Giant cell arteritis (GCA) is an inflammation (swelling) of the arteries, which are the blood vessels that carry blood away from the heart. When arteries swell, it reduces the blood flow through these vessels. GCA affects the arteries in the neck, upper body and arms. It is also called cranial or temporal arteritis because it affects the head (cranium).

Because these blood vessels also help nourish your eyes, reduced blood flow can cause sudden, painless vision loss. This is due to a lack of blood flow in the nerve that connects your eye to the brain. This condition is called anterior ischemic optic neuropathy (AION).