Floaters
These look like dark spots or "cobwebs" floating across your field of vision. They move when the eyes move, but not precisely. Floaters are tiny bits of material from the eye, suspended in the gel-like substance called the vitreous that fills most of the eye. A floater is actually the shadow of the material, cast on the light-sensitive retinal tissue on the back of the eye. Floaters are common and usually disappear or diminish on their own over days or weeks. Usually they are nothing to worry about, with the exception noted in When to See an Eye M.D., below.

Flashes
You may seem to see tiny sparks of light or long streaks, like lightning. The lights are not really there, but actually result from the vitreous pulling on the retinal tissue. (People with migraines see different, longer-lasting light patterns, and the causes are different, as well.)

When to See an Eye M.D.
If the floaters suddenly become more numerous and are accompanied by flashes, you should see an Eye M.D. immediately, as you may be experiencing a retinal tear or detachment. This is more common in people who are very nearsighted (myopic) and those who have undergone intraocular surgery, or have had eye infections or trauma. Retinal tears or detachments can be treated and vision loss prevented. The sooner treatment begins, the better the outcome is likely to be.

Last reviewed and updated in August, 2009,
by the American Academy of Ophthalmology.