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Lasik

Detailed Lasik Information, video, and comparison to PRK, LASEK, Epi-Lasik and other alternatives..


Click to see video of Lasik. Lasik applies laser energy under a flap of corneal tissue to correct nearsighted vision, farsighted vision, and astigmatism. Click for video.

 

Lasik is the most often performed surgery in the US. Conventional or wavefront custom Lasik is a surgical procedure that changes the shape of the cornea to reduce the need for glasses or contacts. Lasik has many distinct advantages over other refractive surgery procedures, but also has limitations that may indicate something else or no surgery is best for an individual patient.

The most you can expect from Lasik is the convenience of a reduced need for corrective lenses. To achieve that convenience, you must accept some risk. We hope to help you minimize that risk, but risk cannot be eliminated.

This document discusses in detail the history of Lasik, some of Lasik's advantages, and many of Lasik's disadvantages. This long and detailed article is to help a potential Lasik patient understand in depth what Lasik can do, might do, and when it is likely to do what is desired. Much of this discussion compares Lasik with other refractive surgery procedures, including PRK, LASEK, Epi-Lasik, P-IOLs, and RLE.

The primary difference between Lasik and other cornea based procedures is where the excimer laser ablates: under a flap of corneal tissue. Lasik is actually the combination of Photorefractive Keratectomy (PRK) and Automated Lamellar Keratoplasty (ALK). As you will see, the Lasik flap is both Lasik's strength, and its weakness.

As with nearly all excimer laser based refractive surgery, Lasik can be performed with both conventional ablation and wavefront-guided ablation.

In The Beginning

ALK was developed in the 1950s as a method of refractive surgery. A mechanical microkeratome is affixed to the eye with a suction ring. A plate flattens the cornea and a very sharp metal blade passes through the top of the flattened cornea, creating a thin slice of tissue. In original ALK, additional shavings of the cornea were removed to cause a net flattening of the central cornea. Flattening the center of the cornea will cause a change in the way light bends through the cornea, correcting myopia (nearsighted, shortsighted). The more tissue that is removed, the more the center becomes flat, and more refractive correction occurs.

ALK was refined over the ensuing decades, but complexity of the microkeratome, unpredictable results, and difficulty of the procedure kept its adoption out of the mainstream. The development and popularization of Radial Keratotomy (RK) in the 1980s provided a more reliable means to correct refractive error, although ALK still had its fans in ophthalmology and the technology behind ALK continued to advance.

The Laser Is Introduced

Lasers have been used successfully for eye care for decades. A laser is only highly condensed light and just about everything your eye doctor does deals with light. PRK was the first refractive treatment to use an excimer laser to remove tissue. An excimer laser changes the chemical nature of the molecules that hold together the cells of the cornea. The change causes this "glue" to release the corneal cells, and they rapidly escape from the cornea in a plume that looks very much like an atomic bomb blast, but is significantly different in its cause and effect. The excimer laser does not "burn" the cornea or cut the cornea. It makes the corneal fall apart, microscopic layer by microscopic layer. You cannot talk about Lasik without talking about PRK. Detailed PRK Information

The Cornea Responds

A major problem with PRK in its early development was corneal haze. PRK related haze continues to be a problem to this day, although some techniques have been developed to control its severity and treat its occurrence. Corneal haze is caused by the cornea's wound response. Surgery is an insult to the cornea, and your cornea really doesn't care if you want this insult, it is going to respond as if it has been wounded. A part of that wound response causes opaque cells to form. This presents as white hazing of the cornea, restricting light from passing through, and reducing the quality of vision.

PRK haze does not normally form for corrections that require a moderate amount of tissue removal, generally less than about 6.00 diopters of refractive error. That is good news for moderate and low myopia and virtually all hyperopes (farsighted, longsighted), but bad news for those needing higher corrections. As a general rule, if you need less than 6.00 diopters of correction, you should consider PRK as an option.

Different Depths, Different Responses

It was noted that wound response to laser ablation deeper in the cornea is significantly different than when the ablation is performed at the outer surface of the cornea. The idea was formed to creating a flap of corneal tissue using ALK methods, perform the PRK ablation under the flap and deeper in the cornea, then returning the flap over the ablated area. Thus Lasik was created as a combination of ALK and PRK.

