The Complete Book of Laser Eye Surgery Mass market paperbound - 2002 - 1st Edition

Excerpt

Chapter 1
What Can Corneal Refractive Eye Surgery Do for You?

The ancient Greeks explained the mystery of sight by declaring that perception occurs when “internal fire” from the eye mixes with “external fire” from an object.
— ”The Sense of Sight,” National Geographic

It was a fresh spring morning. I had awakened early because a robin outside my bedroom was chirping away in wild abandon. Carefully removing my clear plastic eye patch, I glanced at my digital clock, which was about to start buzzing. No longer a total blur, the inch-high numbers on its face were now in focus. Without the aid of glasses for nearsightedness, I silenced the alarm, jumped out of bed, and flung open my second story window. Taking a deep breath of the heavy, gloriously scented air, I gazed at my Formosa azaleas. Covered with dark pink buds, they were about to burst into bloom. I turned and bounded across my bedroom toward the bathroom door and, for once, didn’t run into my coffee table.

Looking in the mirror, I clearly beheld my unmade face without thick-edged glasses for the first time in my adult life. What a shock. Although my curly dark hair was standing on end, my eyes sparkled, and my cheeks were rosy. Slowly, a huge unstoppable grin spread from one ear to the other. I look healthy, I thought. No one would ever guess that I had eye surgery recently. After examining my teeth, I reached for my toothpaste. With surprise, I noticed that I could read the label without holding it two inches from my nose. Another small pleasure.

As I turned on the shower, I discovered that I could see the soap dish. Even the water marks on the glass door didn’t bother me. That morning — two days after my eye surgery — was the beginning of one of the happiest days of my life. I could see! Not only could I see the coat hangers in my closet, but I could see my bright yellow egg on my breakfast plate.

As I drove down the street without glasses, I waved at my neighbor. Approaching the feeder road, I noted the intense color of the red stop light. More sure of my vision — and thus my ability to react — the cars flying by on the freeway were less frightening than before my operation. I opened my sunroof and pushed the accelerator almost to the floor. Like a hummingbird let out of a dim covered cage, I was free. I felt like the luckiest person in the world. But the truth was — luck had nothing to do with my miraculous new eyesight. Over fifty years of dedicated determination on the part of hundreds of people had changed my life.

— Karen

The Elusive Dream of Perfect Vision

The eye has a passion to see. Forty percent of the input to your brain comes from your eyes. Your vision affects every aspect of your life. Through your sight, you behold the flutter of a butterfly wing, the icy chill of a confidant’s betrayal, and the adoration in your lover’s smile. Penetrating your mind like a swift sword, a single image can unleash a cascade of shattering emotions. In the batting of an eye, a compelling look has weakened the mightiest will, commanding its total surrender. Focused shafts of light, amplified by your retina and interpreted by your brain, can trigger a complex series of chemical reactions within your body. Turning up the heat, adrenaline quickens your pulse. Your heart pumps primal hormonal messages throughout your bloodstream. Capable of igniting love at first sight, a mere glance can break your vulnerable heart or steal it for a lifetime. Only with your eyes, can you completely capture the moment. If you miss the magic, it is gone in an instant, never to return.

If you are nearsighted or farsighted, you may fantasize about waking up in the morning able to see the landscapes of your world without glasses or contact lenses. Like Karen, you probably yearn to have clear, comfortable, binocular vision without sticking something in or in front of your eyes. The simple pleasures of keen eyesight that many people take for granted elude your gaze.

Today, the realization of a long-awaited goal — the dream of relatively accurate unaided vision — is now possible by surgically treating the eye. At last, modern medical technology is able to answer the prayer for reduced dependence on corrective lenses for nearsightedness, far sightedness, and astigmatism (see fig. 7).

As much an art as a science, an amazing new refractive eye operation that can now refocus your eyes is changing lives forever. By harnessing the power of today’s sophisticated computers and the remarkable precision of the laser, a specially trained ophthalmologist can improve your vision without glasses.

Looking at the surgical field through the high magnification of a microscope, a refractive surgeon can reshape your cornea — the transparent window of the eye — using a cool, invisible light scalpel called an excimer, or crystal, laser. The difference of a tiny fraction of a millimeter in the steepness of this corneal lens can dramatically improve the quality of your life. By bringing shimmering oak leaves, pink rose petals, and your child’s angelic face into more perfect view, better vision can set you free to take in the world around you.

