Glaucoma

Cross-sectional view of a human eye.

Glaucoma per country in 2002: affected by every 100,000 inhabitants: without data less than 25 25-50 50-75 75-100 100-125 125-150 150-175 175-200 200-225 225-250 250-350 more than 350

Glaucoma is a group of diseases that can damage the optic nerve and the retina of the eye and can cause loss of vision. It is generally caused by a pathological increase in intraocular pressure, due to lack of drainage of the aqueous humor and has as a common end condition an optic neuropathy characterized by the progressive loss of the nerve fibers of the optic nerve and changes in its appearance.

Most affected people have no symptoms in the early stages of the disease; Later, defects in the visual field and progressive loss of vision appear. The appearance of these symptoms may mean that the disease is at an advanced point in its evolution. Eye pain is unusual in chronic glaucoma, but is common in acute glaucoma (angle-closure glaucoma), which can cause severe symptoms from the start.

One of the main factors that can influence the appearance of glaucoma is high intraocular pressure, although there is no exact correlation between glaucoma and intraocular pressure, since some people can develop the disease with intraocular pressure values considered normal and, however, on other occasions there are high figures without any ocular repercussions.

There are several types of glaucoma, each of which has a different origin and evolution, so the general definition previously exposed may not correspond to all forms of this disease. Most of the cases correspond to the so-called simple chronic glaucoma (open-angle glaucoma).

Classification

Depending on the amplitude of the iridocorneal angle, it can be classified as:

• Closed-angle glaucoma. There is a decrease in the iridocorneal angle, which is formed by the root of the iris and the cornea. It is usually acutely, with abrupt elevation of intraocular pressure, intense pain, decreased visual acuity, vision of halos around the lights, redness of the eye (red eye), dilation of the pupil (midriasis), nausea and vomiting. This often occurs when the pupil is dilated, which causes in people with an iridocorneal angle closed a blockage of the trabecular network by the outer area of the iris. This situation requires urgent and immediate treatment.

• Open-angle glaucoma. The iridocorneal angle is normal. Evolution is slow, there are no apparent symptoms, but the vision gradually deteriorates.

According to the origin, it is classified as:

• Primary. If there is no other disease that causes it. This section includes simple chronic glaucoma, which is the most common form of the disease.

• Secondary. When there is another disease that causes it. This section includes the following:
  • Neovascular glaucoma, for the formation of new vessels in the iris.
  • Facolytic glaucoma, for a cataract of long evolution and duration.
  • Pseudo-exfoliative glaucoma.
  • Ghost cell glaucoma, for a vitreous hemorrhage.
  • Inflammatory glaucoma, caused by an inflammatory process inside the eye.
  • Postoperative glaucoma.
  • Traumatic glaucoma. After trauma to the eye, a hemorrhage can occur in the previous chamber or hipema that triggers an eye hypertension by blocking in the reabsorption of aqueous humor in the trabecular network.
  • Lenticular glaucoma, caused by poor crystalline position.
  • Cortisonic glaucoma, caused by prolonged therapeutic use of cortisone or derivatives.

According to the moment of appearance, it is classified as:

• Congenital glaucoma. It is a rare problem that affects 0.05% of the population. Symptoms may appear in a period of time between birth and age 3. 66% of the cases are affected in both eyes. There are different types of congenital glaucoma, the most common being primary congenital glaucoma. Another type of congenital glaucoma is hydrophthalmy. On other occasions it is associated with a set of abnormalities of different eye structures, such as Peters' anomaly, Rieger's syndrome, Axenfel syndrome and aniridia.
• Young or infantile glaucoma. In most cases it is of hereditary origin and is characterized by an eye abnormality in the birth responsible for an increase in intraocular pressure (PIO). It often occurs within the first three years of life. In the embryo the filtration angle is formed by a cleft between the corneal elements and the iris elements, whose growth is slow. An incomplete cleft, which does not allow the normal development of the angle, prevents the normal exit of the aqueous humor and causes child glaucoma.
• Adult glaucoma. It develops in adult life.

Epidemiology

The total number of people with this disease is high, since its prevalence ranges between 1.5% and 2% in those over 40 years of age. It is one of the main causes of irreversible blindness in the world.

The most common form, which accounts for 60% of cases, is primary open-angle glaucoma, also called simple chronic glaucoma.

