Laser Refractive Surgery for High Myopia

While LASIK and lenticule extraction with SMILE are both known to deliver excellent visual results, find­ing differences between the two procedures requires drilling down to take a more detailed look at available data. 

Doing so definitively shows LASIK results in faster visual recovery, according to Edward E Manche MD.

“LASIK has the fastest visual recovery of any keratorefrac­tive procedure,” Dr Manche said. “The speed of visual recov­ery after SMILE has improved with use of lower femtosec­ond laser energy settings, but even with that modification, visual recovery is still faster after LASIK.”

On the other hand, there are reasons to prefer SMILE, according to John So Min Chang MD.

“SMILE seems to have better refractive predictability than LASIK; some studies show refractive stability is better after SMILE, and SMILE has additional advantages of eliminating flap concerns and causing less postoperative dry eye.” 

Time to achieving 20/20 UCVA

Providing evidence to support his conclusion, Dr Manche cited data from selected studies, beginning with results from the clinical trials that led to US FDA approval of SMILE for treating spherical myopia and myopic astigmatism. In the spherical myopia trial, only 63% of eyes achieved 20/20 or better UCVA at one week. By one month, the percentage was still just 79%, and it only rose to 83% by three months. The myopic astigmatism study results showed 20/20 or better UCVA was achieved by only 44% of eyes at one week, 66% at one month, and 83% at three months.

Dr Manche noted multiple prospective studies directly compared LASIK and SMILE, and he discussed three trials that used different LASIK approaches.

One study published in 2016 compared wavefront-optimised LASIK to SMILE and included about 200 eyes with a mean preoperative spherical equivalent (SEQ) of about -5.2 D in both groups.1 SMILE was performed with a laser energy setting of 180 nJ, which was the manufacturer’s recommendation when the study was conducted. On the first day postoperative, 20/20 UCVA was achieved by 73% of LASIK-treated eyes compared to 55% of those treated with SMILE. By one week and throughout follow-up to month six, UCVA was 20/20 or better in 95% of LASIK-treated eyes, only reaching that level in the SMILE group at month three.

A more recent study performed by Dr Manche and col­leagues compared wavefront-guided LASIK with SMILE in 80 eyes (40 patients) with a mean SEQ of about -3.9 D.2 The energy settings for SMILE ranged from 130 to 160 nJ. By day one after surgery, 95% of LASIK patients saw 20/20 UCVA versus only 49% in the SMILE group. In this study, the SMILE-treated eyes caught up to the LASIK group by month one when 89% achieved 20/20 or better UCVA.

Another study compared topography-guided LASIK versus SMILE with the procedures performed in fellow eyes of 30 patients.3 Mean SEQ for eyes in this study was about -4.0 D, and the laser energy setting for SMILE was 125 nJ. At one day postoperative, UCVA was 20/20 or better in 100% of LASIK-treated eyes but only 60% of eyes treated with SMILE. At one week, 86% of SMILE-treated eyes achieved 20/20 or better UCVA.

Benefits with SMILE

In his review of the literature, Dr Chang observed that in addition to evidence showing SMILE has better predict­ability and stability than LASIK, various studies found statistically significant differences favouring SMILE for resulting in better mean BCVA, less change in corneal spherical aberration (SA), and better corneal biomechanics.

Focusing on results from analyses of data for pa­tients treated at his centre, Dr Chang reported better predictability with SMILE was the only statistically significant difference found between the two proce­dures. Data on mean postoperative SEQ showed more overcorrection after LASIK than with SMILE (+0.45 D and +0.29 D, respectively).

The review included 202 eyes of 124 patients treated with SMILE and 201 eyes of 120 patients treated with LASIK. Preoperative SEQ was greater than or equal to -6.0 D in all eyes. He reported finding no statistically significant differences between groups in mean post­operative UDVA, BCVA, or cylinder. Induction of SA was slightly greater after LASIK compared with SMILE (mean change 0.11 and 0.05 microns, respectively), with a trend towards statistical significance.

“Other studies comparing the two procedures for correcting mild and moderate myopia have also report­ed less SA induction with SMILE,” Dr Chang said.

In addition, an analysis of enhancement rates for a cohort of almost 2,000 eyes treated for any level of myopia over a recent two-year period showed no statistically significant difference between the two procedures. All SMILE cases were performed with the VISUMAX 800 laser. Enhancement rates were 0.18% for SMILE and 0.23% for LASIK.

Drs Chang and Manche spoke at AAO Refractive Surgery Subspecialty Day 2023 in San Francisco, US.

1. Liu M, Chen Y, Wang D, et al. “Clinical Outcomes After SMILE and Femtosecond Laser-Assisted LASIK for Myopia and Myopic Astigmatism,” Cornea, 2016; 35(2): 210–216.

2. Chiang B, Valerio GS, Manche EE. “Prospective, Random­ized Contralateral Eye Comparison of Wavefront-Guided Laser In Situ Keratomileusis and Small Incision Lenticule Extraction Refractive Surgeries,” Am J Ophthalmol. 2022; 237: 211–220.

3. ClinicalTrials.gov. Identifier: NCT05611294. Personal com­munication: Majid Moshirfar MD.

John So Min Chang MD is Director of the Guy Hugh Chan Refractive Surgery Centre of Hong Kong Sanatorium & Hospital, Hong Kong. John.SM.Chang@HKSH.com 

Edward Manche MD is Professor of Ophthalmology at the Byers Eye Institute, Stanford School of Medicine, Palo Alto, California, US. lasik.manche@stanford.edu