Flashes of light are caused by tension between the vitreous gel in the eye and the retina. As the gel pulls on the retina, the retina is stimulated, sending signals to the brain that are interpreted as flashes of light. As a person ages, the vitreous gel liquefies and separates from the surface of the retina. Imperfections in the gel may cast shadows on the retina that appear as fine dots, strands, and strings in your vision. Since these seem to float, they are called floaters.
Flashes and floaters are a normal factor of aging, and generally become less noticeable with time. However, patients should be examined if these symptoms occur. Flashes and floaters can be a warning sign of more serious conditions as well such as a retinal tear, posterior vitreous detachment or retinal detachment.