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Carefully evaluate patients before proceeding with LASIK enhancement
Consider binocular and night vision, ocular surface issues and progression to presbyopia.
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Comanagement of laser vision correction is typically straightforward, and with today’s wavefront-guided treatments and femtosecond laser flaps, most patients can expect to achieve excellent visual results without complications. However, what happens when that is not the case?
We would all like to avoid enhancements, but the reality is that a percentage of patients will benefit from a second procedure. Comanaging optometrists should be able to identify patients who desire and could benefit from an enhancement as early as possible after the primary procedure, adequately discuss the risks and benefits of a secondary procedure and help guide their patients through the enhancement.
Enhancement rate study
We looked at the rate of enhancements in nearly 340,000 consecutive primary LASIK procedures performed at Optical Express centers from 2008 to 2011. The data include both myopes and hyperopes (with and without astigmatism) undergoing primary LASIK. All treatments were performed with the Visx Star S4 IR Excimer Laser System (Abbott Medical Optics). Subjects ranged in age from 18 to 70 years old.
From this large group of primary treatments, we identified 19,113 eyes that went on to have an enhancement procedure, for an overall 12-month enhancement rate of 5.6%. It should be noted that for enhancement rates to have meaning and be comparable, they must be calculated and reported in the context of some defined postoperative interval following the primary procedure. For example, rates of enhancement that occur within 2 years of primary treatment will be higher than rates that occur within 1 year (approximately 2% higher in this data set). As your population of treated patients grows and matures, more patients will experience subsequent changes in their vision and seek enhancement.
Mitch Brown
Eighty-three percent of the enhancements were performed as CustomVue (AMO) wavefront-guided procedures. The median time to enhancement was 10 months after the primary surgery, with nearly 70% of the enhancements performed within the first year. In 30% of the cases, the flap was lifted; the other 70% underwent PRK over the flap.
Not surprisingly, eyes that were enhanced had significantly worse uncorrected visual acuity (UCVA) 1 month after their primary surgery. Only 46% of the eyes that went on to enhancement had 20/20 or better UCVA at 1 month, compared to 85% of the nonenhanced eyes. For comparable levels of preop sphere, the enhancement rate for hyperopes was nearly triple that of myopes.
Other factors associated with a higher likelihood of enhancement were higher preoperative sphere or cylinder and older age, although the relationship with age may be confounded by a higher prevalence of hyperopia, presbyopia and monovision correction in older patients.
Following enhancement, UCVA improved significantly: it was 20/20 or better in 80% of the flap-lift enhanced eyes (at 1 month postop) and 73% of the PRK enhanced eyes (at 3 months postop).
In patients who had primary LASIK, we found that refractive stability was achieved in many cases by 1 week and in the vast majority of cases by 1 month postoperative. For this reason, we recommend that potential enhancement candidates be identified at about 1 month, with a target of enhancing at 3 months, assuming stability (≤0.5 D change in sphere or cylinder between two exams, 1 month apart).
We also found that for primary LASIK patients, a flap-lift enhancement performed within 12 months of the primary procedure offers the best results, with higher refractive predictability, better UCVA, less loss of best-corrected visual acuity and a similar complication rate to that of PRK enhancement. While there may be some valid reasons for performing PRK over a primary LASIK flap, we conclude that when lifting the flap is a viable option, this is preferred.
The risk-benefit conversation
It is important to be able to distinguish and explain to patients when the benefits of an enhancement outweigh the risks – or vice versa. The potential benefits of a primary procedure are typically high – it is in many cases a life-changing procedure – while the risks are quite 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 for the primary procedure.
Some patients will report a difference between the two eyes simply as an observation. They think the doctor should know that one eye is not “perfect”; they may even believe that an enhancement should be performed to make both eyes equal or perfect. Often, the symptoms are only bothersome with one eye covered, and the patient is actually quite satisfied with the binocular vision. This is a great opportunity to educate the patient about the risks of a second surgery and the potential for some discrepancy between the two eyes even after an enhancement.
