Lasik information - LASEK, epi-lasik, intra-lasik, wavefront

If you've looked at the name of this page and all the names of procedures that look similar to LASIK, but you’re proceeding with trepidation because this looks like too much to digest, just bear with me! Once you have an understanding of LASIK, the other procedures will become very clear to you as I explain them. They are all just iterations of conventional LASIK and each procedure has its own particular risks and benefits.

The term LASIK is an acronym for Laser Assisted In-situ Keratomileusis. This procedure has corrected the refractive error of millions of people around the world. In fact, over a million people each year undergo LASIK in the United States alone. It is the second most commonly performed surgical procedure in the U.S., being second only to cataract surgery.

LASIK works well for most types and degrees of refractive error (myopia, hyperopia, and astigmatism), however, it certainly has its limitations as all procedures do! Most refractive surgeons would probably agree that LASIK works very well or extremely well in myopes with refractive errors up to about –5.00 or –6.0 diopters. At approximately –6.0 to –8.0 diopters of myopia, LASIK works well but poses a greater risk of reduced contrast sensitivity and night vision aberrations (I’ll review this in detail shortly). I believe that the majority of refractive surgeons do not recommend LASIK when myopia is greater than –9.0 or –10.0 diopters and above due to high risk of reduced contrast sensitivity and night vision aberrations.

For the hyperope (farsighted), LASIK works quite well up to approximately +3.0 or +4.0 diopters, however, this number is certainly debatable even among the most distinguished refractive surgeons. Again, I believe most refractive surgeons would agree that LASIK in the hyperopic patient has never shown as spectacular results as in the myopic (nearsighted) patient. This is because of the inherent relative ease of flattening the central cornea (as is the case in the myope) versus the inherent difficulty in steepening the central cornea (as must occur in the hyperope). However, the addition of tracking devices, which track the movement of the pupil during the procedure, and wavefront technology (see Chapter Nine), have certainly improved the outcomes of hyperopic LASIK. A number of refractive surgeons have begun to recommend conductive keratoplasty in hyperopes with refractive errors between approximately +0.5 and +2.5 diopters and they utilize LASIK for hyperopic refractive errors greater than +2.5 in patients under forty, and some refractive surgeons recommend clear lens replacement (Chapter 13) for patients over forty because this group already has presbyopia. This has considerable merit and I’ll refer the reader to Chapter 11 and 13 for more on CK or conductive keratoplasty and clear lens replacement (CLR), respectively.

LASIK combines the sophisticated precision of the excimer laser to reshape the cornea with a protective flap, the latter of which is created by either a mechanical microkeratome or a second type of laser known as the femtosecond laser (this procedure is known as “IntraLASIK”, which I’ll review in detail in this chapter). Let’s take a look next at the indications for LASIK, the pre-operative evaluation, and then the procedure itself.

LASIK may be used to treat nearsightedness (myopia), farsightedness (hyperopia), and astigmatism. However, not all Excimer lasers are presently FDA approved to treat all three types of refractive errors. For example, some Excimer lasers are not yet FDA approved to treat farsightedness. Your surgeon can provide this information to you at your request.

LASIK is an elective procedure, which, like any procedure, has potential risks and benefits. In general, indications for surgery must include an appropriate level of nearsightedness, farsightedness, or astigmatism, as well as an educated and properly motivated patient with realistic expectations. The best candidate for LASIK is an individual who desires to be less dependent on glasses or contact lenses, is willing to accept the risks of the procedure, and understands that an enhancement procedure may sometimes be required.

The primary potential risks include postoperative glare, halos or starburst around lights at night, and infection in the cornea with loss of best-corrected visual acuity. Fortunately, risks that threaten vision in the eye, such as infection in the cornea, are very rare. An in-depth discussion of the risks of LASIK is presented below.

There are a number of basic criteria that must be met before an individual can be considered for LASIK or, in most cases, any type of laser vision correction procedure. Given below are the general criteria that must be met in order to be considered a candidate, however, as you will read in other chapters (see Chapter Six), I have made recommendations that supercede this list as it regards choosing a procedure based on refractive error. With respect to age, eye disease, medical conditions, and concurrent medication use, this list must be respected. Here is the list of basic inclusion criteria:

· Myopia between – 0.50 and – 14.0 diopters (see Chp. Six for my recommendations)

· No concurrent eye disease or history of: keratoconus, herpes simplex keratitis, unstable refractive error, irregular astigmatism, corneal disease or scarring, cataract, glaucoma, or diabetic retinopathy

· None of the following medical conditions: collagen vascular disease (e.g., lupus), autoimmune disease (e.g., rheumatoid arthritis), immunosuppressive disease (e.g., AIDS, certain cancers), presently pregnant or breastfeeding, history of keloid formation, or diabetes mellitus (relative contraindication… discuss with your EyeMD)

· Must NOT be taking any of the following medications: Accutane, Imitrex, or amiodarone (Cordarone)

Patients who wear soft contact lenses or rigid gas-permeable contacts should discontinue their contact lens wear at least 3 days or 3 weeks prior to the evaluation, respectively. Prior to the LASIK procedure, one or more careful refractions (determinations of eyeglass correction needed) will be completed.

Contact lens wearing patients who are believed to have an unstable refraction will be asked to discontinue contact lens wear and return for a repeat refraction in one to three weeks. When back-to-back refractions are stable (equivalent), the procedure may be scheduled. Corneal topography, or a detailed surface map of the cornea, will also be completed to rule-out keratoconus and irregular astigmatism of the cornea. A complete and thorough eye examination including determination of eye pressure, slit-lamp examination, and dilated retinal evaluation will be completed.

