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FAQ Lasik


How Does LASIK Work?

LASIK surgery works by sculpting the cornea in a precise manner to correct refractive error. By changing the corneal shape, light becomes focused on the retina, allowing clear vision. During LASIK surgery, a very thin flap is created on the front of the cornea. The flap is then folded back, and the laser applied to the underlying corneal tissue in a precise manner that can correct nearsightedness, farsightedness and/or astigmatism. The flap is then replaced, protecting the reshaped cornea underneath. LASIK is the most commonly performed refractive surgical procedure today, with more than two million procedures performed worldwide each year.

Who are candidates for LASIK surgery?

LASIK surgery helps correct the vision of people with myopia, hyperopia, and/or astigmatism. In fact, a large majority of people who wear glasses or contacts and suffer from such refractive errors as these could be candidates for LASIK surgery and other excimer laser refractive surgery such as PRK.

In general, candidates for LASIK should be:

  • 21 years of age or older: younger people may still have eyes that are growing. In certain cases, individuals younger than 21 may have LASIK surgery.
  • There is no upper age limit for LASIK.
  • Dissatisfied with wearing glasses or contact lenses.
  • Have had no change in glasses or contact lens prescription for at least a year.
  • Have otherwise healthy eyes.
  • Be willing to accept a small amount of risk associated with surgery.
  • Understand that glasses and/or contacts are occasionally still needed for some activities after surgery.
  • Not have excessively thin corneas or extremely high levels of refractive error. Your doctor will test for these conditions on your evaluation exam.

These conditions may prevent you from undergoing LASIK. You should alert your eye surgeon if you have one or more of these conditions so that he or she can help you make the best choice about undergoing refractive surgery:

Condition: Reason for caution:


Reason for caution:

Autoimmune diseases (ex: Rheumatoid arthritis, Sjogrens syndrome, Lupus, scleroderma)

May result in poor or inadequate healing after LASIK. LASIK may cause activation of these diseases in the eye.


May result in poor or Inadequate healing after LASIK. Poorly controlled diabetes can cause unstable refractive error

Immune deficiencies (ex : HIV/AIDS, history of an organ transplant, undergoing chemotherapy for cancer, taking oral corticosteroids

May increase chance of a severe eye infection after the surgery.

Personal or family history of corneal diseases, such as Keratoconus or Pellucid Marginal Degeneration

May result in unstable corneal shape and irregular warpage of the cornea after surgery.

History of Herpes Simplex or Zoster eye infections.

May cause reactivation of the infection.

History of other eye diseases (Glaucoma, Fuchs Dystrophy, Macular degeneration, Cataract, Ambylopia or lazy eye)

May decrease the chance of success of LASIK.

Pregnancy or Nursing

Can cause temporary changes in the shape of the cornea.

Certain medications: Accutane® (isotretinoin), Cordarone ® (amiodarone)

May interfere with corneal healing after LASIK.

Dry Eyes

May worsen after LASIK.

Examination prior to LASIK:

Before you arrive at the doctors office:
If you are a contact lens wearer, you should stop wearing you lens for at least 2 weeks if you wear soft contacts or 1 month if you wear hard contacts. Contact lenses can cause mild warping of the corneal shape, which can interfere with the preoperative measurements of the eye and calculations for LASIK surgery.

Tests you may have at the doctor’s office:
The evaluation for LASIK surgery typically includes a complete eye exam of the front and back of the eye, plus several additional tests. Your vision with and without glasses will be tested, as well as a refraction to determine if your current vision differs markedly from the vision corrected in your current glasses. If they do differ markedly, you may need to return for another visit several weeks later for a repeat refraction to insure that your prescription is not changing. The thickness of your corneas will also be tested. Since LASIK surgery removes some corneal tissue during the reshaping process of vision correction, a minimum amount of corneal thickness is required. Your pupil size will also be examined. People with large pupils may be at increased risk for night vision symptoms, such as glare and halos, after refractive surgery. Lastly, several machines may be used to assess the shape of your cornea, including a topographer and/or a tomographer and possibly a wavescan abberometer. Your doctor will review the information from these machines in order to determine if your corneas are regularly shaped. Individuals with abnormally shaped corneas may not be ideal candidates for LASIK, though other excimer laser refractive surgeries, such as PRK may still be an option.

