mechanisms of vitreous haemorrhage
- vitreous haemorrhage may be caused by the following mechanisms:
- retinal vessels that are vulnerable to bleeding
- rupture of normal retinal vessels due to stress
- extension of blood from an adjoining source
- abnormal retinal blood vessels prone to bleeding :
- occurs as a result of neovascularization in response to ischemia
- is induced by vascular endothelial growth factor (VEGF), etc
- is seen in diseases such as:
- diabetic retinopathy
- sickle cell retinopathy
- retinal vein occlusion
- retinopathy of prematurity
- ocular ischemic syndrome
- these newly formed vessels:
- are fragile
- are prone to spontaneous bleeding
- can rupture due to vitreous traction that occurs with usual movements of the eye
- rupture of normal vessels
- occurs when mechanical force is greater than their structural integrity
- e.g posterior vitreous detachment with or without a retinal tear or detachment
- retinal detachment
- can be caused by direct injury to intact vessels
- trauma (blunt /perforating)
- main cause in age less than 40
- may be associated with Terson’s syndrome
- a rare cause
- associated with subarachnoid hemorrhage
- sudden increase in intracranial pressure can cause retinal venules to rupture
- extension of blood through the internal limiting membrane into the vitreous from an adjoining source
- these hemorrhages may arise from :
- macroaneurysms of the retina
- choroidal neovascularization
- tumors
Reference:
(1) John P Berdahl, et al, vitreous hemorrhage: diagnosis and treatment,eye net magazine, © American Academy of Ophthalmology, 2007