FS Laser: Not Ready For Prime Time
Looking at outcomes for evidence of a superior technology, this surgeon says the femtosecond laser has not reached its potential.

Constructing the lamellar corneal flap is the most important part of a LASIK procedure, and to that end, microkeratomes have been the state of the art for the past 10 years. During this time, they've made significant developmental leaps. With respect to safety and efficacy, today's mechanical devices bear little resemblance to the manual microkeratomes of earlier days.

This new generation of mechanical microkeratomes is now facing a challenger in the form of the IntraLase femtosecond (FS) laser. In this article I'll recount my experiences with both technologies.

FS Laser Overview

The IntraLase uses pulses of FS laser (10-15) at near-infrared (1,053 nm) wavelength. The pulses are focused to a diameter of approximately 3 microns in the target corneal tissue. As a low-pressure suction ring holds the eye, approximately 10,000 pulses are placed in a contiguous fashion to create the lamellar dissection. The pulses are stacked vertically around the flap periphery to create the gutter, with sparing of one peripheral section for the hinge.

The flap size, thickness, edge angle, hinge width and hinge location can be varied according to the surgeon's preferences.

Accuracy and Risk

While I don't own a FS laser, I've used one; and I've also managed complications that have arisen from cases in which they've been used by other surgeons.

On first glance, the FS laser offers some advantages. For instance, some surgeons suggest that the laser is more accurate than a conventional microkeratome, and that less risk is involved. The questions are: Are these advantages real, and are there problems with the FS laser that we don't see with the newest generation of mechanical microkeratomes?

For the past 5 years, I've been using the Amadeus microkeratome, which I believe best represents the new generation of microkeratomes. The Amadeus provides a tremendous degree of flexibility, security and quality of flap formation, and it enables me to adjust patient parameters to achieve optimal results. The ability to adjust hinge thickness, flap size, suction and translation speed as well as cutting rate enables me to fine-tune the LASIK flap in a qualitative manner.

Increased accuracy of flap thickness is a supposed benefit of the IntraLase FS laser keratome, however, the only quality paper I've seen on this subject (Binder PS. Flap dimensions created with the IntraLase FS laser. J Cataract Refract Surg. 2004;30:26-32) shows an 18.5-micron variability in flap thickness standard deviation using the IntraLase. This is about the same as we've experienced and published using the Amadeus microkeratome.

The IntraLase may be somewhat more accurate in flap thickness, but I don't think it's dramatically more accurate. Because it's easy to use and may have a slight edge with respect to producing accurate flap thickness, it may prove beneficial to surgeons who don't regularly use a microkeratome.

On the other hand, surgeons who perform a moderate volume of LASIK procedures a month and are very facile with a microkeratome probably make a flap that's as good as or better than an IntraLase flap.

The FS laser is predicated on the idea that it's a bladeless procedure and because of this feature, its marketing suggests that it's a safer procedure. However, it's important to note that no long-term studies exist to support this assumption. Having managed a series of complications arising from cases in which other surgeons have used the FS laser, I question the connection between reduced risk and absence of a blade.

In comparing the FS laser with state-of-the-art mechanical microkeratomes, we need to look at visual acuity outcomes, complications, visual recovery timeline and cost.

By all accounts, reports of visual acuity outcomes achieved with the FS laser are essentially indistinguishable from the outcomes I achieve with the Amadeus. And reports of increased FS-related diffuse lamellar keratitis (DLK), bed dehydration and delayed visual recovery have made their way into the anecdotal annals of refractive surgery -- although not, as yet, into the literature.

The overriding downside, however, that the FS laser has in comparison to mechanical microkeratomes is cost.

Is There Added Value?

At about $300,000, the FS laser costs roughly six times what a mechanical microkeratome costs. While microkeratomes have the additional cost of disposables, the FS laser has a per-procedure user fee of about $150. In addition to the obvious concern that the laser is a much more costly piece of equipment to buy, there's another concern that it's a much more costly piece of equipment to operate. This concern stems from the fact that it takes significantly longer to perform LASIK using the FS laser than it does to perform LASIK using a mechanical microkeratome.

