Methods of diagnosing glaucoma

Early detection of glaucoma is very important, as successful treatment is possible at the very beginning of the disease. Changes in the early stages of the disease are sometimes difficult to distinguish from normal variants that do not pose a threat. When diagnosing glaucoma, a symptom complex of five leading symptoms is taken into account, such as:

1. difficulty and deterioration of moisture outflow;
2. instability of intraocular pressure (daily fluctuations are normally no more than 5 mm Hg; they are detected during loading and unloading tests using elastotonometry);
3. increased intraocular pressure;
4. glaucomatous excavation;
5. decreased visual function.

For a long time, a patient with glaucoma may not notice any changes in vision, but during the initial examination by an ophthalmologist, significant changes are already detected. And in rare cases, an acute attack of glaucoma forces the patient to go directly to the clinic, when with a sudden increase in intraocular pressure, headaches, nausea, vomiting, visual impairment, redness of the eyes appear,

It is recommended that every person undergo an examination by an ophthalmologist when problems with vision arise or any symptoms from the eyes (pain inside or redness of the eyes, double vision) appear. The first examination by an ophthalmologist should be carried out at the age of 40, when, as a rule, most people have problems with vision when reading and need glasses. However, if certain symptoms appear or there are patients with glaucoma in the family, as well as other risk factors listed above, an eye examination is recommended earlier.

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Ophthalmological examination

Currently, there are all modern technologies that allow for painless, safe methods to conduct an eye examination of a patient.

First, visual acuity, the level of necessary optical correction and potential susceptibility of the eye are checked using tables and various objects. V of healthy people is designated 1.0 (100%). If vision is impaired, it is necessary to find the cause. With glaucoma, visual acuity may not suffer for a long time. But if a patient with glaucoma has other eye diseases (for example, cataract), then vision is reduced.

After determining visual acuity, a slit lamp examination is performed.

A slit lamp is a special ophthalmological microscope that is equipped with a light source. The slit lamp rotates so that the eye and its internal areas can be examined from different angles. Usually, the light beam is shaped like a slit, so the eye can be examined layer by layer, i.e. in "optical sections". The fundus and posterior sections of the eye are examined with a slit lamp equipped with a strong convex lens. To examine the posterior section of the eye, the pupil is dilated (a few drops of mydriatic are instilled into the eye). After 15-20 minutes, when the pupil is sufficiently dilated, the examination is carried out.

Measuring intraocular pressure - tonometry - is described in detail above. The normal level of true intraocular pressure varies from 9 to 21 mm Hg, the standards for a 10 g Maklakov tonometer are from 17 to 26 mm Hg, and for a 5 g tonometer - from 11 to 21 mm Hg.

After a steady increase in intraocular pressure, visual function begins to deteriorate, but there may be glaucoma with normal or low pressure. Non-contact devices are used to measure intraocular pressure, which use a stream of air to flatten the cornea. An optical sensor records when and how quickly the cornea has changed its curvature to a given degree. The device then converts the amount of time required for flattening into millimeters of mercury. This method does not require local anesthesia. However, this study is not as accurate. If the data obtained by non-contact means are in doubt, they should be rechecked by a contact method of examination.

Anterior chamber angle examination

The anterior chamber angle is the narrowest part of the anterior chamber. The anterior wall of the anterior chamber angle is formed by Schwalbet's ring, the TA and the scleral spur, the posterior wall is formed by the root of the iris, and the apex is formed by the base of the ciliary crown. Wide angle (40-45°) - all structures of the anterior chamber angle are visible (IV), medium-wide (25-35°) - only a part of the apex of the angle is determined (III), narrow (15-20°) - the ciliary body and scleral spur are not visible (II), slit-like (5-10°) - only a part of the TA is determined (I), closed - the structures of the anterior chamber angle are not visible (0).

The pigment is deposited in the angle of the anterior chamber by the breakdown of cells of the pigment epithelium of the iris and ciliary body.

The examination of the anterior chamber angle is called gonioscopy. It is examined to determine the causes of increased intraocular pressure or when there is concern that the angle may close and cause an acute attack of glaucoma. Since the periphery of the cornea is opaque, the anterior chamber angle is examined during gonioscopy using a special gonioscopic lens that is in contact with the eye. After instillation of a local anesthetic, gonios, a conical lens is placed on the eye, and a whole system of mirrors inside the gonioscopic lens is used for examination. With this technique, the chamber angle is examined for the presence of a substance that should not be there (pigment, blood, or cellular material), which is a sign of inflammation. It is also necessary to check for adhesions in any part of the iris. By assessing the width of the angle, it is possible to predict the threat of angle closure and determine the presence of congenital anomalies inside the anterior chamber angle.

