1:22PM BST 17 Oct 2014
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Signs and symptoms
Glaucoma can develop slowly over a number of years causing gradual loss of vision from the periphery and typically causes sensitivity to light.
Bono is most likely suffering from the form of the disease known as chronic open angle glaucoma which is the most common and develops very slowly.
It develops so slowly that often people do not notice their peripheral vision is failing. The area of vision becomes narrower as the disease progresses.
Other forms can come on suddenly, as a result of injury or infection or are present from birth.
Treatment
It can be treated with eye drops, lasers and surgery and is most often caused by a build-up of pressure in the eye.
A more serious glaucoma
Chronic open-angle glaucoma affects up to two in every 100 people over 40 years old and around five in every 100 people over 80 years old.
It is caused by a blockage in the eye preventing fluid from draining away and causing increased pressure.
It is often not known why a blockage occurs.
This pressure causes damage to the optic nerve and the light sensitive nerves as the back of the eye.
The disease is responsible for one in ten cases of visual impairment.
