How do eye floaters cause symptoms?

You never actually see a floater. What you notice is the change it makes to the light on its way to the retina, the light-sensitive layer at the back of the eye. A dense clump blocks light and casts a shadow. Most everyday floaters, though, are clear strands of collagen that are thought to bend light rather than block it, so they appear as pale, glassy outlines with darker and brighter edges. How much a floater bothers you depends on several things, including how close it sits to the retina, how small your pupil is, what you are looking at and whether it is moving. In some people floaters also scatter enough light to make vision look hazy or washed out, even when the eye chart result is normal or only slightly reduced.

Written by Dr Simon Chen MBBS, BSc(Hons), FRANZCO

Cataract and retinal surgeon, Vision Eye Institute Chatswood, Sydney

Published 27 September 2026

Cutaway of the eye: a beam of light enters through the pupil and passes floaters in the clear gel, which cast matching shadows on the retina. — Light entering through the pupil passes floaters in the gel. What you notice is the pattern each one leaves on the retina, not the floater itself.

Why can't you see the floater itself?

The front of the eye works like a camera lens. The cornea and the natural lens bend light from the outside world so that it comes to a sharp focus on the retina. That system can only focus on things in front of the eye. A floater sits inside the vitreous, the clear gel that fills the space between the lens and the retina, and there is nothing behind it to focus its image. What reaches your brain is not a picture of the floater but the pattern of light and dark it leaves on the retina. Doctors call this kind of sensation an entoptic phenomenon: something you perceive that comes from within your own eye.

Shadows on a wall behave the same way. Hold your hand just in front of a wall under a single bare bulb and its shadow is dark and crisp. Move your hand towards the bulb and the shadow becomes larger, softer and paler until it almost disappears. Swap the bare bulb for a large lampshade, or a window on a cloudy day, and every shadow softens. In the eye, the retina is the wall, the floater is the hand and the pupil plays the part of the lamp. As the next sections explain, what matters is how close the floater is to the retina and how large the pupil is.

Do floaters block light or bend it?

Both happen, and which one dominates depends on what the floater is made of.

Blood cells, pigment and some inflammatory cells absorb light. They behave like tiny opaque objects and cast true shadows, which is why the floaters from a bleed inside the eye often look like dark dots or a sooty haze. What eye floaters are made of describes these different materials in more detail.

The common age-related floater is different. The vitreous is about 98% water held in place by a scaffold of very fine collagen fibrils. Individual fibrils are only 10 to 25 millionths of a millimetre across, far too small to disturb visible light. With age the gel partly liquefies and the fibrils clump together into bundles large enough to matter.

Conceptual enlarged views comparing fine separated collagen fibres with thicker bundles of fibres. — Enlarged and not to scale: the fine collagen framework of the gel (left) and the thicker bundles it can form with age (right). The bundles are still nearly clear.

Most troublesome floaters come from these bundles, from a Weiss ring, or from the back surface of the gel after it has separated from the retina. Bleeding is a much less common cause.

The bundles are nearly transparent, but their refractive index, the property that determines how much a material bends light, is slightly different from the fluid around them. They therefore seem to act like weak, irregular lenses. Light passing through a strand is bent away from some parts of the retina and piled onto others. Nothing is lost overall; it is redistributed.

You can see the same thing at the bottom of a swimming pool on a sunny day. The water is perfectly clear, yet the ripples on its surface bend the sunlight into a net of bright lines with darker gaps between them on the pool floor. Clear collagen strands do this on a much smaller scale.

That explains why so many people describe floaters as transparent threads, rings or "glassy worms" with a dark line and a bright line running along their edges, rather than as solid black shapes. A computer model of the eye published in 2022 found that a floater does not need to be opaque to cause symptoms: a small difference in refractive index is enough, and even a speck about a hundredth of a millimetre across can produce a noticeable pattern if it lies close to the retina.

Why does distance from the retina matter so much?

It helps to follow the light backwards from a single point on the retina. That point receives a cone of light whose base is the pupil, as seen from inside the eye, and whose tip is the retina itself. A floater matters only if it sits within that cone, and its effect depends on how much of the cone it fills. Close to the retina the cone is narrow, so a floater lying there fills a large part of it and blocks or bends most of the light reaching that spot. The result is a dark, sharp-edged shadow. Further forward the cone is wide. The same floater now intercepts only a small part of the light arriving at each point, and its partial shadow is spread thinly over a much larger area. The shadow becomes a faint, soft blur, and beyond a certain distance it is too weak to notice at all.

