The vitreous fluid fills about 80% of the eye and slowly shrinks over time. These strings can cast shadows on the retina. There are other causes of floaters like infection, inflammation (uveitis), hemorrhaging, retinal tears, and injury to the eye.
Some floaters that are so dense that vision is affect, a vitrectomy can remove floaters from the vitreous floaters. This surgery removes all the vitreous gel and the floaters from the eye and then replaces it with a salt solution.