IntraLASIK in Our Practice
Practical advice for surgeons adopting, or considering adopting, the femtosecond laser for flap creation.
BY CHARLES C. MANGER III, M.D.

Our experience in more than 12,000 cases in the past two and a half years is that IntraLASIK offers highly consistent flap thickness and architecture. Because of this, our incidence of flap-related complications has been reduced, and our enhancement rate has dropped from 4% to 5% to less than 2% (ASCRS presentation, May 2004). The IntraLase FS laser keratome has been relatively easy to integrate into our practice and has added to the practice's "advanced technology" image. In this article, I'll elaborate on several aspects of our experience.

The Procedure

The femtosecond laser utilizes a focused infrared beam to create photodisruption below the corneal surface, without generating heat or ablating tissue. To begin the process, the surgeon attaches the suction ring to the patient's eye and applies approximately 29 mmHg of pressure (compared with 60 to 80 mmHg with a typical microkeratome). The IntraLase docking cone should be brought down right over the center of the pupil. By squeezing the suction ring the surgeon expands it a little bit to "grab" the docking cone and adjoin the laser to the cornea. When everything is aligned, centration can be adjusted by using first the IntraLase joystick and then the computer mouse to center the corneal cap on the pupil. Excessive mouse centration movement will reduce the corneal cap diameter.

After achieving proper centration, the surgeon steps on the foot pedal to start the bed cut. The laser puts down a layer of bubbles in a single predetermined plane at whatever flap depth has been set. The size of the hinge is also preset. In my case, I generally set a 65š hinge. After the bed cut, the laser moves directly into the side cut. I prefer an almost vertical, 80š side cut. There is no consensus on this among IntraLase surgeons, however, and some use a much more oblique angle.

In making the side cut, the laser joins the surface of the cornea to the bottom of the bed at the periphery to form the outline of a completed cap. The last step, which we perform in the excimer room right before the ablation, is to lift the cap. Some of the tissue attachments are still there, but the laser bubbles have weakened them so that a spatula can easily lift the cap. Lifting the IntraLase cap requires more force on the spatula than lifting a microkeratome flap. The main difference is that with the steep IntraLase side cut I prefer, it's a little more difficult to atraumatically get into the bottom of the gutter and across the bed with the spatula.

Clinical Advantages

The greatest clinical advantage of this laser is the degree of precision in cap thickness. We looked at IntraLase cap thicknesses in more than 1,000 eyes between May and July 2004. In all cases, cap thickness was set for 120 microns. The mean cap thickness, measured intraoperatively, was 120 microns, with a standard deviation of just 9 microns.

In many patients, the actual flap depth compared with intended is not important. But in a highly myopic eye or thin cornea, when the amount of tissue available for ablation is key, being able to more precisely predict your flap depth can mean the difference between a successful case and an eye with surgically induced keratoconus.

The smoothness of the corneal bed following an IntraLase cut is another advantage because it leads to rapid visual recovery. The technology has improved dramatically over the past 3 years since its initial reputation for somewhat rough beds and slower visual recovery. Still, proper calibration of the laser is essential to ensure smooth corneal beds and excellent 1 day post-LASIK visual acuities.

In a study I presented at last year's AAO meeting, 1 day postoperative acuity with the IntraLase keratome was statistically better than our outcomes with the Hansatome. In fact, more than twice as many IntraLase patients as Hansatome patients saw 20/15 uncorrected the first day after LASIK surgery.

Finally, the IntraLase laser provides the surgeon with a uniformly dry corneal bed on which to do the laser ablation. With a metal keratome, some fluid is invariably introduced into the bed while making the microkeratome cut. Even small amounts of fluid can subtly alter the ablation, so a dry bed provides for much more predictable tissue removal by the treatment laser. This may have contributed to the lower enhancement rate we have experienced.

Cap Anatomy

No keratome is complication-free, but the IntraLase complication rate is much lower than with traditional keratomes. I believe this is due to the anatomy of the cap.