As the history of vision correction surgery shows, realizing the dream of clear, unaided eyesight has never been easy. When most people think of refractive surgery to refocus the eye, they think of “radial keratotomy,” or RK — the first operation to correct nearsightedness. This procedure, which was brought from Russia to the U.S. in the late 1970s, is not laser-based. The surgeon attempts to improve his patient’s vision by cutting spoke-like radial incisions in the cornea with a guarded diamond-tipped knife (see fig. 8). The tiny slits are invisible to the naked eye. Although RK has helped many patients, this surgery, as we discuss in detail later, has limitations.

Surgeons performed the first laser-based procedure in the late 1980s. After extensive clinical trials, ophthalmologists looked with great hope to the cool new excimer laser to provide patients with rapid, predictable results. But, unfortunately, the original operation, called “PRK” (photorefractive keratectomy), has failed to live up to many doctors’ early expectations.

During this procedure, surgeons remove the thin, gel-like outer corneal layer called the epithelium. Laser pulses are aimed at the newly exposed surface of the cornea to vaporize microscopic layers of tissue, thereby changing the curvature of the eye’s transparent outer lens (see fig. 9). Although many mildly and moderately nearsighted patients have been helped by this operation, for reasons we will discuss in detail later, PRK patients sometimes hesitate to recommend it to their friends.

Throughout this book, we refer to focusing errors as “mild,” “moderate,” and “severe,” based on “diopters,” a measurement unit used to quantify the light-bending power of a lens. Diopters define the exact amount of correction you need. A 1 diopter lens can bring light rays to a focus one meter away from the lens. So if you have a —1 diopter lens prescription (written as -1D), your eye focuses clearly without correction at one meter, or approximately the length of your arm. If you need a -2 diopter lens, which is twice as strong, you can focus light at only half a meter. This means that you can see clearly without glasses about halfway down your arm. If you need a -10 diopter lens, your eye focuses light at about two inches from your nose.

We sometimes tell patients to think of diopters in relative terms; the more out of focus the eye, the higher the number used to represent the refractive error. For a further explanation see insert 1, What Are “Diopters”? on page 22 and insert 2, Measuring Visual Acuity: What Is 20/20, or “Normal,” Eyesight? on page 24 (see the Snellen eye chart in fig. 10).

Insert 1
What Are “Diopters”?

To write your glasses or contact lens prescription, your doctor must determine your exact refractive error. Your correction is expressed in diopters that measure how much a corrective lens must bend light to focus it on your retina to normalize your vision. A lens that can bend parallel light rays to a focal point of 1 meter is said to have a power of 1 diopter (1.00D). A 2-diopter lens can focus light rays at a point 0.5 meters away from itself.

If you are blessed with normal eyesight, your eye doctor will write in your chart that your “sphere” is 0.0D, or “plano” (pl). This means, of course, that you have no refractive error. Department store sunglasses without power are plano lenses. Only curved surfaces bend light; flat surfaces do not.

If you have a myopic correction of -1 diopter, you are focused at 1 meter, or approximately the length of your arm. Without glasses, objects farther away than your hand will be slightly blurred and will become progressively more indistinct the further in the distance you look. With this refractive error, and no other visual defects, you should be able to read most street signs in good light. If your refraction is -2 diopters, you are focused at 0.5 meters, and you can only see clearly halfway down your arm. With this refractive error, you dare not drive without glasses. Nonetheless, you can see better in the distance than a person who is more nearsighted — someone, for example, whose correction is -3 diopters.

If you are farsighted, your amount of correction is expressed in positive numbers (+1 diopter of hyperopia, e.g.).

With nearsightedness, a refractive or focusing error less than -5 diopters is considered mild “myopia.” Myopia is the medical term for nearsightedness and is corrected with a “minus” lens. Five to 7 or 8 diopters is in the moderate range, and greater than 7 or 8 is called severe. About 90 percent of nearsighted people have a refractive error of less than -6 diopters. Only about one nearsighted person in ten has severe myopia. Nevertheless, even if you have only -4 diopters of nearsightedness, you may feel that your correction is severe because you are almost totally dependent on your glasses or contact lenses. With astigmatism, less than 1 diopter is considered mild. One to 2 diopters is moderate. Two to 3 diopters is severe, and greater than 3 diopters is extreme. With farsightedness, greater than +5 diopters is called severe “hyperopia,” the medical term for farsightedness. This refractive error is corrected with a “plus” lens. See insert 3, Reading Your Eyeglasses Prescription, on page 25.

