Eyesight by a Thousand Cuts

Eyesight by a Thousand Cuts

A cure for nearsightedness may leave you farsighted

The technique was discovered by a Russian doctor by accident in 1971. Treating a man whose cornea had been cut when his glasses were smashed in a fight, the surgeon Svjatoslav Fyodorov discovered that the patient’s sight had improved.

Fyodorov hypothesized that the scoring of the man’s eye by the shattered glass had flattened the cornea, which is the transparent dome about the thickness of a credit card that covers the front of the eyeball. When a person is nearsighted, or myopic, the eyeball becomes too long, which causes light rays to focus short of the retina, resulting in blurred distant vision.

By flattening the cornea, Fyodorov realized, an eyeball could be restored to a rounder shape, thereby altering its local length so that light focused on the retina itself, eliminating the myopia.

Over the next several years, Fyodorov carefully developed the surgical technique now known as radial keratotomy, in which a series of tiny but deliberate incisions are made in the surface of a patient’s cornea to flatten the eyeball and reduce the nearsightedness.

American surgeons trained by Fyodorov performed the first radial keratotomies here in 1978, and today hundreds of thousands of such operations are performed in the United States annually, at a rather accessible cost. According to a study sponsored by the National Institutes of Health over a 10-year period, the technique successfully eliminated nearsightedness in 70 percent of patients, “with a reasonable level of safety.”

Eyesight. Photo by Elena

Of the several hundred patients followed by a decade, about 70 percent had no need for eyeglasses of contact lenses to correct for nearsightedness, 53 percent of the eyes studied had uncorrected vision of 20/20 or better, and 85 percent of the patients could see at 20/40 or better, which is what is required for a driver’s license in most places. Vision-threatening complications occurred in only 3 percent of the cases, and in all but three cases, the eyes could be corrected to 20/25 vision with glasses.

Farsightedness was another matter, however. Ten years after surgery, 43 percent of those whose eyes were studied had become farsighted bu 1.00 D or more. (D stands for diopter, a measure of lens power indicating the need for a new prescription.) In many cases, the study found, the onset of symptomatic presbyopia – a condition where the eye loses natural flexibility – appear to have been accelerated by radial keratotomy, often leading to the need for reading glasses.

One way to offset this drift toward farsightedness is to shorten the lengths of the incisions made in the cornea, the study group concluded. Most of the vision gain from radial keratotomy comes from the incision’s middle portion and not from the edge, and the longer the incisions, the more pronounced the farsightedness is, according to the NIH study.

The shift to farsightedness can be at least partly compensated for by intentionally undercorrecting for myopia in the initial radial keratotomy operation. Over time, the shift toward farsightedness and the undercorrecting for nearsightedness sometimes balance one another out, resulting in virtually normal vision.

Before deciding to get a vision overhaul with radial keratotomy, consider this, however: Once your corneas are slit in the procedure, wearing contact lenses comfortably can be very difficult. That means that if your nearsightedness is not adequately corrected or if you develop complications from the surgery, you are likely to be stuck wearing eyeglasses all the time.

A new treatment also is on the horizon for the nearsighted that leaps into the world of laser surgery. The process, known as photorefractive keratoktemy, uses an excimer laser to flatten the cornea’s contours and erase nearsightedness, the same way radial keratotomy does. The procedure takes 15 to 30 seconds and is appealing because it removes very little tissue – typically less than 10 percent of the cornea’s thickness – and relies more on automation than on the skill of individual surgeons. Approved for use in 35 countries, photorefractive keratectomy was recommended for approval in the United States by an FDA advisory panel late in 1994. The use of laser surgery to treat mild to moderate nearsightedness was approved a year later.

A Shift to Farsighted

A diopter is the unit of measurement of change in one’s vision. A one-diopter change indicates the need for a new eye-wear prescription in the immediate future.

Beware Extended-Wear Contacts

Sleeping with your lenses in can lead to corneal damage

Extended-wear contact lenses, touted for their ability to be worn as long as a week without removal or cleaning, aren’t so carefree, after all, according to several studies. Researches have found that the risks of an infection known as ulcerative keratitis, which causes severe inflammation of the cornea and can lead to permanent vision loss, were twice as great for conventional soft extended-wear users as for daily-wear users. Wearers of disposable lenses, which are designed to be worn without removal for up to two weeks and then thrown out before dirt and debris build up, were 13 times as likely to develop a corneal infection as those who regularly removed their contacts for cleaning.

Researchers writing in Archives of Ophthalmology found that most of the increased risk was the result of extended-wear users keeping their lenses in overnight and not following proper cleaning procedures. From a half to three-quarters of the corneal infections that now develop could be stopped by not wearing disposable lenses overnight, the group argued.

“Even adequate lens care, although recommended, does not protect against the excess risk of overnight wear,” says Dr. Oliver Schein, an ophthalmologist at John Hopkins University and co-author of the study. The message for the five million Americans who now favor the convenience of extended-wear lenses: Remove your lenses and disinfect them while you give your eyes a rest each night.