In front of the retina is a chamber called the vitreous body, which contains a clear, gelatinous fluid called vitreous humor. Light rays pass through the vitreous before reaching the retina. It is strongly adherent to the retina at the vitreous base in the periphery, the optic nerve head, along the blood vessels and around the macula. With aging, the portions of the vitreous may liquefy and detach in a condition called posterior vitreous detachment (PVD).
Video | Anatomy: Vitreous