Insert 2
Measuring Visual Acuity: What is 20/20, or “Normal,” Eyesight?

You probably remember reading the big E on your doctor’s Snellen eye chart at your last appointment. Many people confuse their eyeglasses prescription, which is measured in diopters, with their eye chart readings, which assess visual acuity (VA). By ascertaining the smallest line of figures that you can distinguish at a specified distance, your physician can determine your VA. If you can read the 20/20 line at 20 feet (about 6 meters), your visual acuity equals 20/20 (or 6/6 in meters), which is normal. If you read the 20/40 line at 20 feet, you see at 20 feet what the normally-sighted person sees at 40 feet.

Your VA, as measured by the Snellen eye chart, cannot be accurately converted to diopters. Nonetheless, assuming that your eyes are healthy, and you have no refractive error affecting distance vision, you should be able to read the 20/20 line or better. If your myopic refraction is -1 diopter, you should be able to read the 20/40 or 20/50 line of the eye chart. If you have significant astigmatism, however, you probably wouldn’t have 20/20 visual acuity. In addition, if your eye has some underlying pathology — even though light is perfectly focused on your retina — you may be unable to read the 20/20 line.

Now, after years of research, ophthalmologists finally have a “patient friendly” procedure that, in exquisitely skilled hands, delivers excellent, relatively stable results in a more elegant fashion than the older refractive operations. Known as LASIK (an acronym for laser in situ keratomileusis), this new excimer laser outpatient procedure is one of the first operations in the history of medicine to use a computer-driven light scalpel to reshape part of the human body. The Greek word keratomileusis is literally translated as “carving of the cornea.” (Kerato means “cornea” and mileusis means “carving.”) During LASIK, an ophthalmologist uses an electromechanically controlled surgical blade to cut a round “hinged” flap from the surface of the anesthetized cornea, the eye’s curved window (see fig. 11). Leaving one uncut edge of the protective flap attached to the eye, the doctor carefully folds back this thin tissue, exposing the delicate inner corneal layer called the stroma (see fig. 3). To correct myopia, he then aims the cool, ultraviolet laser directly over the light-gathering pupil to remove microscopic layers of corneal tissue. For most nearsighted patients, the laser beam is concentrated on the eye only ten or twenty seconds, although larger refractive errors require more treatment. After the cornea’s curvature is thus remodeled, the physician gently puts the living flap back in place. No stitches are necessary. (See chapter 2 for a detailed description of this operation.)

Insert 3
Reading Your Eyeglasses Prescription

When your eye doctor hands you a prescription for glasses or contact lenses to correct nearsightedness, farsightedness, astigmatism, or age-related presbyopia, how do you read the esoteric notation? As you know, your prescription, which is measured in diopters, is the power that must be put in each corrective lens to counteract your refractive error in the respective eye. Your prescription is expressed with the following formula:

Sphere (D) + or - Cylinder Power (D) at Cylinder Axis (in degrees)

This simply means that if you have -3 diopters of nearsightedness in your right eye and -3.5 diopters of myopia in your left eye — and no astigmatism — your glasses prescription might read:

O.D. (right eye) -3.00(D) and O.S. (left eye) -3.50(D)

If you also have 0.25 diopters of myopic astigmatism in your left eye, your prescription may read:

O.S. -3.50(D) -0.25(D) at 180 degrees axis.

This means that to correct your left eye (O.S.) you need a minus (concave) -3.5 spherical lens combined with a -0.25 cylindrical lens at an axis of 180 degrees. Since the axis is at 180 degrees, the astigmatism is horizontal. By looking at this glasses prescription, your doctor knows that both meridians of your cornea bend light too much: the flattest meridian refracts light short of the retina by 3.5 diopters, and the steepest one by 3.75 diopters. Put another way, with this prescription, you would have -3.5 diopters of myopia combined with -0.25 cylinder astigmatism. If you also need bifocal correction for age-related presbyopia, your doctor might write:

Add = +1.50(D)

This means that you need +1.5 diopters more plus power in the lower portion of your glasses to help you focus to read. Added algebraically to the -3.5 diopter prescription of your left lens, the power in your bifocal prescription in that eye would be:

-2.00D (-3.50D plus +1.50D equals -2.00D).

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“With this book, you will have a better chance of realizing your long-awaited dream — the dream of excellent vision without glasses or contact lenses.”
— Spencer P. Thornton, M.D.