Glaucoma is a chronic degenerative disease that affects the optic nerve, characterised by damage to the nerve fibres that constitute it and the consequent loss of the visual field. If left untreated, the progressive reduction of the visual field may lead to blindness.
Glaucoma is a major social problem: it is the second leading cause of blindness worldwide and affects about 60 million people, making more than 8 million blind. In addition, approximately 50% of subjects with glaucoma are unaware of suffering from it.
It is an insidious disease because we often discover the disease when vision changes are already very advanced while we do not notice any symptom before . However, if diagnosed early and treated appropriately, it can be controlled effectively, allowing good vision for the rest of the patient's life.
There are many risk factors associated with the onset of the disease. The main ones are:
- high intraocular pressure (IOP),
- old age,
- familiar predisposition.
The IOP value is determined by a liquid that circulates inside the eye, the aqueous humour. In a healthy eye, the ratio between the aqueous humour produced and that eliminated is such to maintain a constant intraocular pressure, typically between 11 and 20 mmHg. While in the presence of glaucoma, this ratio is altered due to a reduction in the elimination outflow of the aqueous humour which occurs at the level of the trabecular meshwork (a structure that allows the outflow of this fluid from the eye).
Glaucoma can be classified in several ways:
- according to etiology, glaucoma can be primary, when it occurs in the absence of other eye or systemic diseases, or secondary, when combined with pre-existing conditions;
- according to the alteration of the outflow of aqueous humour, we distinguish the open angle glaucoma, due to an increased outflow resistance at the level of the trabecular meshwork and angle closure glaucoma, where there are anatomical problems that prevent the arrival of the aqueous humour to the trabecular meshwork;
- based on the value of the main risk factor, the IOP, we distinguish high pressure glaucoma and normal pressure glaucoma.
Then there are congenital or acquired glaucoma, if the IOP is higher than normal since birth, and infantile glaucoma if it arises during the first few years of life.
The increased intraocular pressure and the resulting damage which the optic nerve undergoes are not perceptible and, therefore, the main symptom is a progressive narrowing of the visual field. Unfortunately, however, in the early stages, it is not possible to be aware of such limitation without an eye examination.
There are several useful tests to exclude or diagnose the presence of glaucoma:
1. tonometry, used to measure intraocular pressure;
2.ophthalmoscopy, which allows an objective examination of the optic nerve;
3. perimetry (or visual field test), which allows an evaluation of the overall visual function;
4. pachymetry, which measures corneal thickness;
5. OCT, which evaluates the thickness of the nerve fibre layer.
Apart from the measurement of IOP, some of these tests are necessary to monitor the evolution of the disease.
Glaucoma therapy involves two types of approach, surgical and pharmacological.
Pharmacological treatment represents the first choice and uses glaucoma medications whose target is the reduction of the main risk factor of glaucoma, intraocular pressure.
These drugs are taken in chronic therapy, which is administered in a regular and constant way throughout life. Full compliance to therapeutic prescriptions is essential for the treatment to produce its effects.
In cases where drug therapy alone is not able to reach IOP target, it is possible to resort to parasurgical therapy (laser treatment), or alternatively, to surgical treatment. The most common surgery carried out is called trabeculectomy and allows the creation of an artificial channel for the aqueous humour outflow.