Refractive Errors and Laser Vision Correction

About 120 million people in the United States wear eyeglasses or contact lenses to correct nearsightedness, farsightedness, or astigmatism. This article will outline some refractive errors that cause people to wear vision correction devices, and may lead to their decision to have laser eye surgery.

The vision disorders, called refractive errors, occur when the curve of the cornea is incorrectly shaped (too steep or too flat) for the length of the eye. When the cornea has a correct shape and curvature, it bends light onto the retina with precise focus. However, when the curve of the cornea is not correct, it bends the light so it is not sharply focused on the retina, making images appear blurry. By placing corrective lenses, either glasses or contacts, in front of the cornea, the light is bent slowly to compensate for the refractive error of your cornea.

Myopia, or nearsightedness, affects more than 25 percent of all adult Americans. When the cornea is curved too steeply, or if the eye is too long, faraway objects will appear blurry because they are focused in front of the retina.

Hyperopia, or farsightedness, is the opposite of myopia. Distant objects are clear, and close-up objects are blurry. With hyperopia, images focus on a point beyond the retina. Hyperopia results from an eye that is too short or a cornea that is too flat.

Astigmatism is a condition in which the uneven curvature of the cornea blurs and distorts both distant and near objects. A normal cornea is round, with even curves from side to side and top to bottom. With astigmatism, the cornea is shaped more like the back of a spoon, curved more in one direction than in another. This type of curving causes light rays to have more than one focal point and focus on two separate areas of the retina, distorting the visual image. Two-thirds of Americans with myopia or hyperopia also have astigmatism.

Presbyopia commonly affects people as they enter their 40s, and it occurs as the lens inside the eye becomes less flexible and the muscles controlling the lens weaken. People with presbyopia may experience blurred vision when performing everyday "close-up" tasks, such as reading, sewing, or working at the computer. This is why some people with presbyopia need reading glasses or need to hold objects farther away to see them.

Correcting the curvature of the cornea is different for each condition previously mentioned. Glasses and contact lenses are designed to compensate for the refractive errors caused by myopia, hyperopia, and astigmatism. Many people, however, want to reduce their dependence on glasses and contacts. The reasons people find eye glasses or contact lenses are diverse.

There are a number of highly advanced surgical procedures available that effectively reduce the need for glasses or contact lenses. However, not everyone is an ideal candidate for these procedures. It is best to consult an experienced laser eye surgeon in your area to see if you are a good candidate. For more information read another article of mine titled "Different Types of LASIK."