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LASEK Preoperative Considerations

Robin F.Beran, MD, FACS

Columbus Laser and Cataract Center

Columbus, OH

INTRODUCTION

All refractive surgical procedures demand appropriate preoperative patient selection and patient preparation to achieve optimal postoperative results. This principle is extremely important when performing laser subepithelial keratomileusis (LASEK), because the characteristics of this technique are considerably different than the more popular procedure, laser in situ keratomileusis (LASIK). Patient selection includes consideration of candidate age, personality characteristics, occupational and recreational activities, as well as a number of specific ocular considerations. Preoperative patient preparation focuses on patient education and optimizing the ocular status for surgery. Failure to address these issues may reduce one’s chances for the best and safest outcome.

PATIENT CHARACTERISTICS

The patient selection and evaluation process should begin with the initial patient contact. This contact is usually via phone, although there will be visitors and walk-ins. In addition to obtaining the vital personal information to permit continued contact, the staff member should record any comments regarding the encounter with the candidate that they believe to be pertinent. The candidate’s personality is important in determining which procedure is preferred, or even if one is a good refractive surgery candidate. An experienced and sharp staff member may pick up on personality characteristics that may be helpful. This awareness by the staff to access the patient’s interest and demeanor should persist throughout all aspects of the testing and evaluation process. The amount of contact time with the patient is limited and, thus, every minute is valuable.

Table 1 summarizes certain personality traits that may favor LASEK vs. LASIK. Patient preference for the choice of procedure should never be overlooked. Many refractive surgeons are surprised at the number of patients who are uncomfortable and concerned about the idea of cutting a flap in their cornea. A significant portion of refractive surgery candidates has refrained from having laser vision correction because of safety concerns and lack of confidence. LASEK does satisfy some of these candidates’ fears regarding potential flap complications and potential for ectasia. Thus, providing LASEK as an option for patients can definitely increase the number of individuals electing to have surgery.

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exist, and the following are those that seem important to use in accessing one’s candidacy for the procedures.

Table 2. Lifestyle and Occupational Characteristics.

Corneal Thickness

Corneal thickness considerations are mandatory in the choice of laser vision correction procedure. The presence of inadequate corneal thickness in performing LASIK has the potential to lead to corneal instability and corneal ectasia. This has been documented in the literature over the past 3 years. There is still not a concrete understanding of the absolute limits and, as mentioned, surgeon comfort levels range from 200 microns to 300 microns of residual intact posterior stroma. Skeptics and those using lower amounts of tissue raise issues regarding the reported cases of ectasia and claim inaccurate microkeratome cuts, improper patient selection (early keratoconus), and incorrect measurements as reasons for this complication. At this time, it appears that the majority of surgeons feel comfortable with 250 microns of stroma as their limit. More conservative surgeons lean toward 300 microns as their limit.

Another issue is the potential structural changes caused by the construction of a lamellar flap in a thin cornea. With lamellar keratoplasty for hyperopia, “controlled steepening (ectasia)” was achieved with a single, deep cut. A 160-micron flap in a 460micron cornea may possibly in and of itself create a degree of structural weakening. The best guideline at present seems to be using 500-micron total corneal thickness as the minimal limit for LASIK.

To enable candidates who do not meet the aforementioned criteria to still undergo LASIK, surgeons will consider the use of a thinner corneal flap. Again, a number of questions arise, including the actual achieved flap thickness, the flap consistency of the microkeratome, potential for increased flap complications during construction, and a potential increase in striae or folds.

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Corneal Tissue Integrity and Quality

Corneal tissue integrity and quality are important with respect to maintaining the strength of the cornea postoperatively. The only gauge available to access the quality or “normality” of the corneal tissue is topography. The presence of either the anterior or the posterior surface abnormalities suggestive of keratoconus can alert one to the likelihood of an abnormality of the stromal tissue. Unfortunately, the ability to routinely and simply obtain and analyze corneal tissue to identify abnormalities in the collagen structure is not available. Surface ablation is a better consideration for suspicious cases, because most would agree it is less likely than a lamellar procedure to induce weakening.