Six simulated squares of retina. A clear strand 0.5 mm from the retina shows as a glassy outline with dark and bright edges; at 2 mm it is a faint smudge and at 6 mm it has almost disappeared. A dense clump 0.5 mm from the retina casts a dark, sharp shadow; at 2 mm the shadow is grey and blurred and at 6 mm it is a pale haze. — The same two floaters at three distances in front of the retina, calculated with a simple optical model. Close to the retina the clear strand shows as a glassy outline and the clump as a sharp shadow; further forward both fade.

The effect is steep. A published geometric model calculated that with a typical daylight pupil of 3 mm, a floater 1.5 mm in front of the retina has to be more than about 0.2 mm across to cast a complete shadow, while one in the middle of the eye would have to be about 1.5 mm across, roughly the size of the optic nerve head. Most floaters fall well short of that, so they only produce a partial shadow, and the further forward they are, the fainter it becomes.

Line chart from a teaching simulation. A dense clump blocks about 90% of light when it lies within about 1 mm of the retina. With a 2.5 mm pupil its shadow is about 60% dark at 2 mm, about 28% at 3 mm and about 10% at 5 mm. With a 6 mm pupil it falls sooner: about 50% at 1 mm, 15% at 2 mm and under 5% beyond 4 mm. — How dark the clump’s shadow is at different distances. The darkness drops steeply within the first few millimetres, and faster still when the pupil is large.

These figures come from optical models rather than measurements in patients, and no clinical study has yet related a floater's measured distance from the retina to how much it bothers someone. Ultrasound shows that after a PVD the detached back surface of the gel can hang quite close to the retina in one eye and much further forward in another, which may be part of why the same diagnosis troubles people so differently. The soft partial shadow is not harmless either: it has been suggested that this blurred fringe may disturb vision more than a small, sharp full shadow. The principle, though, fits what people describe: the floaters that trouble them most are usually the crisp, well-defined ones, and a floater drifting forward, away from the retina, tends to soften and fade.

Why are floaters worse in bright light and against a blue sky?

Two things change when you step outside on a bright day.

First, your pupil becomes small. A smaller pupil makes the cone of light narrower, which has the same effect as moving the floater closer to the retina: its shadow becomes sharper and darker. It is the bare-bulb effect again. In dim light the pupil widens, the cone broadens and the same floater blurs into the background, as a shadow does under a large lampshade.

You can try this yourself. Make a pinhole in a piece of card and look through it at a bright, plain sky or a white wall, never at the sun. The pinhole acts as a very small pupil, and floaters you barely noticed become sharp and dark.

Second, the background matters. A clear sky, a white wall, snow, a bright computer screen or a white page gives an even field of light with nothing else for the eye to attend to, so a slight dip in brightness stands out. In a detailed scene such as trees, a busy street or a patterned carpet, the floater's faint shadow competes with genuine edges and textures and is much easier to miss. Against a large, evenly lit background, most people can detect a brightness difference of about 1%, which is why even a pale, partial shadow can be seen against a plain background.

Four simulated squares of retina. With a small pupil, a clear strand 0.8 mm from the retina shows a crisp glassy outline and a dense clump 1.5 mm from the retina casts a dark, fairly sharp shadow. With a large pupil the strand is barely visible and the clump is a pale, blurred disc. — The same floaters with a small pupil, as in bright light, and a large pupil, as in dim light. The small pupil makes each shadow sharper and darker.

This is also why some people are more aware of floaters when reading on a bright screen, and why a darker screen setting or tinted glasses outdoors can make them less noticeable. That fits the optics, but it has not been tested in trials. Very low-strength atropine drops, which slightly enlarge the pupil, have also been tried. One small, uncontrolled study found that just over half of those who used them for a week were satisfied; it did not test whether the pupil size was the reason. Can eye floaters be treated without surgery? reviews this and other non-surgical options.

Why do floaters drift and dart away when you look at them?

In young people the vitreous is a firm, clear gel. With age it becomes partly liquid, a change often compared to an egg: firm like a lightly boiled egg in childhood, runny in middle age and more like a raw egg later in life. Floaters are suspended in this mixture of gel and fluid.

When your eye moves, its wall moves at once, but the gel and fluid inside take a moment to follow and a moment to stop. An ultrasound study of the human eye and laboratory models have measured this motion after quick eye movements, and shown that it takes time to die away after the eye stops. A floater is carried along with it, so it lags behind your gaze and keeps drifting after you stop.

Chasing a floater makes this worse. Each time you move your eye towards its shadow, the shadow moves too and the fluid starts swirling again, so the floater darts away, then drifts back when you hold still.

Why do floaters appear suddenly?

The most common reason for a sudden new floater is a posterior vitreous detachment, or PVD. As the gel shrinks with age it separates from the retina at the back of the eye. It usually stays attached around the front edge of the retina, and it may still be attached lower down for a time while it separates above. This is normal and happens to most people eventually, earlier in people who are short-sighted.

