The Pulsion FS Laser, a femtosecond laser from IntraLase Corporation of Irvine, California, is the first new modality for lamellar flap creation since José I. Barraquer first devised the microkeratome in the late 1950s. Though the Pulsion laser is intended to replace the microkeratome, surgeons who have used it feel that the two technologies will coexist. The question is, will the femtosecond laser remain a glorified microkeratome, or will its applications expand beyond its current approval to change the way we do LASIK?
How It Works
Approved by the FDA in December of 1999, the Pulsion FS Laser, according to Trudy Larkins, Vice President of Marketing at IntraLase, is a focal laser that uses a beam of light to focus on a predetermined depth within the corneal stroma. It delivers pulses of light in a spiral pattern to create a horizontal or vertical cleavage plane on the cornea. This creates a microplasm that vaporizes approximately 1 µm of corneal tissue. A tiny bubble of gas and water forms, separating the corneal lamellae as it expands. The by products of this photodisruption are carbon dioxide and water, which are absorbed by the action of the endothelial pump. Thousands of laser pulses are then connected together in a spiral pattern to create a cleavage plane. “It creates a planar dissection in the stromal bed,” Larkins says. Gas and water are then either absorbed or released when the corneal flap is lifted.
Custom Flaps
The Pulsion FS Laser allows surgeons to customize flap parameters by programming the system's software to any desired diagram. Larkins explains how the laser is programmed to leave an uncut section on the top of the cornea for a hinge. “Really, you can place the hinge anywhere you want on the cornea,” she says. “You can make the hinge as wide or as narrow as you want; you can also adjust the architecture of that side cut, which of course is impossible with a blade and microkeratome.” Lee Nordan, MD, of Carlsbad, CA, adds that the surgeon can set the laser for a temporal flap, a nasal flap, or a superior hinge, and that he or she is able to determine the thickness and depth of the flap. He says that surgeons can also change the edge to a beveled or perpendicular cut. Stephen Slade, MD, of Houston, TX, says that the laser positions the flap interface “very close to where you want the depth to be,” which in most cases is 180 µm deep.
Another benefit that the laser offers for flaps is consistency in cutting. With the laser, surgeons will always get an accurate measurement of their cut, whereas microkeratomes may not produce the exact desired flap thickness, or may produce a flap that's thinner in the center than on the sides. “With many microkeratomes,” says Dr. Nordan, “I think that when they try to cut a 160 µm flap they really cut 140 µm. The flaps may be a lot thinner than we think. If you try to cut a 130 µm flap and you actually cut a 110 µm flap, the chance of inducing irregular astigmatism will go way up. Using the laser makes it easy to know that we have a thinner-than-normal but legitimate 145 µm flap.” IntraLase says that their product addresses this increasingly important issue for surgeons. “If they ask for a 160 µm depth, they're going to get 160 µm depth with our laser cut, as opposed to the microkeratome,” says Larkins.
Larkins also adds that the Pulsion laser is very precise in making flaps. She explains that when the spots are consecutively lined up next to each other, the result is very good tissue dissection that is comparable to the precision of a microkeratome blade. “Dr. Dishler has very good flap separation with his laser, and his flaps pull back just like they would with a regular keratome,” she says.
Safety
Safety is one of the laser's major selling points. Because the surface of the cornea is the last layer reached by the laser, any mishaps during LASIK surgery, such as a break in suction, can be resolved—the surgeon only has to interrupt the procedure until the bubbles created by the laser dissipate, and then the procedure can resume. “If you had to stop for any reason, you could wait a half hour and do the case all over again,” says Dr. Nordan. Dr. Slade thinks that this aspect of the laser is appealing. “It does have a very nice safety aspect to it,” he says. “Whereas with a keratectomy, you cut into the eye, then cut across, then cut out—with this, you make the actual bed of the flap as the first step, so you're not really disturbing the surface of the eye until the last pulses.”
Larkins points out that the laser eliminates the waiting time that the microkeratome requires if there is a complication during LASIK. “We don't abort procedures with the laser approach,” she says. “There's no waiting as with the microkeratome; if the keratome jams half way across, you have to put the partial flap back down and wait approximately 3 to 4 months until it heals before you can recut.”
