Flap over Flaps: What is the Best Way to do LASIK?
What are the advantages of the Femtosecond LASER over the mechanical microkeratome when it comes to making a flap for LASIK surgery? Simple, predictably making thin (110-120 micron) flaps with a much smaller standard deviation compared with the mechanical microkeratome (140-200 micron) reduces the risk of ectasia. Also, reducing the risk of lamellar transection either posteriorly or anteriorly substantially reducies the risk of scaring. Moving the flap hinge temporally may offer additional benefit against traumatic dislocation as well as offering the best geometric location for patients with nasal pupils. We have enjoyed this technology over the past 6 years at the Duke Center for Vision Correction. I don’t know of a single refractive surgeon today who would choose to have LASIK performed on their own eye with a mechanical microkeratome over a flap created with a femtosecond LASER. The following article is a nice review of this subject matter.
The LASIK procedure involves two steps. First, a thin layer of tissue called a flap is constructed on the surface of the cornea. Second, the flap is lifted and laser energy is used to reshape the bed of tissue beneath the flap to correct nearsightedness, farsightedness, and/or astigmatism. The flap is then laid back in place and allowed to heal.
There are two methods of flap construction: the mechanical microkeratome, which is a very fine, rapidly oscillating blade, and the femtosecond laser, which is a source of pinpoint light energy. Debate continues today as to which method is best. According to a 2010 survey of members of the American Society of Cataract and Refractive Surgery, 50% of LASIK in the US today is performed with the microkeratome and 50% is performed with the laser.1
While many refractive surgeons prefer to use a microkeratome for creating a LASIK flap, market indicators appear to be pointing toward a shift to reliance on femtosecond technology. Published studies continue to show at least equal visual outcomes for these two technologies that are used to create LASIK flaps.2
A review of published peer-reviewed, comparative scientific studies on the relative safety of the microkeratome versus the laser shows equivalence. For example, an 18-month study performed at the John A. Moran Eye Center, Department of Ophthalmology, University of Utah demonstrated that the complication rate was 14.2% in the microkeratome group and 15.2% in the femtosecond laser group (P = .5437).3Similarly, investigation has shown that healing is the same regardless of the method used for flap construction.4
Studies of effectiveness have also generally shown equivalence of the microkeratome and laser. For example, a study performed at the Mayo Clinic showed that the method of flap creation did not affect visual outcomes during the first 6 months after LASIK. Patients did not perceive a difference in vision.5 Another study published in the American Journal of Ophthalmology last year demonstrated that there were no differences in corneal total high-order aberrations, spherical aberration, coma, or trefoil between methods of flap creation at any examination over 4- and 6-mm-diameter pupils. Uncorrected and best-corrected visual acuity did not differ between methods at any examination and remained stable postoperatively through 3 years. The femtosecond laser flap did not offer any advantage in corneal high-order aberrations or visual acuity through 3 years after LASIK.6 Other authors have concluded that corneal aberrations after myopic LASIK are similar after mechanical microkeratome and femtosecond laser flap creation. Visual acuity, refraction, and the optical quality of the cornea after LASIK remain stable through 4 years postoperatively regardless of the method of flap construction.7
There may, however, be advantages for the laser in certain circumstances. One recent publication showed slightly better results in hyperopic LASIK,8 and another showed faster recovery in uncorrected acuity with the laser.9 Authors have also reported slightly better contrast sensitivity at higher spatial frequencies after laser flap construction.10 The one situation in which using the laser makes sense is when there is a limit to the refractive effect due to the thinness of the cornea. Surface ablation (for example, PRK) which does not require the construction of a flap at all may make the most sense in these cases, but the laser does have the ability to safely create a thinner flap and may allow the faster recovery time which is a significant benefit of LASIK.
LASIK remains a wonderful procedure to reduce or eliminate the need for glasses and contact lenses for good candidates, whether a laser or a microkeratome is used to construct the flap.
1. Leaming DV. 2010 Survey of US ASCRS Members. http://www.analeyz.com/AnaleyzASCRS2010.htm (Accessed April 28, 2011).
2. Femtosecond laser use in US increasing, but some still prefer microkeratomes. OCULAR SURGERY NEWS U.S. EDITION June 10, 2009; http://www.osnsupersite.com/view.aspx?rid=40118 (Accessed April 28, 2011).
3. Moshirfar M, Gardiner JP, Schliesser JA, Espandar L, Feiz V, Mifflin MD, Chang JC. Laser in situ keratomileusis flap complications using mechanical microkeratome versus femtosecond laser: retrospective comparison. J Cataract Refract Surg. 2010 Nov;36(11):1925-33.
4. Patel SV, McLaren JW, Kittleson KM, Bourne WM. Subbasal nerve density and corneal sensitivity after laser in situ keratomileusis: femtosecond laser vs mechanical microkeratome. Arch Ophthalmol. 2010 Nov;128(11):1413-9.
5. Patel SV, Maguire LJ, McLaren JW, Hodge DO, Bourne WM. Femtosecond laser versus mechanical microkeratome for LASIK: a randomized controlled study. Ophthalmology. 2007 Aug;114(8):1482-90.
6. Calvo R, McLaren JW, Hodge DO, Bourne WM, Patel SV. Corneal aberrations and visual acuity after laser in situ keratomileusis: femtosecond laser versus mechanical microkeratome. Am J Ophthalmol. 2010 May;149(5):785-93.
7. Muñoz G, Albarrán-Diego C, Ferrer-Blasco T, García-Lázaro S, Cerviño-Expósito A. Long-term comparison of corneal aberration changes after laser in situ keratomileusis: mechanical microkeratome versus femtosecond laser flap creation. J Cataract Refract Surg. 2010 Nov;36(11):1934-44.
8. Gil-Cazorla R, Teus MA, de Benito-Llopis L, Mikropoulos DG. Femtosecond Laser vs Mechanical Microkeratome for Hyperopic Laser In Situ Keratomileusis. Am J Ophthalmol. 2011 Apr 18; [Epub ahead of print]
9. Tanna M, Schallhorn SC, Hettinger KA. Femtosecond laser versus mechanical microkeratome: a retrospective comparison of visual outcomes at 3 months. J Refract Surg. 2009 Jul;25(7 Suppl):S668-71.
10. Montés-Micó R, Rodríguez-Galietero A, Alió JL, Cerviño A. Contrast sensitivity after LASIK flap creation with a femtosecond laser and a mechanical microkeratome. J Refract Surg. 2007 Feb;23(2):188-92.
KA: Mark Packer, MD, CPI, FACS, is Clinical Associate Professor, Casey Eye Institute, Department of Ophthalmology, Oregon Health & Science University School of Medicine, and in practice with Drs. Fine, Hoffman & Packer in Eugene, OR. He serves on the Cataract Clinical Committee of the American Society of Cataract and Refractive Surgery (ASCRS). In 2005 he was elected to membership in The International Intra-Ocular Implant Club.