Lasik Outcomes in Myopia and Hyperopia
Daniel Epstein
Laser in-situ keratomileusis (LASIK) took the ophthalmic world by storm in the second half of the 1990s and has since become by far the most widely performed corneal refractive procedure worldwide.
Arriving on the scene after several years of extensive experience with photorefractive keratectomy (PRK), it was obvious from the start that LASIK provided a much faster recovery of best spectacle-corrected visual acuity (BSCVA) than PRK. Ironically, this rapid visual rehabilitation has made it more difficult to obtain long-term follow-up on LASIK patients, because high levels of immediate satisfaction proved a disincentive for participation in prolonged studies. Accordingly, no 3-year or 5-year analyses of LASIK results can be found in the peer-reviewed literature.
As in all refractive surgery, the interpretation of reports on LASIK outcomes is somewhat tricky. For example, some patients may have a postoperative uncorrected visual acuity (UCVA) of 20/20 with a poor optical quality (e.g., ghosting), and others may have crisp 20/20 vision. But both types of patients are bundled together under the “20/20” rubric, and the reader is unable to obtain an accurate picture of the quality of the visual results.
Similarly, when reporting on postoperative lost lines of BSCVA, it is rarely made clear how rigorously visual acuity (VA) was registered preoperatively. If a patient is tested only to the level of 20/20 preoperatively, a 20/20 result postoperatively would indicate no loss of BSCVA. But most refractive surgery patients have a preoperative BSCVA of 20/16 to 20/14, and if the postoperative result is only 20/20, the failure to register the maximal preoperative VA would result in a misinterpretation of the safety of the procedure. In other words, even a 20/20 outcome may represent a loss of BSCVA.
A further unsatisfactory aspect is that low-contrast VA, which has been shown to decrease after corneal excimer surgery, is almost never reported in outcome papers.
Nevertheless, sufficient documentation is available to assess the outcomes of LASIK procedures over a wide range of refractive errors.
LOW TO MODERATE MYOPIA AND MYOPIC ASTIGMATISM
LASIK refractive and visual results in this category of patients are generally good to excellent even if the definition of low to moderate myopia is not identical in all studies (perceptions on this issue range from about −1 D to about −8 D). The cylinder component of the preoperative refraction is often identified only as a mean (no range); and an alarming number of studies fail to report vital preoperative or postoperative data. (Table 78-1 lists representative outcomes.)
These studies and numerous other publications (8, 9, 10, 11, 12, 13, 14, 15) on patients with similar preoperative refractive errors collectively show that LASIK can effectively correct low to moderate myopia with or without a fair amount of astigmatism. As the procedure improved with the advent of better microkeratomes and lasers, investigators were able to focus on more ambitious results. Whereas an accuracy of ±1 D of emmetropia or aim and an UCVA ≥20/40 initially were considered acceptable treatment goals, the gold standard now requires that results be reported within 0.50 D of aim and that postoperative UCVA be stated in terms of ≥20/20.
Regression of effect after the correction of moderate myopia, a major reason for retreatments in the early days of LASIK (16,17), appears to have become much less of a problem, most likely because of improved ablation profiles. Although retreatments are still part and parcel of LASIK surgery, they are now usually used as enhancements in cases of undercorrection (18, 19, 20).
The American Academy of Ophthalmology (AAO) prepares Ophthalmic Technology Assessments (OTAs) to evaluate new and existing procedures, drugs, and diagnostic and screening tests. The goal of an OTA is to evaluate the peer-reviewed literature, and to distill what is well established about the technology. OTAs are submitted to the AAO’s board of trustees for consideration as official academy statements.
TABLE 78-1. REPRESENTATIVE OUTCOMES OF MYOPIC LASIK STUDIES | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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The OTA on myopic LASIK, published in January 2002 (8), drew the following conclusion:
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