The 10 Most Common Reasons for Refractive Enhancements
Refractive enhancements are a holdover concept from the old RK days when results were unpredictable and the procedure was imprecise. Today, improved diagnostic devices, precise excimer lasers, sophisticated nomograms, and a better general understanding of the variables that affect surgical outcomes have made it possible to nearly eliminate refractive enhancements from your practice.
Having performed RK and ALK procedures, participated in several FDA trials of excimer laser platforms for LASIK, and worked with the Refractive Surgery Consultant Elite software program (Refractive Consulting Group, Inc., Paradise Valley, AZ), I have examined hundreds of databases of refractive outcomes worldwide using all excimer laser platforms. The trends are exciting. Current data show that committed surgeons can reduce their enhancement rates to between 1% and 3% by using available technologies. Some have even eliminated enhancements entirely.
Refractive enhancements cost money and increase the risk of complications. Moreover, the advent of wavefront-guided LASIK and overzealous marketing campaigns have raised patients' expectations to new heights. If you charge patients a premium for customized ablation, they will certainly demand to see well after surgery. Although attorneys state that a poor surgical outcome does not constitute malpractice, common sense says that most LASIK lawsuits occur when the surgical results do not meet patients' expectations.
If your enhancement rate exceeds 3%, evaluate your overall methodology and make improvements. This article incorporates the thoughts of several practitioners whom I interviewed and describes the 10 most common reasons behind refractive enhancements. This knowledge should help you achieve an enhancement rate of 1% or less.
1. BAD NOMOGRAMS
All excimer lasers differ, as do all refractive surgeons and patients. It is necessary to factor these variations into the programmed treatment. Data show that computer-driven Optimized Nomograms (from the Refractive Surgery Consultant Elite software program) can dramatically reduce enhancement rates, even without addressing the issues described later in this article. Simply put, Optimized Nomograms detect and compensate for the factors that affect outcomes.
Old spherocylindrical nomograms with adjustments for patients' ages are no longer adequate. Surgeons must separately adjust programmed amounts for sphere and cylinder, and they should also make age adjustments based upon a statistical analysis of their prior outcomes in the same treatment range as the current eye. I advise using separate nomograms for each optical zone and for other significant variations in technique. Most importantly, sharing nomograms among surgeons, especially when they are not using the same excimer lasers, can lead to improper adjustments. As most refractive surgeons know and as Herman Sloane, MD, of Oak Brook, Illinois, succinctly stated, “Using someone else's nomogram, or using static nomograms that don't take into account ongoing changes in the environment, technique, or equipment, is the most frequent cause of enhancements.”
Creating a nomogram requires only approximately 50 eyes with 1 month of follow-up. The software mentioned automatically performs the calculations and associates the best nomogram with each technique. The process is relatively simple and can eliminate the need for the majority of enhancement procedures from any refractive practice.
2. FAILURE TO CONSIDER COUPLING
A separate but related issue to nomogram adjustments is correcting for defects in the internal laser algorithm, especially sphere/cylinder coupling. Ideally, the cylinder and sphere treatments would be independent. As it is, lasers attempt to compensate for coupling by reducing the amount of spherical ablation when the surgeon adds cylinder to the treatment. The calculations used were created mathematically and tested on plastic, not curved corneas, however. For this reason, with most lasers, you must consider the cylinder treatment when you adjust the programmed treatment amount for sphere, and vice versa. Failing to understand and compensate for coupling causes many refractive surprises, especially in cases involving large amounts of cylinder or in which the amount of cylinder exceeds that of sphere. Figure 1 illustrates this issue with a STAR S2 laser (VISX, Inc., Santa Clara, CA), but the point is equally valid for most current excimer laser platforms.
3. INACCURACIES FROM OPTICAL ZONE ADJUSTMENTS
The recent introduction of 0.1-mm optical zone choices has exacerbated the problem associated with changing optical zone size. Increasing the optical zone diameter alters many parameters of the ablation. Namely, it adds more laser pulses, deepens the ablation, lengthens the treatment time, and results in more lost energy from the peripheral cornea due to surface reflection. Engineers primarily used mathematics with little or no clinical testing when determining these adjustments in the ablation for optical zone size. Complicating matters, the laser manufacturers added in fudge factors in an attempt to compensate for issues such as corneal drying—a method that introduced new and inconsistent variables into the laser treatments. As a result, any change in treatment diameter alters the nomogram significantly. For that reason, the best refractive surgeons select a single (or at most two) optical zone size and treat all eyes at that diameter. This strategy permits them to pool data into large sets and develop solid nomograms for each diameter. Brian Boxer Wachler, MD,1 of Los Angeles has recommended making adjustments to the optical zone in 0.5-mm increments while using a separate nomogram for each zone size (Figure 2).
Deciding instead to provide the maximum optical zone for every eye and adjust optical zone measurements in 0.1-mm increments fails to take into account the inconsistent, nonlinear variation built into excimer lasers for each zone size. Because corneal curvature, plume smoke, reflectivity, and other factors decrease the accuracy of optical zone adjustments to approximately ±0.25 mm,2 adjustments of 0.1 mm are inaccurate. Avoid them at all costs.
4. DELEGATION OF SURGICAL PLANNING TO NONSURGEONS
The key decision in surgical planning is determining the targeted refractive outcome. Doing so entails considering your prior results in the treatment range in question, the patient's age, his tolerance for under- or overcorrection, and any relevant occupational considerations. You, therefore, are the only professional qualified to set the correct target. Creating the surgical plan is as much a part of surgery as making the flap. You cannot expect office personnel to understand the issues involved.