Fool's Paradise

Lasik literally "fools" the cornea into not knowing it has been wounded. This is why Lasik normally provides no pain, has an almost instant vision recovery, and almost never causes corneal haze; the cornea doesn't know it has had surgery. You could call this microsurgery's own "ignorance is bliss". This major advancement allows correction of very high refractive error without a high risk of corneal haze and subsequent loss of vision quality.

More Than One Way To….

Due to new demand caused by the creation of Lasik, rapid advancement in mechanical microkeratome technology has provided much better quality corneal flaps with more predictability of size and thickness. Additionally, the femtosecond laser has been refined to create flaps with laser energy, rather than a metal blade. Intralase is the first company to introduce this technology to the US and Lasik with a laser created flap is often called Bladeless Lasik or "all laser Lasik". Detailed Bladeless Lasik Information

Not All 20-Minute Miracles

The only way to describe the implementation and popularity of Lasik is as an explosion. Ophthalmologists were rushing to lean how to perform this new procedure that promised to give patients freedom from glasses with no pain and almost instant results. Patients were flocking to clinics looking for freedom from glasses and contacts. That was the theory of what would happen. There is nothing that can screw up a perfectly good theory faster than reality.

Reality Sometimes Bites

While the vast majority of patients received a seemingly miraculous improvement in uncorrected vision, a small but very important minority had complications ranging from nuisance to vision debilitating. Much was learned by the early problems with Lasik. The range of refractive error treated today is significantly more narrow than in the early years. You will virtually never see a 20.00 diopter myope have Lasik today. This was not always the case.

Refinements in technology and technique have reduced the severity and probability of complications, but even with continued refinement, no surgery is perfect and there will always be some who will have unexpected and undesired outcomes. The primary purpose of the our organization is to help prospective patients become informed of the issues that contribute to poor outcomes, avoid those problems, and find the best qualified doctor available.

Back To The Future

The basics of Lasik today are virtually the same as when first created: make a flap, zap the cornea, and replace the flap. The range of variables in this three-step process is ever increasing, as are the number of options. What we discuss here are some of the options available today – old and new – and their relative advantages/disadvantages. If you visit our article on Intralase, you will learn the details of the creation options of the corneal flap, but all flaps have potential problems, no matter how they are made. The first problem of the Lasik flap is the existence of the flap itself.

If the flap exists, there will be the possibility of flap related problems. Those potential problems do not stop when you leave the surgery suite. Once you have had Lasik you have always had Lasik and you must always consider that your eye is fundamentally and forever changed. Change can be a good thing, but sometimes not.

There is a movement in ophthalmology back toward the surface ablation techniques of PRK and its cousins LASEK and Epi-Lasik because surface ablation eliminates the Lasik flap. If you eliminate the flap, you do not just reduce the possibility of a flap complication, you eliminate it completely. Everybody likes eliminating the possibility of a problem.

The advantage of surface ablation techniques go beyond just eliminating the possibility of flap complications. Study after study have shown that PRK produces long-term results that are equal to or superior than Lasik. A part of the reason for these better outcomes is the availability of enhanced ablation patterns with wavefront technology. Long term, PRK is often better for a patient than Lasik. The problem is, we don't "see" long term.

Lasik and PRK Recovery

The recovery from PRK is vastly different than Lasik. With Lasik, it is probable that fully functional vision will be almost instantaneous, there will be almost no pain, and you can resume most normal activities almost immediately. PRK, on the other hand, provides "fuzzy functional" vision for 3-6 days, functional vision for about another 2 weeks, and you won't get the really good crisp vision you desire for about 6-8 weeks after surgery. Not everyone can afford this much time with compromised vision. There is much more discomfort associated with PRK, and even today PRK has limitations due to haze, but let's consider how the haze situation has improved.

LASEK and Epi-Lasik

The ideal situation would be to have surface ablation with no pain, little probability of haze, and instant recovery. In other words, Lasik without the flap that reduces the probability of these limitations and speeds vision recovery. The answer to Lasik without the flap may be in changing the depth the flap.

The epithelium is the outermost layer of the cornea. These are the fastest reproducing cells in the human body. Before the laser can remove corneal tissue with PRK, all epithelial cells must be removed over the treatment area. The epithelial cells will regenerate and cover the treatment area in about 3-6 days. They will thicken over the ensuing 2 weeks, and smooth at about 6-8 weeks. Those time periods sound familiar? That's right, all the slow vision recovery of PRK is directly related to the epithelium recovery. Also, comfort is related to epithelium recovery.