Another feature of the Pulsion is that it has an extremely low rate of inducing astigmatism, causing an epithelial defect or abrasion, or any of the other flap-related complications that microkeratomes sometimes experience. “Nothing is traveling across the top of the cornea; [the laser] is focused down into the stroma, therefore, it's almost impossible to get an epithelial defect or an abrasion,” says Larkins. In a multi-center clinical trial in which Drs. Slade and Nordan participated, 314 eyes received LASIK surgery using the laser keratome, and then were followed for 6 months postoperatively. According to the abstract published in the 2001 ISRS summer conference program, there were no reported complications or adverse events. Results of visual acuity were consistent with published data on LASIK outcomes, with 91% of eyes having UCVA of 20/20 or better, and 78% of eyes within 0.5 D of emmetropia at 6 months.1
So does the laser really improve on the safety of the microkeratome? Dr. Slade doesn't think it's a question of one option being better than the other. “It doesn't necessarily improve upon the safety of the microkeratome,” he says. “We can't say one is safer than the other, we can just say that they have different safety characteristics.” With the laser you can control the diameter, the edge and angle, and the depth very precisely. But the microkeratome would give you a smoother cut and a more complete bed.” When interviewed, Dr. Slade was using a beta model Laser, which sometimes produced adhesions when trying to lift the flap. Jon Dishler, MD, of Englewood, CO, also experienced this flap “stickiness” with his beta laser. “You really had to tug on it pretty well to lift it up, and those patients had some mild edema or swelling the first week after their surgery,” he says. IntraLase has since modified the laser to address those early concerns, and Dr. Dishler says that he's very happy with the results of the current production model laser. “We've been using it for about a month,” he continues, “and the amount of stickiness is much less. The flaps lift up more easily and there's very little edema at one day.” Larkins attributes the improved results to the production model's fine-tuning, which she says provides better spot size maintenance and better overall reproducibility.
Other Improvements
One other postoperative effect of the beta FS Pulsion Laser that Dr. Nordan noticed was that visual recovery took slightly longer than with a traditional microkeratome blade. He felt that with the beta model, visual recovery tended to be about one line less than the microkeratome blade in the first few days following the procedure. However, this delayed “wow” effect has also been improved in the production model, and Dr. Dishler reports that the laser is “very comparable to traditional microkeratome flaps in terms of patient vision and patient satisfaction at one day.” Dr. Dishler says that on average, about half of his laser patients are seeing 20/20 at one day postoperatively, and most (about 95%) are seeing 20/40 or better. “Now, I think that recovery is just as quick or nearly as quick as with the standard microkeratomes,” adds Dr. Dishler.
According to Dr. Nordan, long-term results for the femtosecond laser also seem to be equal to those of the microkeratome. He has performed surgery on approximately 500 eyes with the femtosecond laser over the past year, and says that the long-term results are virtually identical to his microkeratome cases. “The majority of the patients are out more than 6 months,” he says, “and it's statistically identical to the microkeratome.”
Time in Surgery
One other note that Dr. Nordan makes about the laser is that it might take a little longer to use during surgery than the blade, but he doesn't see this as a negative aspect of the laser. “It might take a minute or two longer to do the case, maybe 2 minutes per eye,” he says, “but I don't see that as a real drawback.” He says that the all-laser procedure takes approximately 2 minutes to prepare, and to make the flap takes about 1 minute, whereas the microkeratome might take 30 seconds.
Quality and Control in the Cut
Dr. Nordan feels that the differences between the femtosecond laser and the microkeratome blade don't really relate to quality, but reiterates that safety is the main issue. “An excellent microkeratome case and an excellent laser case do equally well,” he says. The benefit of the laser lies in the fact that the chance of inducing irregular astigmatism or of having a problem with the flap is remote. In addition, the technology has been proven to be accurate within 5 µm, according to the company. However, Dr. Nordan feels that the femtosecond laser does not offer any more surgical control over the microkeratome blade other than the ability to customize the flap.
The Laser and the Blade: Domination or Coexistence?
