Customized ablation – the wave moves forward

But keep an eye on a newly-developing technique: laser epithelial keratoplasy or LASEK.

As I have written over the past 2 years, the outlook for performing customized ablation based on wavefront or ray tracing diagnostic technologies continues to be bright. At last year’s American Society of Cataract and Refractive Surgery, we saw the first indications that the diagnostic technology was moving forward, and now, at the International Society of Refractive Surgery (ISRS) and Refractive Surgery Interest Group (RSIG) meetings held in conjunction with the American Academy of Ophthalmology meeting, we learned of the results of the first customized treatments and the approaches each company was taking.

One thing appears evident. Correction of higher order aberrations is not going to be easy. There are still many unknowns along the path to achieving “super vision” before customized ablations become a reality. Although getting closer yet, as I have written, we are probably still 1 to 2 years from the reality of customized ablation being used in general practice.

On first blush, and based on early reports, photorefractive keratectomy (PRK) customized treatments appear to provide better results than those obtained from customized LASIK. See the Alcon Summit Autonomous clinical results reported below. If this continues to be true — primarily because of the influence of the flap and its as-yet-unknown effect on final outcomes — a relatively new procedure, laser epithelial keratoplasty (LASEK), may become the preferred method for producing customized ablations. In LASEK, first performed by Massimo Camellin, MD, of Rovigo, Italy, but now being used by several surgeons around the globe, an epithelial flap is created, followed by PRK. From what little that has been presented to date, the healing response and restoration of visual stability of LASEK is about 7 days, compared to the 1 to 2 months for standard PRK and 1 to 2 days for LASIK. Thus the combination of wavefront (or ray tracing) analysis and customized PRK using LASEK could eliminate the unknown effect of a microkeratome-created flap, and might just prove to be the right ticket to the next advance in refractive surgery.

There is, as with most things, an alternative approach — two-step LASIK. In this procedure, in order to alleviate the effect of the flap, a LASIK procedure is done first in the normal manner, and then about a week later a wavefront analysis is performed to determine the higher order aberrations yet to be corrected, followed by a “touch up” or enhancement with LASIK to provide the final correction.

It will be up to the marketplace to decide which technique the public will accept — a one-step customized PRK/LASEK or a two-step LASIK.

LASEK

So just what is LASEK? As first described in Ocular Surgery News Europe/Asia-Pacific Edition in the March 1999 issue, LASEK is based on the detachment of the epithelium via the use of an alcohol solution that softens the epithelium and allows it to be “rolled” back into a flap, which can then be repositioned over the cornea following excimer ablation. A pre-incision of the corneal epithelium is made using a trephine with an 80-mm blade, with a blunt portion of about 100° at the 12 o’clock position to circumscribe the flap area. A rotation of about 10° is made to form the incision. Two to three drops of 18% to 20% alcohol solution is placed onto the cornea within the marker and left in place for 30 seconds. The area is then dried and thoroughly washed with water and the precut margin lifted with a modified Desmarres spatula. The epithelial flap is gently detached, gathered, and folded up at the 12 o’clock position. Epithelial trephination is designed to leave a hinge of about 80° to 100° at the 12 o’clock position. (A final irrigation with antihistamine is used to reduce any initial release of histamine induced by the alcohol.) Following a traditional PRK treatment, with light smoothing at its conclusion, the epithelial flap is then repositioned with a small spatula.

According to Dr. Camellin, “The epithelial flap is very elastic. It goes back into place easily and smoothly.” Following the treatment, a soft contact bandage lens is applied for 3 to 4 days to keep the flap in place and allow for re-epithelization. Dr. Camellin noted, “The day after, the epithelium is still perfectly transparent and the patients complain of no more than a slight discomfort, comparable, in my experience, to the effects of LASIK.” He reported that after 24 hours, the flap was perfectly sealed around the edge in all of his patients. He explained that at this stage, the epithelial flap has a tectonic rather than a visual function. The new epithelium, which regenerated within 7 days, enables the eye to reach 100% of visual acuity. Four days after removal of the bandage contact lens, his patients had visual acuities, on average, better than those with traditional PRK, and comparable with LASIK. In his opinion, because of the high dilution of the alcohol solution, only part of the epithelial cells die and the epithelium remains largely vital.

