Myopia is a common refractive error, also known as nearsightedness. Nearsighted people see things best when they are close up but have trouble seeing things that are farther away. Myopia occurs when light entering the eye comes into focus in front of the retina instead of precisely on the retina. This can be caused by a cornea that is too steeply curved, by an eye that is too long, or by a combination of both problems. People with mild to moderate myopia can see things close-up, but people with severe myopia may only be able to see objects clearly when they are just a few inches away.