sight test

Floaters and flashes

What are floaters and flashes?

Floaters are more common than flashes, and look like small, dark spots or strands that appear to float in front of your eyes. Floaters are very common and are normally harmless. They are more common if you are short-sighted or as you get older. Some people notice they see flashes of light. These can be due to movement of the gel inside the eye. Very occasionally, flashes or an increase in floaters can be a sign of a retinal detachment, which needs treating as soon as possible. This is more common as you get older, or in people who are short-sighted or have had eye surgery.

If you get any of the following symptoms and you cannot contact your optometrist, you should get urgent attention, ideally from an eye casualty department at the hospital. It is important that you get advice as soon as you can if you have:

  • a sudden increase in floaters, particularly if you also notice flashing lights
  • a new, large, floater
  • a change in floaters or flashing lights after you have had a direct blow to your eye
  • a shadow spreading across the vision of one of your eyes.

Floaters

Floaters appear as black spots or something that looks like a hair or small pieces of a cobweb. These can be semi-transparent or dark and appear to float in front of your vision. If you have had these for years, your eye and your brain learn to ignore them. Sometimes the number of floaters increases as you get older. Occasionally an increase in floaters can be a sign of problems inside the eye.

Because they ‘float’ in the jelly of your eye, you will find that if you move your eye to try to look at a floater, it will move away in the direction you move your eye. You might only see the floater if you are staring at a light coloured surface or at the sky during the day.

Some people find that floaters can be a nuisance, but most people become used to them. They rarely cause problems with your vision.

Why do floaters occur?

Some people are born with floaters. Other floaters occur as you get older when the gel in your eye, the vitreous humour, naturally shrinks. The gel separates into watery fluid and wavy collagen fibrils. The fibrils are seen as line-shaped floaters. Sometimes the gel shrinks enough to collapse away from the light-sensitive lining at the back of your eye, which is called the retina. Once the gel has collapsed, some people see a large ring-shaped floater.

The collapse of the vitreous gel can pull on your retina. If this happens you would see this as flash of light – see ‘flashes’ later.

Floaters can also be caused by some eye diseases that cause inflammation. This is not very common.

Who is at risk of floaters?

Floaters are more common in people who are short-sighted. They may increase if you have had an eye operation such as cataract surgery, or laser treatment after cataract surgery.

What might happen if I have floaters?

Most of the time floaters are harmless. Sometimes they may be annoying, but treatment is not advised.

Occasionally a sudden increase in floaters – either one or more large ones or a shower of tiny ones – may be a sign of a more serious eye disease such as a retinal detachment. This is when your retina pulls away from the back of your eye, and it may lead to a sudden increase in floaters and possibly a blank spot or shadow in your vision which does not go away. This needs immediate attention.

If you notice these symptoms, you should contact your optometrist straight away. If you cannot do this, you should get urgent attention from an eye casualty department at the hospital. If there is no eye casualty department nearby, you can go to your usual hospital casualty department, but it is best to go to an eye casualty department if you can. An ophthalmologist (a specialist eye doctor) will need to use eye drops and a special light to look inside your eyes to check if your retina is damaged.

Flashes

When we are young, the vitreous gel is firmly attached to the back of our eye. As we get older, the vitreous gel naturally becomes more liquid and collapses away from the retina.

This is called posterior vitreous detachment (PVD). It is very common and more likely to happen as you get older. If you get a PVD you may see flashes of light in front of one of your eyes, like small sparkles, lightning or fireworks. These tend to be in the extreme corners of your vision and come and go but don’t obscure any part of your vision. The flashes don’t last for a set length of time, and you may notice them more if you go from a light to dark environment. They may continue on and off for weeks or months. These are different to the shimmering or zig-zag lines that may be part of a migraine.

Migraine shimmers are a flickering of light, often on only one side of your vision, which then expands to the outside of your vision with a sort of jagged pattern. This will often obscure at least part of your vision (the left or right side). The shimmers usually go away after 10 to 20 minutes and may be followed by a headache, although some people may get migraine shimmers even if they do not have a headache afterwards.

Flashes can also occur if you are hit in your eye.

What might happen if I get flashes?

Sometimes flashes just indicate a tug on your retina and nothing more. However constant flashes may be a sign of a retinal detachment.

A retinal tear or retinal detachment may lead to a sudden increase in floaters as well as flashes. You might notice a shadow at the edge of your vision too. This needs immediate attention. If you notice these symptoms, you should contact your optometrist straight away. If you cannot do this, you should get urgent attention from an eye casualty department at the hospital. If there is no eye casualty department nearby, you can go to your usual hospital casualty department, but it is best to go to an eye casualty department if you can. An ophthalmologist (a specialist eye doctor) will need to use eye drops and a special light to look inside your eyes to check if your retina is damaged.

Who is at risk of a retinal detachment?

Some people are more at risk of a retinal detachment. These are people who:

  • have had eye surgery, such as a cataract operation or laser surgery after a cataract operation
  • are moderately short-sighted (over -3.00D)
  • have had a previous eye injury
  • have a family history of retinal detachment
  • have had a previous retinal detachment in that eye or the other eye
  • are over the age of 50
  • have certain retinal diseases such as lattice or other retinal degeneration
  • have certain systemic diseases such as Marfan syndrome.