Lamellar corneal surgery for the correction of refractive errors has been evolving for more than 60 years.1-5 As we enter the second decade of the third millennium, it is surprising when something “new” is actually a paradigm changer in laser vision correction. The principals in the refractive division of Carl Zeiss Meditec, Inc. (Dublin, CA), I believe, have created a device and concept that could be the next major advance in lamellar corneal refractive surgery. It is unlikely that José I. Barraquer, MD, foresaw this latest advance. Dr. Barraquer began developing lamellar corneal surgery in 1948. It is only through his sheer genius, persistence, and ingenuity that the field of lamellar corneal refractive surgery in the form of LASIK is with us today. Many of his concepts remain the foundation of this aspect of ophthalmic surgery.
Fundamentally, refractive lamellar corneal surgery attempts to remove, add, or modify the corneal stroma so that the radius of curvature of the tear film-anterior corneal interface is altered as desired. Dr. Barraquer’s quintessential contribution was the microkeratome, which functions like a carpenter’s plane not only to access the corneal stroma but also to perform a planar lamellar resection of stromal tissue to induce refractive changes. The success of Dr. Barraquer’s lamellar refractive approach approach did not pan out until the 193-nm excimer laser was married to the procedure as the tool to precisely effect the refractive correction instead of the cryolathe.6-9 The precision by which an excimer laser can remove tissue—0.25 µm per pulse—revolutionized the refractive surgical landscape and allowed for commercialization of refractive surgery across the globe.
The femtosecond laser allows surgeons to change the curvature of the stroma with the excimer laser.10 Through the groundbreaking work of Ron Kurz, Tibor Juhanzs, and Eric Weinberg, the Intralase Corporation (now Abbott Medical Optics Inc., Santa Clara, CA) was able to bring to market a device that made the flap’s creation easier, safer, and more predictable.10 Additional work by Intralase/Abbott Medical Optics Inc., Carl Zeiss Meditec, Inc., and other companies has enabled femtosecond lasers to be designed and utilized for therapeutic corneal surgery. The most recent advance by Carl Zeiss Meditec, Inc., goes beyond the flap’s creation with a curved ocular interface (Figure 1) to therapeutic techniques that use the femtosecond laser for an all-in-one refractive procedure called ReLEx (for refractive lenticule extraction) with the Carl Zeiss Meditec, Inc.’s VisuMax femtosecond laser (Figure 2). No 193-nm excimer laser is needed.
The ReLEx technique can correct any refractive error—simple myopia and hyperopia, compound myopic and hyperopic astigmatism, mixed astigmatism, and more. ReLEx encompasses two different approaches. The first is the femtosecond lenticule extraction or FLEx procedure. The femtosecond laser makes essentially two passes. The first or posterior pass of the femtosecond laser creates the posterior surface of the lenticule that will be extracted. The second or anterior pass of the laser accomplishes three goals: the flap’s side cuts, the side cut to lenticule edge pass effectively creating the peripheral stromal bed, and the anterior surface of the lenticule that will be extracted. After the laser passes, the surgeon lifts the peripheral edge of the flap, dissects the flap from the anterior surface of the lenticule, and then takes hold of the peripheral edge of the lenticule to lift the lenticule from the stromal bed (Figure 3). The flap is then positioned in the normal fashion.
The FLEx procedure diverges from traditional LASIK in that, instead of the excimer laser’s being used for the “refractive step,” the femtosecond laser creates a lenticule of corneal tissue for removal to cause the refractive change (Figure 4). In this setting, the procedure is reminiscent of automated lamellar keratoplasty. The major difference is that the refractive predictability is on par with excimerbased corneal refractive procedures (discussed later).
The second approach to ReLEx is the small-incision lenticule extraction or SMILE technique. Rather than create and lift a hinged flap, the surgeon performs two passes of the femtosecond laser. As in the FLEx procedure, the first pass of the laser creates the posterior aspect of the lenticule and a peripheral stromal bed. The second pass of the femtosecond laser creates the anterior surface of the lenticule and one or two small access incisions. The surgeon can then dissect the remaining corneal attachments of the anterior and posterior surfaces and remove the lenticule through a small incision. The advantages of the SMILE concept are that it is less invasive, there is no chance for flap dislocation, the cornea inherently maintains a greater biomechanical structure, and there should theoretically be a shorter healing cycle.
FDA SUBMISSION FOR US CASES UNDERWAY
To date, no ReLEx procedures have been performed in the United States, but FDA submission for these studies is underway and expected to start domestically in the second half of 2010. Outside the United States, ReLEx procedural development under the guidance of Carl Zeiss Meditec, Inc., is occurring at six sites on three continents. Investigations at all of these sites have shown exquisite refractive results that meet or exceed the best LASIK results to date. Data from the international sites (R. Shah, Vadodara, India; W. Sekundo, Mainz, Germany; M. Blum Erfurt, Germany; O. Ibrahim, Alexandria, Egypt; I. Solomatin, Riga, Latvia; R. Wiltfang, Munich, Germany) mirror current LASIK results, although the visual recovery with ReLEx in general has not been as quick. Refractive predictability with ReLEx is equivalent or superior to current LASIK results; with the former, 95% of the eyes are ±0.50 D from refractive target. Interestingly, the predictability has been just as good for patients with low myopia as it has for those with high myopia. Efficacy rates have shown that 95% of the eyes achieve at least 20/30 uncorrected distance visual acuity at 3 months for even moderate-to-high myopic levels. Importantly, the safety results have been excellent, with only 1% to 2% of eyes losing two or more lines of BSCVA (N = 777 eyes). Refractive stability is essentially achieved at 1 week, and little-to-no change is seen between this interval and the 1- and 3-month data sets (data on file at Carl Zeiss Meditec, Inc.).
Are there unknowns? Yes, long-term data are lacking. Like all surgeons, I would like to see the results in my own hands. It is also currently unclear if very small refractive errors (≤1.00 D) can be treated with the ReLEx procedure. Furthermore, investigators have yet to determine what surgeons can achieve for the typical enhancement cases that are less than 1.00 D spherical equivalent refraction. Can these be addressed with a ReLEx enhancement? As this technique evolves and if other manufacturers want to follow Carl Zeiss Meditec, Inc., new systems must have low energy (approximately 200 nJ per photodisruptive spot), have a high hertz rate (500), not applanate the cornea, and have the ability to scan with incredible accuracy in three dimensions.
From a clinician’s standpoint, it is quite clear that, if designed properly, a femtosecond laser is a breakthrough for corneal microsurgery. Very soon, it should be apparent what impact a femtosecond laser can achieve as a stand-alone refractive surgical device.
John F. Doane, MD, specializing in corneal and refractive surgery, is in private practice with Discover Vision Centers in Kansas City, Missouri, and he is a clinical assistant professor for the Department of Ophthalmology, Kansas University Medical Center. He is a consultant to Carl Zeiss Meditec, Inc. Dr. Doane may be reached at (816) 478-1230; email@example.com.
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- Barraquer JI.Results of myopic keratomileusis.J Refract Surg.1987;3:98-101.
- Barraquer JI.Method for cutting lamellar grafts in frozen corneas:new orientations for refractive surgery.Arch Soc Am Ophthalmol.1958;1:237.
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- Doane JF,Jackson RT,Slade SG.Mechanical microkeratomes versus laser keratomes.In:Brightbill E,McDonnell,PJ, McGhee CNJ,Farjo AJ,eds.Corneal Surgery,Theory,Technique and Tissue.4th ed.Philadelphia,Pennsylvania.2008.