Blood vessels that are prone to bleeding, ruptures in healthy blood vessels and bleeding from an adjacent area can cause a hemorrhage behind the eye, according to EyeNet. Vitreous hemorrhage is painless but does obscure vision.
Medical conditions such as diabetes and sickle cell cause insufficient blood flow to the retina, says EyeNet. The lack of fresh blood and oxygen encourages the formation of new blood vessels that may lack the tight junctions of older vessels. These weaker vessels are more prone to rupture due to stress or to simply leak on their own, causing vitreous hemorrhage.
Even normal blood vessels sometimes rupture due to blunt trauma or perforation, as noted by EyeNet. In patients under 40 years of age, trauma is the leading cause of blood vessel rupture in the rear of the eye. Vitreous detachment and retinal tears also contribute to the rupture of otherwise healthy blood vessels. In rare cases, a subarachnoid hemorrhage puts pressure on retinal blood vessels, causing them to hemorrhage as well.
Vitreous bleeding sometimes results from hemorrhaging in adjacent areas of the eye, according to EyeNet. Bleeding from aneurysms and tumors in the retina can leak through surrounding membranes and enter vitreous space.