When an abnormal connection happens between either of the carotid arteries and the veins just behind the eye, it is called a carotid .
Because the carotid arteries have a greater pressure of blood flow than do the veins, the rush of blood prevents the veins that serve the eyes from draining properly.
The blood pressure starts to build up in the eye, causing it to bulge. The eye turns red. As the condition gets worse, a person may start losing his or her vision. Without treatment, the sight can be lost in that eye.

Coil Embolization for Carotid Cavernous Fistulas:

Treating a carotid cavernous fistula with embolization involves placing small platinum coils where the abnormal connection is. This separates the blood flow of the carotid arteries from that of the veins. As a result, the blood can drain properly from the eyes.
Coil embolization is done in an angiography suite. While the patient is given a general anesthetic, the procedure doesn't require any incision into the head or skull.
During the procedure, a small tube is placed through an artery in the groin. The tube is advanced up to the arteries in the neck. Another smaller tube is threaded through the first one. Small platinum coils are delivered to the abnormal connection through the second tube. The coils separate the blood flowing in the arteries from the blood flowing in the veins.
Coil embolization treatment often completely reverses the disabling symptoms in the eye, if treated early enough.