Laser eye surgery

I grew up in a glasses-wearing family. My parents wore glasses, my two older brothers wore glasses and I, by the age of five, also wore glasses.

In more recent years, my brother Dwight and I switched to contacts, but while contacts may be invisible to others, they’re still glasses, albeit tiny ones stuck to your eyeballs.

But within the last couple of years, Dwight got rid of glasses forever (hopefully). He underwent laser eye surgery to correct his vision. No more glasses –and bragging rights over the rest of us, which in a family of three boys are important rights indeed.

The eye works essentially the same as a camera. Light strikes the cornea, the clear outer surface of the eye, and is bent so that it passes through the pupil and then through the lens, which fine-tunes the light waves to focus on the retina, a layer of nerves that lines the back of the eye. If the light waves entering don’t focus properly on the retina, blurry vision results.

Vision is usually described in terms such as 20/20 or 20/40. Having 20/20 vision means you can see something 20 feet away just as clearly as if it were 20 feet away. Having 20/40 vision means that something 20 feet away shows only as much detail as something 40 feet away would to someone with normal vision. And if, like me, your vision is something well over 20/200, then essentially you can’t see much of anything that’s 20 feet away.

Glasses and contact lenses bend the light rays heading for the eyes before they pass through the cornea. Their refraction added to that of the eye itself results in improved vision. Laser eye surgery goes that one further, actually changing the refraction of the eye itself.

The first surgical procedure to attempt to correct eyesight was radial keratotomy, or RK. In RK, incisions are made by a surgeon, wielding a hand-held knife, in a radial pattern along the outer portion of the cornea. These incisions flatten the curvature of the cornea, changing the way it focuses light. The number and length of the incisions determines the degree of correction.

The excimer laser, which entered clinical trials in 1987, offered a new way of working on the eye. The excimer laser uses a cool, computer-controlled beam of ultraviolet light to vaporize tiny amounts of tissue. (The beam is so precise it can cut notches in a strand of human hair.)

Photorefractive keratectomy (PRK) was the first version of laser eye surgery. In PRK, the outer layer of the cornea is scraped away to reveal the inner layer, or stroma, which is then shaped by the removal of microscopic amounts of tissue. Today, PRK has essentially given way to laser-assisted in situ keratomileusis–LASIK for short (thank goodness). In LASIK, a flap of the outermost layer of the cornea is peeled back rather than scraped off, the stroma is sculpted, then the flap is returned to its place.

LASIK surgery isn’t for everyone. Not everyone ends up with 20/20 vision without glasses or contacts. People who need reading glasses before surgery still need reading glasses afterward. Some people actually end up with worse vision. Many patients don’t see as well in situations of low contrast, such as at night or in a fog, as they did before treatment; some see halos around lights at night.

However, scientists continue to refine the procedure. Current laser surgery only correct major aberrations, not only leaving subtle ones untouched but introducing new ones. So researchers are looking for ways to map and correct these subtle aberrations. One method is to shine light into the eye and analyze the reflections bouncing off the retina. In recent trials, surgery based on this information produced 20/20 vision or better in 93 percent of cases.

Other researchers are using scans to directly measure the shape of the cornea, and one, Jim Schwiegerling, an opthamologist at the University of Arizona in Tucson, is combining both approaches to create a highly detailed computer model of the eye, which is then used to guide the laser during surgery. His goal is to ensure that everyone who has surgery gets at least 20/20 vision out of it. A few may even end up with 20/10 or 20/5 vision.

The technique won’t be available for another two or three years at the earliest. But that’s OK. To recapture vision bragging rights from my big brother, I can wait.

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