LECTURE No. 5. Methodology for examining the condition of the eye (part III)

1. Gonioscopy

Gonioscopy (from Latin gonia "angle") is a special method for examining the angle of the anterior chamber. It can only be carried out with the help of optical gonioscopes. The study of the chamber angle is of great importance for the diagnosis, therapy and prognosis of a number of diseases (glaucoma, uveitis, injuries, etc.). The most important outflow pathway for intraocular fluid begins at the camera angle. The angle can be narrowed, obliterated, foreign bodies, a germinating tumor can be found in it.

A gonioscope is a tetrahedral glass prism or pyramid with mirrored inner surfaces. The front part of the device is intended for contact with the cornea and has a corresponding curvature. A reflecting mirror stands in the path of the rays emerging from the chamber angle in such a way that the opposite angle is visible in it.

Before the examination, drip anesthesia of the eye is performed with a 0,5% solution of dicaine or a 1% solution of lidocaine. The subject is seated in front of a slit lamp and his head is fixed on a facial rig. The combined focuses of the illuminator and microscope are aimed at the cornea. The gonioscope is inserted into the conjunctival cavity, the researcher holds its body with his left hand. An approximate examination of the angle is usually carried out in diffuse light; for long-term gonioscopy, a slit diaphragm is used. In the corner of the anterior chamber one can see Schlemm's canal, corneoscleral trabeculae, and ciliary body.

2. Tonometry

This is a method for measuring intraocular pressure. The study is necessary in all cases when the thought arises that a patient has glaucoma, secondary hypertension of the eye or its hypotension, with various general and local diseases.

Approximate pressure in the eye can be determined by palpation. In this case, it is necessary that the patient looks down, and the researcher, with index fingers located above the level of the cartilage, presses in turn through the upper eyelid (when looking up through the lower) on the eyeball (similar to the study of abscess fluctuation). When analyzing pressure, it is necessary to compare its value in one and the other eye.

If the ophthalmotonus is within the normal range, it is designated as TN if its value is 2835 mm Hg. Art. T + 1, more than 36 mm T + 2, if hypotension of the order of 1522 mm Hg is detected. Art. T 1, less than 12 mm Hg. Art. T 2.

For the quantitative determination of ophthalmotonus in Russia, the Maklakov tonometer is most widely used. It is a cylinder weighing 10 g with a base made of matte porcelain plates. Before measuring intraocular pressure, the plates are wiped with cotton wool moistened with alcohol and smeared with a thin layer of paint (collargol, methylene blue). Intraocular pressure is measured in a horizontal position, asking the patient to look at the ceiling or his own finger. The cylinder, held by a special holder, is placed on the center of the cornea, previously anesthetized with a 0,5% solution of dicaine (or 1% solution of lidocaine) (35 minutes after anesthesia). By lowering the holder to approximately 1/3 of the cylinder (in one touch), the weight is allowed to flatten the cornea. The imprint of the flattening circle obtained on the plate is printed on paper slightly moistened with alcohol. Using a special ruler, the diameter of the circle is used to determine the intraocular pressure in millimeters of mercury.

The numbers of tonometric pressure (1116 mm Hg) are always higher than the true ones (1826 mm Hg), since the tonometer increases the intraocular pressure at the time of measurement.

There are other types of tonometers (for example, Dashevsky), indicators of intraocular pressure during mass examinations.

Using tonometers of different weights (5; 7,5; 10 and 15 g) in ascending order, it is possible to determine the reaction of the eye membranes to different weights. The results of these four measurements can be represented as an ascending elastotonometric curve.

3. Tonography

This is a method for studying the hydrodynamics of the eye. It allows you to determine the state of the outflow of intraocular fluid and is used mainly in the examination of patients with glaucoma or if it is suspected. During tonography, the tonometer is placed on the cornea of ​​the examined eye and kept on it for 35 minutes. As a result of compression, an increase in ophthalmotonus occurs, the outflow of fluid from the eye increases, which leads to a gradual decrease in intraocular pressure. The degree of reduction is different in healthy individuals and in patients with glaucoma, which is reflected in the nature of the tonographic curve. Graphic registration of changes in ophthalmotonus becomes possible due to the connection of a recording device. The data is recorded on a moving paper tape.

The degree of reduction in intraocular pressure during tonography depends on the volume of aqueous humor displaced from the eye, which in turn is associated with the state of the outflow tract. According to the obtained data, using special tables and formulas, it is possible to determine the outflow ease coefficient, which quantitatively characterizes the function of the drainage system of the eye. The outflow easiness coefficient is an important indicator in the diagnosis of glaucoma. A decrease in its value, even with a normal level of ophthalmotonus, may indicate the presence of glaucoma. Tonographic studies are useful for monitoring the effectiveness of medical and surgical treatment of glaucoma.

4. Echoophthalography

To study the optical system of the eye, to measure the anteroposterior and other dimensions, the method of ultrasonic echo-ophthalography is used. It consists in the registration of ultrasonic signals reflected from the interfaces between the media and tissues of the eye with different acoustic properties.

Research is carried out using a diagnostic echoophthalograph device. Before the examination, 0,25% dicaine or 1% lidocaine and sterile petroleum jelly are instilled into the eye, serving as a contact medium between the eye and the device sensor. The sensor is first placed on the cornea. When in contact with the sclera, it is sequentially placed on various meridians, thereby achieving ultrasound probing of all parts of the eyeball. Reflected ultrasonic vibrations are recorded on the screen in the form of echo signals.

With corneal abduction, the anterior wave is determined on the echogram, corresponding to the reflection of ultrasound from the cornea, the second and third waves correspond to reflections from the anterior and posterior surfaces of the lens. The vitreous body is acoustically homogeneous and does not show teeth on the echogram.

The posterior complex of teeth corresponds to the reflection of ultrasound from the fundus and retrobulbar tissues.

Ultrasound examination is also used to detect foreign bodies in the eye, for the purpose of diagnosing retinal detachments, tumors, etc., especially in cases where examination of the fundus is impossible due to clouding of the transparent media.

5. Exophthalmometry

If a patient has exophthalmos or enophthalmos (protrusion or retraction of the eyeball), special devices are used to quantify them and judge the dynamics of the process (orbital tumors, retrobulbar hematoma, orbital bone fractures, etc.). The most common mirror exophthalmometer.

It consists of two frames moving along the rod on a sled. The latter are equipped with mirrors intersecting and placed at an angle of 45° to the visual axis of the eye and with a millimeter scale. There are recesses on the edges of the frames, which, during the study, are attached to the outer walls of the orbit of a sick child. The patient should look straight ahead. The top of the cornea is reflected in the mirror of the exophthalmometer; on the millimeter scale of the ruler, one can see the distance between the center of the cornea and the edge of the orbit. This figure indicates the protrusion of the eye. The degree of protrusion of each eye is alternately determined.

Author: Shilnikov L.V.

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