SCLERA

From Big Medical Encyclopedia

SCLERA [sclera (PNA, JNA, BNA); Greek skleros firm, elastic; synonym white of an eye] — the opaque part of a fibrous cover of an eyeglobe performing protective, basic and drainage functions.

In the embryonal period of S. forms from accumulation of the cells of a mesenchyma surrounding a primitive choroid (see. Eye ).

Anatomy

Fig. 1. A structure of an eye (the vitreous, a part of a crystalline lens and covers of an eye are removed): 1 — sclera; 2 — chorioidea; 3 — retina; 4 — a. ciliaris post, brevis; 5 — n. opticus; 6 — a. ciliaris post, longa; 7 — v. vorticosa; 8 — m. rectus inf.; 9 — circulus arteriosus major; 10 — iris; 11 — cornea; 12 — conjunctiva; 13 — lens; 14 — corpus ciliare; 15 — m. rectus sup.

The page makes 5/6 fibrous covers of an eyeglobe and in front passes into its transparent part — a cornea (see tsvetn. fig. 1 to St. Eye ). S.'s thickness at the adult is various in different sites: normal it averages in the forefront apprx. 0,8 mm, in the field of an attachment of outside muscles of an eyeglobe — apprx. 0,3 mm, at an equator of eyeball — 0,4 — 0,6 mm, at an optic nerve — 0,5 — 1,0 mm. On site S.'s transition in cornea (see) the translucent ring — a limb (limbus corneae) is formed. Anatomically the exact place of transition of S. to a cornea consider the small fillet located at once behind a limb — sulcus sclerae ext., from the inside to it there corresponds deeper fillet — sulcus sclerae int. The collagenic fibers C. terminating at an endothelium of a cornea create corneal and scleral part C. It includes a front boundary ring of Shvalbe, well distinguishable at gonioskopiya (see). Behind it the scleral ledge, or a scleral spur (a back boundary ring of Shvalbe) is located, to a cut the ciliary muscle is attached. Between a front boundary ring of Shvalbe and a scleral spur in triangular space the drainage system of an eye is located: corneoscleral trabeculas (gear sheaf, trabecular reticulum, T.) and helmets channel (venous sine of a sclera, T.), knaruzh from to-rogo are available the intrascleral collector channels going to episkleralny veins. Behind S. terminates at an optic nerve, its periblasts pass into his outside vagina, and the separate collagenic fibers crossing it create a trellised plate of Page. It is the thinnest part C. and the first reacts to increase in intraocular pressure emergence of glaukomatozny excavation (see. Glaucoma ). At distance of 7 — 8 mm from edge of a cornea 4 direct muscles are attached to S.: top and bottom are located on a vertical meridian, outside and internal — on horizontal. Two oblique muscles of an eyeglobe are attached between its back pole and the equator of a kzada from the place of an attachment of sinews of an outside and upper straight line of muscles. The page supports numerous channels — emissariums, on the Crimea there pass vessels and nerves. Through the front emissariums having sometimes the pigmented mouths and attachments of direct muscles of an eyeglobe which are located between the place and a limb there pass front ciliary vessels and nerves. The last can form Aksenfeld's loop. Back emissariums contain 4 — 6 vortikozny veins, 2 long and apprx. 20 short ciliary arteries, and also nerves. Separate branches of back short ciliary arteries, anastomosing among themselves and gathering in a ring around an optic nerve, form tsinn a vascular wreath (circulus arteriosus n. optici). Outside S. is closely connected with a tenonovy fascia (a vagina of an eyeglobe, T.).

Page it is rather poor in vessels and it is supplied with blood at the expense of branches of front and back ciliary arteries. A venous blood flows on scleral and episkleralny veins.

The sensitive innervation of S. is carried out by branches trifacial (see), taking place in structure of ciliary nerves.

Histology

Microscopically in a sclera distinguish three layers: episclera (episkleralny plate, T.), scleral stroma (own substance of a sclera. T.) and brown plate (dark substance of a sclera, T.). Episclera — the periblast adjoining on the subject stroma, outside — with a tenonovy fascia and a conjunctiva. It is created by the fine randomly located collagenic fibers. Thickness of an episclera increases in the field of an attachment of direct muscles of an eyeglobe where the tenonova a fascia is interwoven into it. The episclera contains a large number of vessels. S.'s stroma is created by densely located collagenic fibers, sklerotsita and the main substance. Fibers C. have preferential circular course, but on certain sites the slanting and meridional arrangement is observed. Collagenic fibrilla has thickness from 30 to 220 nanometers and different frequency of cross striation. Sklerotsita have the long branching shoots contacting among themselves. The brown plate is the inner layer of S., adjacent to an idiovascular cover and a ciliary body, it consists of fine collagenic fibers, among to-rykh melanocytes and the pigmented macrophages are located.

Fibers C. (unlike fibers of a cornea) are characterized by a chaotic arrangement and low contents free glycoses-noglikanov that does S. opaque. Glikozaminoglikanovy structures are connected with collagenic fibrilla and create around them amorphous covers.

