The eyes contain a jelly-like substance which inflates the eye called the vitreous humour. This is normally transparent, but as the eye ages it begins to degenerate causing strands precipitate out and cast shadows over the retina. These will appear as small greyish spots, strands, or fragments which float around as the eye moves. This is typically harmless and common. A sudden dramatic increase in floaters can be signs of a retinal detachment and warrants a visit to the optometrist.