The vitreous is the jelly-like structure in the eye located behind the lens. It consists of collagen and hyaluronic acid and serves an optical function. The vitreous can develop opacities from developmental causes or degeneration. Treatment options for vitreous opacities include YAG laser or vitrectomy surgery. Vitrectomy surgery involves removing the vitreous and may be used to treat various conditions like vitreous hemorrhage, retinal detachment, or complications after cataract surgery. Vitreous substitutes like gases or liquids are often used to replace the vitreous during vitrectomy.