Refractive Errors / Focusing Problems

About 180 million people in the United States wear eyeglasses or contact lenses to correct nearsightedness, farsightedness, or astigmatism. These vision disorders--called refractive errors-- affect the cornea and are the most common of all vision problems in this country.

Refractive errors occur when the curve of the cornea (the front dome-shaped window of the eye) is shaped too steep or too flat. When the cornea is of normal shape and curvature, it bends, or refracts, light on the retina with precision. However, when the curve of the cornea is incorrect for the length of the eye, this affects vision.

The refractive process is similar to the way a camera takes a picture. The cornea and lens in your eye act as the camera lens. The retina is similar to the film. If the image is not focused properly, the film (or retina) receives a blurry image. The image that your retina "sees" then goes to your brain, which tells you what the image is.

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

Hyperopia, or farsightedness, is the opposite of myopia. Distant objects are seen more clearly, and close-up objects appear 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 astigmatism, the cornea is shaped more like the back of a spoon, curved more in one direction than in another. This causes distortion of the visual image. Two-thirds of Americans with myopia also have astigmatism.

Refractive errors are usually corrected by eyeglasses or contact lenses. Although these are safe and effective methods for treating refractive errors, refractive surgeries such as LASIK are becoming an increasingly popular option. Click here to find out more about LASIK.

Another focusing problem that eventually affects everybody is called Presbyopia. This is the condition that results in difficulty seeing up close and is usually noticed after age 40. This occurs because the eye's own internal focusing lens hardens as we age, and is less flexible in allowing near objects to come into focus. This lens hardening occurs in everyone without exception, and is why reading glasses or bifocals eventually become necessary.