Amaurosis fugax is a classic sign (more often described than actually seen) for an acute embolus to the ophthalmic artery, a branch of the internal carotid artery
It presents as an acute descending blindness in one eye, as if a shade is being pulled down over the eyelid. It is considered an indication for carotid endarectomy (surgical removal of atheromatous plaque in the carotid artery.)