THE HUMAN EYE AND HOW VISION WORKS
NONSURGICAL VISION CORRECTION OPTIONS
Eyeglasses
Eyeglasses have been around for hundreds of years. As early as the thirteenth century, inventors in China and Europe inserted magnifiers into frames, making the first prototype for our modern-day eyeglasses. Like the early versions, today's eyeglasses work like magnifying glasses that enhance the eye's ability to focus sharply, whether near or far. The amount of curvature in the spectacle lens determines how light bends before it reaches your cornea. Vision is corrected, depending on the angle of refraction, to compensate for your focusing error.
Eyeglasses have a number of advantages. They are usually affordable, are easy to maintain, and can be adapted for a number of different uses, such as reading, active sports, and driving. They also have disadvantages. Eyeglasses may restrict peripheral vision, the outer part of your field of vision; prove difficult in certain weather conditions, such as rain or snow; and make images appear smaller or larger than they really are. They may cause a number of visual aberrations, including halos around lights, and the lenses usually need to be replaced as your vision changes. Eye glasses may interfere with certain occupations and recreational activities-swim ming, for example. And some people just don't like the way they look in eyeglasses.
Contact Lenses
Contact lenses offer another option for correct ing vision. Like eyeglasses, they make up the difference between the amount of refraction your eye can accomplish on its own and what is needed for sharp focus. Because they are extremely thin and are custom-shaped for your cornea, contact lenses float on the surface of your eye; they are held in place by natural suction and are constantly lubricated by the eye's own moisture.
Contact lenses have some advantages over eye glasses. For example, contacts enable the wearer to have more natural vision (including better peripheral vision), cause little noticeable change in cosmetic appearance, and allow more freedom in recreational activities. On the other hand, contacts may require maintenance-continuous, frequent cleaning. Users must buy cleaning and storage solutions. The lenses may tear easily. They may be inconvenient for traveling, and also are easily lost. Contacts may be uncomfortable for patients with dry eyes or for those who live and work in polluted city air. They may cause visual aberrations (including halos and un even vision) and always carry an increased risk of infection and possible corneal scarring. Individuals who live in higher altitudes may become intolerant of contact lenses over time because of the air's lower oxygen and humidity content.
The variety of contact lenses available today is dazzling. Costs for contacts vary widely, de pending on the type you need.
Orthokeratology
This is a technique for treating myopia, or near sightedness. Ortho keratology uses a series of rigid contact lenses that apply pressure to the cor nea to flatten it. The effects are not permanent and require continued dependence on daily-wear maintenance lenses to retain the reshaping. Ortho keratology is generally only effective, even tempo rarily, for low levels of nearsightedness. The technique is expensive and high maintenance and requires continuous follow-up visits. Long-term effects can include permanently warped corneas. The risk of infection may also be greater than that from normal contact lens wear.
Laser Vision Correction: An Overview