Excessive Corneal Curvatures

Excessive corneal curvatures can increase the risk of an intraoperative flap complication in LASIK. Either extremely steep (>48) or extremely flat (<40) radii of curvature can alter the tissue delivery into the microkeratome and result in free, thin, incomplete, or buttonholed flaps. Some microkeratomes have improved their suction rings to address this, but surface ablation does definitely eliminate this concern.

Depending on the microkeratome, flatter corneal curvatures may reduce the ability to achieve larger diameter LASIK flaps necessary for hyperopic ablation. Again, LASEK is a valuable alternative in these cases.

Small Corneal Diameters

Small corneal diameters can predispose to free caps as well as insufficient flap diameter to permit a complete hyperopic ablation. It is helpful to check this preoperatively with the reticule of the laser microscope. Identification of the inability to construct a large enough flap centered on the pupil enables one to choose LASEK. This will reduce the chance of irregular astigmatism developing, which is seen in LASIK with incomplete and asymmetrical ablations.

Miscellaneous Corneal Pathology

Miscellaneous corneal pathology such as neovascularization, scars, and guttata must not be ignored. LASEK is frequently the best option in these instances. Anterior basement membrane dystrophy may be treated and then LASIK considered; however, in most cases it is probably best not to take a chance on an epithelial defect. PRK is my preference over LASEK because the abnormal epithelium and basement membrane is being removed in the same way that one would treat the problem with a superficial keratectomy.

Pupil Size and Centration

Pupil size and centration are important determining factors in the choice of procedure. A large scotopic pupil size (7–9 mm) may increase the risk for significant glare and halos, especially if a 6.0-mm ablation is used. The effective optic zone size is reduced in LASIK

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as compared to that with surface ablation because of the thickness of the flap tissue. Dr. Mia Pop’s study several years ago demonstrated that in comparable degrees of myopia, the PRK patients related less glare and halo effects than the LASIK patients.

It is helpful to be able to offer LASEK to these patients to improve their confidence in proceeding with laser vision correction.

As mentioned, any decentration of the pupil in a small diameter cornea can compromise the completeness of the ablation pattern. This is more frequent with hyperopic treatments. It is a good practice to preoperatively check the proposed ablation zone with the reticule of the laser microscope to confirm adequate flap coverage if planning LASIK.

Dry Eye patients

Dry eye patients undergoing LASIK are at risk for a neurotrophic keratitis. This is believed to be caused by transection of the corneal nerves. A superior hinge position seems to increase the incidence of this complication as more of the corneal nerves are transected as they enter from the horizontal limbus. Using a nasal hinge does appear to reduce the frequency. Fortunately, this complication tends to be temporary, but may last 6 months or more despite treatment. Possibly because surface ablation only exposes the nerve endings, this condition does not occur, at least not in the same presentation. Despite this advantage, caution still must be exercised when considering laser vision correction in extremely dry eye patients.

The Posterior Segment

The posterior segment is frequently forgotten when performing refractive surgery. The dramatic increase in intraocular pressure occurring with the application of the fixation ring does have implications with respect to posterior ocular structures. The effects on the vitreous, retina, vessels, and optic nerve must all be considered.

Retinal Vascular Changes

Retinal vascular changes of several types have been reported. Both central retinal vein and branch venous occlusions have been identified. One would expect that there were predisposing and pre-existing factors that made these vessels susceptible to closure with increased intraocular pressure. Superficial and intraretinal hemorrhages have also been seen after LASIK. At least one report of a macular hemorrhage has been described.

Lattice Degeneration

Lattice degeneration of the retina raises questions as to the chances of developing a rhegmatogenous retinal detachment caused by the rapid increase and decrease in intraocular pressure causing a shift in the vitreous. Vitreo-retinal traction might then result in a retinal tear. Certainly, this could possibly happen in eyes without lattice degeneration, but the lattice would seem to increase the odds. So far there is no good data to help with this issue.

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The Optic Nerve

The optic nerve may be impacted by the application of the fixation ring and subsequent increased intraocular pressure. Although at least one study reported a damage to the optic nerve fiber layer after LASIK, it seems most would now agree that this was caused by the testing method and not actual loss of nerve fibers. Nonarteritic anterior ischemic optic neuropathy has been reported after LASIK. High-risk eyes may be better-served with surface ablation to minimize alterations in blood flow. For the same reason, if an eye with glaucomatous optic atrophy requires laser vision correction, might not surface ablation be preferred?

