Causes and risk factors for the development of glaucoma

If we summarize the causal factors of glaucoma development, we can form the following picture: dysfunction of the hypothalamus leads to endocrine and metabolic disorders, which in turn cause local disorders. Hereditary glaucoma is associated with dysfunction of the hypothalamus, endocrine and metabolic disorders. Hereditary factors determine anatomical predisposition, disorders of hydrostatics and hydrodynamics, which causes an increase in intraocular pressure.

Theories of Glaucoma Development

The first period (late 19th - early 20th centuries) - the theory of retention, i.e. delay in the outflow of intraocular fluid from the eye. Increased intraocular pressure was explained by the development of goniosynechiae, pigmentation of the angle of the anterior chamber. The information was obtained in the study of enucleated eyes (blind people with absolute glaucoma). Other factors (nervous, vascular, endocrine) were ignored. But it turned out that pigmentation of goniosynechiae does not always lead to glaucoma.

The second period (1920-1950s) is neurohumoral, characterized by the study of various aspects of the life of patients with glaucoma, i.e. the state of the nervous and endocrine systems. Local, mechanical and vascular factors were ignored.

The third period (since the 1950s) is a synthetic approach that takes into account general and local mechanisms of increased intraocular pressure, based on new data: the role of heredity in the transmission of glaucoma, the phenomenon of steroid glaucoma, the immediate causes of increased intraocular pressure (histological, histochemical, tonographic, etc.), the pathogenesis of glaucomatous optic nerve atrophy.

1. Heredity. Genetic predisposition to primary glaucoma exists (at least two genes have been found that contribute to the development of this disease). It has been established that not only one gene is responsible for the development of glaucoma. There are several genes that, if pathological changes are present in them, lead to the disease. The disease, in addition, manifests itself only with other external factors affecting the body, or if mutations are present in several genes at the same time. In cases where glaucoma is quite common in a family, heredity should be considered an important risk factor. It is also important that family members, living together, are exposed to the same environmental factors. And this parade with genetic predisposition plays a significant role in the development of glaucoma. The "steroid test" - an increase in intraocular pressure on the introduction of steroids - complements the genetic predisposition. Predisposition to glaucoma is transmitted by a dominant type. Isomeric tribes do not have glaucoma; in Normandy, Sweden, and Denmark, glaucoma occurs in 2-3% of the population.
2. Neurogenic theory - a violation of the interaction of inhibitory processes of the cortex and subcortex, the balance of excitability of the sympathetic and parasympathetic systems.
3. Violation of the hemodynamics of the eye - the anterior and posterior segments. With age, the pulse pressure of the blood decreases, the peripheral volume of circulating blood decreases, which leads to a decrease in the volume of blood flowing through the uveal tract, the anterior part of the eye. This causes dystrophic phenomena in the trabecula, ciliary body, which leads to a change in intraocular pressure and a decrease in visual function.

S. N. Fedorov, developing the hemodynamic theory, proposed to consider that glaucoma is an ischemic disease of the eye and has three stages, such as:

1. anterior segment ischemia;
2. increased intraocular pressure;
3. ischemia of the optic nerve with increased intraocular pressure.

N. V. Volkov suggested that the ratio of intracranial, intraocular and arterial pressure is the leading factor in the genesis of glaucoma. The normal ratio of intraocular and intracranial pressure is disrupted. Normally, this ratio; if there is an increase of 3: 1, then this leads to the development of glaucomatous atrophy of the optic nerve.

Pathogenesis of primary glaucoma according to A.P. Nesterov

1. Age-related dystrophic and functional disorders in an anatomically predisposed eye.
2. Hydrostatic shifts are changes in the normal ratio of intraocular pressure in various closed and semi-closed systems of the eye (1/4-1/3 of the intraocular fluid swells along the posterior pathway).
3. Functional unit of the eye drainage system.
4. Violation of the hydrodynamics of the eye.
5. Increased intraocular pressure, secondary vascular degenerative changes in the anterior and posterior segments of the eye.
6. Organic block of the drainage system of the eye with atrophy of the optic nerve and loss of visual functions.

