It is filled with a material called vitreous which is similar to clear Jell-O. As we age, the normal jelly-like consistency of the vitreous begins to liquefy. The vitreous may contract and pull away from its natural attachments on the inside surface of the eye. When it pulls free, it is often accompanied by light flashes and the appearance of a new black spot or floater.
This is not dangerous, but it can be accompanied by more serious eye conditions such as retinal tears and vitreous hemorrhage. These occur when the strong attachments of the vitreous to the retina do not separate properly, tearing the retina or retinal blood vessels. This often leads to new floaters and persistent light flashes. It is suggested that anyone with symptoms of a vitreous detachment have an eye examination to make certain that a more serious problem is not present.