Thursday, 24 October 2013

Types of Laser Eye Surgery

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 just a newer type of PRK. All techniques are performed with the patient awake and drops are used to numb the eyes.
The types of laser eye surgery that fall under the category of PRK do so because they 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 used in LASIK procedures. Removing the epithelium is the first step of laser eye surgery. The next step is reshaping the cornea by excimer laser. Here, the model of excimer laser varies as do 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 cornea flap by cutting is undesirable. Drawbacks of PRK include a longer recovery period and more discomfort during healing than with LASIK. The two main advantages are that PRK does not create a cornea flap by microkeratome blade, which is the part of laser eye surgery that carries the most risk, and it does not penetrate deeply into the cornea, reducing the risk of ectasia. (Ectasia is 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 that 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 hastened 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, or the different types of laser eye surgery that create a corneal flap by cutting, either with a microkeratome blade or laser:
LASIK (Laser-Assisted In Situ Keratomileusis) 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: 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 it is likened to a fingerprint. No two surgeries are alike, hence the name. 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 Custom Vue session, those imperfections would not be correctable until a later procedure).

Conventional IntraLasik 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 — the actual reshaping of the eye.

Custom Vue IntraLasik 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 laser eye surgery.

Custom Vue with Wavefront guidance technology cannot be used with all excimer lasers. VISX Star S4 is one type of laser that does accommodate it, and it is a “tissue saving” model as well. Other types of excimer lasers are guided by other wavefront technologies. Some require the pupils be dilated for the mapping process, such as the Alcon LADARVision laser that uses CustomCornea Wavefront technology. Some physicians 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. In FDA clinical trials where nearsighted patients underwent laser surgery and were retested after a 6-month period, 95.8% of those who were treated with VISX Star4 Custom Vue Lasik retained 20/20 vision, compared to 79.9% treated by Alcon LADARVision CustomCornea.

There are many issues associated with laser eye surgery and this article is not intended to be an exhaustive list of those issues nor an endorsement of any particular brand or technology, but rather a guide so that you will be more prepared to ask questions of your ophthalmologist about any options he or she may present. Among the questions you might want to ask: What is the baseline of expectation associated with this type of laser eye surgery? How accurate is the mapping/reshaping process? What percentage of people require a second procedure? What percentage of people have halo, glare, or night vision problems afterwards? Is the laser and procedure 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 from laser eye surgery, though technology is 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. RK predates the excimer laser and people who had RK may benefit from PRK or Lasik.

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