Laser microkeratome may reduce flap complications and improve visual outcome

Laser microkeratome may reduce flap complications and improve visual outcome

Sept 2003 http://www.escrs.org/eurotimes/September2003/7.asp Cheryl Guttman In San Francisco

MYOPIC "IntraLASIK" performed using the femtosecond laser microkeratome (IntraLase) and the Nidek EC-5000 excimer laser appears to produce better refractive and visual outcomes and lower rates of complications and enhancements compared to traditional LASIK, a recent study suggests. G. Peyton Neatrour, MD compared three-month outcome data from 68 eyes he operated on using a mechanical microkeratome, the Moria M2, and 46 eyes using the femtosecond laser. He presented the data at the annual ASCRS Symposium on Cataract, IOL and Refractive Surgery.

The eyes in the mechanical microkeratome group represented a consecutive series of the last eyes he operated on during August 2002. The femtosecond laser group included eyes operated on in December 2002, during the fourth month after he switched to that device for flap creation. The spherical equivalent in both groups ranged up to -7 D. He used the femtosecond laser to create flaps with a temporal or superior hinges with thickness set to 130 microns except in eyes with thinner corneas or needing higher amounts of correction, in which case he created a 100 micron flap. The Moria M2 flaps had superior or nasal hinges created with the 130 head. All data were entered into the Refractive Surgery Consultant (RSC) Elite for analysis, but the ablations in both groups were performed with a pre-RSC nomogram developed by Howard Gimbel MD.

At three months after surgery, the results showed a significant difference favouring the IntraLASIK group for better treatment accuracy, with a smaller standard deviation in the refractive error analyses and a higher rate of eyes corrected to within 1 D of intended. Those benefits translated clinically into better UCVA outcomes, and the all-laser group also experienced fewer flap-related complications and less problematic dry eye.

"With all other surgical factors the same except for the microkeratome used, the overall results were clearly better with IntraLASIK, and we expect the outcomes to be improved even further as we now use RSC software to personalise the nomogram," said Dr. Neatrour. At three months after surgery, UCVA was 20/20 or better in 63% of IntraLASIK eyes and 58% of those having the mechanical microkeratome-created flap. Some 80% of the IntraLASIK eyes versus only 61% of the mechanical microkeratome group had UCVA of 20/25 or better. The corresponding rates for UCVA of 20/40 or better in the two groups were 96% vs. 69%, respectively.

In the IntraLASIK group 67% of eyes achieved SE within 0.5 D of target compared to only 56% that had flaps constructed with the mechanical microkeratome. The difference was more striking in the analysis of eyes within 1 D of intended correction, with 94% of IntraLASIK eyes and only 68% of eyes in the mechanical microkeratome group reaching that goal.

Analyses of cylinder results showed similar scatter and predictability with IntraLASIK and the mechanical microkeratome procedure. Their mean postoperative values of 0.34±0.35 D and 0.28±0.35 D, respectively, in the two groups and nearly all eyes had less than 1 D of residual cylinder. However, in the scattergram plot of intended versus achieved spherical equivalent for examining the effect on the nomogram, undercorrections were much more common in the mechanical microkeratome group, particularly when higher amounts of treatment were attempted.

"With the laser flap creation procedure, we consistently achieve a very dry bed, whereas even after wiping the stroma with a Weckcel sponge following the mechanical microkeratome pass, there is still some residual moisture that can vary in amount and confound the accuracy of the ablation," Dr. Neatrour said. Safety was excellent overall. In both groups, approximately 15% of eyes gained one or more lines of BSCVA. While there were no cases of loss of two or more lines, a significantly higher proportion of IntraLASIK eyes than the standard treatment group temporarily lost one line of BSCVA, 22% vs. 16%, respectively.

However, all other safety analyses favoured IntraLASIK. For example, about twice as many eyes in the mechanical microkeratome group needed punctal occlusion postoperatively compared with the femtosecond laser group, 15% vs. 6.8%, respectively. "We perform punctal occlusion preoperatively in any eye with less than 6 mm of wetting in Schirmer testing, if the patient is symptomatic, or there is clinically significant superficial punctate keratitis. In this series, about 20% of eyes in both groups had punctal occlusion before surgery. We believe the reduced need for punctal plug placement postoperatively after IntraLASIK reflects the fact that the femtosecond laser procedure causes less nerve damage because it is much gentler and reliably produces a flap with a large hinge," Dr. Neatrour said.

