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Laser Vision Correction:
 A LASIK Manual For Patients

 
Introduction
Refractive errors
Do I qualify for LASIK?
What are the contraindications to LASIK?
Will I be able to throw away my glasses?
How do I prepare for surgery?
How is LASIK performed?
What to expect on the day of surgery?
How do I care for my eyes after LASIK?
What to expect after surgery?
What can go wrong?

 
 

Introduction

     Traditionally, imperfect vision has been corrected with glasses or contact lenses. A more recent option is to perform surgery to correct the prescription. The newest and most advanced surgery is called LASIK (Laser In Situ Keratomileusis). LASIK uses an Excimer laser to reshape the cornea and thus change how images are focused. The procedure can greatly reduce or eliminate your dependency on glasses and contact lenses.
     The purpose of this manual is to better inform you about the LASIK procedure. This manual is not intended to persuade or dissuade you from LASIK surgery. It is intended to give the most accurate information so that you can make an informed decision. You should read this information carefully and discuss any questions with your doctor.

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Refractive errors

     Refractive errors are imperfections in the focusing system of some people's eyes that require them to have to wear glasses or contact lenses in order to see perfectly. Refractive errors may affect distance vision (such as nearsightedness, farsightedness, and astigmatism) or near vision (as in presbyopia).
     The cornea is the clear dome-shaped front part of the eyeball. It measures 11 millimeters vertically and 12 millimeters horizontally. Its thickness measures 0.5 millimeter centrally and 1.0 millimeter peripherally. It is made up of perfectly aligned fibers that allow it to be transparent. The cornea is responsible for 71.7% of the total focusing power of the eye. It is this corneal tissue that the laser reshapes to refocus images onto your eyeball.

     Near-sightedness (myopia)

     In myopia, the eyeball is longer than the focal point (or focusing power) of the eye. This causes images to be focused in front of the retina, resulting in blurring of the image. Glasses are used to refocus the image onto the retina to help clear up the vision.

     Far-sightedness (hyperopia)

     In hyperopia, the eyeball is shorter than the focal point (or focusing power) of the eye. This causes images to be focused behind the retina, resulting in blurring of the image. Glasses are used to refocus the image onto the retina to help clear up the vision.

     Astigmatism

     In astigmatism, the cornea is irregularly shaped, rather than being a perfect sphere. This causes images to be focused irregularly on the retina, resulting in blurring of the image. Glasses are used to refocus the image more evenly onto the retina to help clear up the vision.

     Presbyopia

     Presbyopia occurs when a person reaches his late 30's or early 40's. Unlike the first three refractive errors that deal with distance vision, near vision is dependent on the flexibility of the lens inside your eye and on a muscle inside the eye that has to contract. Both of these mechanisms wear down as you age. At some point, everyone will start having difficulties seeing things up close, such as reading and writing. This is independent of your distance vision. In other words, when you reach you 40's, you may still be able to spot a tick on a hound 200 yards away, but you would not be able to read or write well without reading glasses. For those who already need glasses to see at a distance, they will need a different strength to see up close (in other words, they will need bifocals). Presbyopia is an important concept to understand when considering LASIK, because you will still need reading glasses when you reach a certain age, even if you have had LASIK for distance vision. In fact, some may need reading glasses right after LASIK, even if they did not need it prior to surgery.

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Do I qualify for LASIK?

     There are no set guidelines for which eye qualifies for surgery and which do not. It depends on the health of your eyes, the shape of your eyes, the prescription of your eyes, the thickness of your corneas, the size of your pupils, and your ability to cooperate during the surgery. You need to have an examination to discuss your eyes' potential with your doctor.
     In general, these are the parameters for the laser.
     Myopia: -0.75 to -12.0 diopters
     Hyperopia: +1.0 to +6.0 diopters
     Astigmatism: 0.75 to 4.0 diopters

     Care must also be taken to measure the thickness of the cornea and the size of the pupil in dim light. The cornea must have a certain thickness (based on your prescription). The higher your prescription, the more tissue the laser must remove. It is recommended that the corneal bed must retain a certain amount of residual thickness (at least 250 micrometers). If there is not enough tissue, LASIK should not be performed. Corneal thickness is measured with a pachymeter.
     Also the larger your pupil dilates in dim lighting, the more peripheral aberration you will notice. This is why some people have more trouble at night than others and this is why some people see more glare at night. If your pupil measures up to 6 millimeters in dim light, standard LASIK can be performed. If your pupil measures between 6-8 millimeters, special techniques using larger optical zones should be used. If your pupil measures 8 millimeters or greater, you should be aware of potentially greater difficulties at night after LASIK.

