In a competitive market such as refractive surgery, the introduction of new technologies is a decisive fact. Such is the femtosecond laser, a device initially designed to entirely carry out a refractive procedure—without having to cut a stromal flap. This technology has the potential to revolutionize the way we perform refractive surgery. But, are we too quick to jump the gun? Should the femtosecond laser be considered the gold standard of refractive surgery?

Early clinical trials accomplishing refractive error correction with current-state femtosecond technology have not surpassed the results obtained with excimer laser technology. In fact, several limitations were revealed about the femtosecond laser, which is primarily used for cutting stromal flaps. The use of an excimer laser, however, is obligatory to achieve the desired refractive correction.

With its ability to remove corneal tissue at an accuracy up to 0.25 µm with each pulse, the excimer laser is the most precise tool ever released for vision correction. Its cool (ie, nonthermal) light beam makes the excimer laser ideal for corneal surgery, because it eliminates the risk of thermal damage to the surrounding tissue.

One of the most promising applications for corneal surgery with femtosecond technology is lamellar surgery. In short, the femtosecond laser is the ideal instrument to carry out stromal tissue cuttings, whereas the excimer laser remains the ideal tool to sculpt the corneal stroma.

LASER TECHNOLOGY AND FLAP CUTS
Cutting the flap with a femtosecond laser has certain advantages compared with mechanical cuttings, but it also has certain drawbacks. Here is the implicit question behind this statement: Is it really worth switching from mechanical to laser flap-cut technology? The answer may depend on multiple parameters—including how large one's refractive practice is, how long one has been practicing refractive surgery, and the patient workflow within the practice—but it still seems unobvious today.

The improvement in security claimed by femtosecond laser companies must be balanced with the current rate of mechanical flap cut complications encountered when using a modern microkeratome (eg, Zyoptix XP [Bausch & Lomb, Rochester, New York] and the Moria M2 [Antony, France]). In our institution over the last 3 years, thousands of consecutive flaps were cut using mechanical microkeratomes, without incidence of severe flap-cutting incidents (eg, buttonhole or disrupted flaps). Patients were carefully selected, and we excluded patients in which eye exposure or orbital conformation was judged incompatible for LASIK. Although rare, cases of flap cut complications occurring during femtosecond LASIK are reported.

We studied flap quality by analyzing any changes caused by flap cut in patients scheduled for bioptic procedures. No significant visual impairment due to the mechanical nature of the cut was noted. In some cases, we even noticed a reduced higher-order aberration root mean square after the cut was made.

Increasing flap centration quality is a legitimate way to improve postoperative outcomes, because a decentered flap may significantly increase the higher-order aberration root mean square through direct coma induction or by impairing the proper deliverance of excimer laser treatment on an insufficient stromal bed. Customizing the hinge location to each patient's optical or biomechanical profiles would represent an improved surgical outcome, however, this achievement requires further modeling and clinical studies.

Femtosecond technology does not eliminate interface complications after LASIK, as an interface within the corneal stroma is still created. In fact, an increased incidence of interface reaction after femtosecond cuts—probably due to the biological response to laser energy—may occur. Each impact of delivery in the stromal tissue creates acoustic shock waves; although these phenomena are extremely short and the energy is only several microjoules, they are repeated thousands of times within the stroma to achieve flap creation. The short- and long-term consequences of this, and the plasma effect presiding over the femtosecond-disrupting effect, are not fully known. The exact amount of tissue consumed during plasma generation may vary with the level of energy required to achieve the tissue cleavage. In a patient who had femtosecond flap cuts in both eyes, without subsequent excimer photoablation (ie, bioptic procedure), we noticed a slight decrease in the corneal pachymetry (-10 µm) 1 month postoperatively. It is hard to prove that this reduction would be consecutive to tissue plasmatization or stromal remodelling.

