[charlesbahn]

I'll go on a little further. There are "good" floaters, and "bad" floaters. Good floaters are what we see when we're younger, they are remnants of blood vessels in the jelly of the eye and we see them most prominently against a white or blue background. While sometimes annoying, they are nothing to worry about.

Bad floaters happen when the jelly in the eye (vitreous) shrinks. We call this a posterior vitreous detachment (PVD). This happens to all of us if we are lucky enough to live long enough. These floaters are sudden and different from the good floaters and may occur just out of the blue with no previous strenuous activity or exercise. They may look like a hair or bug in the vision, or they may appear like a spider web or a flock of birds in the vision. They may also be associated with brief flashing lights in the periphery of the vision. Sometimes awareness of these is short lived, and by the next day they may be gone. But the retinal tear that leads to a later detachment may have already occurred.

Also, the risk of a retinal detachment is highest for about two weeks after the onset of new floaters and flashes so most of us council limited activity during this period (jarring head movements such as with running, jogging, tennis, etc). The risk is also higher in people that are nearsighted since they have thinner retinas to start with.

The good news is PVD's are common and happen to almost everyone at some point, and retina detachments are very uncommon, so most don't get one even if they don't see the ophthalmologist. But untreated retinal detachments may lead to blindness, which is preventable. So we don't recommend rolling the dice.