Laser vision correction works by reshaping the cornea to alter its curvature, thus correcting the optics. Each pulse of the laser removes 0.25 microns (0.00004 inch) of corneal tissue.
The laser pulses are controlled with respect to size, shape and location so that after all of the pre-calculated necessary pulses have been delivered, the new shape of the cornea will be correct.
PRK is the laser treatment for refractive error in which an excimer laser reshapes the cornea by removing microscopic layers of tissue from the surface of the cornea. The excimer laser was approved by the FDA for use in the United States in October 1995.
LASIK stands for Laser Assisted In-Situ Keratomileusis. In the LASIK procedure, a corneal flap is created and folded aside temporarily. The excimer laser is then used to precisely remove corneal tissue from the layer immediately beneath the flap. The flap is then replaced in its original position. Initially, LASIK was used to treat only the extremely high ranges of nearsightedness, but in recent years, because of its lack of pain and rapid visual recovery, and as excimer laser accuracy has increased, LASIK has been utilized to correct virtually any refractive error.
With PRK, it usually takes 4 days for the vision to reach a functional level. This is due to the fact that in PRK, the surface layer of the cornea is removed and it takes approximately 4 days for this layer to regenerate. (In LASIK, this surface layer is preserved because it is part of the flap.) During this time, the eye can also be considerably uncomfortable, although new medications have significantly reduced the discomfort during recovery. The visual recovery with PRK is more gradual with the best vision usually being achieved by 2-3 months, although most patients can function after 4 to 5 days. The quality of the vision at three months after PRK is generally as good as it is with LASIK.
One of the potential side effects of PRK is haziness of the surface of the cornea in the area where the laser treatment is applied, although recently developed drugs have largely eliminated this issue. If haze occurs, it’s due to an interaction between the treated cornea and the newly healing surface. This tends to be dose related; that is, the higher the prescription, the higher the laser treatment and the higher the likelihood for corneal haze. This phenomenon does not occur in LASIK because minimal surface healing is required.
LASIK is clearly a more complex operation, and there are more factors which the surgeon must control, especially with regard to the flap; but in the hands of an experienced surgeon, the benefits of LASIK are worth the additional complexity.
To understand Custom LASIK, one first needs to understand conventional LASIK. In conventional LASIK, we measure your prescription as if we are going to make your best-ever pair of glasses. That prescription is entered into the excimer laser, and it then reshapes your cornea so that you will see as if you are wearing those best-ever glasses. This technique has worked very well for hundreds of thousands of people since the dawn of LASIK back in the 1990’s.
In Custom LASIK, we take all of the same measurements as we do in conventional LASIK, however, we also measure your eyes with a device called an aberrometer. This device was originally developed to analyze the optical quality of high-powered telescopes but it has been adapted to do the same kind of analysis on the complete optical pathway of the human eye. What the aberrometer actually detects is an optical wavefront (custom treatments are sometimes called "wavefront driven"). This is accomplished by shining a low energy laser into the eye, which is then reflected back out of the eye. The exiting rays (which form a wavefront) are then collected and their direction in space determined. With this information the aberrometer then calculates what are called higher order aberrations or HOA’s. You can think of HOA’s as subtle abnormalities in the eye’s optical pathway that are not detectable in a regular exam for glasses. (Nearsightedness and astigmatism are lower order aberrations and they are detectable in a regular exam for glasses and are, as you recall from above, the basis for the treatment in conventional LASIK). HOA’s are responsible for things like glare, halo, ghosting, and, if significant, may prevent an eye from being able to see 20/20 even with best-ever glasses in place or after conventional LASIK. Once the aberrometer has measured the HOA’s, it then calculates a refinement to the laser treatment to correct them.
What this means clinically is improvements in three main areas. First, there is a higher chance of seeing 20/20 (or even better). Some people who may not have been able to see 20/20 even with their contacts or glasses may be able to do so after Custom LASIK. Secondly, the re-treatment rate drops to about 1% (compared with about 5% for conventional LASIK). But the biggest advantage of Custom LASIK over conventional LASIK is the quality of vision, especially at night or in dim/low contrast conditions. With custom, we see much fewer problems with haloes, glare and ghosting. Haloes are faint circles of light seen around things like headlights and streetlights at night and traditionally have been more of a problem in people with higher prescriptions and larger pupils.
The microkeratome is a mechanical device and at first glance it somewhat resembles a miniature electric hair clipper. It contains a number of precisely machined moving parts. Successful operation of the microkeratome depends upon meticulous cleaning, assembling and testing operations personally before each case. I take what I like to call the 747 pilot’s approach to LASIK: that is, if the equipment does not pass the check list, we don’t fly. Using this disciplined approach in every case has never failed to produce a good flap.