The LASIK procedure is completed under topical (eye drop) anesthesia and is typically entirely painless during and after the procedure. A few seconds to a few minutes prior to the procedure, anesthetic eye drops will be applied to numb the eye and prevent discomfort during the procedure. These anesthetic drops work extremely rapidly, so one shouldn’t be surprised if the surgeon places the drops just moments before the actual procedure. Furthermore, many surgeons prefer to utilize the drops just 60 seconds or so prior to the procedure because the anesthetic drops cause tear production to be reduced, which may result in poorer initial vision following the procedure. A speculum is placed to hold the lids apart, thereby preventing blinking during the procedure. In LASIK that utilizes a microkeratome (rather than the femtosecond laser) to create the flap, the surgeon places a ring on the surface of the eye, which is designed to hold the eye steady and increase the pressure in the eye. This effect is achieved by way of vacuum that is created once the surgeon engages the unit. The microkeratome, which utilizes a highly polished, thin, oscillating blade, is then utilized to create a protective flap of the corneal surface. This surface flap may run the gamut in thickness from approximately 80 microns up to approximately 180 microns (roughly 1/4th to 1/3rd the corneal thickness). The surface flap is gently folded to one side in preparation for the laser refractive "cut." The laser, being computer driven for accuracy and precision, is pre-programmed based on the patient's refractive error (nearsightedness, farsightedness, astigmatism).

The laser delivery is completed next, and takes less than one minute for most patients. Laser delivery may take slightly longer for patients with hyperopia (farsightedness). Finally, the surface flap is returned to its original position restoring the surface integrity of the eye. The surgeon will often observe and re-evaluate the eye under the laser microscope for up to 2 to 3 minutes or more to be certain the flap is securely in position. The speculum is removed and the patient may typically leave the laser center within the hour. Many patients now have both eyes treated with LASIK on the same day.

Post-operatively, most patients will be instructed to use antibiotic and anti-inflammatory eye drop medications for 3 to 7 days. A shield is usually worn over the operated eye while sleeping for the first 24 hours and even up to seven days or more following surgery. The patient is also typically instructed to avoid rubbing the eye for the first few weeks following surgery.

Post-operative visits are typically minimal, but vary widely from one surgeon to another. Most patients will only require one to three post-operative evaluations, which take place in the first six months following surgery. Patients who are over-corrected, or under-corrected, may require an "enhancement," utilizing a procedure similar to the initial LASIK. Depending on the chosen time frame for an enhancement (when necessary), the surgeon may elect to lift the original flap or create a new flap with the microkeratome.

Your eye or eyes (if both are treated) will likely be quite blurry immediately after your LASIK surgery. Do not be alarmed. This is natural and expected. You will likely awaken the next morning after your LASIK surgery with much improved vision. Your vision should also improve over the first two to three weeks following surgery. It is best to carefully protect your operated eyes with shields or goggles while sleeping during the first day or more, or as your surgeon advises. Also, be sure to use the eye drop medications in the manner that your surgeon prescribes. Be very cautious not to rub your operated eyes for the first few weeks after surgery, as this may cause the flap to dislocate. In general, after the first few days, it is very unlikely that you could dislocate your flap by rubbing your eye, but be cautious nevertheless.

LASIK patients do not generally have any postoperative discomfort. If your eye begins to hurt or your vision deteriorates rather than improves, contact your surgeon immediately. We now know that dry eye syndrome commonly follows LASIK procedures, at least transiently. This may make your eyes burn, sting, dry or gritty, or even blur your vision. Many surgeons advise using non-preserved artificial tears for the first few weeks after LASIK. Other surgeons are now recommending placement of tiny tear duct plugs preoperatively to help prevent the complications of dry eyes following LASIK. Tear duct (punctal) plugs are tiny silicone plugs that may be simply and conveniently placed in one or more of the tear drainage ducts to prevent drainage of tears from the surface of the eye via that duct. The plug can just as easily be removed at a later date if too many tears seem to be present or if for any other reason the plug is not desirable.

The answer to the above question depends on many, many factors. However, I’ll do my best to present some useful data to you. I don’t want to leave you with “individual results may vary”, but at the end of the day, that statement is true!

The majority of LASIK procedures in the U.S. today are being completed on VISX excimer laser machines. As such, I’ll report their findings in one of the latest studies using the VISX Star S4 Excimer laser with the Wavescan wavefront-guided laser ablation system (more on this in Chapter Nine). Please realize that these are very carefully chosen patients under the most optimal conditions. The wavefront-guided Wavescan system is presently only FDA approved to treat up to –6.0 diopters of nearsightedness and up to 3.0 diopters of astigmatism.

From the VISX website (www.visx.com), regarding LASIK outcomes with the above mentioned machines, it states that “of the 277 eyes eligible for the uncorrected visual acuity (UCVA) analysis of effectiveness at 6 months, 100% were corrected to 20/40 or better, and 95.8% were corrected to 20/20 or better” in the eyes with myopia (nearsightedness) only. Of the eyes that had combined myopia and astigmatism, which actually is much more common, the studies “found that 99.5% were corrected to 20/40 or better, and 93.2% were corrected to 20/20 or better”[i]. In these FDA multicenter trials, which initially included 351 eyes of 189 patients at six centers, the mean preoperative myopia was –3.6 diopters and the mean preoperative astigmatism was 0.7 diopters. The safety data showed that, at six months postoperatively, 64% of eyes had a gain in best-corrected visual acuity (BCVA), which denotes the best vision obtainable with or without glasses. No eyes lost more than one line of BCVA. To illustrate what this means, if a patient had a BCVA of 20/15 preoperatively, and a BCVA of 20/20 postoperatively, this indicates a drop of one line of BCVA, because it is one line lower on the Snellen visual acuity chart used in most eye practitioners offices. This is an important statistic because it demonstrates that many patients actually have improved BCVA following LASIK with these machines.

With regard to night vision, patients were also very satisfied with the results. In fact, preoperatively only 65% of patients were satisfied with their night vision vs. 85% of patients at the six-month mark postoperatively.

With respect to hyperopic (farsighted) treatment, the FDA trials evaluated 144 eyes that underwent wavefront-guided LASIK, again using the VISX Star S4 excimer laser and the Wavescan wavefront system, known as CustomVue™. The Physician Information Sheet (Visx.com), referenced above, states that “of the 131 eyes eligible for the uncorrected visual acuity (UCVA) analysis of effectiveness at six months, 97.3% were corrected to 20/40 or better, and 66.2% were corrected to 20/20 or better” in the eyes that had hyperopia only. In the eyes that had combined hyperopia and astigmatism, “93% were corrected to 20/40 or better and 56.1% were corrected to 20/20 or better”.