Two eye cross-sections. Left: the vitreous gel has separated from the upper and back retina but stays attached lower down, with a few floaters and a faint ring-shaped floater near the optic nerve. Right: a retinal tear with the upper retina lifted from the eye wall. — Left: the gel separates from the retina above and behind, releasing floaters and often a ring of tissue from around the optic nerve. Right: where the gel pulls hard enough, it can tear the retina, and fluid passing through the tear can lift it.

When the gel pulls away, it releases condensed collagen into the space in front of the retina and often carries a ring of tissue from where it was attached around the optic nerve. That ring, called a Weiss ring, is a common source of a single large, round or C-shaped floater. The same separation can tug on the retina as it goes. No light is involved: the retina responds to being pulled by producing the sensation of a flash. Flashes are therefore a different mechanism from floaters, and new flashes with new floaters are a reason to be examined urgently, the same day if possible (see the urgent advice below).

The flashes, floaters and a curtain article explains how a retinal tear or retinal detachment is recognised and why an examination is needed even when the symptoms settle.

Why do some floaters fade while others keep catching your eye?

The brain is very good at ignoring anything that stays perfectly still on the retina. The clearest example is the retina's own blood vessels. They lie in front of the light-sensitive cells and cast shadows all the time, yet you never see them, because those shadows never move relative to the retina.

A block of healthy retina: fine blood vessels run across its inner surface, above the layers of light-sensitive cells beneath. — The retina’s blood vessels run across its inner surface, in front of the light-sensitive cells. Their shadows never move, so you never see them.

Experiments that hold an image perfectly still on the retina show that it fades quickly, and vessel shadows can vanish in a fraction of a second.

Floaters escape this filtering because they move. Every eye movement shifts their shadows across the retina, so the brain keeps registering them as something new. This link has not been tested directly in people with floaters, but it is a reasonable explanation for why a floater you had forgotten suddenly reappears as soon as you glance across the sky.

Most people find that the floaters from a new PVD become much less noticeable within about three months. Two processes probably contribute: the floaters tend to drift forward, away from the retina, so their shadows soften, and the brain learns to disregard them. Some people do not improve, and they tend to be the ones who were most bothered from the start. In one study of people whose floaters were troublesome enough to be diagnosed as affecting their vision, only about 4 in 10 reported clear improvement without treatment, over an average of about 17 months. Improvement was less likely in short-sighted people, in those with more than three floaters, and in those with string-like or block-like floaters.

Can floaters reduce vision even when the eye chart is normal?

Yes. The eye chart measures the smallest high-contrast letters you can read. Floaters often leave that result normal or only slightly reduced, even when they are troublesome. What they can change is contrast: how well you see faint, low-contrast detail such as a grey step, a face in shade or light text on a pale background.

A cloud of floaters scatters light in all directions. Some of that light lands on parts of the retina where it does not belong, adding a veil of stray light over the image. In a study of 15 people with floaters in one eye, stray light was measurably higher in the affected eye than in the fellow eye, although the difference was modest, and their eye chart results did not reflect their complaints. Small studies from one research group found that people needed about one and a half times as much contrast to see a pattern after a PVD, and that contrast sensitivity returned to normal after vitrectomy in those who chose surgery. When floaters degrade vision in this way, the condition is sometimes called vision degrading myodesopsia.

ClearWith floaters

Floaters against a bright scene

Grey dots, fine threads, worm-like strands and cobweb shapes drift across a bright view. They move with the eye and can dart away when you try to look directly at them.

These results come from small numbers of patients, largely from one research group, so they show what floaters can do rather than what every floater does. They are a useful reminder that a normal eye chart result does not mean a patient's floaters are imagined or trivial.

Why do floaters bother some people much more than others?

The factors above combine differently in each eye. A floater close to the retina and near the centre of vision intrudes more than one further forward or out to the side, and people who spend long periods on bright screens or outdoors meet them more often.

Glasses prescription matters too. In a survey of 603 smartphone users, 76% said they saw floaters and a third said they noticeably affected their vision; both short-sighted and long-sighted respondents reported moderate or severe floaters more often than people without a prescription. Other studies show that short-sighted eyes have earlier and more extensive vitreous change. It has not been shown that short-sighted eyes see larger shadows from the same floater.

How much a floater matters is also personal. In a study of 266 people with floaters in Singapore, many were prepared to give up a small share of their remaining life, or accept a small risk of death or blindness, to be rid of them; on one measure, people aged 55 or younger were slightly more troubled. People with troublesome floaters score higher for anxiety, stress and low mood than people without them, and the effect is greatest in those most disturbed. Younger people sometimes worry about careers built on reading and screen work. In a large online survey, the drawings people made of their floaters did not predict how much they suffered.

