Eye stroke occurs when there's a lack of sufficient blood flow to the tissues in the optic nerve's front part. It can cause sudden vision loss, and other symptoms include loss of visual contrast and light sensitivity. Although an eye stroke can occur from a total blockage of a blood vessel, it's more commonly also caused by a lack of pressure or perfusion of the tissue. Stroke can lead to losing vision in one eye, too, which is why if you suddenly start seeing darker in one eye, then immediately visit a doctor. Most people with eye stroke notice a vision loss in one eye upon waking in the morning with no pain. Some people notice a dark area or shadow in their vision that affects their visual field's upper or lower half.