Refractive errors are the most common eye disorders. Most people have a refractive error, but it is usually too small to affect their vision significantly. For the eye to see clearly, light rays must be bent, or refracted, by the cornea and the lens and focused on the retina. The retina receives the light rays and converts them to neural signals that are transmitted by the optic nerve to the brain, where the signals are translated into images.
Like a camera, the human eye must be properly focused to see an image clearly. If light does not bend or refract correctly and focus directly on the retina, the result is blurred vision, or a refractive error.
The four most common refractive errors are:
- myopia, or nearsightedness,
- hyperopia, or farsightedness,
- astigmatism, and
It is possible to have more than one refractive error, such as having both myopia and astigmatism.
The loss of visual acuity that results from a refractive error is measured by numbers. For example, 20/20 generally describes seeing clearly at 20 feet away what normally should be seen at that distance. People with 20/80 vision must be as close as 20 feet to clearly see objects that those with normal vision can see from a distance of 80 feet.