According to estimates made by the World Health Organization in the early 1990s, the number of people in the world with high intraocular pressure would be 105 million, new cases of glaucoma identified around 2.4 million per year and the number of blind people due to this disease would be 8 million, which would place it as the third cause of blindness worldwide, only surpassed by cataract and onchocerciasis.

Diagnosis

There are two key aspects to suspect the diagnosis of glaucoma: Elevation of intraocular pressure above 21 mmHg and the presence of an excavated papilla. Any of these two circumstances make the diagnosis probable, especially if there is a family history of the disease and the age is over forty years.

Once the diagnosis is suspected, other studies can be performed, such as a complete ophthalmological examination to check visual acuity and observe all the structures of the eye, both in the anterior and posterior poles, and campimetry or assessment of the visual field, to look for the existence of blind zones or scotomas.

Technologies for the study of glaucoma

HRT: A new imaging technique that uses laser scans to obtain a tomography of the optic disc. The acronym HRT comes from English (Heidelberg retinal tomograph) and means Heidelberg retinal tomography. There are several versions depending on the software used and the resolution of the test.

HRT is a new non-invasive technique that is capable of evaluating optic disc anatomy in three dimensions. It provides information on the structural changes of the optic nerve and enables early diagnosis and imaging monitoring of glaucoma. However, this technology is still in the development and improvement phase and currently has limitations (2010). It is not a widely used test for the evaluation of glaucoma.

Pachymetry: this test is used to measure the thickness of the cornea and thus correct errors in ocular pressure measurement caused by differences in resistance between thin and thick corneas.

Gonioscopia.

Gonioscopy: measures the iridocorneal angle and allows glaucoma to be classified into its two classic forms, open angle or closed angle.

High-resolution ultrasound: allows studying the structure of the eye, the anterior chamber, the ciliary processes and the papilla.

Biomicroscopy: uses a fundamental instrument called a slit lamp, which allows viewing highly magnified details of the eye and examines the fundus and optic disc in three dimensions with the aid of special lenses.

Applanation tonometer: allows you to measure eye pressure in millimeters of mercury. It is usually incorporated into the slit lamp. The most widely used tonometer worldwide is the Goldmann tonometer. There are tonometers that ignore the corneal thickness error factor. There is the Pascal Tonometer, which does not take into account the thickness of the cornea and thus an intraocular pressure not affected by this parameter is obtained.

Perimetry in glaucoma: its purpose is to check the width of the visual field. Initially, perimetries are requested with diagnostic intent and very sensitive strategies and programs must be used. Subsequently, the perimetries are used with the intention of assessing the evolution of the disease. To do this, the test is performed at regular time intervals using highly reproducible strategies and so-called progression programs.

Risk factors

The most frequent form of presentation is primary open-angle glaucoma, also called simple chronic glaucoma, which represents 60% of all cases. This type of glaucoma is not related to other eye diseases and is usually bilateral, although the degree of involvement of each eye is generally different. The main risk factors that make its appearance more likely are elevated intraocular pressure, a family history of glaucoma, and age over 40 years.

Elevated intraocular pressure values are considered to be those greater than 21 mmHg. When this circumstance occurs, the risk of developing glaucoma is very high. However, the relationship between elevated intraocular pressure and the development of glaucoma is not exact, since there are people who keep their eyes healthy despite having high pressure figures and others in whom visual field defects and alterations in vision appear. optic nerve head with normal intraocular pressure levels. It is what is called low-tension or normal-tension glaucoma.

When there are first-degree relatives with glaucoma, the risk of developing the disease is higher than in the general population. There is no clear pattern of inheritance, as different genes seem to be involved. The frequency of glaucoma also increases with age, with the highest risk being over 40 years of age, and multiplying by 7 after 60. Other risk factors are the male sex, the existence of myopia or diabetes, and ethnicity. black.

For all these reasons, preventive control of intraocular pressure can be recommended for people over 40 years of age, especially if they have a family history of glaucoma or have other diseases, such as myopia or diabetes mellitus.

In other types of glaucoma than simple chronic glaucoma, there are various factors involved. For example, a variant gene, termed LOXL1, has been discovered that confers a significantly increased risk of developing pseudoexfoliative glaucoma. The abnormality consists of a variation in the genetic sequence that occurs very frequently in this type of patient. The variation is located in an intron of the gene that codes for an enzyme that produces elastin, involved in the deposition of fibrous material and that somehow facilitates the appearance of this special type of glaucoma. These are variants of the disease that do not respond well to the usual treatments.

