Causes
The most common cause of glaucoma is excessive intraocular pressure. Intraocular pressure is generated in the chambers of the eye between the cornea and the lens. The chambers of the eye contain a fluid, known as the aqueous humour, which is formed in the eye itself. It flows continuously from the posterior to the anterior chamber of the eye and from there out again through a very fine channel. This circulation ensures a constant pressure in the healthy eye.
If the aqueous humour is no longer able to drain properly, it builds up, resulting in an increase in intraocular pressure. This process strains the optic nerve and there is a risk of nerve cells dying off. The resilience of the optic nerve determines whether the increase in intraocular pressure leads to damage or not.
Fortunately, the optic nerve is only susceptible enough to actually become damaged in some of those experiencing increased intraocular pressure. However, if the aqueous humour no longer flows at all, the intraocular pressure suddenly increases excessively; the reason for this is that drainage of the aqueous humour is completely blocked in such cases (known as narrow-angle glaucoma).
The intraocular pressure is measured in mmHg (millimetres of mercury) – this is the same unit that is used for measuring blood pressure. “Healthy” intraocular pressure is between 10 and 21 mmHg. However, intraocular pressure in glaucoma is not always above normal levels. In almost half of all people suffering from glaucoma, damage to the optic nerve can be detected, but no increased intraocular pressure can be observed. In the medical profession, this form of glaucoma is known as “normal tension glaucoma”, because it is assumed that normal intraocular pressure is already too high for those affected.
Inadequate blood supply to the optic nerve can also be the cause of glaucoma. In this case, the nerve cells are not adequately supplied with oxygen and nutrients. Glaucoma can also occur as a consequence of inflammation, injuries and vascular diseases. Experts refer to this as secondary glaucoma. And there are even rare cases where glaucoma is congenital.
In addition, old age, family history, severe short-sightedness and diabetes increase the risk of glaucoma.