Astigmatism of the Human Eye

About Astigmatism of the Human Eye

Overview
Astigmatism is a common eye condition, but severe forms can cause blurred vision. Astigmatism usually coexists with one or more other eye problems, such as myopia or hyperopia. It is easily diagnosed with a conventional eye exam, and several means of correcting the condition are widely available.
Significance
Almost everyone has some degree of astigmatism. Very minor forms usually cause no problem and need no correction. Astigmatism is one of three so-called refractive vision problems. The other two are nearsightedness, or myopia, and farsightedness, or hyperopia. In all three conditions, the eye makes errors when it bends (refracts) the incoming light.
Effects
The human eye should be shaped like an apple or orange. The cornea, or outer covering of the eye, and the lens, which lies right behind the cornea, should be curved evenly in all directions. The light that enters the eye is then properly focused on the retina, located on the eye’s rear inner wall. But rather than an apple, the eyes of people with astigmatism are shaped more like pears or figs. When the cornea or lens is warped or misshapen, the eye can’t properly focus the incoming beams of light. Result: everything looks fuzzy, whether it’s close up or far away.
Identification
The diagnosis of astigmatism can be made during a routine ophthalmologic exam and refraction test. The doctor may also measure the curvature of the cornea with a procedure called keratometry, a very exact procedure. If you plan to get contact lenses, keratometry will probably be necessary.
Prevention/Solution
Eye doctors can treat astigmatism in one of four ways: eyeglasses, contact lenses, orthokeratology and laser or other surgical procedures. Most people choose eyeglasses. The lens is designed to correct for the abnormal curvature of the eye. In addition, the lens can also have additional corrections for myopia or hyperopia, if necessary.
Contact lenses are another option for many people with astigmatism. Orthokeratology, also called Ortho-K, is a process in which a person wears a hard contact lens overnight and removes it in the morning. The lens reshapes the cornea—at least temporarily—and the person usually has normal vision the next day. The benefits are short-lived, and the lens must be worn regularly to maintain the benefit.
If you have astigmatism, you may also be a candidate for a laser procedure. You’ve probably heard of LASIK, a surgical procedure that involves removing tissue from the inner layer of the cornea. A similar procedure, called LASEK, involves a thinner layer of the cornea and leaves the eye less vulnerable to injury. LASEK may be recommended to people who play sports. Another laser procedure, photorefractive keratotomy, or PRK, takes tissue from the both the outer and inner layers of the cornea. In both situations, the goal of surgery is to make changes in the cornea that allow entering light to be more accurately focused before it hits the retina.
Warning
Soft contact lenses may not be the best choice for astigmatism because they take the shape of the eye. Because the astigmatic eye is misshapen, this defeats the purpose of the corrective lens. Some people with astigmatism have good experiences with soft toric lenses, and it may be worthwhile to ask your doctor about these. Rigid gas permeable contact lenses apparently give the best correction for people with astigmatism because they don’t conform to the eye’s shape.
Resources
American Optometric Association
MayoClinic.com
MedlinePlus
University of Michigan Kellogg Eye Center