From NHS Choices:
Glaucoma is a term that describes a group of eye conditions that affect vision. Glaucoma often affects both eyes, usually in varying degrees. One eye may develop glaucoma quicker than the other.
Glaucoma occurs when the drainage tubes (trabecular meshwork) within the eye become slightly blocked. This prevents eye fluid (aqueous humour) from draining properly.
When the fluid cannot drain properly, pressure builds up. This is called intraocular pressure. This can damage the optic nerve (which connects the eye to the brain) and the nerve fibres from the retina (the light-sensitive nerve tissue that lines the back of the eye).
Read more information about the causes of glaucoma.
Types of glaucoma
There are four main types of glaucoma:
- chronic open-angle glaucoma – this is the most common type of glaucoma and develops very slowly
- primary angle-closure glaucoma – this is rare and can occur slowly (chronic) or may develop rapidly (acute) with a sudden, painful build-up of pressure in the eye
- secondary glaucoma – this occurs as a result of an eye injury or another eye condition, such as uveitis (inflammation of the middle layer of the eye)
- developmental glaucoma (congenital glaucoma) – this is rare but can be serious. It is usually present at birth or develops shortly after birth. It is caused by an abnormality of the eye
Read more information about the symptoms of glaucoma.