From time to time, everyone sees small dark specks moving in their vision. These "floaters" are actually condensations of vitreous humor -- the gel that fills the inside of the eye. The more movement a person makes, such as during exercise, the more floaters that can be seen moving. Most of the time, floaters are harmless. However, sometimes floaters indicate the development of a retinal tear. This involves damage to the retina -- the part of the eye that allows you to see.
Vitreous humor is made of collagen, a transparent jelly-like material that over time becomes less solid and more liquid. It contracts and forms clumps that float freely inside the eye and are seen as dark spots, or floaters, moving in your field of vision. They are more common as you age. Any activity, such as rapidly moving your eyes to look at something, can stir up these gel clumps and make floaters more noticeable. Exercise that involves pronounced head movements, such as jogging and trampoline jumping, can have the same effect.
Flashes of light can sometimes accompany floaters. This occurs when the vitreous gel rubs against or tugs the retina. Floaters and flashes that are stirred up through activity usually settle and dissipate after a few seconds. If floaters persist or decrease the vision in your eye, it is not normal. This may mean the vitreous has torn the retina. Exercise has not been found to cause retinal tears, but if you experience symptoms of blurry vision from floaters, you must see an eye doctor for immediate evaluation. Left untreated, a tear or hole in the retina can lead to fluid collecting underneath the retina and detaching it, resulting in loss of vision.