Secondary changes in the eye lead to an increase in intraocular pressure, which in turn causes secondary changes.

Patients with diabetes mellitus are three times more likely to have glaucoma. 35% of patients with glaucoma have protein metabolism disorders and hypercholesterolemia.

Dystrophic changes. Degeneration of connective tissue leads to fragmented disintegration of connective tissue substances in vessels, trabeculae. Dystrophy of the endothelium leads to its proliferation and sclerosis of the trabeculae, resulting in obliteration of the collectors. Disintegration of collagen fibers leads to the trabeculae losing their tone and being pressed into the Schlemm's canal area, the coefficient of ease of fluid outflow C decreases almost 2 times, then the outflow almost stops, secretion is secondarily disrupted.

In the initial stages of glaucoma, the coefficient C decreases to 0.13, in the developed stage of glaucoma - to 0.07, in the terminal stage - to 0.04 and less.

Blocks of hydrostatic and hydrodynamic systems according to A.P. Nesterov and their causes

1. Superficial scleral block. Cause: compression and fusion of episcleral venous vessels.
2. Block of Schlemm's canal graduates. Reason: the inner walls of the Schlemm's canal close the mouths of the collector canals.
3. Blockage of Schlemm's canal. Cause: the inner wall of Schlemm's canal shifts and blocks its lumen, collapse of Schlemm's canal occurs.
4. Trabecular meshwork block. Cause: compression of trabecular gaps, discharge of exfoliative blood pigments. inflammatory and dystrophic changes,
5. Anterior chamber angle block. Cause: anterior displacement of the corneal root, development of goniosynechiae in congenital glaucoma - defects of embryonic development.
6. Lens block. Cause: displacement of the lens towards the anterior chamber, the ciliary body touches the lens, directing it into the vitreous cavity.
7. Posterior vitreous block. Cause: intraocular fluid accumulates in the vitreous body, causing it to move forward.
8. Pupillary block can be relative and absolute. Cause: tight adhesion and adhesion of the cornea to the anterior capsule of the lens - pupillary occlusion.

Risk factors for developing glaucoma

Age plays an important role, especially in primary glaucoma. The age group most often includes patients over 40 years old. With age, an increase in intraocular pressure is observed even in healthy eyes, since the aging process occurs in the trabecular network. During this period, the production of aqueous humor also decreases, so intraocular pressure increases moderately. Intraocular pressure in most patients with glaucoma begins to increase between 40 and 50 years of age, sometimes at a later period.

Gender. Women are more likely to suffer from closed-angle glaucoma, while men are more likely to suffer from pigmentary glaucoma. Women are more likely to have normal-tension glaucoma, although their optic disc is more sensitive to intraocular pressure.

Race. Patients of African descent often have higher intraocular pressure. They have elevated intraocular pressure at an earlier age. Pigmentary glaucoma is most common in people with fair skin. Closed-angle glaucoma is typical for Asia; the Japanese often have glaucoma with normal pressure. People of Caucasian descent living in Northern European countries are most susceptible to the development of pseudoexfoliative glaucoma.

Heredity. The fact of hereditary predisposition to glaucoma has been known for a long time. However, this does not mean that a child whose parents suffer from glaucoma will necessarily develop this disease. Glaucoma can appear spontaneously and without a family predisposition to this disease. Congenital, childhood and juvenile glaucoma are more often hereditary, but spontaneous cases of glaucoma are also observed in this category of patients. However, genetic predisposition to the development of high intraocular pressure and the risk of developing glaucoma sometimes even with normal intraocular pressure are not denied and are of great importance.

Atherosclerosis is one of the major health problems in modern society. The blood vessels of the eye, like any other vessels, can suffer from atherosclerosis. With atherosclerosis, cataracts and macular degeneration (age-related changes in the central zone of the retina) develop more often and at an earlier age. Research shows that atherosclerosis does not increase the risk of developing glaucoma, and yet there is a weak relationship between atherosclerosis and increased intraocular pressure. People suffering from atherosclerosis are more likely to have increased intraocular pressure compared to healthy people of the same age.