Because the FS laser user fee usually is passed on to the patient, I'd argue that patients are not necessarily gaining any extra value for their money. In fact, not only is there no added value, I believe the FS laser may be detrimental because when the flap is created by the laser's microablation of multiple spots, the ablation actually removes tissue from the stromal bed.

Compare this to a microkeratome ablation, where no tissue is removed. You're dissecting within a plane of tissue and when the flap is placed back onto the bed, it can return to its previous position. No tissue has been removed, so the cornea is left as it was before you started.

Interface Irregularity

Once tissue is removed from the stromal bed, the flap can't go back to its virgin position. The flap has to reseat itself, so the interface can't possibly be as smooth as it is with the conventional microkeratome. This is why almost all FS laser users will confirm that the return of visual function takes longer with this technology than with a microkeratome -- because it takes time for the bed to reposition itself and for the surface to become more regular.

Some surgeons report anecdotally that another byproduct of tissue removal by the FS laser ablation is a greater degree of inflammation than when a microkeratome is used. This inflammation is associated with higher incidence of DLK after LASIK with the FS laser than after LASIK with a conventional microkeratome.

Finally, because tissue has been removed and the flap is not sitting in its normal position, it can move within the stromal bed because the bed is now larger than the flap. For this reason, we've seen a number of patients with microfolds following LASIK with the IntraLase laser. The following is an illustrative case.

Slit lamp photomicrograph of the flap folds (OD and OS) at the time of initial consultation.

Bilateral Flap Folds Post FS Laser

Last year, my colleagues and I reported on a case in which a 43-year-old patient had bilateral flap folds from a surgeon who had not previously had a problem with flap folds (Biser SA, Bloom AH, Donnenfeld ED, et al. Flap folds after femtosecond LASIK. Eye Contact Lens 2003;29:252-254).

In this case, preoperative topographic analysis with the Orbscan showed regular astigmatism OU; and the simulated keratometric readings were 46.9 @ 64/46.2 @ 154 OD and 46.2 @ 108/45.5 @ 18 OS. Corneal thickness measured optically with the Orbscan, was 558 µm OD and 554 µm OS. The flaps were created with the IntraLase programmed to 130-micron flaps with a diameter of 8.8 mm and a superior hinge.

Following excimer ablation with the LadarVision laser for a correction of -7.00 -0.50 x 136 OD, -7.00 -0.50 x 180 OS, bandage contact lenses were placed and removed after 2 days. Upon removal of the bandage contact lenses, the patient noted significant visual disability with glare and halos and was diagnosed with corneal striae by the treating physician.

When we examined the patient later, we noted marked vertical flap folds (see photos above). We lifted the flaps and performed 5 minutes of stretching; however, the folds and visual symptoms remained. We then sutured the flaps. Slit lamp examination revealed marked resolution of the corneal striae, and the patient reported improvement in her symptoms. Her uncorrected visual acuity was 20/30 OU, correctable to 20/20 OU.

This case shows that although the FS laser may indeed provide increased accuracy in flap creation, large visually disabling flap folds can develop.

Promise Not Yet Fulfilled

The IntraLase FS laser is a wonderful technology that has improved dramatically over the past 2 years, and I expect it will continue to improve. However, until some evidence suggests that it provides visual acuity benefits over those of conventional microkeratomes along with its additional cost and the additional time it takes to perform and recover from, I won't consider offering it to my patients.

Essentially, I think many surgeons who have invested in a FS laser are using it as a marketing tool similar to how 'up/down LASIK' or 'flying spot LASIK' were used to suggest to patients that a particular technology would effect a more precise outcome. Today, surgeons are using the concept of bladeless LASIK to attract patients, but they're using it without documented evidence that it is better.

Dr. Donnenfeld is in private practice at Ophthalmic Consultants of Long Island, in Rockville Centre, New York. He is a consultant to AMO.