Eye Clinic,
Medical Centre
88 Ahuza St
Ra'anana, Israel
Laser Techniques Explained
Copyright All Rights Reserved 2007
Dr Andrew Fink MD of
(Feel free to reproduce this article and page contents, but do respect the copyrights of the author. The article should be in its entirety, without changes to the text, with active links, and the article source credit below reprinted with the link active).
Is there no end to the variations and types of laser treatment available today for those of us who wear glasses? Whether its LASIK, superLASIK, intraLASIK, PRK, LASEK, or epiLASIK, its all extremely confusing even for the most enthusiastic patient who is about to undergo this life changing procedure. Is any technique really better than any other? How do doctors decide what to recommend, and how do you decide what to choose?
The facts are that thousands around the world continue to undergo what continues to be, in the US at least, the most popular procedure in medicine. Despite claims of superiority by most laser centres who assure you that their technique is best, the truth is results are superb from almost anywhere using latest generation technology and experienced surgeons. These days unhappy patients are a distinct rarity.
Laser vision correction treatments work by reshaping the curvature of the transparent layer of the eye in front of the pupil, called the cornea. The laser evaporates corneal tissue elegantly and delicately, making it flatter in short sighted (myopic) people and steeper in the long sighted (hyperopic).
Overall there are really just two laser techniques, the difference being where on the cornea the laser is performed-either on the surface, or deeper under a thin flap of corneal tissue.
The first technique which can be called "surface treatment" as the laser affects the surface of the cornea directly, involves the gentle removal of the outer skin-like layer of cells called the epithelium, exposing the tissue below which then receives the laser. After the treatment there is a period of about 2-3 days when the eyes are tender and watery with slightly blurry vision as the epithelium grows back and the eye surface heals. The original name of this technique is Photorefractive Keratectomy or PRK and is the longest established laser technique with almost 20 years follow up, stable long term results and is extremely safe.
Although first performed in 1987 PRK today is a much better procedure due the very advanced laser technology and more controlled post operative healing and pain relief techniques.
Epi-Lasik and Lasek are almost the same as PRK except both remove the epithelium in such a way (the former mechanically with a blunt instrument which slides across the eye, the latter with dilute alcohol which chemically loosens the tissue) that it can be replaced again afterwards. Some claim that by replacing the original epithelium, the healing is quicker than in PRK when new epithelium grows in, and therefore recovery is faster and more comfortable. These claims are controversial and not universally accepted, as tests have shown that the original epithelium tends to dissolve and is in any case replaced by fresh epithelium growing in. Moreover the safety and ultimate vision are the same for all surface techniques- excellent .
The second group of techniques used in laser vision correction involves cutting a flap in the cornea, a more invasive procedure. The big advantage is that as the laser treatment is under the flap which is immediately replaced after the laser ablation, and not exposed as in the surface treatments, recovery is much quicker, most seeing well the next day with no discomfort beyond the first few hours. The average cornea is slightly more than half a millimeter thick in the centre (500microns) and the flap is usually between 100-160 microns in thickness, which is folded back on a hinge of uncut cornea. See these diagrams
Most laser centres use an instrument called a microkeratome, which consists of a sharp oscillating blade that moves across the eye cutting the flap as it passes. This technique is called LASIK and is the most well known by today's laser candidates. It is also extremely safe, although on the very rare occasions that a problem occurs during laser vision correction treatments, it is usually connected with the flap.
IntraLASIK uses a special laser (femtosecond laser) to cut the flap (and another laser machine to perform the actual treatment of removing the glasses prescription). Supporters of IntraLASIK claim that it is safer than an oscillating blade, and that it creates more accurate and thinner flaps. Most studies seem to support this to some extent, but in fact modern microkeratomes are also extremely safe, can also create thin flaps, and only very rarely cause complications- and even when they do, they rarely cause significant long term problems for the patient. Also there have been on rare occasions complications with the intraLASIK flaps also. IntraLASIK treatments are generally much more expensive than regular LASIK.
Some studies have shown that intraLASIK may potentially give better quality vision afterwards but this is controversial and moreover the importance of the laser machine that performs the actual vision correction treatment itself is far greater. IntraLASIK does cause more eye inflammation than regular LASIK (although it settles without any problems) and is less comfortable for the patient. In adddition the intralasik cut is not as clean as with a sharp blade, and so the flap tends to stick down afterwards more firmly which may make it more trauma resistant, but can make it more difficult to raise if an enhancement treatment is required.
Other marketing terms such as super LASIK or ultra LASIK are just that-marketing terms.
The main long term concern with LASIK and Intralasik is that by cutting the cornea, it becomes structurally weaker, and in about 1 in several thousand cases (exact figures are difficult to determine as not all case are reported), after a few years the cornea can start to bulge out (a condition called ectasia) causing severe astigmatism, irreversible damage to vision and even a need for a corneal graft. Most at risk cases of ectasia can be predicted in advance e.g. candidates with thin corneas, and they can safely be offered a PRK surface treatment instead. But some cases have occurred for no obvious reason.
Conclusion
So what are the considerations when deciding which technique is best for you? Firstly of course any potential candidate needs to be assessed to make sure he is a good candidate for either technique. Some patients only suit surface treatment such as those with thin corneas, which makes the decision easier. In contrast hyperopic (far sighted) candidates (a minority in Israel) tend to have better visual results with Lasik.
For patients who suit both techniques the choice is between two very safe and successful techniques, and both of which give equally superb results. Surface treatment is a simpler operation but healing is slower requiring a few days off work (a small price to pay for the long term benefits) and vision takes a little longer to reach a good functioning level (3-4 days usually).
LASIK is a more complicated operation involving the cutting of a flap which is the main source of the rare problems that can occur in laser vision correction. There is also the issue of the very rare but serious long term problem of ectasia. But with more rapid healing, almost instant results and with little interruption in daily routine it continues to be very popular.
Whilst LASIK continues to be more heavily marketed by the large laser centres as the instant results are very dramatic-a high "WOW" factor-in private practice many more candidates are now seeing the advantages of PRK and opting for a surface treatment.
