TONOMETRYYa (Greek tonos tension + metreo to measure, measure) — measurement of intraocular pressure, to-rogo is the cornerstone definition of ability of eyeglobes to deformation.
T. apply hl. obr. at glaucoma (see), and also at other diseases of eyes (an inflammation of internal covers of an eye, amotio of a retina, etc.), at to-rykh the size of intraocular pressure (see) is an important indicator of a condition of an eye and dynamics of disease. The USSR manufactures a tonometriya to all persons 40 years, seeing the oculist are more senior (in the absence of contraindications).
Methods T. are based on measurement of deformation of an eyeglobe with a pressure upon it from the outside; the more the size of deformation under the influence of the same force, the less intraocular pressure, and vice versa.
Historically the earliest and not lost value in a crust, time is a method of approximate (manual) determination of intraocular pressure. At the same time investigating slightly presses on an eyeglobe of the patient the index fingers imposed on an upper eyelid under edge of an eye-socket; the patient is asked to watch down, without squeezing a century (fig. 1). Results of a research express by means of the following symbols: Tn — the standard intraocular pressure, T - f 1 — intraocular pressure is slightly increased, T + 2 —
the expressed increase in intraocular pressure, T + 3 — its sharp increase (an eye is firm as a stone); By t — 1 — intraocular pressure is slightly lowered, T — 2 — expressed with and an izheniye vn mornings of N of of l and zn oho pressure, T — 3 — falloff of intraocular pressure.
Emergence in the second half 19 — the beginning of 20 century of devices for measurement of intraocular pressure (see Tonometers in oftalmolo-
Fig. 1. Approximate (manual) determination of intraocular pressure: investigating index fingers slightly presses on an eyeglobe through an upper eyelid.
Giya) allowed to increase the accuracy of the results received at the same time sharply. Then also two main methods T were defined. — apilanatsion-ny and impression, corresponding to a type of the deformation of an eyeglobe made by a working part of a tonometer. At applanation T. the working part of a tonometer contacting to an eye has an appearance of the plane (fig. 2, I), at impressioniy — the wall of an eye is exposed to impression (fig. 2, b).
The Applaiatsnonny tonometriya is offered in 1884 by A. N. Maklako-vy. The basic advantage of this method is the minimum influence of specific features of elasticity of covers of an eyeglobe on results of measurement.
Fig. 2. Diagrammatic representation of the principles of an applanation and impression tonometriya: 1 — the working part of a tonometer contacting to a cornea; 2 — a cornea; 3 — an eyeglobe.
For impression T. most often apply Shyotts's tonometer. It is less exact, than Maklakov's tonometer, but use of it in clinic is simpler.
In sovr. ophthalmology the same tonometers or their usover use
shenstvovanny options. Essential improvement of a method of applanation T. the tonometriya on Goldmanna was, at a cut the tonometer fastens on a usual slit lamp (see). At the same time the surface of an eye is deformed with very small force the transparent cylinder, and the size of the flexing area is measured under a microscope. Also methods T are known. using electronic and pneumatic tonometers applanation or impress ionic type. In recent years there were contactless tonometers allowing to measure intraocular pressure but abilities of an eye to be exposed to deformation under pressure of a current of air on it. The dignity of the last — lack of mechanical contact with a cornea of an eye and need for carrying out local anesthesia.
In 1980 M. M. Krasnov, it is offered so-called konveks-tonomet-riya, having common features from applanation T. Sushchnost of this method is that a cornea
of Fig. 3. Carrying out an applanation tonometriya by means of Maklakov's tonometer.
the studied eye it is deformed by a tonometer on the convex sphere, radius a cut almost corresponds to curvature of a cornea. At the same time it is possible to avoid an essential lack of an applanation method T. — movings of a stroma of a cornea to the periphery at its deformation.
As a rule, T. make on a cornea of the studied eye. When it is impossible, napr, at extensive cataracts of a cornea, nek-ry tonometers allow to perform measurements on a sclera (sklerotonometriya), however the accuracy of measurement in these cases is much lower, in particular because of individual distinctions in elasticity of a sclera. At all types of contact T. use surface anesthesia of a front surface of an eye by means of mestnoanesteziruyushchy means, e.g. 0,5% of solution of Dicainum.
During the carrying out applanation T. across Maklakov a tonometer, with nane-
Senna on its basis paint, napr, kollargolovy, lower on the center of a cornea (see) the studied eye on 1 sec. and quickly remove by means of the handle, a shaped loop (fig. 3). The received print is transferred to the paper moistened with alcohol. By means of a special ruler izkhmeryat diameter of a print with an accuracy of 0,1 mm.
Position of the patient at T. can be both vertical, and horizontal, usually it depends on a type of the used equipment. At the same time the difference between sizes of intraocular pressure on the same eye at vertical and horizontal position of the patient can have essential a wedge, value and is the cornerstone of ortoklino-static tonometric test.
T. in combination with other influences approximately, napr, with introduction to a conjunctival sac of pharmaceuticals, makes contents various tonometricheskpkh tests. Many of these tests apply to provoke narrowing of a corner of an anterior chamber of an eye and to cause increase in intraocular pressure. To any way T. nek-ry errors since force deforming an eyeglobe from the outside is resisted not only by the intraocular pressure, but also elasticity of its walls are inherent, varies edges in considerable limits. At a deforkhmation of an eyeglobe pressure in his cavity increases a little, i.e. during T. not true, but so-called tonometric intraocular pressure, a cut always above true is measured.
A contraindication to T. are disturbance of an integrity of an epithelium of a cornea, and also inf. diseases of front department of an eye or conjunctiva (erosion and helcomas, keratitis, conjunctivitis, etc.). Allergic reaction to mestnoanesteziruyushchy means can be a relative contraindication.
T., as a rule, does not lead to any complications, it is very rare at patol. changes of a cornea in senile age or in connection with hypersensitivity to anesthetic there can be erosion of a cornea.
See also Tonometers.
Bibliogrglazny diseases, under the editorship of T. I. Broshevsky and A. A. Bochkaryova, page 44, M., 1977; Krasnov M. M. New principle of measurement of intraocular pressure (konveks-tonometriya and konveks-tonografiya), Vestn. oftalm., No. 1, page 53, 1981; Nesterov A. P., Bunin A. Ya. and To and c of N e l with about L. A N. Intraocular pressure, M., 1974; Adler F. N of Adler's physiology of the eye, clinical application, St Louis, 1975.
M. M. Krasnov.