Abstract: Vitreous haemorrhage occurring in association with subarachnoid haemorrhage is known as Terson's syndrome. It occurs most commonly due to ruptured intracranial aneurism, or after serious brain injury. The pathogenesis of vitreous haemorrhage remains controversial. The proposed theories include directly entering of intracranial hemorrhage and rupture of intraocular blood vessels caused by high intracranial pressure. The vitreous hemorrhage may be caused by a large amount of blood pushed by high intracranial pressure, entering the vitreous cavity near the optic disc. Inside the eye, the blood may spread subinternal limiting membrane and intraretinally. The understanding of pathogenesis contributes to choosing the treatment strategies and predicting clinical outcomes of Terson’s Syndrome.