Eye Floaters and Flashes: When to Worry

Many people experience eye floaters or flashes at some point in their lives. Usually they don’t indicate a serious vision problem, especially if they’ve developed gradually and haven’t changed much over months or years.

But a sudden onset of new floaters or flashes may signal a retinal detachment, retinal tear or other problem involving the retina or vitreous, which requires immediate evaluation and treatment.

Eye floaters

Floaters are black or gray dots, lines, cobwebs, or other shapes that drift or swim in the visual field. They are caused by small clumps of material that block light passing through the vitreous humor, or the clear gel that fills the inside of the eye. These clumps cast shadows on the retina that are perceived as floating spots in front of the eye.

In some people, floaters remain relatively constant for many years. These floaters are typically of little medical concern, and most people eventually become accustomed to them. In other people, floaters fade with time. But some floaters result from a potentially serious condition.

For instance, as people age the vitreous humor (which is connected to the retina at several points) normally detaches from the retina, and when this occurs a sudden flurry of new floaters or a single large prominent floater may develop. This natural separation of the vitreous from the retina, a condition called posterior vitreous detachment, may occur at a younger age in people who are nearsighted or have diabetes, a history of inflammation inside the eye, have undergone yttrium-aluminum-garnet laser surgery of the eye, or had cataract surgery.

Flashes (photopsia)

Flashes are visual sensations of light that are not caused by light sources in the environment. They may appear as quick bursts of light or streaks of lightning that are similar to what happens when one is hit in the eye.

Flashes result when the vitreous pulls on or tears away from the retina and are more common in older people. Flashes occur only in one eye at a time and tend to last only a second or so, though bouts of flashes often recur over a period of weeks or months. Even though most of these bouts occur without significant abnormalities developing in the eye and do not require any treatment, it is important to contact your doctor when flashes occur so that the appropriate management can be suggested.

Some flashes are associated with migraine headaches rather than problems involving the retina. Flashes associated with migraines are distinguished by their unique pattern: They appear as shimmering, jagged lines in both eyes, simultaneously, and last between 10 minutes and 20 minutes. These flashes usually begin in the middle of the visual field and gradually move outward. Often, but not always, a throbbing headache on one side of the head accompanies the end of a bout of migraine associated flashes. Migraine-like flashes that are not followed by a headache are called ophthalmic migraines.

Examination and treatment

People who experience a sudden onset of new eye floaters or flashes should consult an ophthalmologist promptly, even if the symptoms disappear on their own. If floaters or flashes are caused by a posterior vitreous detachment that has resulted in a tear in the retina, then permanent vision loss can occur if the tear is left untreated.

Posterior vitreous detachment may also lead to a retinal detachment, which requires immediate medical attention. Symptoms of retinal detachment include bright flashes of light, especially in peripheral vision; blurred vision; floaters; and shadow or blindness in a part of the visual field of one eye.

To diagnose a posterior vitreous detachment, an ophthalmologist will perform a dilated exam of the eye. In this examination, the ophthalmologist uses special eye drops to dilate the pupils and then views the vitreous and retina with specialized equipment. This procedure may make the eyes sensitive to light for several hours, so the patient may have to arrange for transportation home. You may also have an ultrasound of the eye to assist with diagnosis.

Posterior vitreous detachments, which occur in more than 60 percent of people older than 69, do not require treatment. However, associated retinal tears may require treatment, usually with laser photocoagulation. If a retinal detachment is also present, it can be treated with surgery with anatomic success in up to 90 percent of cases; however, vision may not be fully restored.

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HealthAfter50 was published by the University of California, Berkeley, School of Public Health, providing up-to-date, evidence-based research and expert advice on the prevention, diagnosis, and treatment of a wide range of health conditions affecting adults in middle age and beyond. It was previously part of Remedy Health Media's network of digital and print publications, which also include HealthCentral; HIV/AIDS resources The Body and The Body Pro; the UC Berkeley Wellness Letter; and the Berkeley Wellness website. All content from HA50 merged into Healthcentral.com in 2018.