Custom (Wavefront) vs. Standard Lasik Sugery

The terms “Custom” or “wavefront” LASIK and “Standard” LASIK are descriptions of the computer program used by the excimer laser to change the shape of the cornea. Standard LASIK is the term now used for the older computer programs for the excimer laser. In these programs, the patient’s glasses prescription was the main factor used by the computer to change the shape of the cornea. As such, two different patients who happened to wear the same glasses prescription would receive the same corneal shape change by the excimer laser. In contrast, Custom LASIK, which has been available since 2003, uses a much more sophisticated way of measuring the eye before surgery. A specialized map, called a wavescan, is obtained using an instrument called an aberrometer.

This measures not only the glasses prescription, but many other optical properties of the eye that cannot be measured by a simple glasses fitting. The result is an optical “fingerprint” of the patient’s eye. This data is then used by the computer to correct all the optical aberrations of the eye during the LASIK procedure. No two treatments, like fingerprints, are exactly alike between patients or even between the two eyes of one patient! Results from the clinical trials of Custom LASIK lasers show that more patients may achieve 20/20 or better vision with Custom LASIK than with the older Standard LASIK treatment.

While Custom LASIK is probably the optimal way to have the corneas reshaped for vision correction, not all patients are candidates for Custom LASIK. Uncommonly, a patient with very small pupil size or high degrees of astigmatism or myopia or people interested in monovision treatments may fall outside the treatment ranges for Custom LASIK. Standard LASIK, however, is still a remarkably effective surgery, and offers a very good option for laser vision correction, even when Custom LASIK cannot be used. The procedure for LASIK, that is, what your surgeon does and you experience during the operation, is essentially the same whether Standard or Custom excimer ablation is used.

Is 20/20 vision guaranteed with LASIK?

LASIK surgery is an extremely advanced technology for surgical vision correction. The excimer laser is one of the most precise instruments available for use in modern medicine, and it can be programmed to match exactly the refractive correction your eye needs to see well. As such, the vast majority of people undergoing LASIK surgery are very happy with their post-procedure vision. In fact, a person’s happiness with their vision after the procedure is a far more important measure of success than the somewhat arbitrary “20/20” measurement done in a dark room of a doctor’s office.

However, several factors may lead to a person having vision after the surgery which still requires additional help from glasses or contact lenses. The excimer laser is precise enough to inscribe letters on a grain of sand and could correct an inert object, such as a piece of plastic, exactly as predicted. However, in LASIK surgery, it is not being applied to something inert, but rather, a living tissue, the cornea. Because of this, and because of the individual healing response of each patient, there is some variability of response in patients to the treatment. Additionally, in individuals with higher levels of refractive error, it is harder to hit an exact refractive outcome target. A simple analogy for this is that it is much easier to make a put in golf (or correct a low amount of vision) than make a hole-in-one driving from the t-box (or precisely correct a very high amount of vision).

Data from the clinical trials for the currently used excimer lasers supports the assertion that LASIK surgery works very well for most people. For example, for the most recent trials of the VISX S4 laser, the most commonly used excimer laser in the United States, 92% of eyes with low to moderate amounts of mypopia achieved 20/20 or better at 3 months time and 98%. Higher levels myopia and hyperopia may have a somewhat lower chance of 20/20 vision after the procedure. 20/40 vision is the minimum needed in most states to drive without glasses or contacts (See below).

What are the Risks of LASIK surgery?

The risks of LASIK fall into two main categories: Vision Loss Risks and Nuisance Risks.

Vision Loss Risks

It is very rare to lose vision after LASIK surgery. When vision is lost in an otherwise uncomplicated LASIK procedure, it typically is 1 or less lines on the eye chart of best corrected vision even with extra help from glasses. As such, LASIK surgery has a very good safety profile. Two other ways may exist in which vision could be lost to a more severe degree.

Infection: Since cuts are made on the eye, it is possible that bacterial could gain access to the corneal tissue and start an infection. Scarring from such an infection could lead to vision loss. This is very uncommon as powerful antibiotics are used after LASIK to prevent infection. The risk of severe infection is probably less than 1 in 500.

Progressive corneal warpage (Ectasia): In this condition, the cornea begins to warp in odd directions, leading to loss of vision. Occasionally, a corneal transplant is required to fix this condition. Ectasia, however, typically is seen only in patients with abnormal corneal shapes, or corneal dystrophies, such as keratoconus, even before the surgery is done. Your surgeon will screen your corneas very closely to help identify any preexisting corneal shape irregularity. The risk of ectasia is probably less than 1 in 3500.

Nuisance Risks

Most of the other risks associated with LASIK surgery don’t usually cause a significant loss of vision. Rather, they can cause nuisance problems with the eyes that may not have been present before the surgery.

