The evolution of LASIK surgery over the past several years has been impressive. The ever-increasing safety and accuracy of the procedure has afforded patients unprecedented outcomes in terms of quality and quantity of vision, and in return it has sparked greater interest in laser vision correction. With these improvements have come heightened expectations in terms of visual performance outcomes as well as procedural safety. Despite greater and recent interest in surface-based laser procedures, LASIK remains the procedure of choice for the majority of surgeons and patients. The greater degree of postoperative comfort and rapid visual restoration make LASIK the procedure of choice, and this fact cannot be denied. Although we have developed a greater sophistication in terms of LASIK surgery, we continue to struggle with flap creation techniques and technology; flap safety remains the greatest barrier to successful procedure completion and visual outcome.
Clearly, patients have become sophisticated in terms of their ability to understand the differences between various laser platforms as well as choose a flap creation technology. Traditionally, flap creation—for the purpose of excimer vision correction surgery—has been a potential source of complications including corneal epithelial defect creation, buttonhole formation, epithelial cell ingrowth, flap slippage, striae formation, and diffuse lamellar keratitis. These potential occurrences remain among the greatest threat to a patient's vision following LASIK. Fortunately, these potential flap complications have decreased in frequency by a significant extent, and thereby afford patients enhanced safety.
THIN-FLAP LASIK
Concomitant with procedural safety advancements, the trend has moved toward creating thinner LASIK flaps. Potential advantages of this surgical technique include reduced induction of postoperative dry eye1 and the ability to minimize ectasia risks by allowing a greater in-the-bed residual corneal thickness following laser ablation. Thinner appears to be better: Thin-flap LASIK has neither created greater problems in terms of a surgeon's ability to handle a flap or greater incidences of flap striae or slippage.
Consequently, the importance of consistently thin flaps has grown significantly in recent years. The jury appears to still be out in regard to the appropriate degree of flap thinness, however, current opinions seem to agree that 100- to 110-µm flaps seem safe. At this depth, flaps can also be made consistently.
In terms of technological choices for flap creation, surgeons are now faced with the decision to perform LASIK with a traditional microkeratome or femtosecond laser. Laser technology has clearly evolved and improved over recent years; the speed and consistency of this equipment has made it a viable consideration for surgeons. The significant expense of this technology, though, makes it cost prohibitive for many practices, surgeons, and patients.
Some studies have implicated a potential advantage of LASIK procedures that incorporate femtosecond laser technologies, such as lower incidences of dry eye, greater patient safety, and greater flap stability. But, these comparisons are frequently made in relation to previous-generation mechanical microkeratomes. To make valid comparisons, contemporary studies that compare modern microkeratomes with lasers that create LASIK flaps need to be undertaken. If modern microkeratomes are to be as safe and consistent as femtosecond technologies, then the flaps created with this modality must be as planar as possible and of a predictable and consistent thickness. Examples of such devices include the Carriazo-Pendular (Schwind eye-tech-solutions, Kleinostheim, Germany) and the Hansatome XP (Bausch & Lomb, Rochester, New York) microkeratomes.
Specifically, Schwind's microkeratome has a unique convex-shaped head (Figure 1) that creates greater central applanation as the device is passed over the cornea. This shape affords the creation of a more planar flap than previous-generation microkeratomes (Figure 2). Therefore, these flaps are more uniform than those created by a femtosecond laser. I performed a clinical investigation of the Carriazo-Pendular microkeratome in terms of flap thickness and consistency. Using a 110-µm keratome head, we performed uncomplicated LASIK on more than 200 patients. The average flap thickness was 111.3 µm (standard deviation, 11.8 µm). This measurement compares favorably with femotosecond lasers for flap creation.
OTHER CONSIDERATIONS
Surgeons comparing flap creation technologies must take additional considerations into account. Understandably, one can observe that laser and microkeratome flap-making devices can create epithelial defects, incomplete flaps, central buttonholes, or inconsistently thin/thick flaps. Potentially significant corneal inflammation events can occur in the form of diffuse lamellar keratitis with both technologies, and potentially devastating central toxic keratopathy has been observed with IntraLase (Advanced Medical Optics, Inc., Santa Ana, California) laser technology as well. Initial postoperative patient discomfort does not appear to vary significantly between mechanical microkeratome and femtosecond laser procedures, although it has been my personal observation that patients do report a trend toward greater discomfort in the initial few hours after a femtosecond laser procedure.
Surgeons are faced with continued challenges in laser vision correction. They must continue to evaluate the science as well as the current trends to maintain the greatest patient safety and deliver the utmost visual outcomes. Existing and emerging data support thin-flap LASIK2 for those reasons previously discussed. What is less compelling, however, are the data suggesting that LASIK procedures performed with a femtosecond laser are superior to those performed with the most contemporary mechanical microkeratomes.
Practically speaking, cost will remain a serious consideration until the time that the acquisition of all-laser technologies for most LASIK surgeons becomes competitive with that of a mechanical microkeratome. Further complicating a surgeon's decision is the fact that modern-generation mechanical microkeratomes can make LASIK flaps of a similar and reproducible nature to those made with a laser.
The ultimate decision of which path for flap creation is chosen should be made based on current published data, a surgeon's personal experience and outcomes, as well as documented and proven advantages for patient safety. My current preference is for a modern mechanical microkeratome, because I believe that it offers very acceptable patient safety and a cost-effective means to having LASIK for the patient and surgeon. The fact that a femtosecond laser LASIK procedure is more expensive does not make it better. To those who claim superiority of a femtosecond laser procedure, I challenge them to show me the data that prove an advantage for patients, as this should always be our ultimate consideration. Until such time, the mechanical microkeratome is not dead.
Stephen E. Pascucci, MD, FACS, is Medical Director, Eye Consultants of Bonita Springs, and Affiliate Assistant Professor of Ophthalmology, University of South Florida. Dr. Pascucci states that he is a consultant to Allergan, Inc. (Irvine, California) and AcuFocus, Inc. (Irvine, California) and receives travel support from Allergan, Inc. and Schwind eye-tech-solutions. Dr. Pascucci may be reached at tel: +1 239 949 2021; fax: +1 239 949 1500; or sep@bonitaeye.com.
