenesis imperfecta ), but in infants or very thin sclera normal.
• Yellowing occurs by increased bilirubin due to liver disease or the like.
• A blackish sclera indicates a alkaptonuria.