From Big Medical Encyclopedia

INTRAOCULAR PRESSURE (synonym: intraocular tension, tenziya of an eye) — pressure put by contents of an eyeglobe upon its outside cover. In the capsule of an eye having a certain rigidity at its stretching there are opposite directed elastic forces as a result of which interaction EL is established at this or that level. As rigidity of the capsule depends from very slow changing in time fiziol, characteristics of a cornea and sclera, relative constancy of EL and its fluctuation are connected by hl. obr. with education and outflow of watery moisture (see. Hydrodynamics of an eye ). Circulation of watery moisture in turn depends from hemodynamics of an eye (see), and also from exchange, nervous and other factors. Influence of arterial pressure upon level and regulation of EL is insignificant. Arterial hypertension does not lead to increase in EL. Pressure of blood in vascular system of an eye is completely counterbalanced with a tone of walls of vessels and EL. Only bystry fluctuations of arterial pressure which are followed by changes of a krovenapolneniye of vascular network of an eye can affect the level of EL. So, in particular, there is volume pulse of an eye, synchronous with a pulsation of carotid arteries, registered by an oftalmopletizmograf. Amplitude of fluctuations of EL reaches a maximum if its level is equal to diastolic pressure in arteries of internal covers of an eye; at the same time the volume pulsation of intraocular vessels causing eye pulse, the greatest (see. Oftalmopletizmografiya ). Slowly developing changes of volume of a vascular bed easily are compensated by strengthening of outflow of liquid from an anterior chamber.

Influence of venous pressure on the level of EL is more noticeable. Build-up of pressure in episkleralny veins complicates outflow of chamber moisture through spaces of an angle of iris and a venous sine of a sclera. The prelum of veins of a neck leads to the expressed raising of EL.

True 16,2 mm of mercury are on average equal to EL at healthy people. with extreme options 9,6 — 22,6 mm of mercury. Level of EL is normal identical on both eyes and does not depend on a floor.

The daily fluctuations which are closely connected with a rhythm of exchange processes, change of a tone of the autonomic nervous system, function of closed glands and also with changes of a hemodynamics and hydrodynamics in an eye are characteristic of EL at a postural change of a body. Normal higher EL is more often noted early in the morning; during the day it gradually decreases by 1 — 5 mm of mercury. Relative constancy of EL provides optimal conditions for implementation of a metabolism in tissues of an eye, especially in the crystalline lens and a vitreous which do not have own vessels and nerves. Raised by EL worsens blood supply of internal covers (see. Glaucoma ), persistent hypotonia conducts to an atrophy of an eyeglobe (see. Eye , pathology). A certain rate of strain of the capsule is necessary also for performance by an eyeglobe of optical functions. Deviations of EL from datum level cause a number of changes in optical system of an eye, up to ruptures of a descemete membrane and hypostasis of a cornea (at hypertensia), emergence of folds of a descemete membrane (at hypotension). About the level of EL judge by rate of strain of covers, a tone of an eyeglobe (see. Tonografiya , Tonometriya ). Approximately EL is defined by a palpation of an eyeglobe by eyelids. Tool measurement of EL is performed by means of tonometers of applanation or impression type (see. Tonometriya , devices for measurement of intraocular pressure).

Bibliography Bunin A. Ya. Hemodynamics of an eye and methods of its research, M., 1971; Zayko H. N and Mintz of G. M. Intraocular pressure and its regulation, Kiev, 1966; Merkulov I. I. Introduction to clinical ophthalmology, page 95, Kharkiv, 1964; Nesterov A. P. Hydrodynamics of an eye, M., 1968; Nesterov A. P. and M. B Burgaft. Gage tables for Filatov's elastotono-meter — Kalfa, Vestn, oftalm., No. 2, page 20, 1972; Nesterov A. P., Bunin A. Ya. and Katsnelson L. A. Intraocular pressure (physiology and pathology), M., 1974; Romanovsky M. M. Intraocular pressure and its regulation, Mnogotomn, the management on glazn, Bol., under the editorship of V. N. Arkhangelsky, t. 1, book 1, page 328, M., 1962; Sheva-l e in A. E. Functional condition of the highest departments of the central nervous system and intraocular pressure, Uchen. zap. Ukrainians. in-that glazn, Bol., t. 3, page 187, Kiev, 1955; Becker B. Diagnosis and therapy of the glaucomas, St. Louis, 1970; Sugar H. S. The glaucomas, N. Y., 1957; Wei ter J. J., Schachar R.A. Ernest J. T. Control of intraocular blood flow, Invest. Ophthal., v. 12, p. 327, 1973, bibliogr.

M. S. Remizov.