The vitreous is a gel-like substance that fills the inner eye. When bleeding occurs in the vitreous, it is known as a vitreous hemorrhage. This is often caused by retinal neovascularization, which is when abnormal blood vessels grow in the retina. Neovascularization typically occurs in conditions such as wet age-related macular degeneration (AMD), diabetic retinopathy, retinal vascular diseases, and/or retinal tears. Treatment options can include photocoagulation, cryotherapy, anti-VEGF injections, and vitrectomy.
You can learn more about vitreous hemorrhage from the AAO here.