The study showed that, at the six-month postoperative time point, no eyes lost more than one line of BCVA from pre-op to post-op. Furthermore, none of the eyes had best spectacle-corrected visual acuity worse than 20/25 postoperatively. Again, this shows a relatively high degree of safety in the treatment of hyperopia and hyperopia with astigmatism using LASIK and the Wavescan wavefront-guided VISX Star S4 laser. However, if you will compare these results to the treatment of myopia and/or myopia with astigmatism via LASIK (using VISX CustomVue), you will see that results are substantially better for the myopic group as compared to the hyperopic group. As I mentioned previously, LASIK has never shown as spectacular results for the hyperopes as compared to the myopes.

The VISX CustomVueä treatment is FDA approved to treat up to +3.0 diopters of hyperopia and 2.0 diopters of astigmatism.

One of the most significant potential risk factors in LASIK is actually the post-operative loss of contrast sensitivity that is accentuated under dim-illumination conditions. Only in the past few years has contrast sensitivity been more thoroughly studied as it relates to LASIK and other refractive surgical patients. It is rapidly becoming one of the most important characteristics of vision to be evaluated following refractive surgical procedures, second perhaps only to visual acuity as measured by the standard Snellen chart. Unfortunately, studies of contrast sensitivity are not always readily available in the doctor’s office. However, it is clear that loss of some degree of contrast sensitivity, which ultimately determines one’s absolute clarity of vision, is quite common with LASIK. It is the degree of contrast sensitivity that is lost or gained that ultimately determines a great deal of the value of a refractive procedure.

When significant amounts of contrast sensitivity are lost following a LASIK procedure, patients most frequently complain that the “sharpness” of their vision is decreased and they may have difficulty with night vision. One of the most commonly encountered contrast sensitivity related visual tasks is driving on a dark road at night, particularly on a wet road at night or during the rain at night. This task is often difficult even with the best visual acuity and contrast sensitivity. All LASIK patients should understand that some degree of contrast sensitivity may be lost following LASIK. It is important to realize, however, that advances in the science, technology, and techniques utilized in LASIK have dramatically reduced contrast sensitivity issues.

Along with reduced contrast sensitivity, glare and halos are probably the next most frequently encountered risks of LASIK. These post-op issues actually go hand-in-hand with one another as they relate to pupil size. Patients with large pupils have a greater degree of risk for these visual acuity issues. This is secondary to the fact that pupil size governs the amount of light that reaches the retina and from where that light comes from. The larger the pupil, the more peripheral rays of light (light hitting the peripheral cornea) are allowed to reach the retina. Because the size of the laser ablation on the cornea is limited by the corneal thickness, we have an anatomically limited laser ablation zone size of approximately six to nine millimeters in diameter (and I’ll remind you that the cornea is approximately 12 millimeters in diameter). This is due to the fact that larger ablation zones require relatively deeper central ablation in order to maintain the optical curvature of the intended ablation. It should be clear to the reader that the optical zone size is not limited because of the microkeratome or femtosecond laser that creates the flap or because the excimer laser couldn’t ultimately be programmed to treat a wider zone. It is because, and it is worth repeating, the corneal thickness limits the ablation zone size! I am making this as clear as possible because the size of the ablation zone is critical to night vision.

To get back to why an individual may experience decreased contrast sensitivity, halos, and glare following LASIK: It is ultimately because the pupil size may allow light to penetrate to the retina that is refracted from the peripheral (untreated) cornea. That is, rays of light that reach the retina under mesopic (reduced illumination, such as dusk) or scotopic (dark-adapted; night) conditions may come from central cornea that has been treated with LASIK as well as the peripheral cornea that has not been treated and cannot be treated due to the physical corneal thickness limitations already discussed. The purists will argue that this is not the only reason that patients experience these visual phenomena and that is true, however, for the sake of this discussion and unless you want a twenty-page dissertation (which I doubt), this is some of the basic logic behind these visual aberrations and LASIK. I’ll discuss contrast sensitivity issues and laser technology that has improved this attribute of vision to a further degree in Chapters Eight and Nine. Let’s move on.

Dry eye is a common condition that frequently follows LASIK. Fortunately, the condition should resolve or return to baseline within six months following the LASIK procedure. The reason that LASIK may result in a dry eye condition is because both the creation of the flap and the excimer laser itself can cut corneal nerves. The nerves should fully regenerate within six months, however, and it is at this point that tear production should be restored to baseline. It is worth noting that those patients with dry eye prior to LASIK may need special attention to this condition and, in some cases, may not be good candidates for LASIK. For those that have dry eyes, the surgeon or treating eye care practitioner may prescribe frequent artificial tears and/or tear duct (punctal) plugs may be placed pre- or post-operatively in the tear drainage ducts to preserve more natural tears.

LASIK flap complications may also occur. These include, but are not limited to partial flaps, button-holed flaps, irregular flaps, thin flaps, free flaps (the flap is not hinged in position), and post-operative flap wrinkles or striae, the latter being very fine wrinkles in the flap. When irregular flaps are created surgically, the LASIK procedure must sometimes be aborted and the flap replaced and allowed to heal. The procedure may sometimes be attempted several months later.

When the LASIK flap slips following the procedure, grossly obvious (at the slit-lamp microscope, that is) flap wrinkles occur and the flap must be re-lifted and “floated” back into position under a blanket of saline solution. This complication is frequently very simple to solve if it is present on post-op day one following LASIK and the condition is dealt with immediately. If wrinkles occur following LASIK and remain present for days or weeks without treatment, the condition becomes progressively more difficult to solve as the wrinkles become more deep-set. This is another reason for close post-op follow up. If flap striae (fine wrinkles) in the flap occur, the management is often unclear and will depend primarily on vision and the degree of striae. Many fine striae can be managed with simple “ironing” at the slit-lamp, which consists of rubbing the wrinkles with a flat instrument under topical anesthesia. In some cases, the striae will resolve with time as the overlying epithelium continues to thicken. In either case, the treating ophthalmologist and the patient must make the final decision in management of striae.

Corneal ectasia is a potential complication that may follow LASIK as well. Ectasia is an abnormal bulging of the cornea that may be precipitated by LASIK, although ectasia, such as keratoconus, also occurs without LASIK. Statistically speaking, the risk of ectasia following LASIK is higher in patients with an early form of keratoconus (forme fruste keratoconus), myopia greater than eight diopters, and relatively thin residual corneal beds following LASIK. The corneal bed is the remaining thickness of the cornea after the LASIK flap and the excimer laser ablation have been completed and this number should generally be greater than 250 microns.