Cutaway of an eye with many small creamy-white particles suspended in the centre of the gel, leaving a clear band of gel next to the retina. — Asteroid hyalosis. The particles are held in an intact gel and stay away from the retina, which is why they rarely cause symptoms despite looking dramatic to the examiner.

A striking example of the difference between what the doctor sees and what the patient sees is asteroid hyalosis, in which hundreds of small white calcium and lipid particles hang in the gel. Through a microscope it can look dramatic, yet most people with it have no symptoms. The particles are held in an intact gel and, on ultrasound in a small study, appear absent from the zone closest to the retina, so they may simply be too far forward to cast a noticeable shadow. Another suggestion is that their smooth, round surfaces scatter light less disturbingly than tangled collagen fibres. The reverse also happens. The angle of the examining light makes many floaters hard to see, and an optical model predicts that clear floaters send far more light forwards to the retina than back towards the examiner, so a floater that troubles a patient can look unremarkable through a microscope.

What else can look like floaters?

Not every moving spot is a floater. On a clear blue sky, many people notice tiny bright dots that dart along short, curved paths. These are white blood cells moving through the fine blood vessels of the retina, not floaters, and they are normal.

Flashes of light are also separate from floaters, as described above: they come from the retina being pulled, not from light. Floaters made of blood or inflammatory cells look like other floaters, but they have a different cause and need a different assessment, which is one reason new floaters should be examined rather than assumed to be age-related.

What does this mean for treatment?

The optics explain why the options differ. Many floaters become less noticeable with time and need nothing more than an examination and an explanation. YAG laser for floaters uses a laser to break up or vaporise a floater; it is best suited to a single, well-defined floater such as a Weiss ring that sits safely away from both the lens and the retina, and it cannot clear the diffuse, wispy strands close to the retina that often cause the most trouble. Vitrectomy removes the gel along with its floaters, and it is considered when persistent floaters genuinely interfere with daily life after a period of observation. The eye floaters guide describes these choices and their risks, and YAG laser or vitrectomy for floaters compares the two.

Vitrectomy for floaters

Dr Chen removing the vitreous gel and its floaters during vitrectomy. It shows real eye surgery.

Watch on YouTube →

What should optometrists take from this?

Take the history in optical terms. Worse in bright light, on screens or against the sky, and a sharp, well-defined shape are consistent with a floater close to the retina. A sudden onset, a shower of new floaters, flashes, a shadow in the field or reduced vision point to PVD and its complications.
Examine for the tear, not the floater. In patients referred with acute floaters or flashes, a pooled analysis found a retinal tear in about 14%; a 2024 UK prospective study found a tear or detachment in 9.9% of eyes with PVD at presentation, with a further 3% developing a tear within two months. A Weiss ring was absent in about a third of eyes with a tear. Vitreous haemorrhage, pigment in the anterior vitreous, subjective loss of vision and a large number of new floaters all raise the likelihood. Examine the peripheral retina through a dilated pupil; in the same UK study about 15% of tears were seen only with indentation. Refer the same day when a tear, haemorrhage, pigment or reduced vision is found or cannot be excluded, and tell every patient with a PVD to return at once if the symptoms change, because about 3% of uncomplicated PVDs develop a tear within six weeks.

A single ring-shaped floater beside a cloud of fine, wispy floater strands. — A Weiss ring (left) is a single, well-defined floater and a sign of PVD; wispy strands (right) are finer and more diffuse. A Weiss ring is absent in about a third of eyes with a retinal tear, so its absence does not rule one out.

Expect the slit lamp to underestimate symptoms. The illumination angle limits what can be seen, and clear floaters are predicted to scatter light mainly forwards, so the patient experiences them in a way the examiner cannot see. B-scan ultrasound shows the whole vitreous and confirms a PVD.
Measure what matters when symptoms persist. Acuity is often normal or only mildly reduced; a new drop in acuity with acute floaters is a red flag, not a floater symptom. Contrast sensitivity and, where available, straylight measurement document the effect better.
Explain the mechanism. The microscope offers a familiar comparison: transparent, unstained cells are almost invisible with the condenser aperture wide open, and gain dark and bright edges when it is closed down. A small pupil does the same to clear floaters. Patients are often reassured to learn why their floaters are sharper outdoors, why they dart away when chased and why the eye chart result is normal. The explanation also sets realistic expectations about adaptation.

Where can I read more?

When are new floaters urgent?

Contact your ophthalmologist urgently, or attend an emergency department, if you notice:

a sudden shower of new floaters, or a large new floater
new flashes of light
a dark shadow or curtain spreading across part of your vision
a sudden drop in vision.

These can be signs of a retinal tear or retinal detachment, which needs prompt treatment. An examination with the pupils dilated is the only reliable way to tell a harmless PVD from a tear.

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