The majority of anterior segment eye surgery has historically been performed using various types of metal or diamond blades. Many surgeons predict that very soon most, if not all, ocular surgery will be performed with lasers. Why is this transition occurring now? Lasers that cause thermal photodisruption, such as Argon and Nd:YAG, have established their benefit in most forms of retinal and glaucoma surgery. However, the most common ophthalmic procedures currently performed, cataract and refractive surgeries, until recently still used blades. The new kid on the block is the femtosecond (fs) laser. Having conquered LASIK surgery, the fs laser now sets its sights on the most popular ocular procedure-cataract surgery.
Femtosecond lasers depend on the effects of cavitation created by the rapid expansion and implosion of plasma, which results in the vaporization of surrounding tissue. The primary advantage of modern fs lasers revolves around the quick pulses that allow very low energy levels to create the plasma that excites the electrons to allow tissue vaporization while limiting the heat and surrounding shock waves that could lead to unwanted collateral damage. The extremely short pulse duration (10-15 seconds) and small pulse size (1-5 mµ) of fs lasers allow us to move away from photodisruption (Nd:YAG) and photoablation (excimer) toward level of precision of the photodisection process.
The first commercial application of fs lasers began in 2001 with the approval of the Intralase laser for LASIK flap creation. Over the past decade, five generations of improvements have resulted in lasers that can produce LASIK flaps at a level of safety and precision that far exceed the conventional bladed microkeratome. Table 1 lists some of the many advantages of fs LASIK flaps that have resulted in greater than 82% of the U.S. market share that continues to grow every year.1
There are fewer flap-related complications with the fs method compared with a mechanical metal blade microkeratome.2 Additionally, fs lasers have virtually eliminated common sight-threatening complications seen with mechanical metal blade microkeratomes.3 Femtosecond flaps result in less loss of BCVA and more gain in BCVA.4. Thinner, more predictable femtosecond flaps are biomechanically stronger and more stable than mechanical metal blade microkeratome flaps, possibly reducing the risk of post-LASIK ectasia.5
Femtosecond flaps are more precise, uniform in thickness (planar), and smoother-resulting in better quality of vision as seen in low-contrast visual acuity and contrast sensitivity studies due to fewer induced higher-order aberration.6-9 Naval studies show fs flaps provide LASIK patients with faster visual recovery.10 Patients who have fs laser flaps also report fewer subjective side effects, including night vision disturbances-glare and halo-and dry eye complaints.9,11,12 While it has taken several years, fs LASIK flap creation has become the standard of care.
Femtosecond lasers have also revolutionized corneal transplantation. Fs laser-enabled keratoplasty (FLEK) shows better long-term outcomes with less residual astigmatism and faster visual recovery compared with mechanical trephine corneal transplants in patients with keratoconus.13 Fewer complications, such as wound leaks with less sutures and faster suture removal, result in higher rates of patient satisfaction and quality of life after corneal transplantation.
Fs lasers provide a way to create Intacs intra-stromal corneal tunnels safely and more precisely than previous manual dissection with overall complication rates below 6%.14 While not all patients appreciate increases in UCVA, FAI may delay the need for corneal transplantation and in addition to corneal collagen cross-linking may stabilize the progressive changes associated with keratoconus.
Undoubtedly the most exciting new application of fs lasers is in the cataract surgery arena. The first generation of fs cataract surgery began with the approval of Alcon’s LenSx in August 2009. At least four fs lasers are currently approved in the U.S. for performing three significant parts of cataract surgery including corneal incisions, anterior capsulotomy, and lens fragmentation (see Table 2). The primary benefit of the fs laser portion of cataract surgery is to improve the safety profile by reducing or eliminating the use of phacoemulsification ultrasound energy often associated with many of the sight-threatening complications in modern cataract surgery.15 Other benefits may allow better UCVA after cataract surgery due to more precise IOL power selection because of less variable effective IOL position due to as a result of more precise anterior capsulotomy and incisional residual astigmatism correction compared with manual procedures.16
Future fs laser considerations in ophthalmic surgery include intra-stromal pockets for corneal inlays such as Kamra by Acufocus, and intra-stromal presbyopia correction such as Bausch + Lomb’s Supracor and Intracor procedures. Improvements in OCT structural imaging and patient interfaces will result in faster and safer procedures.
Femtosecond lasers have offered the ophthalmic surgeon an unparalleled level of precision, safety, and control over cataract and refractive surgery procedures. Femtosecond lasers have reinvigorated LASIK surgery, reinvented corneal transplantation, simplified corneal Intacs, and brought a level of precision to cataract surgery previously unimagined. Femtosecond lasers have reduced the learning curve of new surgical residents, thereby reducing the variability of surgical outcomes due to individual surgeon skill and performance. Future improvements in fs technology only promise to enhance our patients’ outcomes in most forms of cataract and refractive ophthalmic surgery.ODT
2012 U.S. Refractive Market Quarterly Update. Market Scope LLC .August 2012
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Will B, Kurtz RM. IntraLase is best. In: Probst LE, ed. LASIK: Advances, Controversies, and Custom. Thorofare, NJ: SLACK; 2004:397-402
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Knorz MC, Vossmerbaeumer U. Comparison of flap adhesion strength using Amadeus microkeratome and the IntraLase iFS femtosecond laser in rabbits. J Refract Surg. 2008 Nov ;24(9):875-878.
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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 Nov;23(9):880-887
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Tanzer DJ, Schallhorn S, Brown MC, et al. Comparison of Femtosecond vs. Mechanical Keratome in Wavefront Guided LASIK. Data presented at: American Society of Cataract and Refractive Surgery Symposium; April 15-20, 2005; Washington, DC.
Durrie D. A randomized, prospective clinical study of LASIK performed with the IntraLase FS laser vs. mechanical microkeratome. Data presented at: American Academy of Ophthalmology; October 23-26, 2004; New Orleans, LA
Salomão M; Ambrósio Jr R; Wilson SE., Dry eye associated with laser in situ keratomileusis: Mechanical microkeratome vs. femtosecond laser. J Cataract Refract Surg 2009 Oct;35(10):1756-1760
Gaster RN, Dumitrascu O, Rabinowitz YS: Penetrating keratoplasty using femtosecond laser-enabled keratoplasty with zig-zag incisions vs. a mechanical trephine in patients with keratoconus. Br J Ophthalmol. 2012 Sep;96(9):1195-9. doi: 10.1136/bjophthalmol-2012-301662. Epub 2012 Jul 11.
Coskunseven E, Kymionis GD, Tsiklis NS, et al. Complications of intrastromal corneal ring segment implantation using a femtosecond laser for channel creation: a survey of 850 eyes with keratoconus. Acta Ophthalmol. 2011 Feb;89(1):54-57
Conrad-Hengerer I, Hengerer FH, Schultz T, et al. Effect of femtosecond laser fragmentation on effective phacoemulsification time in cataract surgery. J Refract Surg. 2012 Dec;28(12):879-883
Rückl T, Dexl AK, Bachernegg A, et al. Femtosecond laser-assisted intrastromal arcuate keratotomy to reduce corneal astigmatism. J Cataract Refract Surg. 2013 Feb 6. pii: S0886-3350(12)01657-4. doi: 10.1016/j.jcrs.2012.10.043. [Epub ahead of print]