Diffuse lamellar keratitis (DLK) is another potential complication of LASIK that is characterized by a sterile (non-infectious) inflammation at the LASIK flap/stromal bed interface. The condition onsets within the first week following LASIK and may cause permanently reduced vision despite the best management. The cause of the condition is often obscure but is theorized to be related to any number of potential stimulants within the flap/stromal interface including debris from the microkeratome, powder from sterile gloves, red blood cells or hemoglobin, particles from the sterile drape, meibomian oil gland secretions, endotoxins from bacteria present on the lid or ocular surface, epithelial defects (that may occur during the procedure), and povidone-iodine solution that is often used to minimize the risk of infection. Management of the condition consists of aggressive topical steroid eye drop use with or without lifting the flap and irrigation of the flap/stromal bed interface.

The last complication I will discuss, and possibly the worst of all, is infection. Fortunately, infection of the LASIK flap/stromal bed interface is rare (one in thousands of cases) but it does occur. These cases run the gamut from very mild with quick resolution to so severe and refractory to antibiotics that the infection penetrates the eye and threatens permanent and irreversible loss of sight. In some cases, the infection results in such severe scarring of the cornea that, ultimately, a corneal transplant is required. However, at least in these cases, vision is preserved as is the general health of the eye.

If you’re still with me at this point, I would like to congratulate you on considering most all of the possible ramifications of LASIK surgery, both positive and negative! As I eluded to in Chapter One, refractive surgical procedures are real surgical procedures. And with surgery comes risk. If you’re intent on undergoing a refractive surgical procedure such as LASIK, you should have a clear understanding of the potential risks as well as benefits. If you don’t understand the risks, you are not a good surgical candidate and you should not undergo the procedure!

Laser assisted sub-epithelial keratectomy (LASEK) is a procedure that was first introduced in 1999 by Italian ophthalmologist Massimo Camellin, M.D. Epi-LASIK was invented by professor Ioannis J. Pallikaris, M.D., Ph.D., of Crete, Greece, in 2003. As surgical procedures, LASEK and Epi-LASIK have distinct similarities to both LASIK and photorefractive keratectomy (PRK), the latter of which entails surface ablation of the cornea without any type of flap and is reviewed later in Chapter Ten.

LASEK and Epi-LASIK are procedures that require creation of only a surface corneal epithelial flap, rather than a deeper stromal flap as required in LASIK. These procedures have extraordinary appeal, in my opinion, because they avoid all the potential risks involved with creating the LASIK flap, including complications like incomplete flaps, button-holed flaps, slipped flaps, free flaps, striae or wrinkles in the flap, epithelial ingrowth, and diffuse lamellar keratitis (DLK). Furthermore, if an infection were to occur, it would most likely be much less potentially devastating because it wouldn’t be under a much thicker stromal flap as we produce in LASIK.

I’m preparing to present some rather complex issues with a bit of medical-technical jargon that may make you want to skip ahead. But, if you will bear with me just for a couple of paragraphs, I think you’ll get the picture and it will bring home some of the most important points in this website!

Perhaps as important, LASEK and Epi-LASIK may have visual benefits that will supersede traditional LASIK. The logic is as follows: Creation of the LASIK flap, when lifted and repositioned, leads to unpredictable biomechanical changes in the cornea, unpredictable changes in the wavefront (see Chapter Eight), and unpredictable increases in what are known as higher order aberrations (HOA’s), the latter of which reduce the optical clarity and contrast sensitivity of the eye. In fact, a recent study by Cox, et.al., showed that creation of the LASIK flap did not result in increased HOA’s, however, once the flap was lifted and replaced, even without completing the excimer laser aspect of the procedure, the HOA’s increased by 30%.[ii] Conventional excimer laser ablation (to treat the myopia, hyperopia, and/or astigmatism) further increased the spherical aberration and this was proportionate to the amount of spherical refractive error that was corrected. That is, the greater the treatment required, the greater the spherical aberration that was induced by the laser treatment. These general results are supported by a number of studies, which indicate that HOA’s increase following LASIK and PRK procedures[iii],[iv],[v],[vi],[vii],[viii]. When correcting a patient’s refractive error, we need to minimize or eliminate lower order aberrations (myopia, hyperopia, and astigmatism) and we must minimize the inducement of HOA’s as much as possible, as this is what leads to clear, sharp, high-contrast visual acuity. Think of this as high-definition vision! If you’re willing to pay for HDTV, you would probably want high-definition vision as well, correct? When all of these goals are met (lower order aberrations and higher order aberrations are eliminated), the patient sees well whether it be daytime, dusk, or nighttime. Now that was worth waiting for, right?

Multiple studies have demonstrated the safety, efficacy, and stability of LASEK[ix], [x], [xi]. In fact, Marguerite McDonald, M.D., clinical professor of ophthalmology at Tulane University in New Orleans where she also is in private practice, recently presented her early LASEK results. On post-op day (POD) #1, the mean visual acuity of 31 eyes treated was 20/40; on POD #3 to 4, the mean visual acuity was 20/30; on POD #7 the mean visual acuity was 20/25; at one month post-op, the mean visual acuity was 20/20+ (slightly better than 20/20); and at the 3 month post-op interval, the mean visual acuity remained 20/20+[xii]. A study out of Stanford University by Partal, et al, showed excellent results for LASEK patients as well and, in fact, this group was very myopic (nearsighted) with a mean spherical equivalent of –7.03 diopters pre-operatively. Here are the uncorrected visual acuities (UCVA) of these patients at the specified intervals: At 3, 6, and 12 months, the UCVA was 20/20 or better in 66%, 67%, and 83%, respectively, and 20/40 or better in 98%, 99%, and 100%, respectively[xiii]. These are very respectable numbers, by anyone’s judgment, when you consider the degree of myopia they were treating.

Another major advantage of LASEK and Epi-LASIK is that these procedures may allow treatment of patients with relatively thin corneas that would not be candidates for LASIK. As stated previously, corneal thickness limits both the laser ablation zone size (the width of the ablation on the cornea) as well as the depth, the two of which are intimately related.