In the September 2000 issue of Ocular Surgery News Europe/Asia-Pacific Edition, Dr. Camellin reported on more than 1 year’s experience with the LASEK technique. He reported on treating 249 patients with the technique, of which 204 were myopic, 41 hyperopic and 29 retreated after PRK haze, radial keratotomy, keratoplasty or LASEK. The longest follow-up was 14 months. Intraoperative flap management was easy in 60% of the cases, average in 28%, and difficult in 12%. All of the difficult cases involved strong adherence of the epithelium to Bowman’s membrane. He found that retreatments were inevitably difficult, although the flap was easily detachable within 3 months, almost as in a primary operation. He believes that this confirms that the presence of a basal membrane reduces scar exuberance and excessive proliferation of new collagen. Postoperative pain appears limited, if any, to the first 24 hours after surgery, with no pain experienced by 44% of patients, some discomfort by 42% and pain by 14%. He attributes the postoperative pain partly to the contamination of the conjunctiva by the alcohol solution. He further noted that almost 90% of his patients achieved 80% of their preoperative best corrected visual acuity (BCVA) by day 10 following surgery.

Other LASEK experiences

At this year’s combined meeting, there were at least two papers on LASEK and one poster. At the ISRS meeting, Sunil Shah, MD, of Birmingham, England, presented on “Alcohol Delamination of the Epithelial Basement Membrane” and Paolo Vinciguerra, MD, of Italy provided, “Laser Epithelial Keratomileusis (LASEK): One-Year Results of a New Excimer Refractive Procedure,” while Chao-Chien Chu, MD, had a poster entitled, “Comparison of Laser Epithelium Keratomileusis (LASEK) and Photorefractive Keratectomy (PRK)”.

In his paper, Dr. Shah described how he treated 178 eyes of 89 patients, with one eye undergoing alcohol debridement and the second eye receiving the epithelial flap. His results showed that the eye with the flap had a higher uncorrected visual acuity Snellen fraction postop for the first 6 weeks following surgery, and then both eyes were equal out for the remainder of the 1 year follow-up. In postop BCVA Snellen fraction, the epithelial flap eye proved better than the PRK eye with debridement after the first week and out for 1 year. The flap eye also had significantly less haze than did the debrided eye.

In Dr. Vinciguerra’s talk, he reported on 432 eyes. According to his abstract (I was not able to attend his talk), 89% of his patients achieved refractive stability within 1 to 2 weeks, and at 12 months the spherical equivalent was –0.10 D±0.7 D. Haze did not exceed trace and the patients reported only postoperative “grittiness.” He concluded that LASEK provided significantly quicker visual recovery and refractive stability than standard PRK, produced practically no haze, and eliminated post-PRK pain.

Dr. Chu’s poster compared performing LASEK in 19 patients and PRK on the fellow eye. The LASEK eyes achieved best UCVA within 1 month, while PRK eyes did that in about 2 weeks. LASEK eyes achieved steady-state refraction in 1 month, and there was no difference in terms of postoperative pain. He concluded that the visual recovery was somewhat slower in the LASEK group, which might have resulted from the disproportional central islands he found in the early post-operative period. (This is surprising, as Dr. Camellin has noted that in his experience the laser should be set at lower values than those normally indicated, as the almost total absence of regression entails a higher correction than that obtained with normal PRK; it is advisable to reduce preset values by 10% when correcting up to 10 D of myopia, and 20% for myopia between 10 D and 20 D, he said.)

Wavefront clinical results

Alcon Summit Autonomous appears to be in the lead in terms of U.S. clinicals (although Asclepion-Meditec, WaveLight and Schwind continue to make progress outside of the United States). At the ISRS meeting, Marguerite McDonald, MD, reported on the treatment of some 59 patients in three groups. In the first group of eyes, treated beginning in October 1999, 23 patients were given bilateral LASIK and 13 patients bilateral PRK. Each patient had one eye treated according to the CustomCornea diagnostic, while the other eye was treated according to standard refraction. With 6 month follow-up, the myopic LASIK subgroup showed that 85% of the customized eyes achieved UCVA of 20/25 or better, compared to 92% who had the standard LASIK treatment. Similarly, in the hyperopic subgroup, 90% of the conventionally treated eyes achieved 20/40 or better, compared to only 80% of the eyes given custom LASIK.

