When the clot breaks up, the blood flow returns, as does the vision. The embolus may be a cholesterol crystal, a calcium deposit, or a true blood clot. Obstruction of the vertebral arteries, which course up the back of the neck and supply the visual part of the brain. People which this problem may notice temporary dimming of vision affecting both eyes, and possibly imbalance. Sometimes even eye movements are enough to induce a temporary loss of vision.
Retinal migraine is a spasm of the artery leading into the eye which supplies the retina.
This spasm can lead to a temporary black-out of vision on one side, and is fairly rare. However, if the clot is large it may not dislodge, and the vision remains blacked-out. Usually this is painless, and the loss of vision is severe. This condition may indicate risk for cardiac disease, and stroke. If a person with this condition rapidly seeks the medical help by an ophthalmologist, things may be able to be done to dislodge the clot before permanent damage occurs.