Three types of ocular hemorrhage (OH) may be associated with SAH. They occur alone or in various combinations in 20–40% of patients with SAH.
1. subhyaloid (preretinal) hemorrhage: seen funduscopically in 11–33% of cases as bright red blood near the optic disc that obscures the underlying retinal vessels. May be associated with a higher mortality rate
2. (intra)retinal hemorrhage: may surround the fovea
3. hemorrhage within the vitreous humor (Terson syndrome).
The pathomechanics of OH are controversial. OH was originally attributed to extension of the blood from the subarachnoid space into the vitreous, but no communication exists between these two spaces. In actuality may be due to compression of the central retinal vein and the retinochoroidal anastomoses by elevated CSF pressure,67 causing venous hypertension and disruption of retinal veins.