Save The Epithelium!

Obviously, if the epithelium is so helpful, it needs to be saved. Lasik leaves the epithelium in place because the Lasik flap is cut deep underneath the epithelium in the deeper stromal layer of the cornea. Two similar but separate techniques to save the epithelium have been developed; LASEK and Epi-Lasik.

In LASEK, a diluted solution of alcohol is applied to the cornea for a few seconds. This disrupts the epithelial cell's ability to hold on to Bowman's layer, the next layer down the corneal construction. These disrupted, but viable, cells are moved out of the way, the laser does its magic, and then the cells are moved back over the treatment area. In theory, LASEK will hasten recovery, limit pain, and reduce the probability of haze. I'm sure you remember what we said about theories.

The reality is that few of the epithelial cells survive the alcohol. While the dead or dying cells replaced over the treatment area do provide extra protection and appear to reduce discomfort, vision recovery is not significantly improved. Improved, yes, but nothing like a Lasik recovery. While a reduction in corneal haze was noted, this may be attributed more to the advancement in laser quality than the LASEK procedure. Doctors are seeing less haze with PRK today, even thought PRK does not keep the epithelium. Detailed LASEK Information

The latest in the attempt to save the epithelium is Epi-Lasik. This technique uses a mechanical microkeratome with a blunt, rather than sharp, blade that slides across the front of the cornea. This blunt blade scrapes up a sheet of epithelium at the surface of the stronger Bowman's layer. This is essentially an epithelial flap. The flap is moved out of the way similar to Lasik, the laser treats the exposed area, and then the epithelial flap is repositioned. Early reports indicate that there is improvement in recovery time, comfort, and even the probability of haze, but it is much too early to know if Epi-Lasik is really ready for prime time. Detailed Epi-Lasik Information

Detailing the Details of Detailed Ablations

If you are considering Lasik, you are going to hear about wavefront. You are going to hear a lot about wavefront. You are going to be inundated with wavefront this and wavefront that. Click Wavefront Guided Ablation for a detailed article about whether or not you require a wavefront-guided ablation. In this article we will discuss how wavefront-guided ablation relates to Lasik.

Using a wavefront-guided ablation is often called custom Lasik, custom PRK, CustomVue, CustomCornea, or Zyoptix, depending upon the laser used. The process uses a wavefront aberrometer to evaluate virtually all of the optics that affect your vision. From this wavefront derived information, an ablation profile is created with the intent of reducing the introduction of harmful aberrations to your optics, and reducing those that already exist.

Think of wavefront as a mapping system. If you wanted to travel from Cleveland to Beverly Hills, a map of the whole US showing all the major highways would do just fine. If you wanted to get to a specific street corner on Rodeo Drive, you would need the detail of a city map. Think of conventional laser ablation as a map of the US, and wavefront-guided ablation as a street map.

The wavefront ablation profile of where more tissue needs to be removed here and less tissue needs to be removed there is very nuanced with tiny changes across the treatment area. A problem with Lasik is that you are putting a relatively thick 100-180 micron flap of corneal tissue on top of this fancy nuanced ablation. Like too many blankets on the bed, you lose some of the detail of the shape of who is in that bed.

Yet another reason why there is a push toward PRK in some circles is that the lasers are now able to make these really nice detailed ablations, but some of that detail is muted by the Lasik flap. Also, the Bowman's layer and uppermost layer of cells of he cornea are more dense than the deeper stromal layer. It is opined that this may help in creation of better and better ablations.

Why Not Abandon Lasik For surface ablation?

At first glance, it would seem that everyone should be jumping back on the PRK bandwagon. Not always. There is still that issue of corneal haze. The newer lasers seem to reduce the probability of corneal haze with PRK, but do not eliminate it. LASEK and Epi-Lasik attempt to minimize the limitations of PRK by saving the epithelium, but they may turn out to be just so much expensive luggage.

It has been found that having a patient take 500mg of vitamin C (yes, plain old vitamin C) twice a day for a week before PRK and at least two weeks after surgery significantly reduces the incidence of corneal haze. Isn't it always the simple answer that is the best. This appears to be helpful, but more study is needed to determine just how much help is provided with oral vitamin C supplements. It is really not known if vitamin C is enough for someone who needs 8.00 diopters of correction, but is not enough for someone who needs 10.00. The limits need to be determined.

