• The space between the eye’s natural crystalline lens and the retina is filled with a clear, gel-like substance called vitreous. Frequently tiny particles form from the protein material in the fluid resulting in a shadow being cast on the retina which is perceived as a floater.
  • The arrival of many or new floaters, particularly when associated with flashes or a large shadow of reduced vision could indicate a retinal detachment
  • Retinal detachments must be attended to by an ophthalmologist as a matter of urgency.

Link: http://www.allaboutvision.com/conditions/spotsfloats.htm