It can strike anywhere between ages 20 and 40. About half the people who have it will get multiple sclerosis, a disease that attacks brain cells. It usually affects one eye. You could lose vision for a few hours or days or even months or lose a portion of yoir peripheral vision. You may have pain, blurry vision, and see flashing lights. Colors, especially red, might be less bright. Though it usually goes away on its own, the doctor can give you steroids to ease the inflammation and pain. Your eyesight should be back to normal within a year, but the condition can return.