13 Causes of Red Eye

11. Glaucoma

Glaucoma is a condition in which there is too much pressure in the eye, affecting the optic nerve. Long-term, this condition can result in vision loss or blindness. It is the leading cause of blindness in the United States. Acute glaucoma is when the eye suddenly becomes red, and the cornea swells, leading to blurred vision. A person may see halos as well. This is considered a medical emergency, as it can permanently destroy vision if left untreated.