Red eyes usually are caused by allergy, eye fatigue, over-wearing contact lenses or common eye infections such as pink eye (conjunctivitis). However, redness of the eye sometimes can signal a more serious eye condition or disease, such as uveitis or glaucoma.ed eyes occur when the blood vessels on the surface of the eye expand. The appearance of red eye ranges in severity from a bright red that completely covers the sclera to a few enlarged blood vessels that look like wiggly red or pink lines across the white of the eye.