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There are two fundamentally different types of laser eye surgery: PRK and LASIK. Under these two categories, there are several different flavors or modifications of each type. For example, LASEK (with an "E") is a newer type of PRK. All techniques are performed with the patient awake and drops are used to numb the eye or eyes.
PRK surgeries all involve a surface ablation technique to remove the cornea's outermost layer, called the epithelium, rather than creating a flap via a cutting technique, as is used in LASIK procedures. Removing the epithelium is the first step, and is followed by reshaping the cornea by excimer laser. Here, the model of laser varies, as do the guidance or mapping systems associated with each model. The more precise the mapping and reshaping system, the better the results.
Following is a brief overview of the different types of laser eye surgery that use surface ablation techniques:
PRK (PhotoRefractive Keratectomy) — In PRK, the outermost layer of the cornea (epithelium) is manually scraped away and an excimer laser reshapes tissues located on the underlying (stromal) surface of the cornea. Afterwards, the epithelium layer must grow back. PRK is an option for those with thin corneas where the creation of a flap by cutting is undesirable. Drawbacks include a longer recovery period and more discomfort during healing than with LASIK. The two main advantages are that it does not create a cornea flap by microkeratome blade, which is the part of surgery that carries the most risk, and it does not penetrate deeply into the cornea, reducing the risk of ectasia, a condition of inner eye pressure pushing out against a thinned corneal wall, causing it to bulge resulting in worsening vision over time.
A Canadian version of PRK (transepithelial PRK) uses an excimer laser to vaporize the epithelium, rather than manually scraping it away.
LASEK (Laser Assisted Sub-Epithelial Keratomileusis) — An advanced form of PRK, LASEK uses alcohol in solution to first soften then remove the epithelium. After the excimer laser reshapes the stroma to correct the vision, the epithelium is replaced. The advantage of LASEK over PRK is that the healing process is faster while still avoiding the use of a cutting blade to create a cornea flap.
Epi-LASEK — This modified LASEK procedure uses a "separator" to preserve a living layer of epithelium, which is replaced after the excimer laser reshapes the stroma. Epi-LASEK seeks to reduce discomfort and healing time even further than LASEK.
Following are examples of LASIK, which create a corneal flap by cutting, either with a microkeratome blade or laser:
LASIK (Laser-Assisted In Situ Keratomileusis) — This type uses a microkeratome metal blade to cut the cornea flap and an excimer laser to reshape the eye. After the procedure, the flap is returned to its position. This is painless for most patients, and unlike PRK techniques, vision is immediately corrected, though some blurriness may be present for the first 24 hours and vision will improve for a period of weeks.
Custom Vue Lasik — This surgery uses the same hardware as conventional LASIK, but the excimer laser is guided by advanced software called Wavefront. In this procedure, vision is measured by mapping the optical system using technology that is 25% more accurate than traditional methods. The map is so exact that it is likened to a fingerprint and no two surgeries are alike. Because of the precision, it can be used to correct vision or to correct imperfections created by other laser procedures. Reportedly patients can expect 20/20 vision using Custom Vue Lasik, with many people experiencing even better results. The need for a second procedure is less common, but if the microkeratome blade causes imperfections during the session, those imperfections would not be correctable until a later procedure.
Conventional IntraLasik &mash; IntraLaski Uses a femtosecond Intralase laser to make the corneal flap, rather than a metal blade. This allows a much thinner flap to be created, and eliminates imperfections caused by a metal blade. This is regarded as a far superior method for corneal flap creation. The only drawbacks are that it takes about a minute to create a flap, rather than seconds, and it is more expensive. Also, if an excimer laser is used without Wavefront technology, imperfections can still result from the second step of the procedure &mash; the actual reshaping of the eye.
Custom Vue IntraLasik &mash; This type of laser eye surgery combines the best of all worlds. It uses a laser to create a cornea flap, and Custom Vue's Waterfront technology to guide the excimer laser for the best possible results. It is also the most expensive type of surgery.
Custom Vue with Wavefront guidance technology cannot be used with all excimer lasers, and some types are guided by other Wavefront technologies. Some require the pupils be dilated for the mapping process. A number of eye surgeons report that dilation can cause the center of the pupil to shift, offsetting the preciseness of the Wavefront map, resulting in less than optimal results.
There are many issues associated with laser eye surgery, and a brief article cannot provide an exhaustive list of those issues nor act as an endorsement of any particular brand or technology. Patients should be prepared to ask questions of their ophthalmologist about any options he or she may present. Among the questions someone might want to ask are what the baseline of expectation associated with the particular type of laser eye surgery is, how accurate the mapping/reshaping process is, what percentage of people require a second procedure, and what percentage of people have halo, glare, or night vision problems afterwards. Patients should also make sure that the laser and procedure are 100% FDA-approved.
Most reputable centers for eye laser surgery note that 20/20 vision from laser-corrected surgery may not be like 20/20 vision with corrective lenses. Some haze or other side effects can result, though researchers are always working to eliminate these. The most advanced techniques that carry the least amount of risk for side-effects are often more expensive. RK (Radial Keratotomy) is an obsolete form of corrective eye surgery that reshaped the cornea by making a series of radial slits. It predates the excimer laser, and people who had RK may benefit from PRK or LASIK.
Not everyone is a candidate for laser eye surgery. Though it is considered safe, serious risks can be involved. For more information, patients should consult an ophthalmologist.