The laser creates a planar cap, with uniform thickness throughout, rather than being thinner centrally, thicker in the mid-periphery and thinner again at the cap periphery. Because of this, striae are less common and, when they do occur, they are less pronounced. So far, I have not had any that were visually significant and required management other than observation, except for an occasional rubbed cap 1 day post-operatively. This is efficiently remedied with smoothing and contact lens placement for 3 days. The planar shape also virtually eliminates buttonholes.

The incidence of diffuse lamellar keratitis (DLK) is extremely rare and less severe than DLK noted with metal keratomes. Surgeons who experience DLK usually do so early in their experience with the laser, when they use higher side-cut energy, or lack experience in lifting the flap gently.

A sharply angled side cut with the IntraLase contributes to a lower incidence of epithelial ingrowth and DLK. Surgeons may also experience a few more of these complications if they are inexperienced at gently lifting the cap.

Technique improvements over the years have reduced the incidence of DLK. For example, we now typically make the side cut with just 3.0 to 3.5 mJ of energy, compared with the 6.0 to 8.0 mJ used early in our IntraLase experience. We found that higher side-cut energy levels resulted in wider gutters and more interface haze and DLK. Higher side-cut energy, flap hydration, and rough tissue handling can result in a large gutter that can promote DLK; the goal should be to achieve a gutter that is as small and tight as possible.

With an IntraLase procedure, the spatula is the only reusable instrument that touches the corneal cap or bed (we use a disposable cannula) so the potential for contamination from a keratome head, cannula, or blade is reduced.

Practice Impact

One disadvantage of the IntraLase laser is a slower overall procedure time. I went from being able to do a bilateral LASIK case in about 15 minutes to about 22 minutes using IntraLase -- a reduction from eight eyes per hour to five or six. The femtosecond laser energy is delivered quickly, in just a little over a minute. However, it also takes time to center and dock the laser and to move the patient through two devices, rather than making the lamellar cut with a microkeratome at the laser.

Initially, I found that I was treating the same number of patients, but that my staff and I were all working longer hours to handle the same case load. My solution to this was to hire an associate ophthalmologist who, in addition to other clinical and surgical duties, now does the cap creation portion of the procedure in a separate room, while I lift the cap and do the ablation in the excimer laser room. The two of us now treat about 10 eyes per hour.

There is a cost to the practice for the laser, of course, but both the fixed cost and the lost time costs have essentially been balanced by an increase in our procedure fee. Because I believe that IntraLase offers the safest and most precise technology, I raised my fees by $300 per eye when we added IntraLase technology.

We use IntraLase on all patients except those with a corneal scar, previous RK, or a small pterygium. I also highly recommend a wavefront-guided procedure on eligible eyes and most of my patients choose this option, despite having to pay an additional fee for the CustomVue technology.

Although it is hard to quantify the effect on practice volume, there are definite marketing advantages with IntraLase. I think refractive surgeons underestimate the number of people who are interested in LASIK but fearful of the flap cut by a metal blade. These patients find the concept of a computerized laser very appealing and easy to understand. In fact, it is our experience that it is much easier to educate patients about the benefits of IntraLase technology than about the extremely important, but more complex, benefits of wavefront technology.

My case volume has certainly increased in the past two and a half years. I think IntraLase is one of several major factors contributing to the increase, including the improved economy and the advent of wavefront technology.

Ultimately, I think our profession will increasingly move towards laser creation of the corneal cap. Much as with phacoemulsification in the 1970s, we are seeing some initial resistance to adoption of this new technology, but I firmly believe that IntraLase provides a safer, more predictable method of creating LASIK flaps.

Dr. Manger is Medical Director of Saddleback Eye Center in Laguna Hills, Calif., and former clinical instructor with Doheny Eye Institute at the USC Keck School of Medicine. You can contact him at (949) 951-4641.