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Inside Eyetube.net | Jul 2011

Long-Term Data on LASIK Versus PRK: LASIK Versus Surface Ablation: Comparison of Efficacy

Most refractive surgeons who perform corneal laser surgery use both LASIK and surface laser procedures such as LASEK, PRK, and advanced surface ablations (ASA). I know experienced LASIK surgeons who are now performing surface treatments more regularly, and, conversely, colleagues who once favored ASA who are now doing more LASIK. I doubt that the majority of surgeons will ever do only one procedure exclusively. Instead, most choose to incorporate both LASIK and ASA into their surgical armamenatariums to achieve the best results in the safest, most effective manner.

In my experience, LASIK is typically the preferred surgical option because of its quick recovery time and the absence of significant discomfort for patients. ASA is typically done when the cornea is too thin to support the intended treatment with a flap-based procedure and still leave a satisfactory residual corneal thickness, in eyes that are dry, in patients who participate in contact sports or hold occupations in which they have an increased risk of eye injury, and in patients who may adversely affect the flap-making process due to excessive anxiety.

It is important for surgeons to have an idea of how their LASIK and ASA outcomes compare over the long term. In this article, I discuss 1-year results of a large study I conducted that compares the outcomes of LASIK and surface ablation. For the purposes of this article, ASA refers to LASEK or PRK with the adjuvant use of mitomycin C in a 0.02% concentration applied for 30 seconds.

METHODS

All procedures were performed with the 200-, 400-, or 500-Hz WaveLight Allegretto Wave excimer laser (Alcon Laboratories, Inc., Fort Worth, Texas). LASIK flaps were made with the Hansatome or Hansatome XP (Bausch + Lomb, Rochester, New York) or the WaveLight Rondo (Alcon Laboratories, Inc.) mechanical microkeratome, or with the WaveLight FS200 femtosecond laser (Alcon Laboratories, Inc.). All procedures were performed at the Wellington Eye Clinic by either me or my partner Mr. Richard Corkin. Only eyes with at least 1-year follow-up have been included in this report. The outcomes for hyperopia are not included because we perform very few hyperopic ASA cases, and, when we do, they are typically for low hyperopia (less than 2.50 D).

RESULTS

During the 5-year study, 9,657 myopic eyes were treated. Of those with at least 3-month follow-up, 6,184 were with treated with LASIK and 1,115 with ASA. Of those with at least 6-month follow-up, 5,042 were treated with LASIK and 880 with ASA. Of those with 1-year follow-up, 2,523 underwent LASIK and 467 ASA.

The demographics of the two cohorts were similar. Preoperative mean distance UCVA was 0.13 (range, 0.001 to 1.6 Snellen) in the LASIK group and 0.17 (range, 0.001 to 1.25) in the ASA group.

The US Food and Drug Administration (FDA) allows up to 5% of eyes to lose 2 or more lines of BCVA to be deemed safe. Based on this parameter, the results of this study suggest that both LASIK and ASA performed with this laser are safe procedures in this range of refractive error, with only 7% of LASIK and ASA eyes losing 1 line or more of BCVA (Figure 1). In the LASIK group, 16% of eyes gained 1 line of BCVA and an additional 3% gained 2 lines. In the ASA group, 20% gained 1 line of BCVA and an additional 5% gained 2 lines. This suggests that ASA is fractionally safer in this cohort than LASIK.

UCVA is a poor metric to use to compare procedures or technologies in a group in which the patients are all-comers and not selected by predetermined minimum BCVA preoperatively. Nevertheless, the postoperative UCVAs in the two cohorts were similar, with 73% of LASIK eyes and 75% of ASA eyes achieving 20/20 UCVA. This includes the entire range from low myopia up to -12.00 D. Similarly, 94% of LASIK eyes and 92% of ASA eyes achieved 20/20 BCVA.

In terms of stability, the spherical equivalent (SE) refractions in LASIK-treated eyes were -4.10 D preoperatively, -0.30 D at the 3- month interval, -0.30 D at the 6- month interval, and -0.40 D at the 12-month interval. In ASAtreated eyes, the SE refractions were -4.80 D preoperatively, -0.10 D at the 3-month interval, -0.20 D at the 6-month interval, and -0.40 D at the 12-month interval. In both groups, the 12-month visit yielded a SE of -0.40 D (Figure 2).

Predictability was also similar in both groups, with 86% of LASIK patients and 81% of ASA patients achieving within ±0.50 D of the targeted refraction (Figure 3). Cylinder outcomes were almost identical in both groups.

Taken together, the outcomes for myopic patients were generally indistinguishable between these two groups of patients.

HIGH MYOPIA

Patients with high myopia (-8.00 to -11.75 D) often do not have enough corneal tissue to allow laser refractive procedures. For these patients, we typically implant phakic IOLs or perform refractive lens exchange. I was interested to see the outcomes for the subset of myopes higher than -8.00 D in this series. Surprisingly, more eyes in this subset gained lines of BCVA compared with the whole study population; however, more eyes lost lines as well.

Of 403 eyes with high myopia, 6-month data was available for 259 LASIK-treated eyes and 89 ASA-treated eyes. The LASIK group was -10.03 D on average, with a mean 0.93 D of cylinder. The ASA group was -9.83 D on average, with a mean 1.52 D of cylinder.

Postoperatively, 45% of LASIK eyes and 49% of ASA eyes achieved a UCVA of 20/20, and 84% of LASIK eyes and 83% of ASA eyes achieved a BCVA of 20/20. Nine percent of eyes in the LASIK group and 14% of eyes in the ASA group lost 1 line of BCVA. More eyes in the ASA-treated group gained 1 line of BCVA compared with the LASIK-treated group (31% vs 24%). Two-line gains were similar between groups, with 7% in the LASIK group and 6% in the ASA group. One eye in the ASA group and 3% of eyes in the LASIK group gained more than 2 lines (Figure 4).

Astigmatic outcomes were similar between the groups, even though the ASA group started out with significantly higher mean cylinder (Figure 5). In both groups, the residual astigmatism was less than 0.50 D with a standard deviation of less than 0.40 D.

Sixty-four percent of LASIK eyes and 61% of ASA eyes were within 0.50 D of targeted refraction (Figure 6). Stability was slightly better in the LASIK group (Figure 7). Fewer LASIK eyes lost lines of BCVA compared with ASA eyes.

CONCLUSION

These data suggest that, for -8.00 D and higher, LASIK is the preferred method if the preoperative corneal thickness is sufficient. In this series, both LASIK and ASA with the WaveLight excimer laser were effective and safe procedures for patients with high myopia. LASIK was slightly more stable over 12 months than ASA, making it the procedure of choice when possible.

Arthur B. Cummings, MB ChB, FCS(SA), MMed (Ophth), FRCS(Edin), practices at the Wellington Eye Clinic & UPMC Beacon Hospital, Dublin, Ireland. Dr. Cummings is a member of the CRST Europe Editorial Board. He states that he is a consultant and clinical investigator for Alcon/WaveLight. Dr. Cummings may be reached at tel: +353 1 2930470; fax: +353 1 2935978; e-mail: abc@wellingtoneyeclinic.com.

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