Dry Eye: Almost everyone undergoing LASIK has some mild dryness, in which the eyes feel somewhat scratchy from time to time during the day. Typically, these symptoms resolve over the course of several months. A small percentage of people, however, have chronically worse dry eyes after LASIK, which may require continuous treatment with drops or dry eye medications.

Night Vision Symptoms: Some patients notice their night vision after LASIK surgery is different than before. Usually, this occurs in the form of halos around streetlights, added glare from oncoming traffic or increased difficulty seeing dimly light shapes in the dark. Typically, these symptoms improve with time. Data from several studies has shown that if 100 patients had such symptoms at 1 month after surgery, only 20 to 30 will still have symptoms by 1 year. Some surgeons believe that a larger pupil size may put a patient at increased risk for night vision problems. However, such complaints can still happen in people with small pupil sizes. Most people with night vision complaints find them only mildly annoying. However, a few individuals may feel that they are unable to function well in low light settings. Medications can be used to change the size of the pupil in low light or nighttime settings, which can help reduce night vision symptoms from LASIK if they occur.

Flap complications: Occasionally, in the process of making the thin corneal flap for LASIK surgery, the flap is made with an irregular edge or a buttonhole in the center. If this occurs, the surgeon will replace the flap on the eye, not perform the excimer corneal ablation, and allow the eye to heal. Little if any vision is usually lost in such a complication. However, it may take several months for the eye to fully heal. Surface laser, such as PRK can often still be an option for laser vision correction several months later if a problem with the flap occurs during LASIK. The LASIK flap may occasionally become dislodged or wrinkled before it is fully healed. If this occurs, your surgeon will do a minor procedure to put it back in place, usually with no loss of vision. Additionally, cells from the surface of the eye may occasionally start to grow under the LASIK flap, which is called epithelial ingrowth. This is rare in primary LASIK procedures, though may occur more commonly in LASIK enhancements. Often, such cells resolve on their own. Sometimes, though, they require the surgeon to lift the flap and remove the blockage in order to maintain excellent uncorrected vision. Lastly, in the first few days after the surgery, the eye sometimes tries to heal the LASIK wound too aggressively, sending too many white blood cells to the cornea. This condition, called Diffuse Lamellar Keratitis (DLK), usually resolves with frequent steroid eyedrops.

Enhancements: Even though the excimer laser is extremely precise, the fact that the eye is a living tissue and that individual healing response can vary means that sometimes LASIK surgery over or under corrects the refractive error of the eye. If this happens, a “touch up” LASIK procedure, or enhancement, can be done several months later to correct the remaining refractive error. Enhancement procedures carry a small risk of all of the above complications, just like the original LASIK procedure. Mostly, though, enhancements are just a hassle, as both the patient and the surgeon would have liked to have gotten all of the vision corrected on the first try! In general, about 5-10% of patients undergoing LASIK will need an enhancement procedure to obtain their vision goals.

What will I experience during the LASIK procedure?

On the morning of your procedure, your surgeon will ask you not to wear any makeup (which may stain the cornea) or perfume or cologne (which may damage the laser). At the laser surgery center, you will usually be given a Valium pill to help you feel calm during the procedure. The LASIK procedure itself usually takes less than 10 minutes an eye. You will lie on a special bed under the laser. A blinking red light serves as your target to look at during the procedure. A lid holder will be placed to help hold your eyelids open. Numbing drops will be placed on the eye. Then, the LASIK flap will be made, during which you will feel some squeezing and pressure on the eye. Your vision will dim out during the flap making process, and may even go completely away for a few seconds, which is normal. The flap is lifted back, at which the vision will return but be blurry. The laser typically takes less than a minute to change the shape of the cornea. The laser tracks the eye, so if small eye movements occur, it will follow and still apply the laser in just the right position. Large eye movements will cause the laser to stop its treatment, helping to ensure that only the correct treatment is performed. The flap is then put back into place and allowed to dry for a few minutes. Last, eye drops are placed in the eye. The eye is closed with paper tape, then the same steps are performed on the second eye.

After the procedure is done, your surgeon may examine your eye, or simply have you go home and take a long nap. The eyes will start to burn and feel irritated about half an hour after the surgery as the numbing medicine wears off. The nap, plus the eye drops your surgeon will give you will help make your eyes feel more comfortable. Your doctor will see you the next day, at which point the eyes are usually feeling pretty comfortable. You will continue using eye drops for several weeks after the surgery, and then see your doctor again in about a month for a vision check. If all is well, as it typically is, your doctor will usually see you again in 6 months to a year for another vision check. During the few months after the surgery, artificial tears should be used regularly to help limit dryness of the eyes while they heal.



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