Floaters are small pieces of debris that float in the vitreous humour of the eye. They occur behind the lens (a small clear structure that focuses the light entering your eye) and in front of the retina (the light-sensitive tissue that lines the back of the eye).
Vitreous humour is a clear, jelly-like substance that fills the space in the middle of the eyeball. It is mostly made up of water (99%). The other 1% is made up of substances that help to maintain the shape of the vitreous.
Floaters occur as part of the natural ageing process. Some people may have posterior vitreous detachment (PVD), which may cause a sudden increase in the number of floaters they have.
Getting older
As you get older, your risk of developing floaters increases. Floaters tend to occur in people who are over 40 years of age and are most common in those who are in their 60s and 70s. However, some younger people may also develop floaters.
As you get older, the vitreous humour in the middle of your eyeball can become less firm and strands of a protein called collagen may become visible within it. The collagen strands may appear to swirl as your eyes move.
Normally, light travels through the clear layer of vitreous humour to reach the retina. The retina is the light-sensitive layer of cells and tissue at the back of your eye that transmits images to your brain via the optic nerve. Any objects that are in the vitreous humour, such as floaters, will cast shadows onto the retina.
Posterior vitreous detachment (PVD)
Floaters can be a symptom of posterior vitreous detachment (PVD). This is a common condition that occurs in about three-quarters of people over 65 years of age. PVD can occur as the result of changes to the vitreous humour as the eye gets older.
With age, the central part of the vitreous humour becomes more liquid and the outer part, known as the cortex (which contains more collagen), starts to shrink away from the retina. Floaters develop as a result of the collagen thickening and clumping together.
As well as floaters, flashing lights can be another symptom of PVD. Flashing lights may occur when the outer part of the vitreous humour pulls on the light-sensitive tissue of the retina. The pulling stimulates the retina, causing your brain to interpret it as a light signal. This creates the sensation of flashing lights.
Retinal tears
In approximately half of all people, the vitreous humour has separated from the retina by the time they are 50 years of age. This does not usually cause any problems and most people are not even aware that it has happened.
In a few cases of PVD, when the vitreous humour pulls on the retina it can cause the tiny blood vessels in the retina to burst and bleed into the vitreous humour. The red blood cells may appear as tiny black dots or they may look like smoke. However, as the blood is absorbed back into the retina, these floaters tend to disappear over the course of a few months.
In some cases, the vitreous humour remains attached to parts of the retina and it tears the retina as it pulls away. If the retina tears, blood that escapes into the vitreous humour can cause a shower of lots of floaters at once. You may also see flashes of bright, white light in your vision that look a little like lightning streaks.
It is important to be aware that flashes in your vision are not necessarily a sign of retinal tears or retinal detachment (see below). They may have another cause, such as a migraine with aura (a headache with a zigzag pattern across your field of vision).
Floaters and flashes do not usually cause long-term visual impairment, but if you experience them it is important that you visit an eye care specialist, such as an optometrist, to have an eye examination.
Retinal detachment
If you have a retinal tear, you will need to be treated as soon as possible because tears can lead to retinal detachment. Retinal detachment occurs when the retina separates from the wall at the back of the eye. If this happens, it can damage your sight.
After the light has passed through the eye and reaches the retina, the retina changes the light into meaningful electrical signals. The signals are sent through the optic nerve to the brain, where they are translated into the images that you see.
If the retina is damaged, the images that are received by your brain will become patchy or may be lost completely.
Retinal detachment is rare, affecting one person in every 10,000 every year. See the Health A-Z topic about Retinal detachment for more information about the condition.
Other causes
If you have had eye surgery, such as a cataract operation, you are more likely to experience floaters, PVD and, more rarely, retinal tears and retinal detachment. In some cases, floaters may also be caused by:
Floaters are also more common in people who:
- have short-sightedness (myopia), which causes distant objects to appear blurred, while close objects can still be seen clearly
- have diabetes, which is a long-term condition that is caused by too much glucose (sugar) in the blood
As floaters and flashes can be caused by a number of eye conditions, some of which can affect your sight, it is always best to have any that develop checked by an eye care specialist. You should also visit a specialist if you have floaters or flashes that get worse.
See Floaters - diagnosis for more information about seeing an eye care specialist.