Understanding Corneal Thickness and Its Implications for Corneal refractive procedures

In the work-up of a patient who is being considered for LASIK (or any other corneal refractive procedure), one of the many required pre-operative tests is a measure of corneal thickness called pachymetry, with an ultrasonic device called a pachymeter. The corneal thickness is measured in microns, which are 1/1000th of a millimeter. The average corneal thickness is 545 microns, or roughly one-half of a millimeter (about 1/50th of an inch). LASIK surgeons know that, in order not to induce post-operative corneal ectasia (abnormal corneal bulging with loss of best-corrected vision), a “bed” of corneal stromal tissue must be left behind that is at least 250 microns. Another rule of thumb sometimes considered is that the “bed” should be 250 microns or at least 50% of the pre-operative corneal thickness. Using an example, let’s say a patient presents with a corneal thickness of just 500 microns (the cornea is thin). If we’re considering LASIK, we’ll need to make a flap, which is typically 160 or 180 microns if we’re using a standard microkeratome. This flap will include the superficial epithelium (about 45 to 50 microns thick) and a layer of underlying stroma. Then, let’s assume, by further example, that the patient is a –10.0 diopter myope (nearsighted). In treating this patient with the excimer laser once the flap has been made, an additional 100 microns of corneal stromal tissue is removed (this is known by consulting the specific laser manufacturer’s nomogram; this number will vary from one excimer laser to another and one program to another). After we add up the flap thickness (160 microns) and the stromal ablation via the excimer laser (100 microns), we see that we will theoretically leave behind a corneal “bed” of just 240 microns:

In this example, we don’t have enough corneal thickness to complete the LASIK procedure without putting the patient at risk of developing abnormal corneal bulging known as corneal ectasia, because the residual stromal “bed” is under 250 microns. In this scenario, the surgeon could consider other alternatives including LASEK, Epi-LASIK (corneal refractive procedures), and an implantable contact lens (phakic intraocular lens). PRK is not an option because the patient is too myopic.

In the LASEK procedure, the surgeon first places alcohol on the cornea for approximately 20 to 40 seconds. Then, a 270 degree shallow trephine ring is used to outline and initiate the edges of the epithelial flap, and this is followed by mechanical lifting of the epithelial flap of tissue that is hinged on one side (for ease of replacement at the completion of the case). As an aside, there isn’t any cutting of a stromal flap with a blade or laser, as occurs in the LASIK procedure.

In the next step of the LASEK procedure, after the epithelial flap has been created, the excimer laser ablation is completed. Then, the eye is irrigated with saline and the epithelial flap is replaced in its original position. A bandage contact lens is placed on the eye and is usually left in place for about 3 to 7 days. The patient will be required to use antibiotic eyedrop medications for several days or more and anti-inflammatory (steroid) eyedrop medications for anywhere from about four weeks to several months, depending on healing factors and the surgeon’s preference.

The Epi-LASIK procedure is very similar to the LASEK procedure, however, alcohol is not used to loosen the epithelium and, instead, a mechanical device called an epikeratome is used to remove the epithelial layer. The epikeratome is an automated keratome that, like the microkeratome used in LASIK, vacuums onto the eye, and then a blunt tipped separator passes over the cornea literally peeling away the roughly 45 micron thick (about 1/250th of an inch) epithelium. There is no cutting involved, no blade, and none of the potentially dreadful flap complications that are rarely associated with LASIK.

The Epi-LASIK procedure has distinct advantages over LASEK because alcohol (used in LASEK) has been shown to be toxic to the epithelial cells and, in fact, one study completed at the Massachusetts Eye and Ear Infirmary at Harvard Medical School showed that a single 20% ethanol (alcohol) solution applied to the eye for 30 to 40 seconds (as used in LASEK) kills 70% of the epithelial cells within about 24 hours[xiv]. In contrast, in the Epi-LASIK procedure, the epikeratome separates the epithelial layer along a natural cleavage plane (Bowman’s membrane) without the use of alcohol and this leaves 87.3% of the epithelial cells viable 24 hours after the mechanical separation[xv]. Use of the epikeratome also renders a fatal injury to the epithelial cells, however, cell death in this case will not take place until about four to five days later. By that point in time, the patients natural epithelial cell regeneration will have largely or completely replaced the fatally injured cells, and the underlying corneal stroma will be well on its way to an uneventful healing. This latter fact means that the corneal stroma is unlikely to heal with any haze or underlying scarring. In fact, Dr. Pallikaris himself (the inventor of Epi-LASIK) recently showed in a study of forty-four eyes that underwent Epi-LASIK that 97% of the eyes had clear corneas or only trace haze three months after treatment[xvi]. For these reasons, Epi-LASIK appears to be the more gentle of the two procedures and the procedure with the most advantages.

· Theoretical optical advantage over LASIK because the epithelial flap does not negate or alter the accuracy of the laser ablation profile

· Decreases the risk of post-operative dry eye complaints because fewer corneal nerves are cut in the procedure as compared to LASIK

· No stromal flap (as in LASIK), therefore, no risk of flap dislocation, wrinkles, or striae (fine wrinkles), etc.

· No use of alcohol (as in LASEK), which is toxic to epithelial cells; therefore, more uneventful healing and much less risk of corneal haze as the eye heals

· More postoperative discomfort than LASIK (however, post-operative pain regimens developed that include dilute topical anesthetics, anti-inflammatory medications, oral pain relievers, and bandage contact lenses have greatly reduced and even eliminated post-operative discomfort)

If you’ve read this section, you’ve probably surmised that I believe Epi-LASIK has already taken a strong foothold in refractive surgery and this procedure may eventually supplant traditional LASIK. Epi-LASIK is “bladeless LASIK” with virtually all of the major benefits of LASIK and, in my opinion, fewer risks. The only significant disadvantages are that the procedure is not as comfortable post-operatively for the first couple of days and visual recovery is a little slower than traditional LASIK. However, if you prefer the procedure with substantially less risk than traditional LASIK with a blade (or laser to cut the flap known as Intra-LASIK… to be discussed next), then Epi-LASIK appears to be an excellent alternative. The procedure is relatively new and is obviously an “offshoot” of LASIK, so only time will tell if this procedure gains widespread acceptance by both ophthalmologist refractive surgeons and the patients who undergo these procedures.

