A Guide to Laser Vision Correction
Dr. Robert Maloney believes that a well-informed patient is key to successful vision correction surgery. He wants to be sure that you fully understand what you can expect from your procedure you choose.
He wants to help you care for and preserve your eyesight in the best way possible. Here, you can find the information that you need to help you make informed choices about health care for your eyes.
Risks and Complications
Undercorrection results when the desired change in your refractive error, or focusing ability, is not fully achieved after the LASIK procedure. A slight undercorrection will not seriously affect your vision and may even be desirable in nearsighted patients over forty to help with their reading vision. More significant undercorrections may require an enhancement procedure, which sometimes included in the original LASIK cost if performed within the first year.
Undercorrection happens more often in patients with higher levels of nearsightedness, farsightedness, or astigmatism. This makes sense if you think in terms of how much sculpting, or reshaping, the laser has to do. For example, a patient with less than 2.00 diopters of myopia has about a 1 percent chance of needing an enhancement procedure because of an undercorrection. On the other hand, a patient with more than 9.00 diopters of myopia has about a 10 percent chance of requiring an enhancement procedure due to undercorrection.
Surgeons who use consistent techniques and constantly analyze their outcomes have significantly lower incidences of undercorrection. This is another reason it is important to find a surgeon who tracks LASIK outcomes, as discussed earlier. If your doctor keeps an up-to-date database of at least 1,000 procedures, he or she will be able to show you the likelihood of your needing retreatment, based on your own degree and type of refractive error.
Overcorrection results when the refractive error is changed more than was intended. An initial, or temporary, overcorrection may occur and usually rights itself in the first month. After a treatment for farsightedness, an overcorrection would make you temporarily nearsighted. In this case, your distance vision would be somewhat blurred and your near vision rather good. Following a treatment for nearsightedness, an overcorrection would make it more difficult for you to see objects up close. Patients can manage a temporary overcorrection by wearing glasses until it resolves.
There are fewer permanent overcorrections than permanent undercorrections. A significant overcorrection can be treated with an enhancement procedure as well. An overcorrection enhancement is usually performed three to six months after the initial treatment, once the patient's vision has stabilized.
In rare circumstances, significant astigmatism results after the initial LASIK surgery. Induced astigmatism causes blurred vision. It can be treated with enhancement surgery, if it is bothersome. Most people can tolerate small degrees of astigmatism. However, if your vision is blurred because of a refractive error after LASIK and does not meet your expectations, there is a 99 percent chance that it can be corrected with enhancement.
As detailed earlier, it is not uncommon for patients to experience a feeling of dryness or grittiness in the eye after LASIK. This is a common side effect from the surgery that will usually decrease over the first few weeks. The use of nonpreserved lubricating eyedrops (artificial tears), punctual plugs, or a medication called Restasis will help alleviate the symptoms of dry eye.
LASIK makes the eyes somewhat drier than before surgery. For most patients this is not a problem, because the eyes have more moisture than needed; so a little dryness is not bothersome. However, in rare cases patients develop more significant dryness after LASIK. These patients experience dryness throughout the day. You are more at risk for this if you have dry eyes before LASIK when wearing glasses. (Many people have dry eyes while wearing contact lenses, but this is not a risk factor if the dry eye is treated before the LASIK procedure.) An important part of the comprehensive examination is an evaluation of tears to ensure that your chance of experiencing post-LASIK dryness is minimal. If you do develop persistent dryness, a variety of treatments are now available. These include taking dietary supplements, using lubricating eyedrops, using eyedrops that improve tear production, and blocking your tear drainage canals with tiny plugs to retain more tears in your eyes.
Approximately 1 to 5 percent of LASIK patients develop a small corneal abrasion, or scrape, caused by friction of the microkeratome. The eye is covered by a thin layer of skin, called the epithelium. This skin is just like the skin on your hand except that it is clear so you can see through it. Occasionally, the minor trauma of surgery causes part of the epithelium to fall away. This is called a corneal abrasion or corneal epithelial defect. This doesn't harm your eye and doesn't interfere with the laser treatment. However, your eye will be uncomfortable while the epithelium heals, just as your hand is after it is scraped.
Your surgeon will know immediately if you develop a corneal abrasion when the LASIK procedure is performed on your eye; he or she will place a very thin contact lens on the eye. This is called a bandage lens, because it serves as a protective layer over the eye surface. The lens increases comfort and promotes healing. It can be removed in one to five days. The abrasions always heal, usually in one to three days. But it may take up to ten days to achieve your best vision if the abrasion is located centrally.
