Flashes and floaters: when are they harmless, and when do they need an urgent check?

One day you wake up and notice a thin thread or a clear ring that drifts in front of your eye whenever you move it, or black dots like tiny flies, and perhaps a quick flash of light at the edge of your vision when you turn your head in a dark room. The first thought is: "Is this serious?" In most cases the cause is a normal change in the eye that comes with age. But in a proportion of cases there is a tear in the retina, which is what makes a timely examination so important. In this article we explain the difference.

What are "floaters" in the first place?

The inside of the eye is filled with a clear, jelly-like substance called the vitreous. It contains very fine protein fibers. Over time these fibers clump into strands and small clusters that cast shadows on the retina, so we see them as threads, dots or rings that move as the eye moves (Kokavec et al., 2017). These are floaters.

Old, unchanging floaters are common, especially in short-sighted people, and most get used to them over time. What deserves attention is a sudden change.

Vitreous detachment: usually a normal change

With age the vitreous becomes more liquid, shrinks, and moves away from the surface of the retina to which it was attached. This is called posterior vitreous detachment. It is a normal change that eventually happens to most people. In a study of healthy eyes, it was present in about 44% of people in their sixties and 74% in their seventies. In people with high myopia, it occurred about ten years earlier (Akiba, 1993).

When the detachment happens suddenly, the patient notices new floaters, and sometimes flashes of light. The flashes come from the vitreous pulling on the retina as it separates; the retina interprets this pull as light.

So where is the danger?

The danger is that the vitreous may be firmly attached at some point on the retina and pull on it as it separates, creating a tear. Fluid can then pass through the tear and collect behind the retina, causing a retinal detachment, a condition that needs urgent treatment.

How often there is a tear depends on where the patient is seen:

• In an analysis of several studies of patients who went to eye doctors with sudden symptoms, a retinal tear was found in about 14% (Hollands et al., 2009).
• In a specialist retina clinic, a retinal tear was found in about 16% of eyes at the first examination (Uhr et al., 2020).
• In a large American study in general eye clinics, the rate was lower: about 5% had a tear and 4% had a retinal detachment (Seider et al., 2022).

In other words, most vitreous detachments are not accompanied by a tear, but the proportion is not small enough to ignore the symptoms. The two situations cannot be told apart by symptoms alone, only by examination.

Which signs raise the risk?

Some signs make a tear clearly more likely:

• Reduced vision together with new floaters, one of the symptoms most linked to a tear (Hollands et al., 2009; Seider et al., 2022).
• A sudden large number of dots, which can mean a small bleed inside the eye (Hollands et al., 2009).
• Blood or pigment in the vitreous, seen by the doctor during the examination. Pigment is one of the strongest indicators of a tear, and blood clearly raises the risk (Hollands et al., 2009; Seider et al., 2022).
• Men, relatively younger people (under 60), and those who have had cataract surgery or laser vision correction were more at risk in a large study (Seider et al., 2022).
• Weak areas at the edge of the retina (lattice degeneration), or a previous tear or detachment in the other eye (Seider et al., 2022).

What happens during the examination?

The pupil is widened with drops, and the doctor then carefully examines the whole edge of the retina, because tears usually occur at the periphery rather than in the center. The doctor also looks for pigment or blood in the vitreous, because they are among the strongest indicators of a tear (Hollands et al., 2009).

If bleeding is so dense that it hides the retina, an ultrasound of the eye may be needed to confirm that the retina is in place.

And if a tear is found? It is usually treated with laser or freezing treatment around it, to seal the retina firmly and stop fluid passing behind it (Kim et al., 2025). If a detachment has already happened, surgery is needed; we explain the options in our article on retinal detachment surgery.

Why might the doctor ask for a second check when the first one was normal?

Because a tear can develop after the first examination. In an analysis of several studies, a tear appeared within 6 weeks in about 3% of patients whose first examination was normal, and the risk was higher when 10 or more new floaters or reduced vision appeared during that time (Hollands et al., 2009). In a large study in a specialist clinic, late tears appeared in about 2.6% of eyes, and about half of them appeared after more than 6 weeks (Uhr et al., 2020).

This risk varies a great deal between patients. In the large American study, late tears or detachments occurred in about 12% of those with blood in the vitreous, weak areas at the edge of the retina, or a previous tear in the other eye, compared with less than 1% of those with none of these factors (Seider et al., 2022). So the doctor sets the date of the second check according to your level of risk (Coffee et al., 2007). The American Academy of Ophthalmology guideline states that people with pigment or blood in the vitreous should be re-examined within 6 weeks, or immediately if new symptoms appear (Kim et al., 2025).

More important than the appointment date: if your symptoms change before your follow-up, with a sudden increase in floaters, a curtain, or reduced vision, do not wait for the appointment; go the same day.

Do floaters go away?

In most cases floaters become less noticeable over time, or the brain gets used to them so that the patient hardly notices them. But for some people they remain bothersome and can genuinely affect quality of life, especially in younger people (Wagle et al., 2011).

Is there a treatment for troublesome floaters?

Floaters alone usually need no treatment. When they are very bothersome and persistent, there are two options, each with its limits:

• YAG laser to break up floaters: in a small trial of one specific type of floater (the large ring that forms after vitreous detachment), symptoms clearly improved in about half of those treated with laser, compared with almost nobody in the sham-treatment group. But the researchers stressed the need for larger and longer studies (Shah and Heier, 2017). This laser does not suit every type of floater or every location in the eye.
• Vitrectomy: this does remove the floaters. In a study of this operation, visual acuity and quality of vision improved on average afterwards (Sebag et al., 2018). But it is surgery with its own risks. In one study, a retinal detachment occurred after about 2.5% of operations, and a cataract developed in half of those who still had their natural lens (Tan et al., 2011). So it is only done for people whose floaters clearly affect their lives, after explaining the risks in detail. We explain this operation in our article on vitrectomy.

There are still no clinical trials directly comparing laser with surgery for floaters (Kokavec et al., 2017).

Questions patients often ask

I've had floaters for years. Do I need an urgent check?

Old, stable floaters that have not changed do not usually need an urgent check, although it is a good idea to have them examined once if they never have been. What calls for a same-day check is anything new and sudden, or a change in the symptoms (Hollands et al., 2009).

The flashes have stopped. Is the problem over?

Flashes stopping is reassuring, but it does not necessarily mean the retina is healthy. The examination is what reveals warning signs; symptoms alone are not enough to rule out a tear (Hollands et al., 2009).

Will the same thing happen in my other eye?

Vitreous detachment usually happens in both eyes over time, though not necessarily at the same time (Akiba, 1993). So the same warning signs apply to the other eye.

Summary

Sudden flashes and floaters are, in most cases, caused by a normal age-related change in the vitreous. But some patients have a retinal tear that can only be found by examination, and treating it early with laser may prevent a retinal detachment. So the rule is simple: new, sudden symptoms deserve a same-day examination, and any change in symptoms after the examination deserves a new examination without waiting for the appointment.

This information is for health education and does not replace a medical examination.