Glaucoma is not a single disease, but rather a group of diseases that result in damage to the optic nerve, responsible for bringing the visual stimuli captured by the eyes to the brain. With the optic nerve injured, the images taken by the eyes do not reach the brain and the result is blindness.
Glaucoma is the leading cause of irreversible blindness in the world. Cataract blindness is more common than glaucoma, but it is a cause of reversible blindness.
An increase in intraocular pressure, or pressure within the eyes, is the main cause of glaucoma, but it is not the only one. There are cases of glaucoma where the intraocular pressure is normal.
Let's understand what intraocular pressure is. Follow the upper figure.
Between the cornea and the lens there is a cavity that is filled with a liquid, called an aqueous humor. Aqueous humor is constantly produced and drained, so that its volume and pressure are always more or less constant.
When any disturbance occurs in this cycle, either by increasing the production of the aqueous humor, or by a decrease of its drainage, the increase of liquid in this cavity causes an increase of the pressure inside the eyes.
Normal intraocular pressure ranges from 8 to 21 mmHg. When it becomes larger than 21 mmHg, there is a risk of optic nerve damage.
The problem with glaucoma is that it is a silent disease because the simple increase in intraocular pressure can not cause any symptoms. Eye pain usually only occurs when the pressure is already high, usually above 40 mmHg.
The aqueous humor that circulates in the anterior cavity of the eye is constantly drained through a porous, sieve-like tissue called the trabecular meshwork.
Closed-angle glaucoma occurs when there is a physical obstruction to the trabecular meshwork and, consequently, to drainage of this liquid. In open-angle glaucoma the trabecular meshwork is free of obstructions, but its drainage capacity is reduced.
For ease of understanding, imagine the trabecular meshwork as the drain and open tap water as producing a new aqueous humor. Closed-angle glaucoma is similar to what happens when we suddenly put a cap on the drain and completely stop draining the water. Open angle glaucoma would be a case in which the drain opening is free, but there is some degree of clogging of the pipes preventing complete drainage of the water, causing it to slowly rise above the level.
Acute (suddenly occurring) acute angle-closure glaucoma is a medical emergency because intraocular pressure rises rapidly, and within a matter of hours, the optic nerve can be destroyed, leading to irreversible loss of vision.
Blindness caused by glaucoma usually occurs slowly and from the outside inward, ie it first affects the peripheral field of vision and progressively becomes more central, as in the illustration below. Sometimes the vision loss process is so gradual that the patient only notices being blinded in advanced stages of glaucoma.
The main symptoms of acute angle-closure glaucoma are:
Severe eye pain
Nausea and vomiting
Blurred vision
Red eyes
Decreased vision, especially if there is low light
Closed-angle glaucoma may also occur in a chronic manner, when obstruction of the trabecular meshwork occurs progressively. In this case the evolution is slower, similar to open-angle glaucoma.
In open-angle glaucoma, as already said, the picture is insidious, progressing slowly without causing symptoms until advanced stages of the disease, when the patient notices losing vision.
Elevated intraocular pressure - The vast majority of cases of glaucoma are associated with ocular hypertension, but for reasons that are not well understood, there are cases of optic nerve damage even with normal intraocular pressure.
Black race - No one knows why, but black people are 6 to 8 times more likely to develop glaucoma than white people. In addition, glaucoma in blacks is also usually more severe
Age - Everyone over 60 is at increased risk of developing glaucoma. Blacks should start having their ocular pressure assessed from the age of 30
Family history of glaucoma - People with first-degree relatives with glaucoma are up to 6 times more likely to develop the disease
Diabetes - Diabetic patients seem to be at higher risk of developing glaucoma
As it is a silent disease, only an evaluation with the ophthalmologist is able to identify glaucoma in the early stages, which is essential to prevent irreversible damage to the optic nerve. During the evaluation of glaucoma, your ophthalmologist should perform several different tests to arrive at the diagnosis
Usually the first test performed is tonometry, used to measure intraocular pressure. This examination should be done routinely in every consultation with an ophthalmologist.
The fundus examination, or fundoscopy, is performed to evaluate the optic nerve. Likewise, the retinography or stereo ophthalmoscope of papilla is an examination where photographs of the optic nerve are obtained for a better evaluation and later comparison with future exams.
Campimetry is used to assess visual field defects caused by optic nerve damage.
Gonioscopy is the test that distinguishes open-angle glaucoma from closed-angle glaucoma.
Glaucoma has no cure and existing lesions can not be reversed. Therefore, the goal of glaucoma treatment is to reduce ocular hypertension and prevent the appearance of new lesions in the optic nerve.
The best treatment is with eye drops. The most commonly used class is beta-blockers, such as timolol. Other options are alpha-agonists such as brimonidine, carbonic anhydrase inhibitors such as dorzolamide and acetazolamide, or prostaglandins such as latanoprost.
In more severe cases, when eye drops no longer work, or in angle-closure glaucomas, surgery may be required to clear the drainage of the aqueous humor.
