Most floaters are harmless and need no treatment, but new ones that show up suddenly and stay are a reason to call your eye doctor. That is the advice of NIH's National Eye Institute, which says floaters can sometimes signal a more serious eye condition.

Floaters are small dark shapes that drift across your vision, the institute says. They can look like spots, threads, squiggly lines or little cobwebs, and they seem to slide away when you try to look at them directly. You may notice them more against something bright, like white paper or a blue sky.

Almost everyone develops floaters with age, according to the institute. They usually come from normal changes, as tiny strands of the gel that fills the eye stick together and cast shadows on the retina. People who are very nearsighted, have diabetes or have had cataract surgery are at higher risk.

The institute lists two warning signs of a retinal tear or detachment: a lot of new floaters that appear suddenly, sometimes with flashes of light, and a dark shadow like a curtain or a blurry area in your side or central vision. Retinal tear or detachment can be a medical emergency, so the institute says to go to your eye doctor or the emergency room right away if you have these symptoms.

An eye doctor can check for floaters during a dilated eye exam, which the institute says is usually painless. If floaters come from aging and do not bother you, you probably will not need treatment. Talk with your doctor about any option that is suggested.