While the abrasion is healing, your vision will be blurred-as if you were looking through a scratched pair of eyeglasses. In rare cases, if the corneal abrasion is significant, the surgeon may decide to postpone doing LASIK on the other eye for one or two weeks, giving the first eye a chance to heal. Postponement of surgery on the second eye ensures that you don't have blurry vision in both eyes at the same time.
Night Glare and Halos
All people, whether or not they have had LASIK, experience some glare or halos at night. These night-vision disturbances occur when you are in a dark environment and look at a small bright light, such as a headlight or a streetlight. Halo is the glow that surrounds the light source, and glare is little spikes of light that appear to emanate from the light source like the rays around a light. Glare and halos occur because the pupil dilates in low-light conditions. The dilated pupil allows more peripheral light rays (rays coming in from the sides) to enter the eye. These rays are more likely to scatter, instead of coming to a precise focus. You perceive the scattered light as glare or halos. Incidentally, this scattering of light from proper focus is why everyone notices that his or her night vision is not as good as their daytime vision.
Some patients experience an increase in these symptoms after LASIK. Although these symptoms do not necessarily interfere with visual sharpness as measured on the Snellen eye chart, they can be bothersome in dim-light conditions, such as driving at night. Some patients may see glare and halos at night during the first month after treatment; however, it is quite uncommon for these side effects to interfere with patients' activities. The effects usually improve in the first three months, and the overwhelming majority of significant glare problems disappear on their own by six months. There are treatment options for patients who experience persistent glare or halos. Weak prescription night glasses can help, as can the use at dusk of eyedrops that reduce the size of the pupils. Wavefront-guided retreatment is also a promising approach.
It's difficult to predict one patient's chances of having these symptoms after LASIK. Patients with more severe refractive errors and astigmatism may be more prone to glare and halo effects. Many eye doctors used to believe that patients with larger pupils had a greater chance of developing glare or halos at night, although a number of major studies have now shown that this is not true. Special programs for the laser that allow for larger treatment zones can help reduce the chance of these problems.
The newer wavefront-guided laser treatment has been shown to significantly reduce night-vision disturbances compared with conventional laser treatment, which is another reason many surgeons recommend it to all eligible patients.
Problems with Quality of Vision
A small number of patients experience a slight loss of quality of vision after LASIK surgery. This is also called loss of best-corrected vision. Loss of best-corrected vision means that, even with eyeglasses, a patient loses some of the visual crispness and clarity he or she had when wearing eyeglasses or contacts prior to surgery. The person may no longer be able to read the 20/20 line on the Snellen eye chart. He or she may also notice some hazy vision or ghost images. Loss of best-corrected vision can be a result of irregular healing or an irregular flap and may improve over the first year. This complication is very rare except in those with very high levels of nearsightness or astigmatism. Careful surgical technique and good follow-up care help minimize the incidence of this problem.
Development of a "Central Island"
Another potential complication from LASIK is the development of a central island, a small raised area in the cornea's treatment zone. Central Island often disappear spontaneously after several months, but some require an enhancement procedure; in this, the corneal flap is lifted and a small amount of excimer laser energy is delivered to the raised area. When the central island is removed by additional laser treatment, crisp vision usually returns.
The surgeon diagnoses a central island by using a corneal topographer, the device that produces a digitized contour map of the corneal surface. To help prevent central islands, some excimer lasers have special software that distributes additional pulses centrally, along with the regular treatment for the refractive error. With the latest generation of excimer lasers, the incidence of central islands is very low.
Corneal Flap Complications
For experienced surgeons, corneal flap complications are rare, occurring in about 1 in 2,000 procedures. This complication is characterized by a flap that is too small, too thin, detached, or irregularly shaped. After the surgeon makes the flap, he or she inspects it. If there are problems with the flap, the surgeon may not proceed with the laser treatment. He or she will replace the flap and terminate the operation. Typically, vision quickly returns to the way it was before surgery. While this complication is frightening, it almost never harms vision if the surgeon handles the problem correctly. The LASIK procedure can usually be successfully repeated in six months, after the eye heals.
Sometimes the corneal flap may shift slightly in the first twelve hours after LASIK surgery. This is why it is important, especially during the first few hours, not to rub your eyes and to keep them well lubricated. If the flap shifts slightly, wrinkles form, just as wrinkles form in a carpet if you step on it and it isn't properly nailed down. The medical term for these wrinkles is striae. If striae are present in the center of the cornea, they may blur your vision. Fortunately, striae are easy to fix with a brief, painless procedure if treated early. The flap is lifted and laid back down smoothly, and the surgeon places a clear bandage contact lens, that holds the flap securely in place, to wear overnight.
