Most refractive errors can be corrected by wearing glasses or, for older children and adults, contact lenses. Glasses are suitable for most refractive errors, are comfortable to wear, and do not cause complications. Contact lenses are also available for many refractive errors, but they are most effective for myopia and hypermetropia. Nondisposable contact lenses require careful cleaning to reduce the chance of an infection of the transparent cornea over which they are placed.
Glasses and contact lenses correct refractive errors in the eye by altering the angle of light rays before the rays reach the surface of the cornea, the transparent front part of the eye. The cornea at the front of the eye and the lens can then focus the rays correctly on the retina. Concave lenses make the light rays diverge (bend apart) and convex lenses make the light rays converge (bend together).
There are three main types of contact lenses: rigid, gas-permeable, and soft. Soft lenses are the most widely used and rigid the least. Some soft lenses are worn only once or for a few days. Nondisposable lenses should be disinfected daily unless worn for an extended period (not usually recommended). If an eye becomes red or painful, you should stop wearing your lenses and consult your optician immediately.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.