Inside the Eye: From Laser Surgery to Macular Degeneration

Five options for laser eye surgery

Published: June, 2002

Only a few years ago, having imperfect vision simply meant that you went to the eye doctor, got fitted for glasses or contact lenses, and went on your merry way. But now, there's an array of laser surgeries to choose from, each with a slightly different procedure to accommodate particular vision problems.

In general, laser eye surgery modifies the cornea, the clear covering of the front of the eye that bends (or refracts) light rays as they enter the eye. For clear vision, the cornea must have the correct shape to focus light rays precisely on the retina at the back of the eye. If the cornea is too steep, too flat, or irregular in shape, the image focuses either in front of or behind the retina — hence, blurry vision. Eyeglasses or contact lenses can compensate for this problem by increasing or reducing the angle of light as it enters the eye.

In 2000 the U.S. Food and Drug Administration approved a procedure, laser thermal keratoplasty (LTK), and it approved another in April 2002 called conductive keratoplasty (CK), which is specifically used to correct farsightedness. The most common procedures are photorefractive keratectomy (PRK) and Laser-Assisted In Situ Keratomileusis (LASIK). As time and experience advances, these techniques become ever more precise and predictable.

The following chart will help you sort out this alphabet soup of laser eye surgery:

Surgery Eye Condition How It Works The Procedure Considerations
Laser Thermal Keratoplasty (LTK) Farsightedness (Distant objects are clear, but the eye can't focus properly on close ones.) Steepens the slope of the cornea, so light can focus on the retina. A laser reshapes the cornea without touching the eye's surface by gently heating the collagen at the periphery of the cornea.LTK takes only a few minutes. Most people feel very little discomfort during the surgery. LTK is best suited for people over 40 who require only reading glasses and whose prescription has changed very little over the last six months. How long the correction lasts depends largely on the amount of correction needed and the patient's age.
Conductive Keratoplasty (CK) Age-related farsightedness (As we age, the lens of the eye becomes less flexible, making it difficult to focus on close objects.) Like LTK, CK steepens the cornea's slope. CK typically lasts less than a minute. Short bursts of radio waves shrink the cornea's collagen fibers to reshape it. While this technique appears to be generally effective, it can take a few months before the full benefits are experienced.
Keratectomy (PRK)
Nearsightedness (Close objects are clear, but the eyeball is too long or the cornea curves too steeply to sharply focus on distant objects.)Astigmatism (The cornea is irregularly shaped, and vision may be blurry at all distances.) Flattens (or reduces the curvature of) the cornea. A laser removes a thin layer from the center of the cornea by vaporizing corneal tissue in very precise amounts. This procedure takes only a few minutes and is usually performed with local anesthetic eye drops. Most people can return to their normal routines in a day or two.
Laser-Assisted In Situ Keratomileusis (LASIK) Severe nearsightedness, farsightedness, and astigmatism Combines surgery and laser to reshape the cornea. The surgeon cuts a flap in the cornea using a knife, and then reshapes the cornea's middle layer with a laser. The flap heals over that layer. While a more complex surgery than PRK, LASIK requires less recovery time. Many patients can see well enough to drive home after surgery. Candidates for LASIK should be at least 18 years old and have stable vision and no abnormalities of the cornea or external eye.
Radial keratotomy (RK) Moderate or mild nearsightedness Reduces the curvature of the cornea. The doctor makes small, radial incisions in the periphery of the cornea to flatten it. The incisions can weaken eye structure. No other procedures to improve vision can be done after RK. Candidates should be at least 18, with stable vision and no corneal or external eye abnormalities.

June 2002 Update

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New Drugs Have Had Impact on Glaucoma Therapy

Glaucoma strikes nearly 4 million people in the United States, and is a major cause of blindness. It is characterized by excessive fluid pressure in the eye, which can damage the optic nerve. The good news is that when caught and treated early, vision can usually be spared.

Glaucoma can be treated either with medications or with surgery. Until recently, physicians primarily treated glaucoma with topical ß blockers, which reduced the amount of fluid, called aqueous humor, produced in the eye. When drugs were not effective, a surgical procedure would be used to improve drainage of the fluid. Over the past five years, however, three new classes of glaucoma medications have come into use: prostaglandin analogues (latanoprost), which remove aqueous humor through the uveal tissues; topical carbonic anhydrase inhibitors (dorzolamide), which reduce the amount of aqueous humor produced in the eye; and α-2 agonists (brimonidine), which decrease production of aqueous humor and increase fluid outflow.

Investigators in Scotland set out to determine the impact that these new classes of drugs have had on the treatment of glaucoma. They reviewed a national registry that recorded the prescription and surgery statistics for Scotland from 1989 through 1999. The researchers found that the number of surgical procedures performed per 1,000 glaucoma patients increased between the years 1989 and 1994, then decreased by 45.9% from 1994 through 1999. During the same period (1994–1999), the number of medications prescribed per 1,000 glaucoma patients increased by 24.9%, mostly due to a rise in the prescription of the new drug classes.

Although the new drugs have altered the medical and surgical treatment of glaucoma, the researchers note that it is still too early to tell whether the new medications will prevent the need for surgery, or only delay it.
March 2002 Update

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New Treatment for "Wet" Age-Related Macular Degeneration

The U.S. Food and Drug Administration (FDA) has recently approved verteporfin (Visudyne) for the treatment of age-related macular degeneration. Verteporfin is used to treat the "wet" (or "classic") form of this disease in which well-defined blood vessels proliferate beneath the retina. These vessels leak blood and fluid, which causes scarring and loss of vision in the center of the eye. Peripheral vision remains unimpaired. Affected individuals experience a sudden worsening and distortion of their central vision and may become legally blind within a few weeks or months of the time symptoms first appear. Only 10% of age-related macular degeneration cases are of this type.

The new treatment is applied in two stages. First, verteporfin, a photosensitive dye, is injected intravenously into the bloodstream over a 10-minute period. The dye is picked up by the abnormal blood vessels behind the retina. The physician then directs a "cold" laser into the eye. This activitates the dye and triggers clotting and constriction of the abnormal blood vessels without damaging the retina. In many people, the effects of this therapy last only a few months, but the procedure can be repeated every three months if necessary.

In a recent clinical trial comparing treatment with verteporfin to treatment with a sugar-water solution (placebo) and the same phototherapy, the patients treated with verteporfin had significantly better outcomes than those treated with placebo. At the 12-month follow-up visit, 61% of the verteporfin group had lost fewer than three lines of vision compared with 46% of the placebo group. The benefit was even greater for those with the purely "classic" form of the disease — 77% of the verteporfin group versus 27% of the placebo group. No benefit was seen in members of the verteporfin group who did not have primarily "classic" macular degeneration.

Side effects of verteporfin treatment include headache, visual disturbances, injection site reactions, and infusion-related low back pain. A small percentage of patients (1%–4%) experienced severe vision loss within a week after treatment, but this loss of vision was not always permanent. Patients who undergo this therapy must avoid exposing their eyes and skin to direct sunlight or bright light indoors for five days so as not to activate any traces of verteporfin still in the bloodstream.

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