Treatment

Although eye pressure is only one cause of glaucoma, reducing eye pressure is the most widely used treatment. There are drugs that decrease the production of aqueous humor or increase its rate of reabsorption. The treatment is basically with drugs that are applied in the form of ophthalmic eye drops, with surgical procedures for refractory cases or acute complications.

Simple chronic glaucoma:

• First line: beta-blockers and prostaglandins
• Second line: laser trabeculoplasty
• Third line: trabeculectomy (connect the inside of the eye with subset space)

Narrow-angle glaucoma:

• Topic hypotensor with no midriatizing effect
• Manitol IV to achieve a low PIO
• Pilocarpina
• Iridiotomy
• Topical Corticoid

Medication

Elevated intraocular pressure can be treated with eye drops that lower the pressure in the eye. There are several classes of drugs to treat angle-closure glaucoma. In open-angle glaucoma, the most common are beta-blockers (blockers), such as timolol, and prostaglandin derivatives. Hyperosmotic diuretics, such as mannitol, are also used in ocular hypertensive crises and carbonic anhydrase inhibitors..

Use of cannabis

Medical cannabis has been shown in case series to reduce intraocular pressure by 24%. These reductions, however, are short-lived and not sustained. The difficulty for its therapeutic use is due to its psychotropic effect and short duration of action. When administered in the form of drops, almost 90% is absorbed through the conjunctiva, so its action is systemic and not local. Since glaucoma is a chronic disease that requires very long treatment, the risks of dependency and other adverse effects on the central nervous system are very high and outweigh the benefits, for which reason it is not used in medical practice, since there are other medications, both topical and systemic, more effective and safe. Studies are being carried out on the possibility of using some synthetic derivatives of cannabis without effects on the nervous system, but they are in the experimental phase.

The National Eye Institute (NEI) and the Institute of Medicine have conducted a detailed study on this topic, reviewing all previous scientific research, and have concluded that there is no scientific evidence to recommend the use of cannabis for the affections of glaucoma.

Drug use generally requires a prescription, and distribution is usually done within a framework defined by the national and regional laws of each country.

Surgery

Both laser and traditional surgery are used to treat glaucoma. Laser trabeculoplasty is used to treat open-angle glaucoma. Argon or Nd:YAG is used in the laser applied to the trabecular meshwork to stimulate the opening of the ducts and thus increase the flow of aqueous humor. Laser peripheral iridectomy is used in patients with angle-closure glaucoma. In it, the laser is aimed at the iris to make an opening in it. This opens a new pathway by which aqueous humor can pass from the posterior chamber to the anterior chamber. There is currently insufficient evidence to show any benefit in using iridotomy versus no iridotomy to slow visual field loss. This is based on analysis of four studies with a sample of 3,086 eyes from 1,543 participants; iridotomy appears to improve gonioscopic findings, but is not shown to be clinically significant.

The most commonly applied conventional surgery in glaucoma is trabeculectomy. Through this procedure, a new conduit is created through which the aqueous humor drains to the subconjunctival space. A popular alternative to trabeculectomy is deep nonperforating sclerectomy (NPPS).

There are other surgical techniques, which are generally reserved for complex glaucoma or when the usual techniques have failed, such as valve implants for aqueous humor drainage. Congenital glaucoma always requires surgical treatment (usually a goniotomy), although additional surgeries and/or medication may be required to control it.

Consequences of glaucoma

Although glaucoma may or may not have significant effects, a common consequence is loss of field of vision, which can be detected by performing perimetry. Vision loss from glaucoma first affects the peripheral part of the field of vision. Moderate or severe vision loss can be verified by the patient by testing her peripheral vision. This can be done by covering one eye and testing vision in all four corners of the visual field for clarity and sharpness, then repeating the test with the other eye. Very often, the patient does not detect loss of vision until he suffers "tunnel vision". If the disease is not treated, the field of vision will narrow more and more, darken the central part and finally degenerate into total blindness in the affected eye.

Vision loss due to glaucoma is irreversible, but its progression can be prevented or slowed with appropriate treatment. If you suspect that you may have glaucoma or that you have risk factors, it is advisable to visit your family doctor or ophthalmologist.