The use of the topical eye drop Mitomycin C dramatically reduces the probability of haze, and can be used to treat haze when it occurs, but this is rather strong medicine. Mitomycin C is appropriate when required, but probably needs to be avoided if possible. Also, Mitomycin C changes how much tissue the laser ablates with each pulse, so the doctor needs to manually change the treatment plan. This requires additional expertise.

Lasik & Many Options

To get the best possible outcome, one must play the odds. You cannot guarantee perfection, but you and your doctor can take many steps to reduce the probability of a bad outcome. Procedure selection is one of those steps. It is not that Lasik is always best, or PRK should be used whenever possible, it is more that depending upon your unique circumstances, Lasik may or may not be the best choice for you. There is nothing wrong with Lasik as a procedure, if it is the best procedure for your situation.

As a gross generalization, Lasik is probably best for someone with more than 6.00 diopters of correction, and almost certainly necessary for someone needing more than 10.00 diopters of correction. Less than 6.00 diopters would make PRK, LASEK, and Epi-Lasik added possibilities. Between 6.00 diopters and 8.00 diopters, LASEK, Epi-Lasik, or PRK with Mitomycin C would be added to the mix. If you require fast recovery and can't handle even a small amount of discomfort, then Lasik and possibly Epi-Lasik are the prime choices. Over 12.00 diopters of myopic correction and over about 3.00 diopters of hyperopic correction would indicate that cornea based surgery is probably not wise and alternatives such as P-IOLs or RLE should be considered. Although Lasik is approved for much higher corrections, that does not mean that very high refractive error should be corrected with Lasik in your case.

Remember, these are gross generalizations and upon examination your doctor may recommend something completely different. And of course, it may be that no refractive surgery of any kind is appropriate for you.

Looking For Best Lasik Surgeon?

If you are ready to choose a doctor to be evaluated for conventional or custom wavefront Lasik, Bladeless Lasik, PRK, or any refractive surgery procedure, we recommend you consider a doctor who has been evaluated and certified by the USAEyes nonprofit organization. Locate a USAEyes Evaluated & Certified Lasik Doctor.

Personalized Answers

If this article did not fully answer your questions, use our free Ask Lasik Expert patient forum.


Recent Lasik Medical Journal Articles...

Related Articles

Post-Laser In Situ Keratomileusis Interface Fungal Keratitis.

Cornea. 2014 Aug 28;

Authors: Mittal V, Jain R, Mittal R, Sangwan VS

Abstract
PURPOSE:: To report outcomes of post-laser in situ keratomileusis (LASIK) interface filamentous fungal keratitis.
METHODS:: This retrospective interventional case series included 6 eyes of 5 patients with microbiologically proven post-LASIK interface fungal keratitis from August 2008 to August 2013. Patients presenting with concurrent bacterial/viral keratitis, systemic illness, prior ocular pathology, or those without a minimum follow-up of 3 months were excluded. Every case underwent microbiological scrapings from residual bed and undersurface of the flap after flap lift at presentation followed by voriconazole interface wash. Flap amputation was performed when required. The outcome measure was complete resolution of infection.
RESULTS:: The mean age was 24 ± 3.1 years. The male:female ratio was 4:1. The mean interval between LASIK and symptom onset was 4.16 ± 2 days; and the mean interval between symptom onset and patient referral was 3.16 ± 1.16 days. Interface scrapings showed filamentous fungal filaments in KOH wet mount. The culture grew Aspergillus in case 1 and case 5. Infiltrated LASIK flap needed to be amputated in 4 eyes of 3 patients. Voriconazole wash (100 μg/mL) of the stromal bed was performed in all cases. A positive response to therapy with resolution of infection was seen in all cases at a mean of 6.5 ± 4.6 days. No intraoperative or postoperative complications after interface scraping or voriconazole wash were observed. The final best-corrected visual acuity ranged from 20/20 to 20/80 at a mean follow-up of 9.1 ± 6.5 months.
CONCLUSIONS:: Post-LASIK interface fungal filamentous keratitis can present early and gives good outcomes with early microbiological diagnosis and appropriate management. Voriconazole is an efficient and probably safe adjunct in the armamentarium of corneal surgeons to treat such cases.

PMID: 25170582 [PubMed - as supplied by publisher]

 


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