Although IntraLase says that the Pulsion FS Laser is intended to replace the microkeratome and turn LASIK into an all-laser procedure, Drs. Nordan and Slade don't think that surgeons will be abandoning their blades just yet. However, they say that there are particular situations in which the laser is a better choice, such as in cases of high ranges of myopia, in which Dr. Nordan prefers the laser; or when a thin flap is particularly favorable, or for those patients who are afraid of a blade procedure. Even so, Dr. Nordan says that he'll continue to use his microkeratome blade in surgery. “There's no doubt that the laser and the microkeratome will coexist. I don't think that one is going to drive the other out; I think they'll both have their place and they'll both be used extensively, but that it will be coexistence rather than domination,” he says. Dr. Slade points out that the microkeratome is a simpler instrument with far fewer moving parts, and that the microkeratome has more of a history than the femtosecond laser. “We have a vast experience with regular microkeratomes,” he notes. He says that right now, he uses the microkeratome for the majority of his cases. Dr. Dishler, on the other hand, believes that there will come a day when surgeons will no longer be using blades to make flaps, and that LASIK with evolve into an all-laser procedure. “If we have a procedure that uses all disposables and also is solid-state, it seems like that's going to have to replace the current technology,” he says.
The laser will be sold on a fee-per-procedure basis, and will include all hardware, software, and service, as well as all disposables. IntraLase has begun rolling the laser out regionally starting with southern California, and plans to officially launch the laser this November at the American Academy of Ophthalmology meeting. Larkins says that next year's goal is to have the laser available in every major U.S. metropolitan area.
What's In a Name
In the hopes that the Pulsion FS Laser will turn the LASIK procedure into a laser procedure, IntraLase has termed the combination of the two technologies IntraLASIK. They will market the name to trigger doctor and consumer recognition between LASIK using a blade and LASIK using the Pulsion FS Laser. “There's a very strong marketing aspect to this,” explains Larkins. “IntraLASIK is a new technology that gives consumers a new level of confidence in the LASIK procedure, which is something that we hope helps the industry grow.”
Future Applications
The femtosecond laser's most interesting aspect may be its potential for other applications. According to Larkins, IntraLase began feasibility studies in April with Arturo Chayet, MD of Tijuana, Mexico for an intrastromal refractive procedure. The technology would enable surgeons to create a refractive correction completely intrastromally, without any flap or wound to the top of the cornea. Dr. Chayet says that so far, they've tested the procedure for very low hyperopia, up to 1.5 D. “You will do an ablation of the tissue and the cornea, the stroma will collapse at that point, and will acquire the new shape,” he explains. Dr. Chayet adds that he is investigating an application for creating the channels for intracorneal rings. “There's no need to do an incision,” he says, “you just create a channel.” He is also looking into applications for penetrating keratoplasties, as well as lamellar transplants, in which the laser would be used to exchange the superficial layers of the cornea that may be damaged by refractive surgery, instead of removing the entire cornea.
Larkins says that the company has also had success with intrastromal hyperopia correction, and that it's starting to work on intrastromal myopia. “If we could correct an area of nearsightedness or farsightedness without creating a flap, no healing would be involved. There would be no pain, and antibiotics would be unnecessary, which is obviously a big deal,” says Larkins. “Taking it to the next step, to see if we can use the laser to correct refractive error without even making a flap, is going to be very exciting, and has a potential that the microkeratome doesn't.” The company will be expanding to other clinical sites outside the United States this year, and presenting those results at the AAO meeting in November, she says.
Dr. Slade is also interested in other applications for the laser. “ I think it's an incredible technology that has tremendous potential,” he says, “maybe doing intrastromal ablations, maybe treating the lens of the eye, or for presbyopia. So far it's been used to make T-cuts, to treat lenses, and as a presbyopia treatment in monkeys.” Dr. Dishler sees potential in combining the laser with wavefront technology. “It could be used with wavefront analyzers to improve aberrations so that people could have very slight modifications made to their eyes to make them see even better.”
Lee T. Nordan, MD is in private practice at the Nordan Laser Eye Medical Group in Carlsbad, California. (760) 930-9696; laserltn@aol.comStephen G. Slade, MD is National Medical Director of the TLC Laser Eye Center in Houston, Texas. (713) 626-5544; sgs@visiontexas.com Jon G. Dishler, MD is in private practice at the Laser Institute of Rockies in Englewood, Colorado. He has performed more femtosecond procedures at time of publication than any other surgeon in the world. (303) 793-3000; jond@dishler.com
Arturo S. Chayet, MD, is in private practice at the Codet Laser Vision Center in San Diego, California, and also at the Codet Laser Vision Center in Tijuana, Mexico. (619) 662-4999; codet@infosel.net.m
1. Slade SG, Nordan LT, Schanzlin D, Chayet AS: Results of a Prospective, Multi-Center Clinical Trial of a Laser Keratome. ISRS Abstract, 2001.