Sometimes patients seek enhancement years after primary laser vision correction, mistakenly believing that their treatment has “stopped working” when they are actually experiencing the onset of presbyopia or lenticular changes. Although it is worth considering a second procedure for eyes that have undergone refractive change, it is also critical to help the patient understand how vision changes throughout life and educate him or her about options such as readers or lens surgery.
I believe there are two good reasons for enhancement. The first is when the patient complains of a functional deficit under binocular viewing conditions. For example, if the patient tells me, “I don’t feel safe driving at night because my distance vision is too blurry,” that is a good reason to enhance.
The second reason is significant visual or other symptoms, such as, “I am bothered by the blur in the left eye, even with both eyes open.” Two good questions to ask are: “Are you able to do all the things you need to do visually without problems?” and “Are you experiencing any symptoms or discomfort related to your vision?”
Pursuing enhancement
Once it has been determined that a patient may benefit from an enhancement, a complete work-up is recommended. Enhancement candidates should have visual acuity testing, manifest and cycloplegic refractions, keratometry, intraocular pressure, pachymetry, WaveScan (AMO), corneal topography or Pentacam (Oculus), and assessments of pupil size and ocular dominance. They should also undergo a full anterior and posterior eye exam with particular attention to the integrity of the tear film and epithelium, condition of the lids and conjunctiva, and clarity of the crystalline lens.
This figure shows enhancement rate by preoperative sphere in 339,740 eyes. It was found that hyperopes and high myopes are more likely to need an enhancement than low myopes.
This figure shows enhancement rate by preoperative cylinder in 339,740 eyes. It was found that greater amounts of preoperative cylinder are associated with a higher rate of enhancement.
This figure shows the uncorrected visual acuity (UCVA) in 19,113 eyes after enhancement. It was found that UCVA was greatly improved after CustomVue enhancement, from 46% seeing 20/20 or better pre-enhancement to 73% or 80% seeing 20/20 post-enhancement in eyes undergoing PRK or flap lift, respectively.
Dry eye is a common source of visual complaints after LASIK, so before moving forward with enhancement, it is important to determine whether the patient’s complaints of blur or fluctuating vision may simply be due to a rapid tear film break-up or poor quality tear film. Artificial tears or more intensive dry eye therapies, such as cyclosporine and topical steroids, may obviate the need for an enhancement. Corneal staining and topography can be useful in examining the ocular surface.
While we recommend that enhancements be performed as soon as possible after the primary surgery, it is imperative to be certain the vision has stabilized. Some eyes take longer than others to reach stability. Primary PRK, particularly for hyperopia, can take significantly longer than LASIK to stabilize. Rapid or persistent postoperative change can be a sign of ectasia, in which case further corneal surgery would typically be contraindicated. Topography or Pentacam imaging can help determine whether some ectatic process is involved.
A common but challenging situation is the patient who has quality-of-vision complaints but objectively good visual acuity. In our data set, almost half the eyes that were enhanced (46%) had UCVA of 20/20 prior to enhancement. The problem may be induced higher-order aberrations. In addition to ruling out dry eye in these patients, one needs to perform a thorough topography and wavefront assessment.
Counseling must take into consideration the risk of overcorrection or of not resolving the problems. In some cases, a PreVue lens generated by the Visx laser can help the patient understand whether a wavefront-guided treatment is likely to resolve their symptoms.
Finally, in the case of a PRK enhancement, optometrists should be prepared for a different postoperative management strategy. Specifically, as with primary PRK procedures, the steroid taper will be longer and there will likely to be a greater role for pain control medications. Pain tolerance after surface ablation varies widely among patients and can be unpredictable.
With these considerations, comanaging optometrists can facilitate the experience for that small percentage of patients who require enhancement after laser vision correction surgery. Ultimately, a positive result for the patient reflects well on all the clinicians involved in the process.
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Disclosure: Brown has no relevant financial disclosures.