The jelly-like fluid in the posterior chamber, which is the space between the back of the iris and the front face of the vitreous, is surrounded by a very thin membrane. The fluid also contains many fibers that are usually invisible. This whole structure is called the vitreous body. Sometimes the fibers in the vitreous body pull loose from where they are normally attached. When this happens, they can make shadows inside the eye. This is what causes the floaters that look like wispy threads.