Nearsightedness and farsightedness. Healthy farsighted and nearsighted eyes have the same average intraocular pressure. However, farsightedness has a higher risk of developing closed-angle glaucoma, while nearsightedness is more likely to develop pigmentary glaucoma. Such eyes are more sensitive to the effects of increased intraocular pressure.

Disturbances of ocular blood flow. The fact that decreased ocular blood flow usually occurs before glaucomatous lesions, and that patients with glaucoma often have circulatory disturbances in other organs, indicates that some of these disturbances are causal,

Some glaucoma patients show changes in blood circulation even at rest, but especially after physical exertion, emotional stress or cold. There are various signs that are most likely due to vascular dysregulation rather than atherosclerotic circulatory disorders. It has been proven that patients with glaucoma suffer from various circulatory disorders much more often than healthy people of the same age. At low intraocular pressure, at which glaucomatous damage develops, there is a possibility that circulatory disorders are also involved in the pathological process. In the most serious cases, insufficient blood circulation (i.e. nutrition of the optic nerve) can lead to structural damage, sometimes even at quite low levels of intraocular pressure. The most common cause of reduced blood supply is atherosclerosis. It can lead to narrowing of blood vessels, thrombosis and embolism. The main reason for the deterioration of ocular blood flow in glaucoma is dysregulatory disorders in blood vessels, including the vessels of the eye. Patients who suffer from vascular dysregulation have a tendency to low blood pressure (hypotension), especially at night, and the development of vasospasm.

Blood pressure. High blood pressure, or hypertension, is a known health risk. There is no constant blood pressure. It can change throughout the day depending on physical activity, a person's position (horizontal or vertical), food intake, and medication use.

Glaucoma is often associated with normal blood pressure during the day, but at night it can either decrease or increase, which does not happen in healthy people.

For glaucoma patients, a significant orthostatic drop in pressure (when changing body position from horizontal to vertical) can be quite dangerous.

High blood pressure in glaucoma is not of such serious importance, but chronic high blood pressure leads to the progression of atherosclerosis, which results in the development of ophthalmopathology, including glaucoma.

Temporary drops in blood pressure are common among patients with vasospastic syndrome, since their ocular circulation is very sensitive to drops in blood pressure.

The blood vessels of the eye provide nutrition to various parts of the eyeball. Active regulation of ocular blood flow is carried out in the following way. When light enters the eye of a healthy person, the blood supply to the retina and optic nerve immediately increases. This leads to a decrease in blood pressure in the vessels at the entrance to the retina and causes a deficit in blood supply. To compensate for this deficit, the vessels expand. This is how ocular blood flow is regulated.

Diabetes mellitus. Diabetes can cause irreversible eye damage, especially with the development of glaucoma. Diabetes can cause a significant increase in intraocular pressure, which is considered a complication of glaucoma. There is evidence that glaucoma is less common in diabetes.

Thus, the primary risk factors for increased intraocular pressure and, as a consequence, the development of glaucoma are age, heredity, race, atherosclerosis, and myopia. The primary risk factors for the development of glaucomatous damage are increased intraocular pressure, vascular dysregulation with systemic hypotension and vasospasm, female gender, and race.

Additional factors (anatomical predisposition to the development of glaucoma)

1. Nearsightedness and farsightedness. Healthy hypermetropic and myopic eyes have average intraocular pressure. However, with farsightedness, the risk of developing closed-angle glaucoma is higher, and with nearsightedness, pigment glaucoma is more often observed. Such eyes are more sensitive to the effects of increased intraocular pressure.
2. Minor anterior and posterior axis of the eye.
3. Posterior localization of Schlemm's canal.
4. Small anterior chamber.
5. Large lens.
6. The small curvature of the cornea results in a shallow anterior chamber.
7. Atopy of the ciliary body, weakening of the Brucke muscle, which tightens the scleral spur, which leads to collapse of the graduates.

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