The physiology

S. protects internal covers of an eyeglobe from the damaging influences of the environment. Due to the intrascleral arrangement of drainage system and change of hydration of collagenic fibers C. takes part in outflow of intraocular liquid (watery moisture, T.). The form of an eyeglobe depends on S.'s condition and intraocular pressure. Intraocular pressure (see) promotes a dense prileganiye of a choroid and a retina to S., holds them in normal situation. Intraocular pressure creates a certain tightness of fibers C. Due to elasticity S. is capable to be reduced at reduction of volume of an eyeglobe and to stretch at its increase (see. Short-sightedness , Gidroftaljm ).

Methods of a research

apply To a research C. biomicroscopy of an eye (see), gonioskopiya (see), diafanoskopiya (see) and fluorescent methods of a research (see. Flyuorestseinovaya test ). The biomicroscopy allows to estimate a condition of an episclera of front department of an eyeglobe and its vessels, extent of pigmentation of Page. Define a condition of drainage system of an eye by a gonioskopiya. Fluorescent methods of a research are directed to clarification of a condition of outflow tracts of intraocular liquid. Diafanoskopiya eyes allows to reveal sites of an ectasia of a sclera.

Pathology

Distinguish anomalies of coloring of S. of the inborn and acquired character, damages and diseases of Page.

Anomalies of coloring. At small children of S. bluish that is connected with its small thickness causing raying of an idiovascular cover (horioidea) and a ciliary body. The symptom of blue scleras can be display of the hereditary disease which is transmitted on autosomal dominantly type, a cut in addition to blue coloring of S. is characterized by fragility of bones, dislocations and relative deafness (see. Wang-der-Huve syndrome ).

S.'s melanosis happens inborn or acquired (see. Melanosis ); focal or diffusion accumulation in surface layers of S. of melanocytes is the cornerstone of it. It can be combined with a melanosis of other covers of an eyeglobe.

At an ochronosis (see) 70% of patients have deposits of a pigment (oxidate homogentistic to - you) in S., a conjunctiva and in the field of a limb.

Damages. At a contusion of an eye subconjunctival ruptures of S. in places of its thinnings, most often in the field of a limb, and also under direct muscles of an eye and in the field of a trellised plate can be observed that dictates need of audit of these sites at stupid injuries of an eye. Perforated wounds of S. are followed by loss of internal covers of an eye and damage of a choroid, a retina and other tissues of an eye (see. Eye, damages ). At S.'s wound on edges of a wound put stitches; the extensive gaping deckle-edged wounds demand scleroplastic surgeries.

Diseases. Inflammatory processes in S. almost in half of cases arise at general diseases, a thicket collagenoses or tuberculosis (see. Sclerite ).

At the diseases which are followed by reduction of secretion of intraocular liquid and volume of an eyeglobe and also at a hypermetropia (see. Far-sightedness ) S.'s thickening is observed, a cut it is most expressed at an atrophy of an eyeglobe. Local stretching of S. as a result of an injury or the inflammatory process causing partial death of fibers C. can lead to formation of ectasia of S. and staphylomas (see), to-rye are sometimes observed also at short-sightedness of high degree.

Tumors Pages meet extremely seldom. From benign tumors are described fibroma, neurinoma (see), Ota's nevus (see. Nevus ). Treatment their operational. Forecast favorable.

Malignant tumors of S. develop for the second time, usually at germination in S. of tumors of a conjunctiva or intraocular tumors.

Operations

Surgeries on S. have, as a rule, character plastic (scleroplasty); apply them at short-sightedness for the purpose of strengthening of back department of S. and make by means of plastic materials. Scleroplastic surgeries were widely adopted at to amotio of a retina (see). Often operative measures on S. are a stage of operations on an eyeglobe. Sclerotomy (S.'s section) it is applied, e.g., at extraction cataracts (see), a scleroticectomy (excision of site C.) — at nek-ry antiglaukomatozny operations, napr, at sinusotomies (see). In some cases make excision of a disk C. — trepanation scleras (see).

See also Diaskleralny operations .



Bibliography: Avetisov E. S., Andreyeva L. D. Are also good l of an ova-Maslov of I. P. Electronic and microscopic studying of a sclera of an eye of the person in different age groups, Vestn. oftalm., No. 1, page 24, 1979; Arkhangelsk V. N. Eye diseases, e. 187, M., 1969; Belyaev V. S. A scleroplasty in treatment of the progressing short-sightedness, M., 1977; Kovalyov-with to and y E. I. Eye diseases, page 22, M., 1980; About x r and m e N to about V. E. Effektivnost of a scleroplasty at some diseases of eyes, Oftalm. zhurn., No. 4, page 209,1981; Hogan M. J., Alvarado J. A. a. Weddell J. E. Histology of the human eye, Philadelphia, 1971.


G. G. Ziangirova.

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