My first FDA-monitored study was as an investigator in a 1990 partially sighted eyes PRK study. This led to my involvement as a principal investigator in the FDA-monitored sighted eye trials in PRK, LASIK and SMILE. Having used all three of these procedures in clinical trials and post-approval has shaped my philosophy on their use in my own clinical practice. (See “Patient Education is Paramount,” below.) Since SMILE and LASIK are employed, in general, for the same refractive error and corneal thickness patient population, I am often asked which procedure is “better” and will, therefore, be the future of corneal refractive surgery.

I will start out by saying I think the reason SMILE is the fastest-growing corneal refractive surgery in the world is that it has features that combine what we love about PRK, such as less dry eye, no flap to dislodge, and potentially improved biomechanics, along with what we love about LASIK, such as fast vision return and no risk of corneal haze. With these considerations in mind, I share my thoughts about and experience with SMILE and LASIK and how they coexist in my practice.

SMILE

I prefer to use SMILE when the correction is high enough (-1.00 or higher), the cylinder is -0.75 or higher, and there is no need for either a custom approach to address higher-order aberrations (HOAs) or a topographical-guided approach required to deal with topographical issues. The other instances I prefer to use SMILE are where patients or myself are concerned about dry eye disease, corneal sensation, biomechanical stability or trauma (potential flap dislodgement). SMILE’s benefits:

• Small side cut. It is well understood, through studies on corneal strength, that the depth of incised corneal collagen lamellae matters. The Scarcelli group used Brillouin scattering technology to show that the anterior cornea contains the strongest corneal collagen lamellae.¹ As a result, it is felt that the preservation of the stronger anterior corneal collagen lamellae may lead to improved corneal biomechanics.² The side cut in SMILE is 2 mm to 4 mm, whereas in LASIK, it is typically around 20 mm. Thus, SMILE cuts much less of the anterior corneal collagen lamellae. Also, mathematical modeling showed 75% of corneal tensile strength remained after SMILE versus 54% with LASIK.³

Something else to consider: SMILE’s smaller side cut results in less corneal nerve damage and faster corneal nerve recovery than LASIK.⁴ It has been shown that as a result of this, corneal sensation is improved with SMILE when compared to LASIK. Also, there is less postoperative dry eye disease in SMILE versus LASIK.⁵ Specifically, studies showed that tear break-up time, tear osmolarity, and Schirmer’s test one and two were all better after SMILE when compared to LASIK.⁶

• Low postoperative total HOAs. A large meta-analysis study comparing HOAs after SMILE versus LASIK showed SMILE to have, on average, lower postoperative total HOAs compared to femtosecond laser LASIK in studies combining 1,230 eyes.⁷ SMILE also had lower postoperative spherical aberration compared to femtosecond LASIK in studies looking at the same 1,230 eyes, and the procedure had comparable postoperative vertical coma in 5 studies combining 733 eyes.

Further, my clinical impression of the visual results of SMILE have shown it to compare very well to LASIK results.

LASIK

I find LASIK results are favored over SMILE when patients can benefit from a custom approach via wavefront-guided and topographical-guided LASIK. Regarding the former, Edward E. Manche, MD, and Gabriel Valerio, MD, at the Stanford University School of Medicine, compared the one-year outcomes of SMILE versus wavefront-guided LASIK in a randomized, prospective study of 80 eyes of 40 subjects, presented at the European Society of Cataract & Refractive Surgery this year. LASIK’s benefits:

• Better vision. Wavefront-guided LASIK postop day 1 showed more patients with 20/20 uncorrected vision than those in the SMILE group. Also, at 12-months postoperatively, those who underwent wavefront-guided LASIK had significantly better low-contrast visual acuity versus SMILE. Additionally, as far as patients who gained one line of vision, wavefront-guided LASIK showed superiority over SMILE also. Further, the number of patients who achieved 20/12.5 or better vision was higher in the wavefront-guided LASIK group, and 5% and 25% low-contrast visual acuity was also higher in this group. Finally, there was faster visual recovery in the wavefront-guided LASIK group when compared with the SMILE group.

Additional studies have shown that topographical-guided LASIK has advantages over SMILE too, especially when the patient has topographic irregularities.

Other benefits of LASIK over SMILE:

• Unimpeded patient fixation during the ablation.
• Addressing low corrections. Since SMILE’s FDA labeling is myopia -1.00 to -10.00 and astigmatism -0.75 to -3.00, LASIK is still needed.

The Bottom Line

I feel most corneal refractive patients I see are good candidates for SMILE or LASIK. If I can center the SMILE well, it is my preferred approach, as long as a custom or topographical-guided approach is not needed. Time will tell which one of these procedures win out, but in my opinion, they can coexist nicely in a practice, and patients will appreciate learning about the pluses and minuses of both, as they make their ultimate, life-long vision decision. CP

References:

1. Webb JN, Su JP, Scarcelli G. Mechanical outcome of accelerated corneal crosslinking evaluated by Brillouin microscopy. J Cataract Refract Surg. 2017;43(11):1458-1463.
2. Spiru B, Kling S, Hafezi F, Sekundo W. Biomechanical Properties of Human Cornea Tested by Two-Dimensional Extensiometry Ex Vivo in Fellow Eyes: Femtosecond Laser-Assisted LASIK Versus Smile. J Refract Surg. 2018; 34(6): 419-423.
3. Reinstein DZ, Archer TJ, Randleman JB, Mathematical model to compare the relative tensile strength of the cornea after PRK, LASIK, and small incision lenticule extraction. J Refract Surg. 2013;29(7):454-460.
4. Mohamed-Noriega K, Riau AK, Lwin NC, Chaurasia SS, Tan DT, Mehta JS. Early corneal nerve damage and recovery following small incision lenticule extraction (SMILE) and laser in situ keratomileusis (LASIK). Invest Ophthalmol Vis Sci. 2014;55(3):1823-1834.
5. Reinstein DZ, Archer TJ, Gobbe M, Bartoli E. Corneal sensitivity after small-incision lenticule extraction and laser in situ keratomileusis. J Cataract Refract Surg. 2015 Aug;41(8):1580-1587.
6. Ganesh S, Gupta R. Comparison of visual and refractive outcomes following femtosecond laser-assisted lasik with smile in patients with myopia or myopic astigmatism. J Refract Surg. 2014;30(9):590-596.
7. Yan H, Gong LY, Huang W, Peng YL. Clinical outcomes of small incision lenticule extraction versus femtosecond laser-assisted LASIK for myopia: a Meta-analysis. Int J Ophthalmol. 2017;10(9):1436-1445.

 

DR. THOMPSON is a board-certified ophthalmologist in Sioux Falls, SD, specializing in refractive corneal, phakic IOL, and lens surgery at Vance Thompson Vision. He has relationships with Alcon, Bausch + Lomb, Carl Zeiss Meditec and Johnson & Johnson.