People who are short-sighted are more prone to retinal tears
Prime Minister Gordon Brown has two minor tears in his retina - but how common is the condition and what are the risks?
What is the retina?
The retina is a layer of light sensitive cells at the back of the eye. If the eye can be thought of as a complex camera, then the retina is effectively the film.
When light reaches the cells in the retina they react by generating a series of nerve impulses which are sent back along the optic nerve to the brain, where they are interpreted as a picture.
What is a retinal tear?
Literally a tiny tear in the retina. Often these are minor and have little impact, but more severe tears can cause the retina to become detached from its underlying layer of support cells - and this can have a serious impact on vision.
Detachments happen when a tear is large enough for fluid in the eyeball to seep into the retina and peel it away, rather like a bubble in wallpaper.
What causes tears?
As we age the retina tends to get thinner, and this makes it more vulnerable to damage.
In addition, the clear gel - or vitreous humour - which fills the eyeball in front of the retina starts to shrink and to become more like a liquid as we age.
As the eyeball moves around, pockets of this liquid can stick to the retina.
Usually it comes away again without causing any lasting damage, but sometimes it sticks so firmly to the retina that when it comes away it causes a tear.
Are some people more at risk?
Yes. People who are short-sighted tend to be more prone to retinal tears, as their retina is more likely to thin over time and become fragile.
The risk is also higher as you get older, if you have had complicated cataract surgery, or if you have suffered a serious blow to the eye in the past.
How serious is it?
Minor tears will have little impact on vision but the more severe they are, the more vision will be affected.
A teenage rugby injury left Mr Brown with just 30% vision in his right eye
Retinal tears may lead to shadows in your vision, flashing bright lights when you move your eyes, and spots and specks known as floaters, which seem to drift across your eye.
As long as the hole in the retina is properly assessed for risk, symptoms are normally very short lived, subsiding in days or hours.
Left untreated a retinal detachment can lead to blindness, although this is rare.
How are tears treated?
It is important to assess the situation carefully. Some holes and tears do not need treatment, but in some cases it can be helpful to use laser treatment to prevent detachment.
If a retina does become detached, it can be effectively treated with surgery to seal the holes and reattach the retina. This usually restores some, but not all of your sight.
How likely am I to tear my retina?
Not very. Retinal detachment is uncommon, affecting one in a few hundred people. Retinal tears are more common than that, but still unlikely to happen.