Q. What exactly is a "floater" that you see in your eye?

Floaters create images in your eye that look like specks, filaments, rings, dots, cobwebs or other shapes. Floaters are the most vivid when you are looking at the sky or a white surface such as a ceiling. They move as your eyes move and seem to dart away when you try to look at them directly.

Here's some biology first.

The lens in the front of your eye focuses light on the retina in the back of your eye. The lens is like the one in a camera, and the retina is like the digital sensor that records the image. The space between the lens and retina is filled with the vitreous, a clear gel that helps to maintain the shape of the eye.

Floaters occur when the vitreous slowly shrinks over time. As the vitreous changes, it becomes stringy, and the strands can cast shadows on the retina. These strands are the floaters.

In most cases, floaters are just annoying. When you discover them, they are very distracting. But, in time, they usually settle below the line of sight. Most people who have visible floaters gradually develop the ability to make them disappear by ignoring them.

Floaters are usually nothing to worry about. More than seven in 10 people experience floaters. Floaters are more likely to develop as we age.

When people reach middle age, the vitreous gel may pull away from the retina, causing posterior vitreous detachment. It is a common cause of floaters, and it is more likely in people who are diabetics, nearsighted, had eye surgery, or suffered inflammation inside the eye.

These vitreous detachments are often accompanied by light flashes. The flashes can be a warning sign of a detached retina. Flashes are also caused by head trauma that makes you see stars.

Sometimes light flashes appear to be little lightning bolts or waves. This type of flash is usually caused by a blood-vessel spasm in the brain, which is called a migraine. These flashes can happen without a headache and they are called an ophthalmic migraine.

If your floaters are just bothersome, eye doctors will tell you to ignore them. In rare cases, a bunch of floaters can hamper sight. Then a vitrectomy may be necessary. A vitrectomy is a surgical procedure that removes the vitreous gel with its floaters. A salt solution replaces the vitreous.

The vitreous is mostly water, so patients who undergo the procedure don't notice a difference. However, this is a risky procedure, so most eye surgeons won't recommend it unless the floaters are a major impediment.

Many new floaters can sometimes appear suddenly. When this happens, it usually is not sight-threatening and requires no treatment.

However, a sudden increase in floaters could mean that a part of the retina has pulled away from its normal position at the back wall of the eye. A detached retina is a serious condition and demands emergency treatment to prevent permanent impairment or even blindness.

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