Floaters are movable spots that can appear in your field of vision. Eye floaters may look like black or gray particles that move along with eye movement. Flashes are perception of brief arcs or flashes of light that you may experience even in a dark room where no light is actually flashing.
Floaters and flashes can be caused by any of the following:
Age-related changes of the eyes: Age-related changes in the vitreous (jelly-like material inside the eye) causes it to liquefy and pull away from the interior surface of the eyeball where it is attached to the retina. This process is called posterior vitreous detachment (PVD) and occurs mostly in people between the ages of 40 and 70. The vitreous pull on the retina during PVD can normally be experienced as bright flashes of light. Vitreous becomes clumped, and string-like due to shrinkage and sagging. Pieces of this debris can block some of the light passing through the eye and form shadows on your retina, which you may experience as floaters.
Posterior uveitis: inflammation in the layers of the uvea in the back of your eye
Vitreous hemorrhage: bleeding into the vitreous of the eye
Retinal tear: if the sagging vitreous pulls out with enough force to tear the retina it can cause floaters to appear. Retinal tears can lead to retinal detachment and if left untreated can cause permanent loss of vision.