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What are the contraindications to LASIK?

You should not have LASIK if you:

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Will I be able to throw away my glasses?

     Many advertisements will lead you to believe that you will be completely free of glasses after this procedure. I think of LASIK as more of a procedure to reduce your dependency on glasses. If you look at studies that were performed, 95% of patients achieve 20/40 vision or better, and 65-70% achieve 20/20 vision or better. 20/40 vision is good vision that will allow most people to do anything they wish (including get a driver's license without the corrective lens restriction). If you look at the numbers, theoretically, 25% of patients still need some prescription to achieve 20/20 vision (although the prescription would be very small). However, most of these patients do not feel the need to wear glasses because 20/40 vision is good enough for then to do anything. Some may want a small prescription for night driving.
     Another factor is reading vision. If you are in your late 30's or early 40's, there is a good chance that you will need reading glasses for near work, even if you distance vision is very good. Some get around this problem by choosing monovision. In a sense, we leave one eye a little more nearsighted to allow for near vision (while the other eye is corrected fully for distance vision). This will allow you to retain some near vision for basic activities such as reading your watch, looking at price tags, and opening mail. However, this will not eliminate your need for reading glasses, especially for fine print. The disadvantage is that monovision may reduce your vision for night driving or for sports that require good binocular vision (e.g. golf, tennis, softball). Patients who are currently using monovision with contact lenses without problems are the best candidates. You should discuss this with your doctor and try monovision with contacts before deciding on monovision with surgery. Most people still choose to have full distance vision in both eyes and wear reading glasses when needed.

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How do I prepare for surgery?

     The first step is to have a thorough eye examination. You should ask questions and discuss all aspects of the surgery with your doctor. You should understand and sign the informed consent. You should leave your contact lenses out (I prefer 2 weeks for soft and 8 weeks for hard lenses) for as long as your doctor instructs. You should get a good rest the night before. On the day of surgery, do not wear jewelry, makeup, or perfume. You have to have someone drive you to and from the surgery. Do not make plans for working that day.

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How is LASIK performed?

     The LASIK procedure uses an Excimer laser to reshape the cornea (the clear dome- shaped part of the eye) to refocus images without the use of glasses or contact lenses. A thin blade called a microkeratome is used to make a circular hinged flap in the center of the cornea. The flap is only between 170 to 190 micrometers thick (about 30% of the total thickness of the cornea). The flap is then lifted and flipped over along the hinge. The laser then applies computer-controlled pulses of light energy to the corneal surface; and the flap is flipped back on top and allowed to heal.

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What to expect on the day of surgery?

     When you arrive on the day of surgery, you will have the opportunity to ask any last questions. You are then given some oral medications to help you relax. The technicians will then put some drops into your eyes. The drops are antibiotics and anesthetic drops. The technicians will clean your eyes with a soapy solution. You will be then taken to the laser room where the laser is being calibrated. You will sit in a chair that will recline back like a bed. The chair will then be swung underneath the laser. You will then see a red aiming light beam which you will be asked to look at. The surgeon will then place a lid speculum to hold your eyelids open. This wire speculum does not hurt; but may feel funny for a few seconds. After this, a vacuum device is placed on the eye. You will feel a tightness when the vacuum is turned on. Your vision will also completely black out for about 30 seconds. You will hear a motor device move across your eye. This is the blade that makes the flap. The entire suction apparatus will then release; and your vision will return (although it will be hazy due to edema at this time). The surgeon will then use a forceps to lift the flap and flip it over. The surgeon will then advise you that he is ready to start the laser. You will need to concentrate on keeping your focus still and not look around. The surgeon will then step on the pedal and you will hear the laser fire. There is a suction device on the laser to remove the debris and smell; but some patients may smell burning. Afterwards, the surgeon will then replace the flap and irrigate underneath the flap. The lid speculum will then be removed and the procedure will be over. Many surgeons will walk you to another room and look at your eyes under another more powerful slit-lamp before letting you go home.
     Your vision will be hazy following the procedure due to swelling of the cornea. The vision usually returns quickly, by that evening or the next day. You will be very light-sensitive. You may feel some burning and scratchiness. It is important that you not rub your eyes for this may dislodge the fresh flap.

