The most common vision problems are refractive errors, which is when the shape of the eye prevents light from directly focusing on the retina. Vision occurs when light rays are bent, or refracted, through the cornea and the lens. This light is then focused on the retina, which converts the light into messages sent through the optic nerves to the brain. Refractive errors happen when there is a change in length of the eyeball, a change in the shape of the cornea, or as a result of an aging lens. Learn more about refractive errors including their symptoms and treatments: