Vision Correction

by Food and Drug Administration (FDA)

Vision correction has come a long way since the 13th century when the first pair of spectacles was made by riveting together the handles of two magnifying lenses. Today, surgical developments in vision correction, as well as advances in traditional eyeglasses and contact lenses, can potentially improve a person's vision to better than the optimal range of "20/20."

It's no surprise, then, that people dependent on glasses or contact lenses are visiting their eye-care specialists, hoping to find a quick fix for some age-old vision problems among the array of new techniques, products and technologies. Learning about some of the common disorders that can threaten vision and how the eye "sees" can help you determine the best treatment to correct your vision. It's also important to understand the advantages, disadvantages, and limitations that come with vision correction procedures and aids.

How the Eye Sees

Having 20/20 vision means seeing at 20 feet what a person with normal vision sees at 20 feet. A person who has 20/40 vision can see at 20 feet what the person with normal vision sees at 40 feet. And so on.

The eye does not actually "see" objects. Instead, it sees the light that objects reflect. To see clearly, light striking the eye must be bent or "refracted" through the cornea — the clear window at the front of the eye that provides most of the focusing power. Light then travels through the lens, where it is fine-tuned to focus properly on the nerve layer that lines the back of the eye — the retina — and sent to the brain via the optic nerve. The retina acts like the film in a camera, and clear vision is achieved only if light from an object is precisely focused on it. If not, the image you see is blurred. This is called a refractive error.

Refractive errors usually occur in otherwise healthy eyes. They are caused mostly by an imperfectly shaped eyeball, cornea or lens. There are four basic types of errors:

Myopia or nearsightedness — Close objects appear sharp but those in the distance are blurred. The eyeball is longer than normal from front to back, so images focus in front of the retina instead of on it.

Hyperopia or farsightedness — Distant objects can be seen clearly but objects up close are blurred. The eyeball is shorter than normal, so images focus behind the retina.

Astigmatism — Objects are blurred at any distance. The cornea, lens, or both are shaped so that images aren't focused sharply on the retina.

Presbyopia or aging eye — The eye loses its ability to change focus due to the natural aging process. This usually occurs between ages 40 and 50.

Glasses, contact lenses, and laser eye surgery attempt to reduce refractive errors by making light rays focus properly on the retina.

Laser Eye Surgery — A Popular Alternative

Laser eye surgery is intended for people who want to minimize their dependency on glasses or contact lenses. Laser surgery can provide vision correction similar to what would be obtained with glasses or contact lenses. People under the impression that surgery can improve their vision beyond what they can see with glasses or contact lenses, however, likely will be disappointed.

By far, the largest increase in laser eye surgery interest recently has been in a procedure called "laser in situ keratomileusis," popularly known as LASIK. Advertising for this technique appears prominently on broadcast outlets, including the Internet and in newspapers and magazines. Fortunately, says Terrence P. O'Brien, M.D., a spokesman for the American Academy of Ophthalmology (AAO), most surgeons and medical centers are doing a good job of educating the public about the risks and benefits of LASIK. "But patients need to be very well-informed in advance," he says.

LASIK permanently changes the shape of the cornea, and is performed for varying degrees of nearsightedness, farsightedness, and astigmatism. A surgical knife, called a microkeratome, is used to cut a flap in the cornea, leaving a hinge at one end of the flap. The flap is then folded back to reveal the middle layer of the cornea, called the stroma. Pulses from a computer-controlled excimer laser vaporize a portion of the stroma and the flap is then replaced. By removing this tissue, the shape of the central cornea is changed, and the refractive error is reduced.

O'Brien, who is also director of refractive surgery at the Wilmer Eye Institute at Johns Hopkins University in Baltimore, has performed over 10,000 eye surgeries. Still, he warns that people considering LASIK need to be wary of ads that make excessive promises.

"Price should not be the first factor" in considering to have delicate eye surgery, he says. "People fear blindness second only to cancer, and just as they wouldn't consider a discount open heart operation or budget brain surgery, they shouldn't take a chance with their eyes." The real struggle, he says, is in training doctors. "The most advanced technology and precise laser will give poor results if you don't have an experienced, capable surgeon."

This latest hype about LASIK's now-more-affordable advantage, coupled with some pretty appealing results, makes surgery one of the most exciting vision correction options available. Doctors say that LASIK gives a rapid visual recovery, with minimal pain, and little or no post-operative discomfort. In fact, most people who undergo LASIK, like Beth Polazzo — one of O'Brien's patients — can see well enough to drive immediately after surgery, and usually have excellent vision within a week.

"I had good vision immediately," says the 54-year-old Brooklyn, N.Y., resident, even though eventually one eye had to be retreated. "This is the best I've seen since I was seven years old." The laser does its work on each eye in less than a minute, and patients are typically back to work or normal activities within three days.

About the Author

www.fda.gov
FDA is A United States government body that oversees medical devices, including contact lenses, intraocular lenses, excimer lasers and eyedrops. In the US, these products must be approved by the FDA before they can be marketed.