Flap Technology Review—The Case for Femtosecond Laser Flaps in Laser In Situ Keratomileusis

Ronald R Krueger, Richard Potvin
US Ophthalmic Review, 2012;5(1):18–21

Abstract

Purpose: 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.
Keywords: Femtosecond laser, laser in situ keratomileusis (LASIK), surgery, mechanical microkeratomes
Disclosure: Ronald R Krueger, MD, is Medical Director of the Department of Refractive Surgery at the Cole Eye Institute of the Cleveland Clinic Foundation in Cleveland. He is a consultant for Alcon Laboratories, Inc. Richard Potvin, MASc, OD, is a private consultant providing data analysis and research services to ophthalmologists and the ophthalmology industry. His clients include Alcon Laboratories, Inc.
Received: February 27, 2012 Accepted March 02, 2012 Citation US Ophthalmic Review, 2012;5(1):18–21
Correspondence: Ronald R Krueger, MD, Cole Eye Institute, Cleveland Clinic, 9500 Euclid Ave/i32 Cleveland, OH 44195. E: Krueger@ccf.org
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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 IntraLase® 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 35–40 % 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.

References:
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Keywords: Femtosecond laser, femtosecond laser flaps, laser in situ keratomileusis, LASIK, LASIK flaps, surgery, mechanical microkeratomes, refractive surgery, spherocylindrical refractive outcomes