Nearsightedness, or myopia, is experienced by up to about one-third of the population. These patients have difficulty reading highway signs and seeing other objects at a distance. Symptoms would include headaches or eyestrain and might squint or feel fatigued when driving or playing sports. Myopia occurs when the eyeball is slightly longer than usual from front to back. This causes light rays to focus at a point in front of the retina, rather than directly on its surface. Nearsightedness may be corrected with glasses, contact lenses or refractive surgery. You may need to wear your glasses or contact lenses all the time or only when you need distance vision, like driving, seeing a chalkboard or watching a movie. If you're nearsighted, your prescription is a negative number. The higher the numeral, the stronger your lenses will be. Refractive surgery can reduce or even eliminate your need for glasses or contacts. The most common procedures are performed with an excimer laser. Others include photorefractive keratectomy, or PRK, (laser removes a layer of corneal tissue, which flattens the cornea and allows light rays to focus closer to or even on the retina) and laser-assisted in situ keratomileusis (LASIK) (where a flap is cut through the top of the cornea, a laser removes some corneal tissue, and then the flap is dropped back into place). Then there's orthokeratology, a non-surgical procedure where you wear special contact lenses that slowly reshape the cornea over time to correct your myopia. Another surgical procedure for correcting mild myopia is the implantation of plastic corneal rings, which also alter the shape of the cornea. One advantage of the rings is that they may be removed in case of a problem or adjusted should your prescription change. They can also be left in place permanently.