Usually caused by blow to eye that tears blood vessels at iris root
Other signs of ocular or orbital contusion often come with it: vision loss, diplopia, lid swelling or laceration, ptosis, orbital fractures, rupture of eye, cataract, vitreous hemorrhage, or damage to cornea, retina, optic nerve
Hyphema by itself is a concern because of elevated intraocular pressure and corneal blood-staining