The cornea is covered by a thin, clear skin, called epithelium. This clear skin is made of epithelial cells. When the LASIK flap is lifted and replaced, these cells normally grow back over the top of the flap. About 1 percent of the time, the cells grow under the flap instead. This condition is called epithelial ingrowth. These cells occasionally cause blurred vision or irritation. Epithelial ingrowth is easy to identify and is treated by gently lifting the flap and clearing away the trapped epithelial cells. Epithelial ingrowth is more common following enhancement procedures when the original flap is relifted.
Regression refers to the tendency of the eye to drift back slightly toward the original refractive error. This occurs more commonly in patients with higher degrees of myopia, hyperopia, or astigmatism.
If significant regression occurs, you may require either low-prescription eyeglasses for night driving or an enhancement procedure to "tune up" the original treatment, provided your cornea is thick enough to allow retreatment. Enhancements for regression are usually performed three to six months after the original procedure, to allow time for the patient's vision to stabilize.
This condition, diffuse lamellar keratitis (DLK)-also known as "sands of the Sahara" syndrome-is an inflammation that occurs in the space between the corneal flap and the underlying stroma. This relatively rare condition is typically observed by the doctor the day after surgery. You may have no symptoms, or you may notice some haziness in your vision or a mild irritation. After LASIK, all patients are given a topical corticosteroid, a medicated eyedrop used to suppress inflammation. You will be instructed to apply these drops at least four days after the procedure. These drops prevent DLK from occurring in the great majority of patients.
There is considerable debate about what causes DLK. It is normally easily treated with topical corticosteroids. Most cases of DLK respond promptly to this treatment. More severe cases may require that the surgeon lift the corneal flap and irrigate beneath it to remove the inflammatory cells. Severe cases may cause some blurring of vision that necessitates an enhancement procedure, although these cases are extraordinarily rare. When recognized early and treated properly, DLK resolves quickly.
Keratoconus and Corneal Ectasia
Keratoconus is a naturally occurring disease caused by a weakness in the cornea. Keratoconus naturally occurs in some people as they age. Patients with this condition suffer from increasingly poor vision as their corneas bulge and thin over time due to the pressure put on their weakened corneas. Symptoms often reported by keratoconus patients include nearsightedness and fluctuating vision (irregular astigmatism). This disease is progressive, but does not progress much after age forty. Scientists are not completely sure of the causes of keratoconus, but genetics is believed to play a large part.
Patients who suffer from preexisting keratoconus are not candidates for LASIK, because LASIK in some cases accelerates the progression of the disease. An essential part of your consultation is examining you for keratoconus, using a specialized diagnostic map of the eye called corneal topography.
Corneal ectasia is a disorder that appears just like keratoconus but develops after LASIK. It is also called secondary keratoconus or iatrogenic keratoconus. It is very rare, and its causes are uncertain. Some patients who develop ectasia after LASIK would have developed keratoconus even without LASIK surgery because of their genetic predisposition. Other patients develop it because the surgeon removed too much tissue during the procedure. Poor preoperative screening is often a factor in these cases. To prevent ectasia after LASIK, your surgeon will measure your corneal thickness before surgery. He or she should ensure that you have a minimum of 220 to 250 microns of tissue remaining after LASIK.
Corneal ectasia is very rare. Those who are at higher risk for developing ectasia include people with extreme myopia or whose eyes have an irregular preoperative shape or people who have a particularly thin cornea. It is important to note that corneal ectasia has occurred in patients with no risk factors and after LASIK procedures that appeared to be free of complications.
In its early stages, keratoconus and ectasia are often successfully managed with rigid gas permeable contact lenses. Patients often find they are able to use these lenses for many years with few problems. Intacs, tiny rings inserted into the cornea to correct nearsightedness, are also used to manage keratoconus in early stages of treatment. In more advanced cases, keratoconus may require a corneal transplant. Patients who cannot wear the rigid gas permeable contact lens may also need a transplant. Usually, corneal transplants are very successful. Unlike keratoconus, corneal ectasia is not usually progressive, so even patients who develop it do not usually require a corneal transplant.
Although infection is the most feared complication, it is extremely rare, occurring in about 1 in 10,000 surgeries done by an experienced surgeon. As with any surgery, proper technique is the best way to avoid infection. If your eye does become infected, it will likely occur during the first forty-eight to seventy-two hours after LASIK. This is why it is so important for the first week to avoid any contact with substances that may cause infection, such as eye makeup, hot tubs, and swimming pools. It is also essential to go to all of your follow-up visits, even if everything seems fine. To prevent infection, you will use antibiotic drops postoperatively for a few days to a week.PRK »
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