Glaucoma: what it is and why it occurs

By Cristiano Antonino On May 9, 2023

Glaucoma – also known as “the silent thief of sight” – is a chronic disease that affects the optic nerve

It can lead, if left untreated, to particularly negative consequences such as partial or total loss of vision.

Increased intraocular pressure (IOP) is the main risk factor and the only one currently treatable in almost all cases, especially in the primary forms.

Elevated IOP causes compression and distortion of the posterior ocular structures, particularly the scleral cribrosa plate which contains the optic nerve axons exiting the eyeball.

When there is actual damage to the optic nerve, the visual field begins to decrease starting from the most peripheral portions, proceeding gradually and involving more and more central portions of the visual field until complete loss of vision.

Glaucoma: why it occurs

Inside the eyeball there is a continuous flow of production and reabsorption of an aqueous liquid, which takes the name of aqueous humour, which has an optical function, linked to its transparency, static as it keeps the bulb tonic, nourishing as it it supplies glucose and oxygen and other nutrients to the cornea, to the lens, dynamic as it avoids the formation of adhesions between the structures of the eye and protects against trauma and photochromatic damage.

The outflow of aqueous humor occurs at the trabecular meshwork which, due to a reduction in its functions, can slow down the reabsorption of the aqueous humor produced, causing an increase in intraocular pressure.

The increase in pressure inside the eye, caused by a stagnation of unabsorbed fluid, can cause substantial damage to the optic nerve and, consequently, the development of glaucoma.

Glaucoma: symptoms

As anticipated, glaucoma is also known as “the silent thief of sight” as, in its initial stage, it does not present any symptoms detectable by the patient.

Only from the moment in which the optic nerve begins to be damaged due to the high intraocular pressure – which normally should not exceed 10 – 20 mmHg (millimeters of mercury) – the person suffering from glaucoma will begin to show the first symptoms of the disease: the loss of portions of the visual field.

The loss of portions of the visual field occurs progressively.

The first portion of the visual field that glaucoma will take away from the affected subject is the lateral, superior and inferior one.

Initially the latter may not notice a narrowing of his field of vision.

Glaucoma, unfortunately, is not a linearly advancing disease.

This means that, if these alarm bells are ignored and an ophthalmological examination is not promptly carried out which will diagnose the disease and then treat it, glaucoma could also subtract the central portion of the visual field of the subject, who would be in a state of permanent blindness.

Glaucoma: the diagnosis

The specialist visit assumes fundamental importance since the initial stages of the pathology are not characterized by particularly evident symptoms.

During the visit it will therefore be possible to carry out a tonometry to verify the alteration of the intraocular pressure, and a gonioscopy which allows to visualize the structures responsible for the outflow and production of the aqueous humor and thus proceed to the distinction of the various types of glaucoma.

In addition, pachymetry may be needed to measure the thickness of the cornea.

Fundamental for the diagnosis and to evaluate the progression of the disease are:

Perimetry or examination of the visual field or the evaluation of the extension of the visual field
An OCT (optical coherence tomography) to check the thickness of the nerve fibers that surround the optic nerve.

In other cases you can also use:

A computerized FDT (Frequency Doubling Technology) perimetry to detect visual field deficits or alterations
Evaluation test for the perception of colors and contrasts
A fluorescein angiography (FA) to highlight the possible presence of retinal ischemic areas in the presence of a type of glaucoma defined as neovascular, secondary to systemic or ocular pathologies

Glaucoma: three different types

Once all the specific tests requested by the ophthalmologist have been carried out, it will be easier for the specialist to provide a precise diagnosis to the patient.

If this confirms the presence of glaucoma, a first important subdivision will be between open angle glaucoma, narrow angle glaucoma and congenital glaucoma.

Open angle glaucoma

If the diagnosis confirms the presence of an open angle glaucoma, the course of the disease will be slow and progressive, caused by the alteration of the pressure of the aqueous humor inside the eye.

This type of glaucoma will slowly degenerate causing no symptoms other than the progressive reduction of the visual field

Narrow angle glaucoma

If, on the other hand, the diagnosis confirms the presence of narrow-angle glaucoma – fortunately less widespread disease – the glaucoma will degenerate rather quickly.

In fact, the disease can occur suddenly, caused by an abrupt interruption of the reabsorption of the aqueous humor at the trabecular meshwork.

This abrupt obstruction configuring a picture of so-called “acute glaucoma” will be immediately perceived by the patient, triggering eye pain, nausea, vomiting, blurry vision and halos around light sources.

Treatment must also be timely to avoid irreversible sequelae to visual function.

Congenital glaucoma

This form of glaucoma can manifest itself from birth or in the very first years of the child’s life.

It is due to a malformation of the outflow tracts of the aqueous humor and is among the leading causes of childhood blindness.

Glaucoma: how to cure it

In an initial phase, glaucoma – especially in its open angle version – can be treated with drug therapy based on eye drops.

If this treatment proves insufficient to control the disease and the ocular pressure continues its slow damage to the optic nerve, parasurgical intervention (use of lasers) or surgery is generally used.

Surgical and parasurgical interventions are all aimed at obtaining control of ocular pressure where medical therapy has proved ineffective.

Furthermore, they are many and not all of them are indicated for the different types of glaucoma.

In open angle glaucoma, more or less invasive techniques are often used which have the aim of restoring the outflow paths of the aqueous humor or creating new ones, or of reducing the production of aqueous humor, acting on the structures that release it, obtaining in each case a decrease in intraocular pressure.

The main ones are:

Laser Trabeculoplasty (ALT or SLT)
Cyclodestructive procedures (e.g. cyclophotocoagulation, cyclocryotherapy)
Penetrating filtering surgery (trabeculectomy)
Non-perforating filtering surgery (e.g. canaloplasty)
Shunt procedures (microinvasive anterior drainage techniques, posterior drainage devices)
In the treatment of narrow angle glaucoma are also useful:
YAG laser iridotomy

Cataract surgery

Depending on the type of glaucoma diagnosed, the specialist doctor will reserve the right to direct the patient towards the treatment that best suits his needs.

Glaucoma: how to prevent its occurrence

There is no real way to prevent the occurrence of glaucoma.

However, there are some subjects at risk, who – for prevention – are strongly advised to undergo periodic eye examinations so as to detect any onset of the disease in time.

Patients who have relatives with glaucoma, who have a percentage chance of developing the disease themselves between 10 and 15%

Subjects with reduced thickness of the cornea
Subjects who have an optic disc that appears altered and does not present in its normal anatomy
Subjects complaining of visual field amplitude defects
Patients with ocular defects attributable to the possible appearance of glaucoma
Those with high myopia
Diabetic subjects

Subjects who – due to other pathologies – are forced for a long time to administer cortisone drugs which could cause an increase in ocular tone

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