Floaters and flashes: when are they harmless?

What are you actually seeing?

The specks you see drifting are not on your eye but inside it. The eye is filled with a clear gel, the vitreous. Over the years small condensations form in it — proteins and fibres clumping together. These cast tiny shadows on your retina, and you experience each shadow as a thread, dot or film. Officially they are vitreous opacities; the French name mouches volantes ('flying flies') captures it well.

They move with your eye but with a lag, which makes them appear to float. Look at one and it darts away. They are most visible against bright backgrounds — a white wall, a blue sky, a screen.

Why do they increase with age?

The vitreous liquefies and shrinks over a lifetime. Somewhere between your fifties and seventies it usually separates from the retina: a posterior vitreous detachment. That sounds worse than it is — it is a normal ageing process, not a disease. It does often bring temporarily more floaters, sometimes one striking ring or strand, and sometimes flashes of light as the separating gel tugs on the retina.

When do flashes and floaters warrant an examination?

The great majority of people go through a vitreous detachment without problems. In a small minority, however, the gel pulls hard enough to tear the retina — and that tear can lead to a retinal detachment. From the outside the difference is invisible; it takes an examination with dilated pupils.

The rule of thumb: a sudden new shower of floaters, new flashes of light, or both together — have the eye examined within a day or two. If you see a grey shadow or a curtain moving in from the edge of your vision, call your GP or the out-of-hours service immediately: that can signal a retinal detachment.

Do floaters ever go away?

The opacities themselves rarely disappear completely, but the nuisance almost always fades. They partly sink out of view, and — more importantly — your brain learns to ignore them, just as it filters out the frame of your glasses. Most people eventually only notice their floaters when they deliberately look for them.

For the small group whose vision remains severely hindered by large opacities, treatment options exist: a laser treatment that breaks opacities down, or surgery to remove the vitreous (vitrectomy). Both carry benefits and risks that must be weighed carefully against the nuisance — that is a conversation with an ophthalmologist, not a first step.

What can you do yourself?

Little — and that is good news, because usually nothing needs doing. Floaters are not caused by screens, reading or 'looking too much', and no vitamin or eye drop dissolves them. What does help: knowing the difference between usual (familiar, slowly changing floaters) and new (a sudden shower, flashes, a shadow), and not waiting in the latter case.