Floaters and flashes, and when to worry

Spots, threads or cobwebs drift across your sight and slip away when you look straight at them. They show up most against a bright background such as white paper or blue sky.

Where do they come from?

The inside of the eye is filled with a gel called the vitreous. With age this gel slowly clumps, and the clumps cast shadows on the retina. Nearly everyone gets floaters as they age. They are more likely with severe short sight, diabetes and after cataract surgery.

Sometimes the gel separates from the retina, which is called posterior vitreous detachment. This change is usually harmless and can cause floaters and flashes.

When is it harmless?

Floaters that have been there a long time, are not getting worse and do not affect your sight are generally not serious, and they become less noticeable over time.

When is it urgent?

These signs should be checked the same day:

• Floaters or flashes for the first time
• A sudden increase in them
• A dark shadow or curtain moving across your sight
• Blurred vision or eye pain
• Floaters after eye surgery or an eye injury

These can be signs of a retinal tear or detachment. Retinal detachment is a medical emergency, and delay can lead to permanent loss of sight.

What happens at the exam?

Dilating drops open the pupil so the doctor can look at the back of the eye. Vision stays blurry for a few hours, so do not drive yourself.

Is treatment needed?

If ageing is the cause and the floaters do not bother you, treatment is usually not needed. If they seriously interfere with daily life, a vitrectomy operation can remove them, but it has risks to weigh up with your doctor.