Eye Floaters and Flashes: Causes and When to See an Eye Doctor Urgently

The vitreous fills most of the eyeball. Young vitreous is a transparent gel made mainly of water, collagen fibres and hyaluronic acid. With age, and earlier in short-sightedness, the gel liquefies: collagen separates from hyaluronic acid and clumps into fibres that scatter light. It is the shadows of these fibres and clumps that we see as floaters. The 2016 review by Milston, Madigan and Sebag describes this process as the main mechanism of symptomatic opacities, particularly pronounced in myopia.

With liquefaction the attachment of the vitreous to the retina also weakens. When the back surface of the vitreous finally separates from the retina, posterior vitreous detachment (PVD) results, the most common cause of symptomatic opacities. It is often accompanied by a single dense, ring-shaped or thread-like cloudy area that we see as a large floater, and when the eye moves the vitreous tugs on the retina and produces tiny flashes, because the brain interprets the traction as a light signal.

The mere presence of floaters is not a disease. The 2016 review does point out, however, that the impact of symptomatic opacities on quality of life is greater than once thought, so 'get used to it' is not always an honest answer for a person whose floaters interfere with reading or driving.

This question decides whether you need to hurry. The answer depends on whom we count. The most frequently cited analysis (Coffee et al., 2007) combined the authors' own case series with a meta-analysis of observational studies.

Why two numbers, 8.2% and 21.7%? The meta-analysis pools work from different centres, including ones in which patients who were more severely affected or referred by other doctors reached the eye doctor, and the definitions of a tear and the examination methods differed. The practical conclusion: in one in ten to one in five people with new floaters and flashes examined by an ophthalmologist a retinal tear is found, so 'it is probably PVD' is not enough without an examination.

On the other hand, a few small, stable floaters present for years, without flashes and without changes in the visual field, are usually not an emergency. The eye doctor will assess them at a routine check-up anyway, and for a person over forty a periodic fundus examination is a good habit, especially with short-sightedness or diabetes.

Yes, and this is important, lesser-known information. A first examination that does not detect a tear does not mean the end of the story. In a Boston case series, tears appeared later in some patients.

Limitations: this is a retrospective single tertiary-centre study, so the 7.39% need not correspond to the general population. But the practical conclusion is consistent with other work: after a normal first examination it is worth knowing the warning symptoms and returning immediately if they change, because there is usually no point waiting for a scheduled check-up. According to Coffee et al., new symptoms or haemorrhage at the first examination are the best signals that early follow-up is advisable.

A retinal tear can progress to rhegmatogenous detachment, in which fluid enters through the hole under the retina and detaches it. According to the latest epidemiological reviews the global incidence is about 12.17 cases per 100,000 people per year (about 14.5 in Europe and about 9 in the Americas), and the main risk factors include myopia (risk increased 3 to 39 times depending on severity), age (peak in the 60s-70s), male sex, cataract surgery and trauma. The authors of the review also point to rising incidence, driven by ageing populations and growing myopia.

Differential diagnosis also matters in practice. Flashes in both eyes that take the shape of a shimmering zigzag line and last 20-30 minutes, often followed by a headache, more often come from a migraine aura than from a retinal problem (we write about migraine in our knowledge base). Repeated, brief flashes in one eye, lasting seconds, usually suggest vitreous traction on the retina. Such an assessment belongs to the eye doctor, though, and when in doubt it is better to have the eye examined.

The basis is a dilated fundus examination (pupil-dilating drops), in which the ophthalmologist inspects the entire retina including the periphery, often with gentle pressure on the eyeball to see the farthest regions. After the drops you see worse up close and are sensitive to light for several hours, so it is better not to drive yourself to the appointment. The doctor looks for pigmented cells in the vitreous ('tobacco dust'), haemorrhages and peripheral changes such as lattice degeneration.

If a symptomatic retinal tear is found, the standard is to seal it with a laser (laser retinopexy) or cryotherapy, usually as an outpatient, to prevent detachment. If the retina is already detached, surgery is needed. Detailed recommendations are in the current American Academy of Ophthalmology guide on posterior vitreous detachment, retinal breaks and lattice degeneration, to which we refer interested readers. If there is no tear, the ophthalmologist usually explains how to recognise warning symptoms and sets a follow-up whose timing depends on features such as haemorrhage or pigment.

When urgent causes have been excluded and the floaters still bother you, there are three paths: observation (floaters often fade and the brain gets used to them and notices them less), vitrectomy (surgical removal of the vitreous) and Nd:YAG laser vitreolysis. The evidence for them varies, and the decision always requires a conversation with a specialist, because every procedure carries risk.

The strength of this evidence is limited: it is one small study from a single private practice, concerning a specific type of floater (Weiss ring), and the review by Milston et al. points out that reported laser success rates range from 0 to 100%, whereas for vitrectomy data on a low risk and good success rate are available, although it is a surgical procedure. In an honest conversation with a patient, therefore, laser is an option to be considered, not an obvious treatment. There are, however, no drops, eye exercises or supplements whose effectiveness in dissolving floaters has been proven; such promises in advertising should be treated sceptically.

The opposite myth can also do harm: that every floater means retinal disease. An ageing vitreous gives floaters to almost everyone, and most people with long-standing, unchanged floaters have no problem with the retina. The difference comes down to whether the symptom is new or has changed.

The most important message from the literature is simple: new floaters and flashes are common and usually harmless, but this cannot be judged without looking at the retinal periphery. That is why we recommend, editorially, the rule 'new means get it examined': a short dilated examination costs an hour and usually brings peace of mind, and in a minority of cases it allows a tear to be sealed with a laser before the retina detaches.