Disorders of the Eye and the Visual System

Disorders and disease of the eye and visual system are widely prevalent among Americans. The best currently available figures indicate that more than two—and possibly as many as four—out of every one thousand Americans are legally blind. While many people are concerned about losing their sight, few are familiar with the actual causes of blindness.

In a person with normal vision, several complicated systems function well and in a coordinated fashion. Abnormalities that interfere with normal vision fall into three groups ranging from disorders that can be corrected with eye glasses to blinding diseases caused by birth defects, infections, aging, and injuries.

Improving Refractive Errors



Difficulty in focusing or seeing a clear image is called a "refractive error." These are very common and can be fully corrected with eyeglasses or contact lenses. Some of these active errors frequently treated by eye care professionals include:

1. Myopia or nearsightedness.  Distances are blurred because the eye is longer than normal so that the image is focused in front of the retina.
   
   
2. Hyperopia or farsightedness. Near objects are blurred because the eye is shorter than normal and the image focus is behind the retina.
   
   
3. Astigmatism. Vision is blurred at all distances because the image does not focus in one position on the retina.
   
   
4. Presbyopia. Reading materials and near objects are blurred because the clear lens at the front of the eye gets cloudier as people age.
   

Refractive errors are common in about one in five children in the United States. Myopia, correctable with concave lenses in eyeglasses, is the most prevalent form. Among adults over age forty, presbyopia affects every other person. The usual prescription is "reading glasses."

In the last twenty years, the dramatic advances in the surgical correction of refractive errors have given the patient a dizzying array of options to wearing glasses and contact lenses. Anyone who is considering these alternatives should become well informed about both the ophthalmologist and the surgical procedure that will be performed. Today, surgeons expect to have patients ask about the number of procedures they have performed and their complication rates, including the incidence of infections, performing operations twice, and other adverse results. Being an informed patient means knowing about and discussing with your surgeon the expected positive and negative results of the type of surgery you are anticipating, and reviewing the consent form that you will be asked to sign. Don't forget to discuss the cost, the time period for the operation and recuperation, and whether you will need to bring someone with you to drive you home and care for you the day of your procedure. Information about all of the surgeries listed below, including testimonials of patients, is available from the organizations. Currently; the following procedures are approved in both the United States and Canada to correct refractive errors:

1. Radial Keratotomy (RK) is an outpatient surgical procedure that corrects myopia by reshaping the curvature of the cornea with microscopic incisions made by an ophthalmologist in a radial or spoke like pattern around the cornea. Several hundred thousand patients have had RK since it was introduced in North America in 1978 with 60 percent resulting in 20/20 vision and 87 percent resulting in 20/40 vision after five years. These are the results of the Prospective Evaluation of Radial Keratotomy (PERK) Study conducted by the National Eye Institute, which now considers the procedure "a reasonably safe and effective technique to improve distance vision/'
   
   
2. Astigmatic Keratotomy (AK) is sometimes used in conjunction with RK to correct astigmatism. The procedure involves surgical incisions made in a curved pattern on the cornea.
   
   
3. Automated Lamellar Keratoplasty (ALK) is a type of surgery where the ophthalmologist cuts a flap of tissue across the cornea. If additional tissue under the flap is removed, high levels of myopia can be corrected. If a thin level of tissue is retained and stretched under the flap, there is a correction for hyperopia.
   
   
4. Photo-refractive Keratectomy (PRK) corrects mild to moderate myopia. The ophthalmologist uses an excimer laser to flatten the cornea. The procedure has been performed in Canada since 1978 and was approved in the United States in 1995 as safe and effective.
   
   
5. Laser Assisted in Keratomileusis (LASIK) is the most advanced and effective laser procedure for patients with more severe myopia. The LASIK procedure involves the use of a keratome (scalpel) and excimer laser to remove a thin layer of tissue from the center of the cornea to flatten the center. LASIK is currently undergoing investigational studies by the Food and Drug Administration (FDA) to determine its long-term effects.