What is glaucoma?

Glaucoma (from the Greek glaukos) - "watery blue". The term was first mentioned in the "Aphorisms" of Hippocrates around 400 BC. For the next several hundred years, glaucoma was considered to be a disease of the lens. "The scientific history of glaucoma began on the day when cataracts were given their proper place" (Albert Terson, 1867-1935, French ophthalmologist). The determination of the correct anatomical location of the optic nerve in the cat by a German ophthalmologist in 1894 and the subsequent use of this data by Edward Jaeger (1818-1884) led to the assertion that the optic nerve was involved. In the late 1850s, swelling of the optic nerve as a sign of glaucoma was proven by the anatomist Heinrich Müller. In 1856, von Graefe first described the narrowing of the visual fields and paracentral defects in glaucoma.

Until recently, glaucoma was considered to be present when the intraocular pressure (IOP) was greater than 21 mm Hg (i.e., more than 2 standard deviations above the mean intraocular pressure in a population survey). More recent studies have shown that most people with IOP greater than 21 mm Hg do not have glaucomatous visual field loss. In addition, approximately 40% of people with glaucomatous visual field loss have never had IOP greater than 21 mm Hg. The current concept of primary open-angle glaucoma is a description of a constellation of features commonly found in glaucoma that include intraocular pressure, optic disc appearance, and characteristic visual field changes. The key to diagnosing glaucoma is progressive changes over time in the optic disc, visual field, or both. Many glaucoma experts believe that primary open-angle glaucoma occurs in many diseases with a common pathogenesis at the end stages. It is likely that as the understanding of the disease increases, the definition of glaucoma will improve.

The most modern definition: glaucoma is a pathological condition with progressive loss of ganglion cell axons, resulting in visual field impairment, which is associated with intraocular pressure. Thus, when making a diagnosis, the following aspects should be assessed: anamnesis, the presence or absence of risk factors, intraocular pressure, the state of the optic disc, and also an examination of the visual fields.

A Brief Outline of the Physiology of Ocular Aqueousity and Intraocular Pressure

The ciliary processes (pars plicata region of the retina) form the aqueous humor of the eye. The epithelial cells of the inner nonpigmented layer are the site of aqueous humor production. Aqueous humor is formed as a result of a combination of active secretion, ultrafiltration, and diffusion. Many intraocular agents that reduce intraocular pressure inhibit secretion in the ciliary body. Aqueous humor flows through the pupil into the anterior chamber of the eye, nourishing the lens, cornea, and iris. Aqueous humor flows out through the angle of the anterior chamber, which contains the trabecular meshwork and the surface of the ciliary body.

Approximately 80-90% of the eye's aqueous humor drains through the trabecular meshwork - the traditional outflow pathway, the remaining 10-20% - through the surface of the ciliary body - the uveoscleral or alternative outflow pathway. The trabecular meshwork is considered the place where the regulation of the outflow of intraocular fluid occurs. In the trabecular meshwork, especially under conditions of increased intraocular pressure, the juxtacanalicular region has the greatest resistance to outflow.

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Optic nerve

The optic nerve consists of all the axons of the ganglion cells of the retina. The optic nerve is the structure affected by glaucoma. Functionally, damage to the optic nerve leads to changes in the visual fields. If left untreated, increased intraocular pressure can lead to progressive narrowing of the visual fields and ultimately to blindness.

The meaning of intraocular pressure

Understanding the basics of eye physiology is important for understanding the pathophysiology, diagnosis and treatment of glaucoma. Currently, many doctors and scientists believe that several factors are involved in the pathogenesis of glaucoma: apoptosis, impaired blood supply to the optic nerve and, possibly, autoimmune reactions. However, intraocular pressure is one of the most important risk factors for the development of the disease. In addition, the only method of treating glaucoma, the effectiveness of which has been clearly proven, is to reduce intraocular pressure. Despite the understanding of the physiology of intraocular pressure, it is still not completely clear how the eye regulates intraocular pressure at the cellular and molecular levels. Every year, knowledge of physiological processes increases. Perhaps in the future it will be possible to answer the question that worries many patients: "What is the cause of increased intraocular pressure?"