“SMILE is combining the best of both worlds of PRK and LASIK into one procedure, i.e., performing a PRK without the pain, and having the benefit of a LASIK without a flap.”
Dr. Rupal Shah
Surgical correction of refractive errors is certainly popular. Twenty years ago, the development of photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) using the excimer laser revolutionized the field of corneal refractive surgery.1 Thereafter, refractive lenticule extraction (ReLEx) of intracorneal tissue became possible using a femtosecond laser. Although the clinical results of LASIK have improved remarkably, there are postoperative complications, among which LASIK-inflicted ectasia is the foremost concern. As most complications are believed to be associated with the corneal flap, recent efforts have focused on the development of new procedures that avoid the flap creation.2
Recently, small incision lenticule extraction (SMILE) has been established as a ‘flapless’ procedure in which an intrastromal lenticule is cut by a femtosecond laser and manually extracted through a peripheral corneal tunnel incision. SMILE is a minimally invasive, laser vision-correction procedure, and excellent visual outcomes with high predictability have been recorded in patients with myopia and astigmatism.3
Several studies have demonstrated a lower reduction and faster recovery of corneal sensitivity and sub-basal nerve fiber density after SMILE as compared to LASIK4 – this is because the anterior stroma is disturbed only by the small incision. The potential biomechanical advantages of SMILE have been modeled based on the nonlinearity of tensile strength through the stroma.5 SMILE offers a variety of clinical advantages, and a recent meta-analysis of published studies concluded that the incidence of transient dry eye syndrome following surgery is lower in SMILE, as compared to LASIK.6 As a minimally invasive approach, SMILE offers the potential for more biomechanical stability of the cornea, thereby facilitating rapid wound healing.7
Dr. Rupal Shah, the group medical director for New Vision Laser Centers in India, is one of the global pioneers of SMILE. She shared insights into her decade-long experience as one of the first corneal laser refractive surgeons in the world to use the ZEISS (Carl Zeiss Meditec, Jena, Germany) platform for SMILE procedures.
“I’ve been performing laser surgery since 1994, and I have extensive experience in corneal laser refractive surgery. For the past 11 years, I’ve been performing femto-LASIK and SMILE procedures,” shared Dr. Shah. “I am one of the pioneers of SMILE as I got a chance to study the procedure in its infancy.”
She recalled the early years of refractive surgery in India: “What we basically do in corneal refractive surgery is to do a corneal reshaping so that the focusing of the rays of light happens exactly on the retina, to match patients’ expectations. Previous procedures involved creating a flap, because the epithelium can regenerate, so you somehow need to go underneath the epithelium to achieve a stable shape. Microkeratome LASIK would offer a much faster visual recovery with less need to take steroids. However, it has the disadvantage of flap-related complications which can be worrying.”
Dr. Shah said femto-LASIK came like a breath of fresh air. “It was a huge step ahead of microkeratome LASIK. However, in a country like India, it is difficult to justify investing in a femto-LASIK, as this significantly increases the cost of the procedure. There is still flap formation, and this takes considerable time to heal. So, SMILE is like a new paradigm because it removes the need to create a flap, while ensuring quick recovery of the LASIK procedure. Therefore, it’s safer and it comes without pain.”
While noting its key advantages, Dr. Shah said: “I can describe SMILE as combining the best of both worlds of PRK and LASIK into one procedure, i.e., performing a PRK without the pain, and having the benefit of a LASIK without a flap.”
Dr. Shah explained that during SMILE eye surgery, a lenticule is created inside the intact cornea using the VisuMax femtosecond laser (Carl Zeiss Meditec, Jena, Germany) and extracted through a small incision. “The lenticule is removed, thereby achieving the desired vision correction,” Dr. Shah said. “SMILE will most likely be the future of corneal refractive surgery.”
Given its importance in corneal refractive surgery today, Dr. Shah stated that SMILE is an important technique that should be learned by all corneal surgeons. “This procedure is more difficult to learn compared to LASIK, but there is a finite learning curve. In addition, there is only one company that makes these lasers, which is ZEISS, so training is not widely available.” However, she stressed that: “For a surgeon with an established refractive practice, this can be a good addition. And the extra time invested in learning SMILE and the excellent results in patient outcomes will be worth it.”
Editor’s Note: In October 2018, the US FDA Premarket Approval (PMA) for ReLEx SMILE expanded myopia treatment to patients with astigmatism.
References
- Vestergaard AH. Past and present of corneal refractive surgery: a retrospective study of long-term results after photorefractive keratectomy, and a prospective study of refractive lenticule extraction. Acta Ophthalmologica. 2014;92(5):492-493.
- Chansue E, Tanehsakdi M, Swasdibutra S, McAlinden C. Efficacy, predictability and safety of small incision lenticule extraction (SMILE). Eye Vis (Lond). 2015;2:14.
- Liu M, Chen Y, Wang D. et al. Clinical Outcomes After SMILE and femtosecond laser-assisted LASIK for myopia and myopic astigmatism: A prospective randomized comparative study. Cornea 2016;35(2):210-216.
- Denoyer A, Landman E, Trinh L, Faure JF, Auclin F, Baudouin C. Dry eye disease after refractive surgery: Comparative outcomes of small incision lenticule extraction versus LASIK. Ophthalmology 2015;122(4):669-676.
- Seven I, Vahdati A, Pedersen IB, et al. Contralateral Eye Comparison of SMILE and flap-based corneal refractive surgery: Computational analysis of biomechanical impact. J Refract Surg. 2017;33(7):444-453.
- 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):1436-1445.7 Wang D, Liu M, Chen Y, et al. Differences in the corneal biomechanical changes after SMILE and LASIK. J Refract Surg. 2014;30(10):702-707.
