A floater is a small clump of gel that forms in the vitreous, the clear jelly-like fluid which fills the cavity inside the eye. Floaters may be seen as dots, lines, cobwebs or spiders and are most often noticed when reading, looking at a blank wall or gazing at a clear sky.
Although floaters appear to be in front of the eye, they are actually floating in the fluid inside the eye. Sometimes, floaters do not interfere with vision at all. However, when a floater enters the line of vision the light is blocked and a shadow is cast on the retina. (The retina is the thin lining at the back of the eye that converts images to electrical impulses which are then sent by the optic nerve to the brain.)