Previous Ocular Surgery

Previous ocular surgery can make it difficult to obtain adequate suction with the fixation ring. In eyes having had a scleral buckling procedure, one may not achieve good vacuum. The same is true for an eye that has undergone a trabeculectomy. Aborted LASIK procedures may be better served with surface ablation. Consecutive hyperopia in previous radial keratotomy eyes may have less chance of developing irregular astigmatism with LASEK than with LASIK. Concerns regarding the development of corneal haze seen with myopic surface ablation after PRK should be lessened for hyperopic surface ablation because the treatment zone is peripheral to the visual axis.

The Degree of Refractive Error

The degree of refractive error has played a role in the choice of procedure. The preferred treatment for higher degrees of myopia has been LASIK to reduce the incidence of haze and regression. LASEK results have shown similar success to LASIK patients even for the higher ranges of myopia. Thus, it is an acceptable option for those patients or eyes having any characteristic best treated with surface ablation.

Everyone is familiar with the general contraindications for laser vision correction: unstable refraction, younger than age 18 years, autoimmune/connective tissue disease, as well as neurotrophic/herpetic keratitis. Patient preference for LASIK with its quicker visual recovery and minimal postoperative discomfort is definitely a contraindication for LASEK. A relative contraindication for LASEK is anterior basement membrane dystrophy. It is prudent to remove the diseased epithelium and basement membrane rather than to replace it. My personal experience has been that LASEK in anterior basement dystrophy significantly prolongs the postoperative visual recovery.

PATIENT EDUCATION

The importance of education cannot be overemphasized! Patient education can only begin after the surgeon, staff, and co-managing physicians understand the LASEK procedure and the education process.

It may seem ridiculously obvious; however, the surgeon must be the first to be educated, not only about the LASEK technique but also about the importance of the office process to provide a quality experience for the patients. It is imperative that the

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surgeon has a total commitment and confidence in the results of surface ablation. Only then will the staff be able support the patients during their evaluation and treatment.

During the initial contact, it is helpful if the staff member conveys the concept that there is not just one refractive surgical procedure that is best for all candidates. One should not go into great detail, but should simply in the appropriate circumstance plant the seed that LASIK is not the only available procedure. This prepares the patient to begin the thought process required in selecting their procedure. This is not an easy transition for those practices in which LASIK has been the only procedure offered or used. In these cases, when you do try to explain to patients that they are good LASIK candidates, they will always be hesitant to have surface ablation because they perceive it as an inferior procedure. By using this concept of multiple procedures, one will not get into this predicament, thereby reducing patient confusion.

It is inevitable that all LASEK patients will come into contact with patients having undergone LASIK. If the LASEK patient does not understand why LASEK was chosen, doubt will arise as to the surgeon’s competence and reasons for performing a procedure with a longer visual recovery and more postoperative discomfort. The patient must be able to easily explain the reason for LASEK to the individuals having had LASIK. This ensures satisfied patients who will refer friends, to their LASEK surgeon.

The greatest problem with performing LASEK is communicating the nature of the postoperative course to the patient. Most patients are saturated with the rapid, painless, dramatic visual recovery after LASIK. Therefore, it is necessary to emphasize to all patients that the postoperative visual recovery may be 1 or 2 weeks and also that there is the potential for significant discomfort for the first 3 to 4 days. I explain that by 1 week after surgery, approximately 80% of eyes will be 20/40 or better, and by 1 month 98% to 99% will be there. Adequate preparation by the patient for this delayed recovery will spare both you and them the distress created if they become compromised during this time.

Preoperative ocular findings such as increased intraocular pressure, lattice retinal degeneration, blepharitis, and dry eye syndrome are all addressed and treated appropriately before proceeding with surgery. A topical fluoroquinolone is initiated four times per day beginning 24 hours before surgery. Finally, patients are instructed not to wear cosmetics or perfumes to surgery.