The most common cause is obstructive lesions in the carotid arteries but other causes can occur.
Changes in the anterior segment:
(1) conjunctival and episcleral injection
(2) corneal edema
(3) corneo-scleral melting
(4) spontaneous hyphema
(5) iris atrophy
(6) fixed semi-dilated pupil or sluggish reaction to light
(7) anterior and posterior synechia
(8) uveal ectropion
(9) rubeosis iridis
(10) neovascular glaucoma
(11) iridocyclitis
(12) asymmetric cataract
Changes in the posterior segment:
(1) narrowing of retinal arteries
(2) dilation of retinal veins
(3) retinal hemorrhages
(4) microaneurysms
(5) macular capillary telangiectasia
(6) retinal arteriovenous communications
(7) cotton-wool spots
(8) cherry-red spot
(9) neovascularization on the disc and elsewhere
(10) choroidal neovascular membrane
(11) vitreous hemorrhage
(12) cholesterol emboli
(13) spontaneous retinal arterial pulsations
(14) anterior ischemic optic neuropathy
(15) cobblestone degeneration and wedge-shaped areas of chorio-retinal atrophy