The IntraLASIK group also had lower rates of other complications compared with the mechanical microkeratome group, including epithelial defects (1.7% vs. 6%), diffuse lamellar keratitis (7% vs. 3.5%), and peripheral striae (<2% vs. 9%). "The side architecture of the femtosecond laser flap is like a manhole cover, and that allows for better repositioning with a reduced rate of peripheral striae. Having recently adjusted our procedure by lowering the Intralase energy levels for the raster and side cut, we also expect to see further reduction in the rate of diffuse lamellar keratitis using IntraLASIK," Dr. Neatrour said.

In presenting enhancement rates, Dr. Neatrour noted that the duration of follow-up is only up to seven months in the eyes with mechanical microkeratome-created flaps and only three months for the femtosecond laser group. Against that background, he noted the overall enhancement rates have been 3% of eyes in the traditional LASIK group and 1.2% of the IntraLASIK group. Dr. Neatrour acknowledged his associates Mark A. Lipton, OD, and Guy M. Kezirian, MD, for their help with data analysis.

G. Peyton Neatrour MD Virginia Beach, Virginia, US info@beacheyecare.com

Is Intralase Better Than Microkeratomes?

Walt Bethke, Managing Editor http://www.revophth.com/index.asp?page=1_606.htm

When the Pulsion femtosecond laser first arrived, its manufacturer touted its increase in precision, along with a decrease or elimination of flap complications such as epithelial ingrowth and buttonhole flaps, as comparative advantages over mechanical microkeratomes. Recently, Intralase users have begun reporting that the laser yields better visual outcomes after LASIK, as well. Is the device preferable to mechanical microkeratomes, or do the latter still have a place? Here’s what surgeons on both sides of the debate have to say.

The Pros and Cons Kansas City, Mo., surgeon Dan Durrie, MD, says Intralase has proven its worth both in terms of flap quality and outcomes.

“You can control things with the femtosecond laser that you can’t with a microkeratome,” he says. “You can control the depth, the diameter and the position of the flap relative to the treatment zone, and you really can’t control these as precisely with a microkeratome. So, the original things that people were pushing the Intralase for, such as preventing buttonholes, incomplete flaps and epithelial defects, and enabling surgeons to control the depth better, those have proven to be true. But a lot of people, myself included, said, ‘So what? Does that translate into better quality vision?’ Now, the data is starting to be pretty convincing that it’s at least as good, if not better, than a keratome in terms of quality of vision postop.”

As evidence, Dr. Durrie offers a prospective, randomized comparative study he performed, in which 51 patients (102 eyes) received Alcon CustomCornea LASIK in both eyes. The flap of one eye of each patient was created with the Intralase and the other flap was made with a mechanical microkeratome (Hansatome, Bausch & Lomb). The patients’ average error was -4.11 D (range: -0.75 D to -7.38 D), and average cylinder was 0.46 D. (The six-month uncorrected vision results appear in Figure 1.)

“The longer we followed the eyes,” says Dr. Durrie, “it became obvious at one day, one week, and now at three and six months, that the Intralase eyes had a better quality of vision in terms of contrast sensitivity, uncorrected visual acuity and improvement of lines of best-corrected visual acuity. The Intralase was also better in terms of patients whose uncorrected vision postop was better than their best-corrected vision preop.” There were no complications in either group. Dr. Durrie says he now only uses a keratome for patients who might not be good candidates for Intralase flaps due to corneal opacities.

Another recent study found similar results with the Intralase. In the retrospective report, researchers compared the LASIK outcomes in patients with Intralase flaps (106 eyes) to those with flaps made by Moria’s Carriazo-Barraquer microkeratome (126 eyes) and the Hansatome (143 eyes).1 At three months, there was no significant difference between the groups in terms of uncorrected or best-corrected acuity. However, 91 percent of the Intralase eyes were within ±0.5 D of the intended refraction, compared to 73 percent and 74 percent of the CB and Hansatome groups, respectively. Also, when programmed for a 130-µm flap, the mean flap thickness for the Intralase group was 114 µm ±14, compared to 153 µm ±26 for the CB with a 130-µm plate, and 156 µm ±29 for the Hansatome with a 180-µm plate.