Examination of the optic disc

The intraocular part of the optic nerve is called the head or disc, which is a section of the nerve 1-3 mm long. The blood supply to the disc depends to some extent on the level of intraocular pressure. The optic disc consists of axons of the retinal ganglion cells, astroglia, blood vessels and connective tissue. The number of nerve fibers in the optic nerve varies from 700,000 to 1,200,000, and it gradually decreases with age. The optic disc is divided into four sections: superficial (retinal), prelaminar, laminar and retrolaminar. In the laminar section, connective tissue is added to the nerve fibers and astroglia, which forms the cribriform plate of the sclera, consisting of several perforated sheets of connective tissue separated by astroglial layers. The perforations form 200-400 canals, through each of which a bundle of nerve fibers passes. When intraocular pressure increases, the upper and lower segments of the cribriform plate, which are thinner and the openings in them are wider, are more easily deformed.

The diameter of the optic nerve disc is 1.2-2 mm, and its area is 1.1-3.4 mm ². The size of the optic nerve disc depends on the size of the scleral canal. With myopia, the canal is wider, with hyperopia, it is narrower. In the optic nerve disc, a neural (neuroretinal) ring and a central depression are distinguished - a physiological excavation in which the fibroglial strand is located, containing the central vessels of the retina.

The blood supply to the optic nerve head is segmental, due to the existence of zones of division of the vascular network. The blood supply to the prelaminar and laminar sections of the optic nerve head is carried out from the branches of the posterior short ciliary arteries, and the regional section is supplied from the system of the central retinal artery. The dependence of blood flow on intraocular pressure in the retrolaminar section of the optic nerve head is due to the existence of recurrent arterial branches coming from the intraocular part of the optic nerve head.

Examination of the optic disc is the most important part of glaucoma diagnostics. First, the size of the optic disc is assessed - a large disc has a more pronounced physiological excavation than a small one, but this is not a sign of the disease. The shape of the excavation is assessed. Its shape determines whether the excavation is congenital or has developed as a result of a pathological process.

Atrophy around the optic disc indicates glaucoma, although it can also be observed in other diseases and even in normal conditions.

Glaucomatous excavation, atrophy, develops as a result of prolonged elevated intraocular pressure. Obstruction of blood flow leads to depression of the cribriform plate, displacement and compression of the optic nerve fibers occur, plasma flow through the perineural spaces is disrupted, chronic ischemia of the optic nerve develops, which leads to glial atrophy.

Glaucomatous excavation is vertical-oval, there is a bend in the vessels at the edge of the optic nerve, the excavation expands in all directions, but still more in the lower or upper temporal directions. The edges of the excavation can be steep, undermined or gently sloping (saucer-shaped excavation).

In glaucoma, these changes can be observed dynamically.

At the initial stage, the vascular bundle shifts to the nasal side, then the optic disc begins to atrophy, its color changes, the number of vessels falling on the optic disc decreases. A small hemorrhage in the neuroretinal ring of the optic disc is almost always a sign of glaucoma. Hemorrhages on the disc are specific signs of developing glaucomatous damage. Local narrowing of the retinal vessels is another sign of glaucoma, but they can also be observed with other disc damage. If the vessel bends sharply when crossing the edge of the excavation, this gives even more grounds to suspect its glaucomatous nature.

Simultaneously with the atrophy of the optic nerve, visual functions are impaired. These disorders are initially transient, unnoticeable to the patient and slowly progressing, they are detected only after the loss of 30% or more of the nerve fibers in the optic nerve disk. The impairment of visual functions is expressed in a change in the field of vision, tempo adaptation, an increase in the threshold of the critical frequency of flickering, a decrease in vision and color perception.

The examination of visual fields is called perimetry, and the state of the entire visual field or its central section within 25-30 from the point of fixation of the gaze is assessed. When examining the visual field of a glaucoma patient, the following changes are found:

1. an increase in the blind spot, the appearance of paracentral scotomas in the area located 10-20 from the point of fixation of the gaze. They can be transient. Measuring the boundaries of the blind spot is important in load tests. On an empty stomach, the blind spot is measured using a water-drinking test: in the morning on an empty stomach, you need to quickly drink 200 g of water, the examination should be done after 30 minutes. If the blind spot increases by 5 arcs, the test is considered positive;
2. peripheral visual field begins to suffer from the superonasal quadrant;
3. the field of view is concentrically narrowed;
4. light perception with incorrect light projection;
5. Initial changes in the visual field are reversible.

The average duration of glaucoma is about 7 years (without treatment, serious complications and blindness occur).