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How do I care for my eyes after LASIK?

     The main restriction is that you cannot rub, press, poke, push, or prod on your eyes for at least 1 week. In fact, I give patients goggles or patches to wear when they go to sleep to avoid accidental rubbing and hitting in their sleep. You also cannot swim for 1 week. You cannot wear mascara around your eyes for 1 week. There will be some eyedrops to use for a few days after surgery. You will also be given sunglasses to protect your eyes in the sun. You can use your eyes for seeing and reading as you normally would.

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What to expect long-term after surgery?

     Usually your vision will be good enough to function and drive the next day. The vision however may still fluctuate somewhat until 3 to 6 months after surgery. This is the time when your doctor will determine the end-result and whether or not an enhancement is necessary. The LASIK procedure does not alter the normal changes your eyes go through with aging. Even if you have had the procedure, you will start needing reading glasses for near work when you approach your 40's. LASIK also does not protect your eyes from developing cataracts. When this occurs, usually in the 60's and 70's, your vision will change again due to the cataract.
     Studies show that the regression rate for LASIK is less than 10% after ten years. This is opposed to 33-40% rate of regression for RK surgery. Sometimes, it is difficult to determine whether a change in your eyes is due to regression or to the natural changes with aging.
     Many people have light-sensitivity for a few weeks after the procedure. Sunglasses are very helpful at this time. It is also normal to develop or worsen the symptoms of dry eyes for a few weeks to a few months after surgery. Many require the use of lubricant drops. Many also experience glare and haloes (especially around lights at night) for a few weeks to a few months after surgery. A small percentage (less than 2%) may have glare last longer than 1 year. Many patients report that this is no different than what they experience with their contact lenses at night.

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What can go wrong?

     No surgery is risk-free or guaranteed. In general, about 1-5% may experience some complications. Less than 1% may experience severe sight-threatening complications.
     During the procedure, the most common complications have to do with the creation of the flap. Sometimes, depending on the type of microkeratome used, the flap may be irregular-shaped or too thin. If this is the case, the surgery cannot be performed until it heals. Rarely, the blade may go too deep and cut into the eye. Again, surgery would have to be postponed until the eye heals (usually 3-6 months).
     Immediately after the surgery, the flap may droop or develop folds and wrinkles. If this is the case, the surgeon would have to relift the flap and smooth out the folds and replace it. This is why it is important not to rub the eye for a few days after surgery. Epithelial ingrowth occurs when corneal cells grow into and underneath the flap because the flap does not heal tightly. This may affect vision and require lifting the flap and irrigating out the cells.
     DLK (Diffuse Lamellar Keratitis) may occur at any time postoperatively. It is a nonspecific inflammation of the flap that may cause redness, pain, and blurred vision. Some feel that it may be an immune reaction to debris or oil (from eyelashes, makeup, surgical instruments, etc.) that gets underneath the flap. This has to be treated with steroids or debridement, depending on the severity.
     Corneal infections are very rare with LASIK, but can be severe leading to scarring and loss of vision.
     Retinal detachment, a serious condition requiring further surgery, is also extremely rare. In fact, many now question whether or not this is a true complication of LASIK. Since the risk of retinal detachment is increased in people who are very nearsighted, many now wonder whether the extremely low incidence of retinal detachments after LASIK is attributable to the surgery or just to the fact that most patients undergoing LASIK are apt to be nearsighted to begin with.
     Finally, there can be undercorrection or overcorrection. How can this be if the laser is computer-controlled? One important aspect is the measurements of your eyes prior to surgery. Factors such as contact lens wear can greatly affect the measurements. I usually have patients completely stop wearing contact lenses (2 weeks for soft contacts and at least 4 weeks for gas-permeable contacts) prior to making any measurements for surgery. Astigmatism is also more variable and more difficult to treat than near-sightedness. Far-sightedness is also more difficult to treat than near-sightedness. Fortunately, we can now perform enhancements in many cases to get closer to perfect for you. I usually wait between 3-6 months when the prescription stabilizes before making the decision on enhancements.
     Even if all measurements are correct, the largest unknown variable is the corneal healing characteristics of your eye. This will vary from person to person and from eye to eye and is unpredictable and uncontrollable. If the cornea develops irregularities during healing or due to the surgery, this may permanently affect the quality and crispness of your vision. Many irregularities improve over 6-12 months. Some may be correctable with more surgery.

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