Though studies such as Dr. Durrie’s and the other mentioned above seem to give an edge to Intralase, other data render the decision less than clear cut. Atlanta surgeon Trevor Woodhams compared LASIK patients with flaps created by the laser to those with flaps made by AMO’s Amadeus microkeratome. The preop errors were -6.5 D and less, and all were operated on with Visx’s CustomView system.

At the time of his interview, Dr. Woodhams was preparing the study for presentation at the European Society of Cataract and Refractive Surgery, although he shared the observation that, at the end of three months, 94 percent of the microkeratome patients see 20/20 or better uncorrected, compared to 90 percent of the Intralase patients.

Dr. Woodhams was also disappointed with his Intralase as a result of what he considered an inordinate number of Intralase-LASIK patients reporting photophobia postop.

The photophobia appears to be an adverse event unique to the femtosecond laser, and has been reported by several surgeons under a variety of names, such as track-related iridocyclitis and scleritis syndrome (TRISC) and transient light sensitivity syndrome (TLS). However, no other surgeon thus far has reported an incidence as high as Dr. Woodhams’, which was 20 percent at three months. “This doesn’t mean that all these patients came in with two pairs of sunglasses on,” says Dr. Woodhams. “But it does mean that some came in with light sensitivity that wasn’t in line with our typical postop findings.”

Dr. Woodhams says the photophobia often occurs in the late postop period, several weeks to two or three months postop. Often, the slit-lamp appearance can be very good, with very few, if any, cells in the interface. The condition responds to steroids, though Dr. Woodhams claims that he’s had to use extensive steroids for a few weeks in some cases.

Because of the TRISC, Dr. Woodhams has stopped using his Intralase, as he awaits a new laser from the company.

“The company has done a very good job in responding to my problems,” he says. “They’ve been entirely forthright and helpful … My understanding is that I’ve seen a greater percentage of TRISC patients than other Intralase users, but not necessarily a greater degree of photophobia.”

San Diego surgeon Perry Binder, MD, Intralase’s medical director, has helped the company prepare a white paper on the transient photophobia.

“It’s a fraction of 1 percent of the cases in my practice and in the practice of North Carolina surgeon? Karl Stonecipher, who has also studied it,” he says. “It’s not debilitating and it’s temporary. It doesn’t require any repeat surgeries, there’s no morbidity, no loss of vision and it’s totally reversible … what’s happening in Dr. Woodhams’ experience has been way out of proportion to what anyone else has had, so much so that Intralase is changing out his laser.” • Logistics. Dr. Durrie is convinced that Intralase gives him better clinical results than microkeratomes, and says that the negatives to Intralase are actually all logistical: “it’s expensive $340,000, plus $160 per-case fee?, it takes an extra room and it slows down the procedure taking about 55 seconds to make a flap?,” he says. However, these logistical concerns can add up for certain practices.

“Intralase increases the cost per case by about $300,” estimates Minneapolis surgeon Richard Lindstrom. “And it’s slower, meaning a solo surgeon couldn’t do as many cases in as efficient a fashion … And if you buy an Intralase and you want to let your community know about it, then you have to market it. So, what can happen with a practice that purchases an Intralase is its costs go up by $300 per eye, plus it has to market it, so its annual costs may increase by about $400,000-$500,000 if it was performing 1,000 cases per year.

“If you believe that, in your market, you can raise your prices by $400-$500 per eye, then maybe it will work. Or, if you believe your volume’s going to grow, maybe it will work. But, after an objective analysis of several markets, including ours here in Minneapolis, we haven’t found that to be the case.” Dr. Lindstrom wasn’t able to share the specific results of his analysis, as he is planning to present them during the refractive surgery Subspecialty Day Meeting at this year’s meeting of the American Academy of Ophthalmology. Perhaps Dr. Lindstrom’s data and other studies presented at the meeting will clear up some of the uncertainty surrounding the decision to purchase an Intralase, and enable surgeons to make the right choice.

1. Kezirian GM, Stonecipher KG. Comparison of the Intralase femtosecond laser and mechanical keratomes for laser in situ keratomileusis. J Cataract Refract Surg 2004;30:4:804-811.

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. http://www.ophmanagement.com/article.aspx?article=86197 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.