As previously reviewed in this chapter, LASIK corneal flaps are traditionally created using a mechanical microkeratome. This has generally been a safe technique. However, the microkeratome produces a meniscus-shaped flap of variable overall thickness and always thinner in the center than at the edges. Occasionally, a corneal abrasion or an irregular, incomplete, or button-hole flap results.

The IntraLase™ femtosecond laser virtually eliminates the risk traditionally involved in creating a LASIK corneal flap. The LASIK surgeon programs the desired thickness, diameter, and hinge placement. Then, without using a blade, the IntraLase™ laser creates a predictable uniform-thickness flap. The next step in LASIK, of course, is to complete the laser refractive ablation. That is, an excimer laser is still required to perform the refractive ablation, the latter of which is the aspect of the procedure that reshapes the cornea such that the patient will see better without glasses or contacts.

laser and excimer laser combined) LASIK vision treatment that minimizes the possibility of flap complications while maximizing comfort and safety. However, there are still risks associated with the flap itself, such as the possibility of infection, striae (wrinkles), flap dislocation, and the concerns that creating a flap at all, once lifted, induces higher order aberrations. But, if you’re considering LASIK, it certainly is true that creation of the LASIK flap is much safer with the IntraLase femtosecond laser. Let’s look a little further into this issue.

So what about visual acuity outcomes? Could visual acuity actually be better with IntraLase versus a bladed microkeratome? Several studies have addressed this issue and here are the major results.

David Tanzer, M.D., reported outcomes from a prospective study that compared vision outcomes from groups of LASIK patients that had flaps created either by the IntraLase femtosecond laser or by bladed microkeratomes. This study was conducted at the Naval Medical Center in San Diego and the results were presented at the 2005 American Society of Cataract and Refractive Surgeons (ASCRS) convention[xvii].

There were three patient groups in this study: those with IntraLase created flaps, Hansatome (by Bausch & Lomb) microkeratome created flaps, and Amadeus (by AMO) microkeratome created flaps. There were 50 patients in each group. All patients were treated with the VISX Star S4 CustomVue laser. He found patients in the IntraLase group had better postoperative visual acuities at one month than patients in either of the microkeratome groups. At three months post-op, the visual acuities were similar in all three groups, however, the IntraLase group gained one line of best-corrected visual acuity (BCVA), the latter of which indicates that vision was one line better on the Snellen visual acuity chart postoperatively when compared to pre-op BCVA. Furthermore, he found that the IntraLase group performed better on mesopic (dim light) contrast sensitivity testing as compared to the microkeratome groups.

Dan Durrie, M.D., conducted a similar study comparing visual outcomes of patients who underwent LASIK surgery with an IntraLase flap in one eye and a Hansatome microkeratome flap in the opposite eye. His results showed that postoperative visual acuity was better at all time points measured with the IntraLase treated eyes[xviii]. Contrast sensitivity was better in the IntraLase treated eyes and there was a patient preference for the IntraLase treated eyes as well.

Dan B. Tran, M.D. at the Coastal Vision Medical Group, Inc., in Irvine, California, conducted a study that compared the objective wavefront aberration (see Chapter Eight for detail) as well as the refraction (glasses prescription determination) after LASIK flap creation with a microkeratome (Hansatome) vs. a femtosecond (IntraLase) laser. In this most interesting study, the surgeons completed the flap creation, studied the effect that creation of the flap had on the eyes’ visual function, and 10 weeks later lifted the flap and completed the excimer laser refractive ablation. They again completed studies of visual function.

They found statistically significant changes in total higher-order aberrations (HOA’s) (trefoil and quadrafoil…for the optical physicist readers!) after flap creation in the microkeratome group, but no significant changes in HOA’s after flap creation in the IntraLase group[xix]. A hyperopic (farsighted) shift occurred in the Hansatome microkeratome group after flap creation but no refractive error shift occurred in the IntraLase group. After the flap was re-lifted in each group and the excimer laser ablation procedure was completed, a statistically significant increase in coma (yet another type of HOA, think comma shaped visual aberration) occurred in the microkeratome group but not in the IntraLase group. The authors concluded, “The creation of the LASIK flap alone can modify the eye’s optical characteristics in low-order aberrations and HOA’s. A significant increase in HOA’s was seen in the Hansatome (microkeratome) group but not in the IntraLase group.”

Maria Chalita, M.D., also presented results comparing IntraLase vs. Moria microkeratome treated eyes (for flap creation) at the 2005 ASCRS convention. Both groups underwent LASIK using a wavefront-guided excimer laser. However, in this case, there was no statistically significant difference in postoperative visual outcomes between the two groups, nor was there any difference in the induction of higher order aberrations (HOA) between the two groups[xx].

Another study, conducted by Edward E. Manche, M.D., director of cornea and refractive surgery at the Stanford University School of Medicine, showed rather similar results between the IntraLase and microkeratome flap-created eyes[xxi]. Both groups showed quite a high degree of safety and efficacy, however, many more eyes were evaluated in the microkeratome group. In this study, 36 eyes were treated with IntraLase and 140 eyes were treated with the Hansatome microkeratome. The uncorrected visual acuities were better postoperatively in the group whose flaps were created with the IntraLase than in those whose flaps were created with the microkeratome. Dr. Manche reported that 100% of the eyes in the IntraLase group had 20/40 or better, 94% were 20/20 or better, and 64% were 20/16 or better. In the microkeratome group, almost 99.5% were 20/40 or better, 88% 20/20 or better, and 36% 20/16 or better.

