Glaucoma is an eye disease characterised by loss of vision caused by damage to the optic nerve. It is very hard to detect until it has already reached an advanced stage.
The mechanisms behind the disease are not fully understood, although the evidence points to raised intraocular pressure, which is why treatments aimed at lowering that pressure are very effective at preventing sight loss.
It is important to understand that the damage caused by glaucoma is irreversible, which makes prevention and early diagnosis essential.
Glaucoma is one of the leading causes of blindness, and it is avoidable if diagnosed and treated in time. It is a disease of the optic nerve, the bundle of nerve fibres that carries visual information from the eye to the brain.
In glaucoma the optic nerve is progressively damaged, irreversibly losing nerve fibres. As a result vision is lost slowly, first at the edges of the visual field and later in the centre. Unfortunately, people with glaucoma only notice this loss when the disease is well advanced, and they consult an ophthalmologist when it is already too late.
What causes it?
Most glaucomas are caused by raised pressure inside the eye. Intraocular pressure is measured in millimetres of mercury; when it reaches 22 or above we speak of ocular hypertension. Finding raised pressure calls for further assessment to establish whether glaucoma has developed. If it has not, the ophthalmologist will decide whether to start preventive treatment or simply monitor the patient.
In some people glaucoma occurs without raised pressure; in those cases the main cause is poor blood supply to the optic nerve or an unusual susceptibility of the nerve itself.
The risk of glaucoma rises with age, so regular eye checks matter: every two years between the ages of 40 and 60, and every year from 60 onwards.
Close relatives of someone diagnosed with glaucoma are at higher risk than the general population, so they should also be checked regularly.
Types of glaucoma
The commonest form is primary open-angle glaucoma. In this form the pressure is generally mildly or moderately raised.
In other cases, known as secondary glaucomas and also open-angle, there is a specific cause raising the pressure.
Finally, less common in our part of the world, there is angle-closure glaucoma, which can be acute (causing pain and rapid loss of vision) or chronic.
Establishing which type of glaucoma is present matters a great deal, because the treatment differs.
Symptoms
The great danger of this disease is that it has no symptoms. According to the Spanish Society of Ophthalmology, more than one million Spaniards over 40 have glaucoma, and half of them do not know it. After diabetes, it is the second leading cause of blindness in industrialised countries.
The real problem, experts say, lies with that 50 % who remain undiagnosed. Because the disease produces no recognisable symptoms, those who have it are unaware and have never been given a diagnosis. This is why glaucoma is known as «silent blindness».
Diagnostic tests
The key tests carried out at ICOA are:
- Examination of the optic nerve and retinal photography.
- Measurement of intraocular pressure (applanation and air tonometry).
- Examination of the iridocorneal angle (gonioscopy).
- Measurement of corneal thickness (pachymetry).
- Computerised visual field testing (perimetry).
Treatment
Modern eye drops (used alone or in combination) are the first-line treatment for controlling glaucoma. These medicines lower the pressure by reducing the production of aqueous fluid inside the eye or by improving its outflow through the drainage angle or the uveoscleral route.
When medication is not effective, other techniques are used:
- Laser: such as Argon laser trabeculoplasty. The laser widens the drainage channel to help control the pressure inside the eye.
- Conventional surgery (surgical trabeculectomy): the ophthalmologist uses microsurgical instruments to create a new drainage channel through which aqueous fluid can leave the eye, lowering the pressure.