The key to understanding refractive surgery is to understand how the eye works.

Normal Vision

Sharp, clear vision is the result of light rays passing through the cornea, pupil and lens of the eye and focusing directly on the retina. If the cornea is not round, or is too steep or too flat in relation to the length of the eye, light rays focus either in front of or behind the retina. This results in "refractive errors" such as nearsightedness, farsightedness, and astigmatism. Laser vision correction improves the way the eye focuses light by modifying the curvature of the cornea and re-focusing the light directly on the retina.

Nearsightedness

Nearsightedness, or myopia, occurs when the curvature of the cornea is too steep or the eyeball is too long. With nearsightedness, the eye's strong refractive power forces the image to be focused in front of the retina, rather than on it. When light focuses in front of the retina, near objects can be seen clearly, but far objects appear blurry. Myopia can be treated by flattening the cornea with LASIK, PRK or LASEK.

Farsightedness

Farsightedness, or hyperopia, is caused when the curvature of the cornea is too flat, or the eyeball is too short, forcing light to focus behind the retina. With farsightedness, the eye's weak refractive power causes far objects to be seen more clearly and near objects to appear blurred. The eyes may have to strain to maintain things in focus. The first appearance of hyperopia is strongly age-dependent; younger patients have much less difficulty with hyperopia. Hyperopia can be corrected by steepening the central cornea with LASIK, PRK or LASEK.

Astigmatism

Astigmatism occurs when the cornea is irregularly shaped - like a football or a teaspoon - preventing light from converging on the retina. Parts of the image may focus on the retina, while others focus behind it or in front of it. This has the effect of bending light inconsistently and causing blurred or distorted images. Astigmatism can occur alone or in addition to either nearsightedness or farsightedness. Although astigmatism can complicate refractive surgery, it can be effectively corrected with LASIK, PRK or LASEK.

Higher-order Aberrations

Several types of visual imperfections, referred to as lower- and higher-order aberrations, can exist within the same eye and affect both visual acuity and the quality of vision. Lower-order aberrations, like nearsightedness, farsightedness, and astigmatism, contribute to approximately 80% of refractive errors. They affect how much you see. Higher-order aberrations account for the remaining 20% of error and affect how well you see. They can be compared to smudges or spots on your glasses and have been linked to halos and glare that cause vision problems at night. Higher-order aberrations have not been treatable by conventional laser vision correction procedures. Now, Wavefront technology and Custom LASIK can quantify and correct these higher-order aberrations.