Guy Kezirian, M.D. and Karl Stonecipher, M.D. compared LASIK results obtained with the femtosecond laser (IntraLase) to those obtained using two popular microkeratomes (Moria and Hansatome)[xxii]. Visual acuity results, including uncorrected visual acuity (UCVA) and best spectacle corrected visual acuity (BCVA), were not statistically significantly different between the groups at post-op day one or at three months. However, they did find that the IntraLase flaps were significantly thinner (as programmed) (P< .01) and varied substantially less in thickness than the flaps created with either of the two microkeratomes (P < .01). The microkeratomes caused epithelial abrasions or loose epithelium in 9.6% of the eyes in the Moria microkeratome group and 7.7% of the eyes in the Hansatome microkeratome group but in none of the eyes in the IntraLase group (P = .001). To understand what this means, however, one must realize that an epithelial abrasion or loose epithelium usually heals within the first 24 hours following LASIK and generally only results in a foreign body sensation until healed. However, a small number may subsequently develop a complication known as epithelial ingrowth – a condition that may require lifting the flap and removing the epithelium. The microkeratomes also caused more induced astigmatism than did the IntraLase (P< .01). The authors conclusions: “The IntraLase demonstrated more predictable flap thickness, better astigmatic neutrality, and decreased epithelial injury than 2 popular mechanical kicrokeratomes.”

If you were to do a thorough job of researching the IntraLase laser, you might come across a condition called “transient light sensitivity syndrome” that has been associated with the use of this laser. I believe the term was coined by IntraLase company officials when an ophthalmologist had a fairly high rate of IntraLase patients in his practice that complained of light sensitivity (photophobia). The ophthalmologist did note that the light sensitivity resolved after treating with topical steroid eye drops (which are normally used for a brief period of time after LASIK). This issue was addressed by IntraLase medical director, Perry Binder, M.D. “It {transient light sensitivity} is a fraction of one-percent of the cases in my practice and in the practice of (North Carolina surgeon) Karl Stonecipher, who has also studied it,” said Dr. Binder. “It’s not debilitating and it’s temporary. It doesn’t require any repeat surgeries, there’s no morbidity, no loss of vision and it’s totally reversible,” he said. He elaborated that what happened in the ophthalmologist’s practice that reported the high incidence of light sensitivity was “way out of proportion to what anyone else has had, so much so that IntraLase is changing out his laser”[xxiii]. Apparently, about 1% of patients whose flaps are cut with the IntraLase laser develop transient light sensitivity (TLS), which may manifest itself as an extreme sensitivity to light without any loss of visual acuity. The onset of this light sensitivity usually occurs about 2 to 6 weeks post-LASIK and may last approximately 2 to 6 months if not treated aggressively with topical (eyedrop) steroids such as Pred Forte.

The exact cause of TLS is still uncertain, however, it has been theorized that the inflammation is caused by cellular debris or inflammatory cytokines (mediators of inflammation) that develop within the tissues of the eye itself as a response to the surgery. Dan Durrie, M.D., refractive surgeon in Overland Park, Kansas, states, “It was scary when we didn’t know what it was – frightening to the surgeon and the patient. Now that it’s been identified, I can put a name to it and say, ‘Oh, you have TLS. This is a known condition. It responds to steroids and then goes away for good.[xxiv]’”

LASIK has been associated with the development of a dry eye syndrome as well that may be minimized with IntraLase. But let’s take a look at why: With “standard” microkeratome (blade) LASIK, the blade must cut through corneal nerves. This leads to denervation and less corneal sensation that, in turn, translates to decreased tear production. The problem is certainly temporary and, in most cases, corneal sensation returns to baseline (along with tear production) within six months. Microkeratomes generally make corneal flaps in the 140 to 180 micron range. However, with IntraLase the flap can be programmed to be 120 microns or even less. This translates to less corneal nerves being transected and, therefore, better corneal sensation postoperatively and less dry eye.

There are far less surgically induced complications with IntraLase as well. Three studies presented at the 2003 American Society of Cataract and refractive surgery convention showed no serious flap complications in 208, 300, and 5,000 cases using IntraLase (Lee T. Nordan, M.D. and Stephen G. Slade, M.D.; Jonathan D. Christenbury, M.D.; and Brian Will, M.D., respectively)[xxv].

So, if you’re thoroughly confused by all of the new and complex terminology, you’re not alone! This is no doubt a difficult subject. I’ve tried to give as much detail here as I felt our most avid readers would desire to investigate this most important issue. Let me summarize with a list of the benefits of using the IntraLase laser to create the LASIK flap as compared to the standard microkeratome.

·Reduces the induction of higher-order aberrations (HOAs) as compared to the microkeratome

I would have to submit to you that, if you’re choosing to have LASIK, you might want to strongly consider “all laser LASIK”, better known as IntraLASIK. The IntraLase laser, used to create the LASIK flap, obviously has many advantages over the traditional, mechanical, bladed microkeratome. However, to keep this in perspective, I would also submit to you that most surgeons who are very experienced with a microkeratome have a very low complication rate. LASIK in an experienced surgeon’s hands with a microkeratome can still be very good or even excellent, however, the risks are still higher, as I’ve laid out for you in this chapter.

One final consideration: IntraLASIK with the IntraLase machine will probably cost you about $400 to $600 dollars or more per eye than LASIK with a microkeratome. Why? Because the IntraLase femtosecond laser has an up-front cost of approximately $375,000.00 plus a fee of about $160.00 per eye for the disposables. Compare this to the microkeratome’s cost of approximately $40,000 to $65,000.00 and a case fee of approximately $80.00 for the disposables for both eyes. Ultimately, your surgeon must pass this cost on to you, if he is to stay in business. Is it worth it to you to have IntraLASIK instead of microkeratome LASIK? With most surgeons, you probably won’t have a choice. They’ll either offer LASIK with a microkeratome or LASIK with the IntraLase. They’ve made a decision based on their own reasons, which clearly must also involve finances. If you feel strongly about this issue one way or another based on the studies I’ve presented, you should ask if the surgeon you’re considering offers LASIK using IntraLase (IntraLASIK).

Again, I submit the contents of this chapter for your own edification. I think the results are clearly in favor of IntraLASIK (when compared to microkeratome LASIK) when it comes to both safety and visual acuity outcomes. However, you should be your own judge. Look at the summaries of these studies and draw your own conclusions.

If you’ve decided that you would prefer to have IntraLASIK rather than microkeratome LASIK (or vice-versa), don’t click away from this website just yet! In the next chapter, we’ll look at conventional vs. wavefront-guided LASIK. You have yet another decision to make!

