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What Causes Eye Floaters?

Scheie Eye Institute, University of Pennsylvania
A view inside the eye showing floaters. Copyright 2019 Rendia, Inc
Many people see some floaters in their vision and wonder whether they should be concerned. Learn what floaters are, what causes them, and when an eye doctor should be consulted.

Clumps of Vitreous Jelly

Floaters are little black spots that you can see best against a brightly lit white background, or when looking at the sky on a sunny day. When you move your eyes, they also move, but there is a time lag: they seem to move shortly after your eyes move. The reason for this time lag is that they are usually caused by thickened clumps of vitreous jelly.

The vitreous jelly is the substance that occupies the center of the eye. When we are young, the vitreous is usually clear, but over time, some small clumps made of contracted collagen fibers form. They block light coming from the front of the eye and cast shadows on the retina, the light-sensing nerve tissue in the back of the eye. Since the vitreous is a thick jelly, it has inertia (resistance to change in motion), so that it moves slightly after any eye movements, causing the floater time lag.

Most Floaters are Normal

Most of the time, floaters are not concerning, especially if they are unchanging from day to day. They may occur in one or both eyes, and you can figure out which eye has them by covering one eye at a time and looking for them.

Video: Eye Floaters

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When A Doctor Should be Consulted

However, if they are new, become more numerous over time, have a reddish color to them, or are associated with flashing lights, then they may represent a serious problem that should prompt a call to your ophthalmologist,

Retinal Tears and Detachment

Retinal tears or detachments often cause flashing lights and new floaters. The flashing lights are usually seen in an arc at the edge of the visual field and are caused by the vitreous jelly pulling on the retina. If you have these symptoms, you should call your ophthalmologist right away.

A retinal detachment is painless if it occurs spontaneously, or may be associated with eye pain if caused by getting hit in the eye. As a retinal detachment progresses, it looks like a black curtain coming across your vision, usually over the course of hours or days. It usually starts at the edge of the visual field and moves toward the center.


Some people have migraines that cause flashing lights in the center of the visual field followed within about 30 minutes by a severe headache on one side of the head. This is different from the retinal detachment symptoms.

Vitreous Bleeding

Sometimes bleeding into the vitreous can cause floaters, which may have a reddish appearance. This is most likely to occur in diabetics who have new, abnormal blood vessels growing on the surface of the retina and into the vitreous. These vessels can leak and bleed, sometimes filling the vitreous with blood or blood spots. If you have these symptoms, you should call your ophthalmologist right away.

Severe Inflammation

Severe inflammation in the eye can cause white blood cells to enter the vitreous, and this can look like floaters. These are more common in patients with autoimmune diseases like lupus or sarcoid.

Rare Diseases

Very rare disease-causing floaters can occur with ocular lymphoma, where cancerous white blood cells grow in the vitreous. Even rarer is retinoblastoma, a form of cancer seen in babies that can cause white vitreous floaters that make the pupil look white in photographs (normally it would look red).


In summary, eye floaters are caused by thickened clumps of vitreous jelly. Many people have vitreous floaters, which are usually not concerning if they are stable and not associated with any other symptoms. However, if they are new, increasing in number, or associating with flashing lights or eye pain, then call your ophthalmologist right away.


This content was first posted on: June 2, 2020

The information provided here is a public service of the BrightFocus Foundation and should not in any way substitute for personalized advice of a qualified healthcare professional; it is not intended to constitute medical advice. Please consult your physician for personalized medical advice. BrightFocus Foundation does not endorse any medical product, therapy, or resources mentioned or listed in this article. All medications and supplements should only be taken under medical supervision. Also, although we make every effort to keep the medical information on our website updated, we cannot guarantee that the posted information reflects the most up-to-date research.

These articles do not imply an endorsement of BrightFocus by the author or their institution, nor do they imply an endorsement of the institution or author by BrightFocus.

Some of the content may be adapted from other sources, which will be clearly identified within the article.

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