What Causes Floaters in the Eye? A Practical Guide from St. Thomas Eye Hospital

If you’ve noticed small specks, threads, or cobweb-like shapes drifting across your vision, you’re not alone. Many people search for what causes floaters in the eye because the experience can be distracting—especially against a bright background like the sky or a white screen. 

In most cases, floaters are a common part of how the eye changes over time. However, a sudden change in floaters can sometimes be a sign that your retina needs urgent assessment.

This guide explains what floaters are, what causes floaters in the eye, when to seek medical advice, and what to expect if you come in for an examination—using a reassuring, hospital-appropriate approach.

What Eye Floaters are (And Why You “See” Them)

Eye floaters are tiny shadows cast onto the retina (the light-sensitive layer at the back of the eye). They usually come from small clumps or strands within the vitreous—the clear, jelly-like substance that fills most of the inside of the eye.

Because floaters sit inside the eye, they can appear to move when you move your eyes. You may notice they drift away when you try to look directly at them—this is typical.

People often describe floaters as:

• Dots or pepper-like specks
• Fine threads or hair-like strands
• Transparent rings
• A light “cobweb” that moves with eye motion

Floaters are especially noticeable when looking at:

• A bright sky
• A plain wall
• A computer screen
• A well-lit page

Why Floaters Develop Inside the Eye

To understand what causes floaters in the eye, it helps to know what the vitreous does.

When we’re younger, the vitreous is more uniformly gel-like and clear. Over time, it gradually changes: parts of it can become more liquid, and the microscopic collagen fibres within it may clump together. These tiny condensations are what commonly create the shadows you perceive as floaters.

This is not something you “cause” by reading, using screens, or straining your eyes. In most people, it’s simply a normal age-related change.

What Causes Floaters in the Eye: The Most Common Causes

Aging-related vitreous changes (the most common reason)

For many adults, natural aging of the vitreous is a major contributor to eye floaters.

Common age-related processes include:

• Vitreous syneresis: the gel becomes less uniform and more fluid in places
• Collagen clumping: tiny fibres aggregate and cast shadows
• Posterior vitreous detachment (PVD): the vitreous can separate from the retina as it changes

A PVD is common and often not harmful by itself. However, because the vitreous is close to the retina, a sudden change (particularly with flashes) should be assessed to make sure there’s no retinal tear.

Eye injury or trauma

A knock or injury to the eye can disturb the vitreous and sometimes trigger new floaters. Trauma can also be associated with retinal problems, which is why a professional assessment is important if symptoms appear after an impact—especially if there is a sudden increase or associated flashes.

Inflammation inside the eye (uveitis)

Inflammation in the eye can lead to floaters because inflammatory cells and debris can circulate in the vitreous. People with uveitis may also notice discomfort, redness, light sensitivity, or blurred vision—though symptoms vary.

Retinal-related causes (important to rule out)

Sometimes floaters are linked to changes at the retina, such as:

• Retinal tear
• Retinal detachment
• Bleeding into the vitreous (for example, from fragile retinal vessels)

These are less common than age-related floaters, but they matter because prompt assessment can protect vision.

When Floaters are Usually Harmless vs When to See a Doctor

Floaters are often harmless, especially if they are stable and have developed gradually. The key is noticing change.

Floaters that are often reassuring

• A few floaters that have been present for a long time
• Gradual onset over weeks or months
• No flashes of light
• No shadow or “curtain” in vision
• No reduction in vision

When to seek urgent eye assessment

Contact an optometrist or eye emergency service urgently if you notice:

• A sudden increase in floaters (especially many new ones at once)
• Flashes of light, particularly in the peripheral vision
• A shadow/curtain-like effect moving across vision
• Sudden blurred vision or a noticeable drop in vision
• Floaters after eye injury

These symptoms don’t automatically mean something serious is happening, but they do warrant a same-day or urgent evaluation to check the retina.

What Happens During an Eye Exam for Floaters

If you attend for an assessment, the goal is to understand what causes floaters in the eye in your specific situation and, importantly, to ensure your retina is healthy.

An eye assessment commonly includes:

• History and symptom review: when it started, whether it’s changing, and whether there are flashes or shadows
• Vision check: how clearly you can see
• Pupil dilation: drops to widen the pupil so the clinician can examine the vitreous and retina thoroughly
• Retinal examination: careful inspection to look for tears, weak areas, bleeding, or detachment
• Additional tests if needed: sometimes imaging scans are used to support the clinical view (depending on what’s seen)

You may have blurred vision and light sensitivity for a few hours after dilation, so it’s sensible to plan accordingly.

Treatment Options (And What Most People Actually Need)

It’s understandable to want floaters “removed,” but treatment depends on the cause and how much the floaters affect daily life.

Most floaters: monitoring and reassurance

For common age-related floaters, many people find that:

• The brain gradually adapts and notices them less
• Floaters can settle lower in the vitreous over time
• Symptoms become less intrusive

If the retina is healthy and symptoms are stable, treatment is often not required.

If there’s an underlying eye condition

If inflammation, bleeding, or retinal disease is found, treatment is directed at the underlying cause. This is why prompt assessment of sudden changes is so important—management is tailored and time-sensitive when the retina is involved.

Procedures (selected cases only)

In a small number of cases where floaters are severe and persistently interfere with quality of life, specialist teams may discuss procedural options. These are not suitable for everyone and are considered carefully because any intraocular procedure carries risk. 

If this is relevant, it should be a shared decision after full assessment and discussion of benefits and risks.

FAQs

1) What causes floaters in the eye as you get older?

Most commonly, the vitreous gel naturally changes with age. Small collagen fibres can clump, and those clumps cast shadows on the retina—seen as floaters.

2) Are floaters permanent?

Some may persist, but many become less noticeable over time as they shift position and as the brain adapts to them.

3) Can stress or screen use cause floaters?

Stress and screen use don’t typically cause floaters. However, people may notice floaters more when staring at bright, plain backgrounds (like screens or white walls).

4) Do floaters mean I’m going blind?

Most floaters are benign. The key concern is a sudden change—especially with flashes or a curtain-like shadow—because that can signal a retinal problem that needs urgent assessment.

5) Is it normal to see floaters more in bright light?

Yes. Bright, uniform backgrounds make the shadows from floaters easier to see.

6) What if I have floaters in only one eye?

Floaters can occur in one eye or both. A new onset in one eye still deserves attention—especially if sudden, increasing, or associated with flashes.

7) When should I treat floaters as urgent?

If there’s a sudden increase, flashes of light, vision loss, or a shadow/curtain across vision, seek urgent eye assessment.

When in Doubt, Get Checked

Floaters are common and often harmless—but changes matter. If you’re worried, if symptoms are new, or if you’ve noticed a sudden increase, flashes, or any shadow in your vision, it’s appropriate to seek expert advice. 

At St Thomas Eye Hospital, our team can assess your symptoms carefully, check the vitreous and retina, and guide you with clear, reassuring next steps based on what we find.