In this chapter, we’ve reviewed LASIK, LASEK, Epi-LASIK, and IntraLASIK, all in substantial detail. All of these procedures have pros and cons. In the final analysis, all of these procedures are excellent in the right hands. However, I do believe that Epi-LASIK has some safety and optical advantages over traditional LASIK because it utilizes only an epithelial flap rather than a deeper stromal flap (as in LASIK or IntraLASIK) that may alter the intended laser ablative contour changes in the cornea with consequent induction of higher-order aberrations. Furthermore, in my opinion, IntraLASIK shows greater safety and visual outcomes than microkeratome (bladed) LASIK.

So what about Epi-LASIK vs. IntraLASIK? Tough question! I really can’t answer that question with any sort of clinical study to back me up. So let me just state that they’re both excellent procedures. I would choose either one, depending on what my surgeon was most comfortable with.

[i] Physician Information Sheet. VISX Wavefront-Guided LASIK for Correction of Myopic, Hyperopic, and Mixed Astigmatism (CustomVue LASIK Laser Treatment). Visx.com. 07/01/2003.

[ii] Cox, S. What Causes The Increase in Higher Order Aberrations After LASIK? The Cut, The Flap Manipulation and /or the Ablation? Invest Ophthalmol Vis Sci 2004;45: E-Abstract 211

[iii] Oshika T, Klyce SD, Applegate RA, Howland HC, El Danasoury MA. Comparison of corneal wavefront aberrations after photorefractive keratectomy and laser in situ keratomileusis. Am J Ophthalmolol 1999;127:1-7.

[iv] Thibos LN, Hong X. Clinical applications of the Shack-Hartmann Aberrometer, Optom Vis Sci 1999;76:817-825.

[v] Williams DR, Yoon GY, Porter J, Guirao A, Hofer H, Cox I. Visual benefit of correcting higher order aberrations of the eye. J Refract Surg 2000;16:S554-S559.

[vi] Mrochen M, Kaemmerer M, Mierdel P, Seiler T. Increased higher –order optical aberrations after laser refractive surgery: a problem of subclinical decentration. J Cataract Refract Surg 2001:27:362-369.

[vii] Endl MJ, Martinez CE, Klyce SD, et al. Effect of larger ablation zone and transition zone on corneal optical aberrations after photorefractive keratectomy. Arch Ophthalmol 2001;119:1159-1164.

[viii] Moreno-Barriuso E, Lloves JM, Marcos S, Navarro R, Llorente L, Barbero S. Ocular aberrations before and after myopic corneal refractive surgery: LASIK-induced chanes measured with laser ray tracing. Invest Ophthalmol Vis Sci 2001;42:1396-1403.

[ix] Safety, efficacy, and stability indices of LASEK correction in moderate myopia and astigmatism. J Cataract Refract Surg. 2004 Oct;30(10):2130-7.

[x] Analysis of the efficacy, predictability, and safety of LASEK for myopia and myopic astigmatism using the Technolas 217 excimer laser. J. Cataract Refract Surg. 2004 Oct;30(10):2138-44.

[xi] LASEK: results after 1 year. Retrospective analysis based on the dioptric power matrix for moderate myopic and astigmatic correction. Ophthalmologe, 2005 Mar; 102(3):235-40.

[xii] M. McDonald. LASEK and Epi-LASIK: An Update. Ophthalmic Hyperguide. Mar. 2004, Video Presentation.

[xiii] Analysis of the efficacy, predictability, and safety of LASEK for myopia and myopic astigmatism using the Technolas 217 excimer laser. J. Cataract Refract Surg. 2004 Oct;30(10):2138-44.

[xiv] Chun CC, et al., Human Corneal Epithelial Cell Viability and Morphology after Dilute Alcohol Exposure. Invest Ophthalmol Vis Sci. 2002;43:2593-2602.

[xv] M. McDonald. LASEK and Epi-LASIK: An Update. Ophthalmic Hyperguide. Mar. 2004, Video Presentation.

[xvi] Ioannis G. Pallikaris, M.D., Ph.D., et al., Epi-LASIK: Preliminary clinical results of an alternative surface ablation procedure. Journal of Cataract and refractive surgery, May 2005, Vol 31, Issue 5, pp. 879-885.

[xvii] Tanzer DJ. Comparison of visual outcomes with femtosecond and mechanical microkeratomes for wavefront-guided LASIK. Program and abstracts from the American Society of Cataract and Refractive Surgery 2005 Symposium on Cataract, IOL, and refractive surgery; April 15-20, 2005; Washington, DC.

[xviii] Durrie DS. Clinical and anatomical outcomes of LASIK performed with an intralase femtosecond laser versus a mechanical keratome. Program and abstracts from the American Society of Cataract and Refractive Surgery 2005 Symposium on Cataract, IOL, and refractive surgery; April 15-20, 2005; Washington, DC.

[xix] Tran, DB, et al., Randomized prospective clinical study comparing induced aberrations with IntraLase and Hansatome flap creation in fellow eyes: potential impact on wavefront-guided laser in situe keratiomileusis. J. Cataract Refract Surg. 2005 Jan;31(1): 97-105.

[xx] Chalita MR. Comparison of custom LASIK outcomes with femtosecond and conventional microkeratome. Program and abstracts from the American Society of Cataract and refractive surgery 2005 Symposium on Cataract, IOL, and refractive surgery; April 15-20, 2005; Washington, DC.

[xxi] Manche, E. Femtosecond laser creates more accurate flap thickness. Ophthalmology Times. Jan. 15, 2005.

[xxii] Kezirian, GM, Stonecipher, KG. Comparison of the IntraLase femtosecond laser and mechanical keratomes for laser in situ keratomileusis. Journal of Cataract and refractive surgery. Vol. 30, Issue 4, pp 804-811 (April 2004).

[xxiii] Is Intralase Better Than Microkeratomes? Review of Ophthalmology. Vol. No: 11:10 Issue. Oct 15, 2004.

[xxiv] IntraLase: Changing the LASIK Landscape. Ophthalmology Management. March, 2005.

[xxv] Talamo, JH. Optimizing Flap Outcomes With the IntraLase FS Laser. Ophthalmology Management. May, 2004.

More info> lasiksurgerynews.com

LASIK, LASEK, Epi-LASIK and Intra-LASIK (all laser LASIK)

eye surgery Links

Vision Correction surgery

Vision Correction surgery

Terms of Use | Privacy Statement

Home | Surgery Options

Copyright 2010 © Mark Erickson