Introduction
Glaucoma is one of the world’s leading causes of sight loss.
It becomes more common with age and is present in more than 1 in 50 people over 40 in the UK.
Glaucoma is not curable, but the vast majority of people retain useful vision for the rest of their lives. Severe loss of vision is preventable if the glaucoma is diagnosed and treated early.
There are usually no warning signs. However, its onset can be detected by regular eye tests by your community optician.
Visual Field Loss in Moderately Advanced Glaucoma
What is Glaucoma?
Glaucoma is an eye condition in which there is loss of vision due to damage to the optic nerve, which carries signals to the brain from the eye. The damage is irreversible.
Loss of vision tends to be very gradual, affecting the peripheral vision at first. Both eyes are usually affected, though the degree of damage is often different in each eye.
Even if you have excellent sight, this doesn’t rule out glaucoma because:
- Glaucoma initially destroys the off-centre vision, leaving the central vision unaffected until a later stage.
- Blank patches in the field of vision may go unnoticed as the less affected eye ‘completes the picture’.
- Glaucoma does not affect the ability of the eye to focus and the condition may be present even though vision seems fine without the need for glasses. A considerable amount of peripheral sight can be lost before patients become aware of a problem.
Why does glaucoma occur?
It is thought that there are two mechanisms for damage occurring to the optic nerve:
Raised eye pressure (intraocular pressure). High pressure within the eye pushes on the optic disc. Initially, this may cause no damage – a condition called ‘ocular hypertension’. However, persistently raised pressure may lead to structural deformation of the nerve with subsequent loss of vision – this is ‘glaucoma’. Raised pressure occurs because the fluid within the eye is not drained away quickly enough; this is usually because there is an obstruction within or in front of the drainage apparatus (trabecular meshwork).- Reduced blood flow to the optic nerve. Some patients have optic disc damage and visual field loss typical of glaucoma, but with normal intraocular pressures. The reason this happens is thought to be a lack of blood supply to the nerve. This is known as ‘normal tension glaucoma’.