One crucial element of flap cut quality evaluation is the reproducibility of the cut. Femtosecond lasers have reduced—but not cancelled—the variation in the obtained flap thickness standard deviation, although newer microkeratomes may do similarly well. We have now reached the conviction that some corneas may not benefit from LASIK at all, even in the presence of a thin flap. In these patients with thin and slightly asymmetrical corneas, surface ablation may be the best procedure, in both predictability and safety.

Additionally, I see no clinical benefit of cutting particularly thin flaps for the correction of hyperopia or mixed astigmatism—provided that the total LASIK procedure would leave a posterior stromal thickness of between 250 µm and 300 µm. Positive corrections spare central tissue ablation. Large and thin flaps may increase the risk of flap striae, and slippage in these corrections where the stroma is underlying the flap undergo important geometrical modifications.

The cost associated with the femtosecond flap-cut procedure must be taken into account in the business model of the eye center. Acquiring a femtosecond device and the use of disposable components for each surgical procedure results in an increase of each procedure's cost. This increase must be compensated for; the patient's workflow rate must increase.

Additional expenses aimed at advertising and marketing femtosecond technology may also represent a significant cause of increased expense. In Europe, however, patients tend to select the center—and physician—because they have confidence in their reputation, not because of Internet research or marketing. The latter is the trend in the United States. Whatever the means of selection, a center may see more referrals by acquiring this technology. Most patients find no-blade technology an attractive alternative, however, given the cost of femtosecond technology, the odds of receiving little or no benefit with this advanced technology must be predicted with a good probability before its purchase.

Current femtosecond flap-cut technology does not reduce surgical time. The fastest femtosecond machines deliver flap cuts in approximately 30 seconds, whereas a mechanical microkeratome flap cuts last less than 15 seconds. Moreover, (1) patients must be transferred from the femtosecond bed to the excimer laser bed, and (2) some interfaces require extra time for gas bubbles to clear up. Both cause additional time when compared with conventional mechanical LASIK.

In conclusion, the advantages of the femtosecond laser over mechanical microkeratomes are sound. Each surgeon, depending on practice type and experience, must carefully address the costs and benefits of switching to femtosecond technology. The early promises of full refractive correction with the femtosecond laser have not yet been met. The ergonomy of the combined femtosecond and excimer laser procedure may not be as good as that of conventional LASIK, and the refractive results of an uncomplicated LASIK procedure depend heavily on the excimer laser ablation, not on subtle flap characteristics. Beyond the marketing aspects of the femtosecond all-laser procedure, LASIK remains a challenging technique that requires expertise in preoperative evaluation, technical execution, and postoperative follow-up. The flap-cutting step is only that—a step. Even if its proper execution governs the outcomes of the procedure, it is only one step in refractive surgery. I believe that technologies and techniques aimed at improving proper delivery, centration, and optical efficiency of the excimer laser are probably more important to improve the already very satisfactory results of current LASIK surgery. I see no reason why patients cannot undergo an operation with mechanical LASIK– provided that they undergo careful selection and receive this technique from well-trained surgeons using modern mechanical microkeratomes.

In my opinion, it is still too early to tell if femtosecond laser technology should be the gold standard of refractive surgery. With the right improvements and advancements in its technology, the femtosecond laser may be the gold standard in the future. We will just have to wait and see.

The following two articles, the first by Suphi Taneri, MD, and the second by Emilio Balestrazzi, MD; Luigi Mosca, MD; Romina Fasciani, MD; and Luca Mosca, MD, demonstrate both sides of the argument.

Damien Gatinel, MD, PhD, is a cataract, corneal, and refractive surgery specialist. He is the Scientific Director of the Refractive Surgery Unit and Assistant Professor at the Rosthschild Ophthalmology Foundation and Bichat-Claude Bernard Hospital, in Paris. Dr. Gatinel is a member of the CRST Europe Editorial Board. He states that he has no financial interest in the products or companies mentioned. He may be reached at +33 1 48 03 64 86; gatinel@aol.com.