Flap Technology Reviewâ€”The Case for Femtosecond Laser Flaps in Laser In Situ Keratomileusis
AbstractPurpose: To review the literature concerning the relative advantages and disadvantages of laser in situ keratomileusis (LASIK) flaps created with mechanical microkeratomes versus femtosecond laser systems. Setting: Cole Eye Institute, Cleveland Clinic Foundation, Cleveland, OH 44195. Methods: A review of the literature available related to mechanical microkeratomes and femtosecond laser systems was conducted. Operational limitations, complications, complication rates, and clinical outcomes were compared. Results: Data from the peer-reviewed literature showed that intra-operative complication rates were slightly higher with mechanical microkeratomes, and a training effect was evident. Complication rates with femtosecond laser systems have dropped as the laser spot size and/or energy has decreased and shot frequency has increased. Laser-created flaps showed lower variability in flap thickness and greater variety in programmable flap geometry. Spherocylindrical refractive outcomes were generally similar but higher order aberrations were reported as lower with femtosecond laser flap creation. Conclusion: There is now extensive evidence in the literature comparing these technologies. The results support current femtosecond laser technology as superior to mechanical microkeratomes for the creation of LASIK flaps in refractive surgery.
It has been more than a decade since the femtosecond laser entered the ophthalmic market as an alternative to the mechanical microkeratome for the creation of flaps in laser in situ keratomileusis (LASIK).1 The first device approved in the US was the IntraLaseÂ® Femtosecond Laser (Abbott Medical Optics) in 2001. The early successes of this device generated considerable interest in the technology, such that there are now five femtosecond laser systems available to surgeons, each with slightly different characteristics. Table 1 summarizes the key features of each system.2 The first widely available IntraLase system operated at 15 kHz, a significantly lower pulse rate (with significantly higher pulse energy) than used in more recently available systems. The fundamental theory behind the use of the femtosecond laser for flap creation is that the laser can perform cutting procedures, much like a blade. A focused pulse of the laser causes photodisruption of the target tissue, effectively creating a microseparation that is then followed by an expanding cavitation bubble, which then collapses to a smaller size. When these pulses are contiguously arranged along a common focal plane, they produce a dissection plane. Larger pulses create larger expanding bubbles, which reduce the number of pulses required to cleave the tissue. However, collateral damage from the shock wave in the tissue is higher with these larger, higher energy pulses, and there is a correspondingly higher inflammatory response. 3 A greater number of smaller pulses can achieve the same result. The advantage of a smaller spot size is that the energy per pulse can be significantly lower. To maintain a constant ablation time, the frequency of the laser system must rise as the spot size decreases. The cleavage that occurs with the femtosecond laser is functionally equivalent to that which can be achieved with the cutting of a blade. However, there are histologic differences in the two procedures in both the inflammatory4 and healing5 responses.
By the end of 2008, it was estimated that 35â€“40 % of LASIK surgeries in the US were being performed using a femtosecond laser for flap creation.6 It is estimated that this number has since increased to up to 70 %. There are now more than 50 publications in the peer-reviewed literature comparing the use of mechanical microkeratomes and femtosecond lasers for LASIK flap creation. The evidence in the literature indicates that there is a good case for adopting femtosecond laser technology for all LASIK flaps. Some of the key arguments are outlined here.
- Ratkay-Traub I, Juhasz T, Horvath C, et al., Ultra-short pulse (femtosecond) laser surgery: initial use in LASIK flap creation, Ophthalmol Clin North Am, 2001;14(2):347â€“55, viii-ix.
- Reggiani-Mello G, Krueger RR, Comparison of commercially available femtosecond lasers in refractive surgery, Expert Rev Opthalmol, 2011;6(1):55â€“65.
- SalomÃ£o MQ, Wilson SE, Femtosecond laser in laser in situ keratomileusis, J Cataract Refract Surg 2010;36(6):1024â€“32.
- Sonigo B, Iordanidou V, Chong-Sit D, et al., In vivo corneal confocal microscopy comparison of intralase femtosecond laser and mechanical microkeratome for laser in situ keratomileusis, Invest Ophthalmol Vis Sci, 2006;47(7):2803â€“11.
- Santhiago MR, Wilson SE, Cellular Effects After Laser In Situ Keratomileusis Flap Formation With Femtosecond Lasers: A Review, Cornea, 2012;31(2):198â€“205.
- Bechtel B, Cimberle M, Femtosecond laser use in US increasing, but some still prefer microkeratomes, Ocular Surgery News, June 10, 2009. Available at: www.osnsupersite.com/view.aspx?rid=40118 (accessed March 02, 2012).
- Gimbel HV, Penno EE, van Westenbrugge JA, et al., Incidence and management of intraoperative and early postoperative complications in 1000 consecutive laser insitu keratomileusis cases, Ophthalmology, 1998;105:1839â€“48.
- Doane JF, Stechshulte SU, Moles S, Mechanical Microkeratomes: Creation of a Meniscus, not a Planar Flap, Presented at: ASCRS/AOSA Annual Meeting, April 30, 2001, San Diego, CA.
- Paschalis EI, Labiris G, Aristeidou AP, et al., Laser in situ keratomileusis flap-thickness predictability with a pendular microkeratome, J Cataract Refract Surg, 2011;37(12):2160â€“6.
