Among the wide range of surgical techniques available for the correction of ametropia, laser-assisted in situ keratomileusis (LASIK) has gained considerable international attention over the past two decades and has become the procedure of choice for the correction of refractive errors. Management of laser vision correction is typically straightforward, and with today’s advanced surgical techniques and the evolution of new equipment, most patients can expect to achieve and maintain excellent visual results. In fact, one study analyzing 4,937 eyes indicates that 90.6% of patients still see 20/20 binocularly five years after LASIK surgery (Schallhorn et al, 2016).
However, in the early days of laser vision correction, up to 15% of patients needed additional surgery after the initial healing period to achieve best results (Nataloni, 2000). With improvements to the procedure and advancements in the instrumentation, the percentage of patients who need an enhancement procedure within the first 12 months after surgery can be as low as 1% to 2% (Donnenfeld and Parkhurst, 2016).
While enhancements would best be avoided, optimal refractive surgery outcomes often necessitate that eyes treated with LASIK have a second procedure to yield the best possible vision. Managing clinicians must recognize and monitor patients who could benefit from an enhancement as early as possible after the initial procedure. Discussion of the risks, benefits, and alternatives to an enhancement procedure should take place during the observation period. Should a secondary procedure prove to be the best option, co-managing practitioners must help guide their patients through the enhancement.
Pursuing an Enhancement
Who Needs It? Given that most outcomes today are very close to the intended result, a number of factors impact surgeons’ decisions about whether to enhance, including a patient’s attitude, the amount of enhancement being requested, and the reason why the outcome wasn’t on target (Kent, 2009).
From a refractive standpoint, patient dissatisfaction is likely the most common reason to re-treat. This includes residual refractive error with unacceptable visual acuity, complaints of a functional deficit under binocular viewing conditions, or difficulty with night or dim light vision. Other common reasons for enhancement can include unsatisfactory quality of vision issues that may manifest as nighttime glare, starbursts, halos, and distortion (Nataloni, 2001).
Once it is established that a re-treatment is warranted, it is wise to simulate the resulting vision. Showing patients the anticipated correction with trial frame spectacles can easily produce an adequate simulation. If it is a patient of presbyopic age, he or she must understand the consequences to both distance and near vision; therefore, both distance and near vision should be thoroughly tested with the trial frame. If it is a myopic enhancement in a presbyopic patient, emphasize how the enhancement will have a negative impact on his or her near vision. In some cases, a lens containing a patient’s wavefront scan created by a particular laser can help the patient best understand whether a wavefront-guided treatment is likely to resolve his or her symptoms (Brown, 2014).
The Risk-Benefit Conversation As with all procedures, it is important that patients understand the risk-reward relationship of an enhancement. With a primary procedure, the potential benefits are typically high—and the motivation to undergo surgery is strong—while the risks are low. For enhancement procedures, patients have to accept essentially the same low level of risk, but now the potential gain is typically much less than it was for the primary procedure (Brown, 2014).
Discussion of the risks associated with enhancement should include overcorrection, the possibility of not resolving the problem, and epithelial ingrowth. Epithelial ingrowth is far more common with enhancement procedures than with primary LASIK and must be explained to patients in detail.
Occasionally, patients pursue an enhancement years after their primary LASIK procedure, mistakenly believing that their treatment is no longer effective. Often, these patients’ vision changes are due to natural phenomena that would have occurred if no surgery had taken place, such as presbyopia or lenticular changes. It is important to help these patients understand that LASIK doesn’t prevent the changes that naturally occur with age and to review how vision changes throughout their lifetime. Also, discussing options such as reading glasses, corneal inlays for presbyopia, or lens replacement surgery is necessary.
Other patients may report a disparity between the two eyes simply as an observation and believe that their eyecare practitioner should know about this difference. They may even believe that an enhancement should be performed to make both eyes equal, even though binocular vision is fine and the symptoms are often only bothersome with one eye covered (Brown, 2014). This is a great opportunity to review the risks of a second surgery and to educate patients that the eyes heal differently based upon differences in preoperative prescription, corneal curvature, variation in healing, and other factors.
Residual refractive error following LASIK is a challenging situation, and a comprehensive evaluation is required to determine whether a patient would benefit from additional laser refractive surgery. The initial approach to any patient experiencing subjective change in visual acuity after refractive surgery should include a complete evaluation. Enhancement candidates should undergo assessment of visual acuity, manifest and cycloplegic refractions, keratometry, intraocular pressure, pachymetry, wavefront aberrometry, topography/tomography, and ocular dominance (Moshifrar et al, 2017).
A complete anterior and posterior examination, including a dilated funduscopic examination, should be performed. Corneal evaluation should include judgment of flap-edge alignment, edema assessment, and lamellar interface monitoring. Pay particular attention to the integrity of the tear film and corneal epithelium; the condition of the lids, conjunctiva, and other adnexal abnormalities; and the clarity of the crystalline lens. The patients’ underlying systemic comorbidities, such as hypertension and diabetes mellitus, along with current medications, should be reviewed at this time (Moshifrar et al, 2017).
While I recommend that enhancements be performed as soon as possible after the primary surgery, it is imperative to be certain that the vision has stabilized. Suitable candidates for enhancement should demonstrate refractive stability for an interval that comprises at least two consecutive clinic visits, typically performed three to six months apart. However, specific parameters have not been thoroughly defined (Moshifrar et al, 2017).
Rapid or persistent postoperative change can be a sign of ectasia, in which case further corneal surgery would typically be contraindicated. Corneal tomography should be used to assure corneal stability and thickness. This imaging can help determine whether some ectatic process is involved (Brown, 2014). This testing is more important today because we can treat corneal ectasia early with corneal cross-linking to reduce or prevent the devastating visual effects of ectasia.
After excluding intraoperative flap complications and anatomical causes for visual complaints, such as ocular surface disease, cataract, and macular pathology, evaluate the residual stromal bed. Miscalculations in stromal thickness can result in overestimation or underestimation of the residual stromal bed thickness, which increases the risk of ectasia or inappropriate rejection of candidacy for enhancement, respectively.
Numerous surgical techniques exist for performing a LASIK enhancement, including, but not limited to, flap re-lift, surface ablation, flap re-cut, and femtosecond laser-assisted intrastromal astigmatic keratotomy. Surgeons most commonly use one of two methods: re-lift the flap and perform LASIK, or perform a surface ablation in the form of photorefractive keratectomy (PRK) on top of the flap. Most surgeons believe that the decision comes down to weighing the increased risk of epithelial ingrowth with LASIK versus the slow visual and physical recovery and risk of haze associated with PRK. Appropriate selection is contingent on the accurate determination of several factors, including the postoperative time period, previous intraoperative complications, and preoperative screening parameters (Moshifrar et al, 2017).
Even years after laser vision correction, most patients still enjoy wonderful distance vision from the procedure. Nevertheless, eyes change over time for various reasons, and the presence of residual refractive error following LASIK can be a precarious situation. It is important to understand why the refractive status is changing and how to best manage that refractive change. Most eyes that undergo LASIK re-treatment achieve excellent visual acuity with good stability. LASIK re-treatment allows for further improvement in refractive outcomes in a safe and effective manner. Ensuring post-LASIK stability and accurate stromal bed thickness calculations are paramount for excellent enhancement results. CLS
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