After the front of the eye is completely anesthetized with drops, the patient is positioned under the laser. A device called a vacuum ring is then attached to the front of the eye. This stabilizes the eye and temporarily raises the pressure to aid in the creation of a smooth flap. Next, the microkeratome guides itself across the vacuum ring thereby creating the flap. The microkeratome and vacuum ring are then removed, the corneal flap is folded aside and the laser treatment is applied to the bed underlying the flap. After the laser treatment is completed, the flap is replaced to its original position and allowed to seat for 2 minutes. During this time period the natural vacuum mechanism of the corneal tissue will hold the flap in place. Surface healing usually occurs within 12 hours thereby virtually eliminating any possibility of displacement of the flap. Antibiotic drops are then distilled and a protective rigid shield is placed over the eye. This entire procedure takes about ten minutes.
After the front of the eye is completely anesthetized with drops, the patient is positioned under the laser. A device called a docking ring is then attached to the front of the eye by way of vaccuum. Next, the cone-shaped applanation plate of the Intralase is lowered onto the eye until the cornea is flattened. The clip on the docking ring is then released securely holding the cornea against the applanation plate. A diagram appears on the computer screen of the Intralase showing where on the cornea the flap will be positioned. At this point I have the ability to fine tune the actual location of the flap by manipulating the software. Once I am content with the planned location of the flap, the treatment commences and the microscopic layer of gas bubbles appears in the corneal tissue. At the end of this step, the eye is “undocked” and the applanation plate is elevated off of the eye. The edge of the flap is then entered with a special probe which sweeps across the layer of bubbles, allowing the flap to be lifted and laid aside. The laser treatment is then applied to the bed underlying the flap. After the laser treatment is completed, the flap is replaced to its original position and allowed to seat for 2 minutes. During this time period the natural vacuum mechanism of the corneal tissue will hold the flap in place. Surface healing usually occurs within 12 hours thereby virtually eliminating any possibility of displacement of the flap. Antibiotic drops are then distilled and a protective rigid shield is placed over the eye. This entire procedure takes about ten minutes.
To understand the benefits of the Intralase , one first needs to understand the conventional way to make a corneal flap. Since the dawn of LASIK, the device used to make a corneal flap has been a microkeratome: a mechanical device with a blade and a motor. For years this has been a very dependable device when properly maintained and in the hands of an experienced surgeon. However, on rare occasions, a microkeratome flap would have irregularities that might necessitate a delay in the completion of the surgery or lead to problems that were difficult to remedy. Such problems are virtually impossible with the Intralase because of the way in which it makes a flap. The patient’s eye is "docked" to the Intralase and a glass plate flattens the corneal. The Intralase then deposits pulses of energy at a very precise distance beyond the surface of the glass plate (or, when docked against the eye, at a very precise depth in the cornea). Each pulse of energy produces a microscopic bubble; the pulses are delivered so that an entire sheet of confluent bubbles is produced in the plane of the “flap-to-be.” Next, rings of pulses are stacked around the edge of the bubble layer until the surface of the cornea is reached. At the end of the procedure, the location of a flap has been defined with microscopic bubbles.
the surgeon then uses a tiny probe to "connect the dots" and lifts up a flap without ever having to cut the cornea.
In addition to being safer, the Intralase can make a thinner flap than a microkeratome, so people who, because of their higher prescription or their thin corneas were not candidates for LASIK with a microkeratome, may be able to have surgery utilizing the Intralase.
Will the Intralase ever completely replace the microkeratome? Because there are some cases that cannot be done with an Intralase (such as LASIK in the setting of prior radial keratotomy or other corneal surgery), the microkeratome will probably never be completely replaced with the Intralase. But the clear majority of patients now chose the Intralase.
As an expert in refractive surgery, I will recommend the surgery that I feel will be the most effective in treating your refractive error. In general, the outcome is somewhat dependent on the pre-operative refractive error. For patients with up to -6.00 of nearsightedness, +3.00 of farsightedness and -2.50 of astigmatism, Custom LASIK will yield 20/20 or better in 98% of those patients. For patients outside of that range, 90% of patients should expect to see 20/20 or better. For both groups the remaining 2% and 10% should expect to see in the 20/25 range. For the most part, if I don’t feel that a patient falls at least into the 90% 20/20 range, I will not recommend surgery. In general you can usually expect to see as well after the surgery as you did with your glasses or contact lenses before the surgery, although some cases of Custom LASIK have seen better than 20/20.
LASIK was approved by the FDA in 2001. Technically, all LASIK performed prior to that was considered to be an "off label" use of the excimer laser. In its original studies, (prior to 1995), the FDA approved the excimer laser for PRK when performed according to specific guidelines. Although LASIK was not part of the original study guidelines, the FDA had not said that it couldn’t be performed, hence the use of the term "off label." This is analogous to using a medication to treat a specific condition when it was originally designed to treat a different specific condition. The FDA will allow a physician to use an FDA approved medication or device in an "off label" manner as long as 1) it makes sense medically, 2) the patient understand the concept and 3) it’s within the standard of care for the medical community. The widespread growth in popularity of LASIK among refractive surgeons, and the quality of results I have personally seen, are actually more meaningful than FDA approval; nevertheless, this was achieved in 2001.
