Glaucoma is one of the leading causes of blindness worldwide. It damages the optic nerve, the cable of more than a million fine fibres that carries signals from the eye to the brain. Lost fibres do not grow back. Treatment cannot restore sight that is already lost, but it can protect what remains.
How sight is lost
Glaucoma usually affects side (peripheral) vision first. Over years, the field of vision narrows from the edges inwards. Central vision, the part you read and recognise faces with, is affected last. That is why so many people do not notice anything until the damage is advanced.
There are usually no symptoms in early glaucoma. No pain, no blur, no warning. Only an eye examination can find it.
The role of eye pressure
The front of the eye is filled with a clear fluid, the aqueous, which nourishes the lens and cornea. It is made constantly behind the iris and drains out through a fine mesh, the trabecular meshwork, in the “angle” where the iris meets the cornea.
If the fluid drains too slowly, the pressure inside the eye rises and can damage the optic nerve. Raised pressure is the strongest known risk factor, and the only one that treatment can change. But the link is not simple:
- Glaucoma can develop even when the pressure is in the normal range.
- High pressure does not always mean glaucoma. Some people’s nerves cope with it for years.
- Eye pressure is not the same as blood pressure, and it is not caused by eye strain, reading or diet.
Who is at risk
Glaucoma can run in families, but it also occurs with no family history. The risk is higher if you:
- have a parent, brother or sister with glaucoma
- are older
- are very short-sighted or very long-sighted
- have diabetes or high blood pressure
- take steroid medicines for long periods
- have had an eye injury
If any of these apply to you, regular eye examinations matter even when your eyes feel fine.
How glaucoma is found
- Eye pressure check. A quick measurement of the pressure inside the eye.
- Gonioscopy. A special mirrored lens lets the doctor see the drainage angle and tell which type of glaucoma it is.
- Optic nerve examination and scans. The doctor looks at the optic nerve, and an OCT scan measures the thickness of its fibres. Scans can show damage before you notice any change in vision.
- Visual field test. This maps how much side vision you have. See visual field testing.
A diagnosis rests on several of these together, not on one number.
Treatment
All glaucoma treatment works by lowering eye pressure to a level that protects the nerve. There are three main ways to do it, not always in this order:
- Eye drops, used every day.
- Laser treatment. See laser treatment for glaucoma.
- Surgery, which creates a new drainage path. See glaucoma surgery.
Treatment is for life
Glaucoma is a chronic condition. Treatment works only if it is kept up: drops used every day as prescribed, and check-ups kept even when you feel well. At those visits, repeated field tests and nerve scans show whether the disease is stable or still changing. A normal pressure reading alone is not proof that treatment is working.
This guide explains; it does not diagnose. Your doctor’s advice about your own eyes comes first.