Laser in situ keratomileusis (LASIK) is the gold standard of corneal refractive surgery. This technique has become very successful because of its predictabilty, fast visual recovery, relatively low wound healing response, and the option to retreat patients easily by simply lifting the flap. Compared with mechanical microkeratomes, the use of femtosecond lasers to create LASIK flaps significantly improved morphology and predictability, which also has implications for safety.1–3
Treatment of refractive error is carried out in corneal surgery by removing corneal tissue, which changes the radius of the corneal curvature and, accordingly, the power of the optical system. Some of the significant advantages of LASIK—fast visual recovery and low wound-healing response—are due to the intrastromal removal of tissue with immediate maintenance of the corneal surface. Only a miniscule epithelial defect, the LASIK flap entrance, is created, and this recovers rapidly within a few hours after the treatment.4 Therefore, intralenticular removal of tissue without surface treatment or even without flap creation seems to be a worthwhile new goal in corneal refractive surgery.
A few years ago, the femtosecond laser was introduced to remove corneal tissue, the part of the procedure that was historically done by the excimer laser. As in conventional microkeratome LASIK, the femtosecond laser can be used to create a lamellar incision in the cornea and then the corneal flap is lifted (femto-LASIK). Femtosecond lenticule extraction goes beyond that and uses the femtosecond laser to create a flap and with a second lamellar interface, a refractive lenticule for the removal of corneal tissue. This procedure was developed even further and uses the femtosecond laser to create just a lenticule (without a flap), which is then removed through a small incision. Overall, the solution is now called refractive lenticule extraction.5,6
Several long-term studies have been published and provide evidence to support the hypothesis that the refractive lenticule extraction technique is a viable alternative treatment. This issue includes 2 articles that focus on the advances in refractive lenticule extraction using a full femtosecond laser system.
In the first paper, Blum et al. (pages 1425–1429) report the results of a long-term follow-up of the original study of refractive lenticule extraction. This had been known as an effective procedure to correct myopia; however, the ability of refractive lenticule extraction to correct refractive errors in an effective and stable manner in the long term still has to be demonstrated. The findings by Blum et al. indicate that the refractive outcomes are comparable to LASIK outcomes. The authors even suggest that the techninque may provide superior stability after a 5-year period.
The second paper, by Ang et al. (pages 1415–1424), offers an overview of the transition and outcomes of 3 refractive lenticule extraction techniques: femtosecond lenticule extraction, small-incision lenticule extraction, and pseudo-small-incision lenticule extraction. Although this comparison offers interesting data, the research must be replicated in a wider spectrum of patients and locations to ensure ophthalmic surgeons have the best available information on which to base their recommendations. The findings in both papers provide more evidence to support the hypothesis that this technique offers good efficacy, safety, and stability in the long term.
The refractive lenticule extraction procedure may simplify corneal refractive laser surgery by requiring the use of only 1 laser system. Moving from a 2-laser system to a 1-laser system offers several advantages in terms of reduced workflow and space requirements and, potentially, improvements in patient comfort. However, there remain several concerns about the technique:
- Retreatments for low amounts of residual refractive errors cannot be done yet in the interface. A simple LASIK flap relift is not possible, and retreatments must be performed on the surface with the already reported disadvantage of unwanted haze formation. The use of mitomycin-C seems to be indicated.
- Data on the treatment of hyperopia is rare. Therefore, it is not currently known whether hyperopic patients can be successfully treated.
- Undercorrections of the astigmatic components have been reported.7
- Induction of higher-order aberrations, in particular coma, have been reported. This might be due to a centration issue.8
Looking into the future, refractive lenticule extraction could offer a safer, more patient-friendly solution depending on the outcomes of continued research. Most interesting for the ophthalmic community and the general public is that these advances may be another step in the direction toward even safer refractive corneal surgery.
1. von Jagow B, Kohnen T. Corneal architecture of femtosecond laser and microkeratome flaps imaged by anterior segment optical coherence tomography. J Cataract Refract Surg
2. Durrie DS, Kezirian GM. Femtosecond laser versus mechanical keratome flaps in wavefront-guided laser in situ keratomileusis; prospective contralateral eye study. J Cataract Refract Surg
3. Santhiago MR, Kara-Junior N, Waring GO IV. Microkeratome versus femtosecond flaps: accuracy and complications. Curr Opin Ophthalmol
4. Giessler S, Duncker GIW. Short-term visual rehabilitation after LASIK. Graefes Arch Clin Exp Ophthalmol
5. Sekundo W, Kunert K, Russman C, Gille A, Bissman W, Stobrawa G, Sticker M, Bischoff M, Blum M. First efficacy and safety study of femtosecond lenticule extraction for the correction of myopia: Six-month results. J Cataract Refract Surg
6. Shah R, Shah S, Sengupta S. Results of small incision lenticule extraction: All-in-one femtosecond laser refractive surgery. J Cataract Refract Surg
7. Ivarsen A, Hjortdal J. Correction of myopic astigmatism with small incision lenticule extraction. J Refract Surg
8. Li M, Zhao J, Miao H, Shen Y, Sun L, Tian M, Wadium E, Zhou X. Mild decentration measured by a Scheimpflug camera and its impact on visual quality following SMILE in the early learning curve. Invest Ophthalmol Vis Sci