Floaters and spots in vision: causes, red flags and what to do

The eye is filled with a clear gel called the vitreous, made mostly of water and collagen. RNIB explains that floaters are floating clumps of cells that form in this gel. You see them because they cast shadows on the retina when light enters the eye. They come in many shapes: dots that resemble flies, threads, circles, clouds, spiders or cobwebs, and they seem to drift when you move your eyes and then settle.

They are easiest to notice against a bright plain background, such as a clear sky or a white wall. Many people have a few for years without any problem. What brings people to a clinic is a change: a new floater, more floaters than before, or floaters with flashes of light.

RNIB explains that with age the vitreous becomes more watery and less like a gel, loses its shape and comes away from the retina, shrinking towards the centre of the eye. Once detached it does not reattach, and because we do not need the vitreous attached to the retina to see well, this is generally not a problem. Cambridge University Hospitals describes the same natural ageing process, usually quite sudden, causing floaters and sometimes an arc of flashing light at the side of vision, which may be dim and seen most easily at dusk or in the dark.

RNIB says most people with PVD are over 50, but it can happen in the 40s, particularly if you are short-sighted or have had an eye injury or eye surgery. It often affects one eye first, with the other eye usually following between six months and a couple of years later. The symptoms may last weeks to months and generally calm down as the brain learns to ignore them. Cambridge University Hospitals says the flashing light will usually subside over weeks but may sometimes last several months, and that no treatment is needed for PVD itself.

Occasionally, as the vitreous separates it pulls on the retina and tears it. A tear can bleed into the eye, or let fluid pass behind the retina and lift it away, which is a retinal detachment. The NHS says a detached retina needs to be treated quickly to stop it permanently affecting your sight, and that it is usually caused by changes to the jelly inside the eye with age, with risk higher if you are short-sighted, have had an eye operation such as cataract surgery or an eye injury, or have a family history of retinal detachment.

The symptoms of PVD and retinal detachment overlap, which is why RNIB says to have the eyes examined within 24 hours by an ophthalmologist or optometrist, or at A&E or eye casualty, and that you can call 111 for advice about where to go. RNIB says a retinal tear or detachment can be successfully treated if diagnosed early.

• Bleeding into the vitreous (vitreous haemorrhage), which may cause a shower of dots or a reddish haze; Cambridge University Hospitals says a retinal tear may cause some bleeding inside the eye.

• Inflammation inside the eye: the NHS lists lights in the corner of the eyes or dark spots (flashes and floaters) among symptoms of uveitis, with eye pain, redness and light sensitivity.

• Migraine aura, which can produce shimmering zigzags or spots in both eyes lasting a short while, often followed by headache; it differs from floaters because it fills the vision rather than drifting.

• Diabetic eye disease, which can cause new vessels to bleed in the eye.

• Floaters after eye surgery or injury, which should be reported to the treating team.

The NHS retinal detachment page and RNIB give consistent advice.

• Get help from NHS 111 if floaters (dots and lines) suddenly appear in your vision or suddenly increase in number.

• Get help from NHS 111 if you notice flashes of light in your vision.

• Get help from NHS 111 if a dark curtain or shadow moves across your vision, or if your vision gets suddenly blurred.

• RNIB advises being examined by an optometrist, an ophthalmologist, or at A&E or eye casualty within 24 hours of noticing symptoms.

• Cambridge University Hospitals lists a shower of dot-like floaters, loss of vision and a growing dark shadow from the edge of vision as symptoms to report immediately after PVD has been diagnosed.

• If your symptoms come back after a previous detachment, the NHS says to get medical help as soon as possible, because it is possible to detach a retina more than once.

The clinician asks when the floaters began, whether they appeared suddenly, whether there are flashes, a shadow or any blurred patch, and whether you are short-sighted, have had eye surgery or injury, or have a family history of detached retina. Vision is tested, and drops are used to widen the pupil so the retina can be inspected right to the edge with a lens and bright light.

If no tear is found, you will be told what symptoms to report and that floaters will usually become less obtrusive. If a tear is found, laser or freezing treatment may seal it; the NHS lists sealing a tear with laser or cryotherapy among treatments, and surgery if the retina has detached.

RNIB says that if symptoms are not worsening after your eyes have been checked and PVD is diagnosed, they are not usually a cause for concern. You might remain aware of floaters long term, but they are generally less noticeable than at first. RNIB says that with a large floater, moving your eyes gently round in circles may help. RNIB says very few ophthalmologists offer laser treatment for floaters, that in the UK it is not a routine treatment, and that anyone considering it should ask about the risks beforehand.

Regular eye tests remain important. The NHS recommends everyone has an eye test at least every 2 years.