Creating a uniform corneal flap in the proper location and properly reseating it are two elements that are critical to the success of LASIK. These two steps are very surgeon dependent. Adequate experience in both of these steps is crucial whether the flap is created with a microkeratome or with the Intralase.
I performed my first cases of LASIK in January of 1996 in Shanghai, China. At that time, LASIK was more commonly performed abroad and there was not a good teaching venue for LASIK in the United States. Therefore, four other surgeons and I traveled to Shanghai where I was able to perform my first 8 human cases under the careful scrutiny of an internationally known expert in LASIK. This was an invaluable teaching/learning experience. The techniques that I learned in China, I have refined and built upon in my own practice with excellent results. I am often asked to help “coach” a new surgeon through his first few cases.
At your consultation we will determine your suitability for laser vision correction and determine exactly which procedure will be best for you. We will accomplish this through numerous measurements including your refractive error (prescription), pachymetry (corneal thickness), and topography (corneal contour). Ideal candidates are free of any ocular history or abnormalities other than needing glasses or contacts. There are a few medical conditions that may influence an individual’s suitability for surgery; certain medications should be discontinued before surgery; these issues will be reviewed in detail at your consultation. After your consultation, we will see you one more time for finalized measurements before surgery
Certain corneal conditions may eliminate LASIK as the best choice. These can best be detected by corneal topography, usually at the time of the pre-surgical evaluation. Some refractive errors are outside of the range of laser vision correction; newer technologies are being evaluated for individuals with prescriptions in this category.
Any contact lens will alter the shape of the cornea, some more than others. We will instruct you as to how long you need to be out of contacts before your final evaluation and before surgery. For most types of contacts, about three days is long enough, for others, such as hard contacts, up to two to three months may be necessary.
You will be at the surgery center for about an hour. Most of your scans will be repeated just prior to surgery. You will enter the laser room and your surgery will take about twenty minutes for both eyes. I will then check your eyes (flaps) under a special microscope and then apply your shields and send you home to get to sleep. We will prescribe sleeping pills to aid in your ability to sleep. If you are able to sleep 6 to 8 hours, you will most likely wake up with your eyes comfortable and with 98% of your vision.
Yes. Your cooperation is necessary because you must look at the laser’s fixation light during the laser treatment. However, I usually give my patients a mild oral sedative before the surgery to help them stay relaxed.
There is very little discomfort with the LASIK procedure. The eye may be scratchy for a few hours after the surgery; most patients are comfortable thereafter.
Usually; however, it is almost always feasible to do one eye
at a time if that is your preference. I have never encountered a situation where, in retrospect, I wished I had done one eye at a time.
You will notice an improvement immediately or within a few hours. The morning after surgery, the vision is usually good enough to drive and return to work. In PRK the recovery is a little slower.
Rubbing the eye within the first 24 hours may dislodge the flap in which case it would have to be repositioned. After that time, the flap could only be dislodged by sharp trauma to the eye at the edge of the flap. The likelihood of either event is very remote.
Re-treatment is necessary in about 3% of cases. This is usually due to slight under correction. For LASIK re-treatments, it is usually not necessary to make a new flap, the original flap can be used.
With newer technologies such as Custom LASIK and Intralase, side effects have decreased significantly. All patients having LASIK will have scratchiness and tearing that resolves after about six hours. Most people will notice that their vision in dim light will be slightly diminished and that they may see some halos around headlights or streetlights at night. These side effects tend to diminish over the first 2 to 3 weeks. If the amount of correction is small, these side effects will tend to be insignificant. For everyone, the best vision is always in brighter light. Most patients will experience temporary dryness of the eyes up to 2 to 3 months. For most, these symptoms will resolve spontaneously; however, if the symptoms are significant, there are many adjunctive treatments for dry eye that can help.
Over my many years of involvement with eye surgery, particularly refractive surgery, I have found that complications are best avoided by careful patient selection, proper application of state-of-the-art technology, meticulous attention to detail and conscientious post-operative management. I think of complications as falling into three different categories: First, would include patients having residual refractive error; this occurs in about 3% and is usually resolved by retreatment. Second, would include patients that have some irregularity in the way their corneal tissue and the excimer laser energy interact producing a slightly irregular treatment. These patients are usually slightly less than 20/20 and may not benefit from retreatment; this occurs in about 0.3% or about 1 in 300 eyes. Third, would include events that lead to some significant visual loss that may be difficult to correct or may require significant secondary intervention. These would fall into the category of post-operative infection or microkeratome-related flap complications. Although these types of complication are reported in the literature, I, fortunately, have never personally had to deal with a sight threatening complication caused by refractive surgery.
RK is an incisional procedure that was done for nearsightedness and astigmatism until about 1994 when it was largely replaced with the more stable and more predictable excimer laser procedures. Although many patients have done quite well with RK, some have gone on to be overcorrected, often with hyperopia and astigmatism. Many of these cases can do very well with LASIK or PRK but each case requires individual evaluation.