If your scatter is ±0.35 D when treating 6.00 D of myopia, you should incorporate this information into the setting of the target refraction. In an effort to avoid residual myopia, you may wish to aim for an average outcome of plano in a -6.00-D pilot, because two-thirds of eyes will fall within the range of ±0.35 D. In contrast, the best average outcome for an accountant in the same range might be -0.35 D in order to avoid overcorrection.
It is no longer appropriate to target an arbitrary amount of residual myopia because you do not know your degree of accuracy for a given treatment. With old, paper nomograms, you had no choice. Now, you can take control of the target refraction and eliminate undercorrections as a major source of enhancements by considering the accuracy of your surgical efforts for the same treatment range, based upon your own results.
5. POOR LASER SERVICE
The most dangerous time to operate an excimer laser is directly after the service technician has left. Read the technical service log at the start of each surgical day and be aware of which components received service most recently. Diligently ensure the proper functioning of those systems. For example, if the technician adjusted the optics, carefully check the laser optics' alignment. If he changed the laser cavity, expect a higher energy output and watch for variations in calibration throughout the day.
Reading the service log takes only a few minutes and can be very instructive. Sometimes the log includes comments such as the following from one of my Chicago clients: “could not achieve specified output levels; adjusted settings to highest setting and will come back next week to try again.” As could have been expected, that week's cases were undercorrected.
6. POOR LASER CALIBRATION
Calibrate your laser daily and between cases. An excimer laser that fails to hold calibration is unstable and requires servicing. Poor and unstable calibration can bring disastrous refractive surprises into your practice. As Dr. Sloane commented to me, calibration “should be done against a verifiable ‘known,' not some indirect internal sensor.”
7. POOR REFRACTIONS
Reliable refractions are the basis of accurate outcomes. Karl Stonecipher, MD, of Greensboro, North Carolina, described his procedure as follows: “I only use one or two refractionists. That is one reason why I have a low enhancement rate. I never use the optometrist's refractions other than as a reference. Who knows what vertex distance was used or under what conditions the refraction was performed? Does he or she overminus?”
8. DIFFERING ABERROMETER AND MANIFEST REFRACTIONS
Whereas the first seven issues apply to any excimer laser treatment, this and the following comments relate specifically to wavefront-driven corrections. A significant difference (>0.50 D) between the preoperative wavefront refraction and the patient's subjective manifest refraction is a contraindication to customized LASIK. The aberrometer's refraction is an average of the entire entrance pupil refraction. In contrast, the endpoint chosen by the patient for the manifest refraction is the result that he prefers. If these refractions differ, then the spherocylindrical correction applied by the wavefront-guided procedure will differ from the patient's preference, and the procedure is apt to fail.
9. FAILURE TO NOMOGRAM-ADJUST WAVEFRONT TREATMENTS
Using the aberrometer to determine the preoperative refractive error does not change the fact that all lasers and surgeons differ and therefore require nomogram adjustment. The laser manufacturers have (one hopes) calibrated the aberrometers, software links, and lasers for the average surgeon and laser, but who is average?
If aberrometer-based treatments do not include the additional necessary nomogram adjustments for the surgeon and laser, then the spherocylindrical outcomes will suffer. Stephen Brint, MD, FACS, of New Orleans was the medical monitor for Alcon Laboratories, Inc.'s (Fort Worth, TX) customized LASIK trials. Dr. Brint commented, ?If you can't back off the sphere enough [to compensate for the nomogram] and the difference in the cylinder looks uncomfortable, convert to conventional LASIK.?
10. INATTENTION TO DETAIL
I am amazed at how many refractive surprises are caused by an inattention to detail, or what I call the oops factor. Fortunately, most surgeons implement redundant safety checks in order to minimize such mistakes, but these problems occur nevertheless. Common errors include laser technicians' entering refractions incorrectly, staff members' picking up the wrong patient chart, surgeons' failing to notice the tilting of a patient's head on the laser table, and practitioners' not personally rechecking their numbers prior to commencing treatment.
If you do not have firm policies and procedures in your OR and clinic to guard against errors such as I have described, visit a colleague who does and implement similar safety checks immediately. Your attorney will not be able to defend you in a lawsuit if you operate on the wrong eye, treat the incorrect amount of cylinder, or flip a cylinder axis because you failed to check the numbers.
CONCLUSION
This list is not new to most experienced surgeons, but some choose to ignore the issues this article highlights. Performing refractive surgery well entails doing all you can to eliminate refractive enhancements from your practice. Moreover, happy single-procedure patients are the best referral sources. To illustrate this point, imagine the following conversation at a cocktail party.
Patient Y: “Really? Dr. B did my LASIK, and then I had to wait 3 months for my enhancement procedure.”
Patient X: “Dr. A told me he only reoperates on 1% of his patients.”
Patient Y: “Dr. B told me my chances of a second operation were one in 10.”
This conversation happens worldwide every day. It's no mystery which doctor will receive referrals. n
Guy M. Kezirian, MD, FACS, is a board-certified ophthalmologist. He is President of SurgiVision Consultants, Inc., an ophthalmic consulting company in Thousand Oaks, California, and a partner in Refractive Consulting Group, Inc. Dr. Kezirian may be reached at (805) 493-4200; guy1000@surgivision.biz.
1. Boxer Wachler BS. Strategic outcomes applications: effect of optical zone differences on laser performance [Refractive Consulting Group, Inc., Web site]. Available at: http://www.refractiveconsultant.com/AAOCourse.html. Accessed: October 8, 2003.
2. Partal AE, Manche EE. Diameters of topographic optical zone and programmed ablation zone for laser in situ keratomileusis for myopia. J Refract Surg. 2003;19:528-533.
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