Most eye floaters are harmless. Sudden floaters with flashes are a same-day problem.

Floaters — the small dark specks, threads and cobwebs that drift across your vision — are one of the most common eye complaints, and most of the time they are nothing to treat. But the same symptom, when it arrives suddenly and is joined by flashes of light, is one of the few eye problems that genuinely counts as an emergency. The honest answer to "are floaters dangerous?" is: usually not, occasionally very, and the timing of onset is what tells the two apart.

What floaters actually are

In the plain description used by the National Eye Institute, floaters are small dark shapes that float across your vision and can look like spots, threads, squiggly lines or little cobwebs [s2]. They move as your eyes move, so when you try to look straight at one it seems to dart away, and you notice them most against something bright like white paper or a blue sky [s2].

The usual cause is ordinary ageing. As the eye ages, tiny strands within the vitreous — the gel-like fluid that fills the eye — stick together and cast shadows on the retina, the light-sensitive layer at the back, and those shadows are what you see [s2]. Almost everyone develops floaters as they get older, and the NEI lists three groups at higher risk: people who are very nearsighted, people with diabetes, and people who have had cataract surgery [s2].

The pattern that matters

Trouble starts when the vitreous pulls away from the retina — a posterior vitreous detachment — and, in a minority of cases, tears a hole in the retina as it goes. A retinal tear can progress to a retinal detachment, in which the retina is pulled out of position, and that causes permanent vision loss if it is not treated [s2].

How often does a sudden shower of floaters signal a tear rather than a harmless detachment? A 2009 JAMA review pooled 17 studies to answer exactly that. For patients who present with acute-onset floaters and/or flashes and are referred to an ophthalmologist, the prevalence of a retinal tear was 14% (95% confidence interval, 12%–16%) [s1]. In other words, most people with the sudden symptom do not have a tear — but roughly one in seven do, which is far too high to wait out.

The review also identified the features that raise or lower the odds. The single most important symptom is a subjective reduction in vision, which carried a likelihood ratio of 5.0 (95% CI, 3.1–8.1) for a retinal tear [s1]. On examination, vitreous haemorrhage was the finding most strongly associated with a tear (summary likelihood ratio 10; 95% CI, 5.1–20), while the absence of vitreous pigment was the most reassuring (summary likelihood ratio 0.23; 95% CI, 0.12–0.43) [s1]. New onset of at least 10 floaters was another high-risk feature, with summary likelihood ratios ranging from 8.1 to 36 [s1].

Even a reassuring first examination is not a permanent all-clear. Patients initially diagnosed with an uncomplicated posterior vitreous detachment still had a 3.4% chance of a retinal tear within six weeks, with the risk rising again if new floaters or visual reduction appeared during that window [s1]. That is why any change in symptoms after a first assessment is itself a reason to be seen again.

The red flags, and what to do

Both the NEI and the U.S. National Library of Medicine give the same warning signs. Go to an eye doctor or emergency room right away if you notice a lot of new floaters that appear suddenly, especially with flashes of light, or a dark shadow — often described as a curtain or shade — across your side or central vision [s2]. MedlinePlus is specific about the clock: a retinal detachment is an urgent problem that requires medical attention within 24 hours of the first symptoms of new flashes of light and floaters [s3]. It also notes a detail that catches people out — there is usually no pain in or around the eye, so the absence of pain is not reassurance [s3].

Longstanding floaters that come and go, by contrast, rarely need any treatment, and the NEI says treatment depends on the cause [s2]. The way to know which kind you have is a dilated eye exam, in which the pupil is widened with drops so the retina can be inspected directly [s2].

This article is informational and is not medical advice. If floaters appear suddenly, arrive with flashes of light, or come with a shadow or any drop in vision, treat it as urgent and be seen the same day.

Sources

• Acute-onset floaters and flashes: is this patient at risk for retinal detachment? — JAMA, 2009-11-25
• Floaters — National Eye Institute, 2024-12-04
• Retinal detachment (MedlinePlus Medical Encyclopedia) — U.S. National Library of Medicine (MedlinePlus), 2025-07-24