From Big Medical Encyclopedia

CONTACT LENSES — the lenses which are put on directly a cornea or a sclera for the purpose of optical correction of sight and treatment of some diseases of eyes and also for cover of defects of a front piece of an eyeglobe.

For the first time To. l. were made almost at the same time in 1887 in Switzerland by Fick (And. Fick), in France Kaltom (E. Kalt), in Germany F. Miiller, and in clinic To. l. are used since 1920.

Fig. 1. The scheme of a path of rays in an eye at the wrong astigmatism: 1 — without lens (beams are not focused on a retina); 2 — with a corneal and scleral contact lens (beams agree on a retina).

To. l. have a number of advantages before usual ocular glasses: they more increase visual acuity, correct aberrations better (see. Aberration of an eye ), since make uniform optical system together with an eye and at change of the direction of a look move together with an eye. These lenses reduce or eliminate aniseikonia (see) since are closer located to the front main plane of optical system of an eye that promotes recovery of solid vision. They are more perfect in the esthetic relation and are not visible on an eye. To. l. put on directly a cornea or a sclera; owing to capillary tension they stick to them and are kept by centuries. Usually To. l. have a spherical front surface and index of refraction, almost identical with a cornea and the lacrimal liquid. It promotes correction of irregular shape of a cornea, the set optical power of a lens korrigirut anomalies of a refraction (fig. 1).

There are two main types To. l. — rigid and soft which can be corneal and scleral. Rigid To. l. make of polymethyl methacrylate, and soft — of hydrocolloid or silicone material. Soft To. l., unlike rigid, are more elastic, do not interfere with exchange processes in a cornea, do not demand long adaptation and therefore are more perspective.

Fig. 2. The diagrammatic representation of a corneal contact lens (at the left) and a path of rays in an eye at its use (on the right).
Fig. 3. The diagrammatic representation of a scleral lens (at the left) and a path of rays in an eye at its use (on the right).

Corneal To. l. represent optically the operating meniscuses (fig. 2). Scleral To. l. have the optical part located before a cornea, and basic, gaptichesky, a part, adjacent to a sclera (fig. 3).

To. h.p. are shown by the purpose of correction of sight at high short-sightedness, the expressed astigmatism, a keratoconus, an aphakia and a heterometropia. They are applied at some diseases of a cornea of inflammatory, dystrophic and traumatic character (e.g., at a violent keratopathy), and also to prolongation of effect of some medicinal substances. To. l. appoint also to people of such professions (to actors, athletes, divers, etc.) at which carrying usual eyeglass lenses is undesirable or complicated by working conditions. (At an aniridiya, colobomas of an iris, a leucoma, an inoperable cataract) are applied to masking of defects of front department of an eyeglobe To. l., the imitating pupils, an iris. At some diagnostic methods (an elektroretinografiya, a X-ray analysis of an orbit) for protection of eyes during a roentgenotherapy special types K are used. l.

Contraindication for contact correction conjunctivas, blepharites, dacryocystites, allergic diseases of skin a century and conjunctivas, noncompensated glaucoma are acute and hron.

To. l. it is possible to carry in a row 4 — 16 hours a day depending on individual portability. At long carrying To. l. the irritation of front department of an eye is possible.

To. l. are stored in special plastic cases and will be sterilized by boiling or processing by chemical substances.

Bibliography: Kivayev A. A., etc. Modern methods of inspection and correction of the patients needing contact lenses on medical indications in book: Probl, wedge, oftalm., under the editorship of G. A. Ul-danov, page 23 6, Alma-Ata, 1977; Krasnov M. M., Kasparov A. A. and Ogane-s I am N of c of V. A. Experience of use of soft contact lenses at various diseases of a cornea, Vestn, oftalm., No. 6, page 38, 1975; Orlova E. M and White stotskiye. M. Contact lenses, M., 1961, bibliogr.; In i e of N. a. Lowther G. E. Contact lens correction, L., 1977; Mandell R. B. Contact lens practice, Springfield, 1974; Ruben M. Contact lens practice, L., 1975.

A. A. Kivayev.