When Floaters and Flashes Are an Emergency

Almost everyone has floaters. Most people have had them for years, barely notice them, and would be right not to worry.

A small proportion of floater episodes are the first sign of something that will cost vision permanently if it is not dealt with quickly. Telling those two situations apart is what this page is for, and the distinguishing feature is not what the floaters look like but how suddenly they arrived.

What floaters actually are

The main cavity of the eye is filled with vitreous, a clear gel that helps maintain the eye's shape. In youth it is uniformly transparent and firmly attached to the retina.

With age it liquefies. As it does, the collagen fibres suspended within it clump together, and those clumps cast shadows on the retina. You see those shadows as specks, threads, rings and cobwebs that drift when you move your eyes and settle when you hold still.

This is normal, universal, and in itself harmless.

The event that matters

As the vitreous shrinks, it eventually pulls away from the retinal surface. This is called posterior vitreous detachment, and it happens to most people eventually, typically between fifty and seventy, and earlier in eyes that are highly myopic.

In most cases it separates cleanly. The person notices a sudden increase in floaters, often a prominent ring shaped one, some flashing lights for a few weeks, and then things settle.

The problem is that the vitreous is not equally attached everywhere. Where adhesion is strong, particularly at the retinal periphery and around areas of pre-existing weakness, the separating gel can pull hard enough to tear the retina.

Why a tear is urgent

A retinal tear is a hole in the light sensitive tissue lining the back of the eye. Fluid can pass through it and get behind the retina, lifting it away from the wall of the eye. That is a retinal detachment.

The gap between those two states is where the urgency lives.

A tear caught before detachment is sealed with laser and the eye is generally fine. Once the retina detaches, particularly if it involves the macula, permanent vision loss is likely regardless of how good the surgery is.

The whole difference is timing.

The warning signs

Any of these means same day assessment, not a routine appointment.

• A sudden shower of new floaters, particularly many small dots at once
• New flashing lights in the peripheral vision, often described as lightning at the edge of sight
• A dark curtain, shadow or veil moving across part of your vision
• A sudden drop in vision in one eye
• A sudden increase in floaters accompanied by any of the above

The shower of small dots is worth singling out. Many tiny dark specks appearing at once can indicate a small amount of bleeding into the vitreous, which frequently accompanies a tear.

Why flashes happen

The retina has no way of registering anything except light. Whatever stimulates it, including mechanical traction, is reported to the brain as light.

So when the vitreous pulls on the retina, you perceive a flash, even in a completely dark room. That is why flashes accompanying new floaters are significant: they indicate active traction rather than settled change.

Who is at higher risk

• High myopia, which means a longer eye, a thinner stretched retina and earlier vitreous change
• Previous retinal tear or detachment in either eye
• Family history of retinal detachment
• Previous cataract surgery
• Significant eye trauma
• Lattice degeneration, a peripheral retinal thinning found on examination

Anyone in those groups should treat new floaters and flashes with more urgency rather than less, and should know their own risk status. It is worth asking at your next examination.

What assessment involves

Widefield retinal imaging captures over 80 percent of the retina in a single image, including the peripheral areas where tears occur, which makes it a fast and thorough first look.

Where a tear is genuinely suspected, dilation follows. A dilated examination gives a stereoscopic view of the far periphery that a flat image cannot, and elevation is exactly what distinguishes a tear that has begun to detach from one that has not.

If a tear is found, referral for laser treatment is arranged promptly. If nothing is found, you are given clear instructions about what would warrant coming back, because a tear can develop in the weeks following a vitreous detachment even when the first examination was clear.

The floaters that stay

For harmless floaters, the honest answer is that they generally do not disappear. What happens instead is that they settle lower in the eye over months and the brain gradually stops flagging them.

Most people find them substantially less intrusive after six months and barely notice them after a year. They are most obvious against bright uniform backgrounds, so a blue sky or a white screen will always show them more than a cluttered room.

What the examination involves

Knowing what happens removes some of the reluctance to come in for something that might be nothing.

1. History first, and it is unusually important here. When did it start, how suddenly, how many floaters, are there flashes, is there any shadow. The answers largely determine the urgency.
2. Vision and pupil responses, checking for anything suggesting a larger problem.
3. Widefield retinal imaging, capturing over 80 percent of the retina in seconds without drops.
4. Dilation if a tear is suspected or the imaging is inconclusive. This is the part people want to avoid and it is exactly the situation where it is warranted, because a flat image cannot show elevation.
5. A dilated peripheral examination, sometimes with gentle indentation to bring the far periphery into view. Uncomfortable rather than painful, and thorough.

If a tear is found, referral for laser is arranged immediately rather than at the next available appointment. If nothing is found, you are told specifically what would warrant coming back, because a tear can develop in the weeks after a vitreous detachment even when the first look was clear.

What laser repair is like

Worth describing because people imagine something far more involved.

It is an outpatient procedure taking well under half an hour. Anaesthetic drops, a contact lens on the eye to focus the laser, and a series of laser applications creating small burns around the tear. Those burns scar over the following weeks and weld the retina down around the break, stopping fluid getting behind it.

People describe it as bright and occasionally as a pinprick sensation rather than as painful. You go home the same day. Vision is usually normal, sometimes with some floaters from the procedure itself.

Compared against detachment surgery, which involves an operating theatre, often a gas bubble, and sometimes weeks of specific head positioning, the difference is substantial. That difference is the entire reason for coming in quickly.

After a vitreous detachment

Most people with sudden floaters turn out to have an uncomplicated posterior vitreous detachment, which needs no treatment. What it does need is awareness.

• The risk of a tear is highest in the first six weeks, so a follow up examination in that window is usual even when the first was clear.
• New symptoms during that period, more floaters, more flashes, any shadow, mean returning immediately rather than waiting for the scheduled visit.
• The floaters themselves settle over months. They rarely disappear and they usually stop being intrusive.
• The other eye commonly does the same thing within a couple of years, so knowing the symptoms is worth retaining.

Who should be most alert

• Anyone highly myopic, where vitreous change happens earlier and tear risk is higher
• Anyone who has had a tear or detachment in either eye
• Anyone with a family history of retinal detachment
• Anyone who has had cataract surgery
• Anyone with lattice degeneration, which is found on examination and is worth asking about

If you are in one of those groups, ask at your next examination so you know your own baseline risk. It changes how quickly you should act rather than whether you should.

Floaters that are not vitreous at all

Most floaters are vitreous strands. A few are something else, and the distinction occasionally matters a great deal.

• A shower of many tiny dark dots, often described as pepper or soot, can be red blood cells in the vitreous. That indicates bleeding, frequently from a tear, and needs same day assessment.
• White or grey cells rather than dark strands can indicate inflammation inside the eye, which is uveitis and has its own urgency and its own systemic associations.
• A large single floater appearing suddenly with flashes is the classic vitreous detachment, and it is the common one.
• Floaters accompanied by pain or light sensitivity are not ordinary floaters, because ordinary floaters do not hurt.

You are not expected to make this distinction yourself. What is worth doing is describing what you see accurately rather than just saying floaters, because pepper versus one large strand meaningfully changes the urgency at the other end of the phone.