- Von Jagow B, Kohnen T, Corneal architecture of femtosecond laser and microkeratome flaps imaged by anterior segment optical coherence tomography, J Cataract Refract Surg, 2009;35(1):35â€“41.
- Murakami Y, Manche EE, Comparison of intraoperative subtraction pachymetry and postoperative anterior segment optical coherence tomography of laser in situ keratomileusis flaps, J Cataract Refract Surg, 2011;37(10):1879â€“83.
- Ahn H, Kim JK, Kim CK, et al., Comparison of laser in situ keratomileusis flaps created by 3 femtosecond lasers and a microkeratome, J Cataract Refract Surg, 2011;37(2):349â€“57.
- Javaloy J, Vidal MT, Abdelrahman AM, et al., Confocal microscopy comparison of intralase femtosecond laser and Moria M2 microkeratome in LASIK, J Refract Surg, 2007;23(2):178â€“87.
- Moshirfar M, Gardiner JP, Schliesser JA, et al., Laser in situ keratomileusis flap complications using mechanical microkeratome versus femtosecond laser: retrospective comparison, J Cataract Refract Surg, 2010;36(11):1925â€“33.
- Gil-Cazorla R, Teus MA, de Benito-Llopis L, Fuentes I, Incidence of diffuse lamellar keratitis after laser in situ keratomileusis associated with the IntraLase 15 kHz femtosecond laser and Moria M2 microkeratome, J Cataract Refract Surg, 2008;34(1):28â€“31.
- Kamburoglu G, Ertan A, Epithelial ingrowth after femtosecond laser-assisted in situ keratomileusis, Cornea, 2008;27(10):1122â€“5.
- Kaiserman I, Maresky HS, Bahar I, Rootman DS, Incidence, possible risk factors, and potential effects of an opaque bubble layer created by a femtosecond laser, J Cataract Refract Surg, 2008;34(3):417â€“23.
- Haft P, Yoo SH, Kymionis GD, et al., Complications of LASIK flaps made by the IntraLase 15- and 30-kHz femtosecond lasers, J Refract Surg, 2009;25(11):979â€“84.
- Choe CH, Guss C, Musch DC, et al., Incidence of diffuse lamellar keratitis after LASIK with 15 KHz, 30 KHz, and 60 KHz femtosecond laser flap creation, J Cataract Refract Surg, 2010;36(11):1912â€“8.
- Stonecipher KG, Dishler JG, Ignacio TS, Binder PS, Transient light sensitivity after femtosecond laser flap creation: clinical findings and management, J Cataract Refract Surg, 2006;32(1):91â€“94.
- Krueger RR, Thornton IL, Xu M, et al., Rainbow glare as an optical side effect of IntraLASIK, Ophthalmology, 2008;115(7):1187â€“95.
- Bamba S, Rocha KM, Ramos-Esteban JC, Krueger RR, Incidence of rainbow glare after laser in situ keratomileusis flap creation with a 60 kHz femtosecond laser, J Cataract Refract Surg, 2009;35(6):1082â€“6.
- Al-Swailem SA, Wagoner MD, Complications and visual outcome of LASIK performed by anterior segment fellows vs experienced faculty supervisors, Am J Ophthalmol, 2006;141(1):13â€“23.
- Li H, Sun T, Wang M, Zhao J, Safety and effectiveness of thin-flap LASIK using a femtosecond laser and microkeratome in the correction of high myopia in Chinese patients, J Refract Surg, 2010;26(2):99â€“106.
- Zhang ZH, Jin HY, Suo Y, et al., Femtosecond laser versus mechanical microkeratome laser in situ keratomileusis for myopia: Meta-analysis of randomized controlled trials, J Cataract Refract Surg, 2011;37(12):2151â€“9.
- 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;152(1):16â€“21.
- Tanna M, Schallhorn SC, Hettinger KA, Femtosecond laser versus mechanical microkeratome: a retrospective comparison of visual outcomes at 3 months, J Refract Surg, 2009;25(7 Suppl.):S668â€“71.
- Medeiros FW, Stapleton WM, Hammel J, et al., Wavefront analysis comparison of LASIK outcomes with the femtosecond laser and mechanical microkeratomes, J Refract Surg, 2007;23(9):880â€“7.
- Krueger RR, Dupps WJ Jr, Biomechanical effects of femtosecond and microkeratome-based flap creation: prospective contralateral examination of two patients, J Refract Surg, 2007;23(8):800â€“7.
- Calvo R, McLaren JW, Hodge DO, et al., Corneal aberrations and visual acuity after laser in situ keratomileusis: femtosecond laser versus mechanical microkeratome, Am J Ophthalmol, 2010;149(5):785â€“93.
- Buzzonetti L, Petrocelli G, Valente P, et al., Comparison of corneal aberration changes after laser in situ keratomileusis performed with mechanical microkeratome and IntraLase femtosecond laser: 1-year follow-up, Cornea, 2008;27(2):174â€“9.
- AliÃ³ JL, PiÃ±ero DP, Very high-frequency digital ultrasound measurement of the LASIK flap thickness profile using the IntraLase femtosecond laser and M2 and Carriazo-Pendular microkeratomes, J Refract Surg, 2008;24(1):12â€“23.