In the second group of 13 patients given either customized or conventional PRK, 85% of the customized eyes achieved UCVA of 20/20 or better compared to only 65% of the standard PRK eyes. In a third group of 23 patients treated with customized and conventional LASIK, after the algorithms had been adjusted, but with only 1 week follow-up, 70% of the customized eyes achieved 20/20 or better, compared to 78% of the conventional LASIK eyes.

Even with very early data, it appears that there is a decrease in higher order aberrations with customized PRK (46% decrease) compared to only 26% decrease with customized LASIK. Could this lead to a PRK comeback, especially when combined with LASEK?

Visx

At the ISRS meeting, Keith Williams, speaking for Visx, presented on four patients who had had previous unsuccessful refractive surgeries, and had undergone wavefront analysis to correct the problems incurred. All four got markedly improved acuity results, albeit after only 1 week of follow-up. The patients were first measured with conventional manifest refraction, and then again with Visx’s WaveScan wavefront diagnostic. The surgeon then ablated a plastic lens, the PreView lens, with which the patient could “test” his or her new refraction to determine if it provided better acuity. If the wavefront method was preferable, the patient was treated with a second LASIK, using the Visx Star S3 variable spot scanning laser. Of the four retreated patients, ranging in pre-op UCVA from 20/30 to 20/200, all achieved improved results, with three achieving 20/15 1 week postop, and the 20/200 patient improving to 20/30. All were corrected to their best preop BCVA. The only negative was that contrast sensitivity was slightly worse postop. (It should be noted that the PreView lens used by Visx, and shown on the floor at the AAO meeting, was first used by Asclepion-Meditec, whose AWACS [Asclepion Wavefront Aberration Correction Simulator] process involves placing a wavefront imprint onto an optical plastic slide for previewing a patient’s wavefront guided correction. According to company sources from both companies, Asclepion came up with the idea first.)

Bausch & Lomb

Stephen Slade, MD, made the case for use of Bausch’s Zyoptix system, which incorporates its Zywave wavefront aberrometer and the Technolas 217Z laser. According to Dr. Slade, more than 400 patients have been treated to date in Europe, but results on only 32 patients enrolled in a prospective pilot study in Germany were presented. In each patient, one eye received standard LASIK while the other received a wavefront-guided ablation. The results showed, on average, a 1 line increase in BCVA in eyes treated with the wavefront-guided ablation. Of the 32 patients, 7 had no difference between the two eyes; 4 had worse BCVA in the custom eye; and the remaining 21 had better BCVA in the custom eye. These early results are promising, but they only compare BCVA and not UCVA, to allow a comparison to results with both the Alcon Summit Autonomous and VISX systems. Bausch & Lomb hopes to begin its U.S. clinical trials soon.

LaserSight

Jack Holladay described what LaserSight was doing in custom ablation. It turns out that the company is planning to do all of its work with its AstraMax system, which is similar to Bausch & Lomb’s Orbscan device, aiming to achieve prolate corneas with less tissue removal. The AstraMax provides only stereographic topographic diagnostic information, and does not yet have wavescan ability.

WaveLight

Theo Seiler, MD, made the case for WaveLight, stating that “SuperVision” was not the main goal, but that correcting almost everyone to 20/15 was probably good enough, while the use of wavefront technology was most useful for correction of problematic eyes. Wavefront corrects both refraction and aberration. Some of the problems remaining are to achieve centration of the treatment — aligning the measurement and the treatment, while adjusting for cyclotorsion — the difference from measuring while sitting and treating while the patient is lying down. He reported on his patients with at least 3 months follow-up, achieving no loss of more than 1 line of vision, but getting an increase in RMS error on average of 1.44 ± 0.74, a 44% increase, a suboptimal result. (Is this due to the effect of the LASIK flap?) Standard LASIK results in an increase of 5 to 25 times. Fifteen percent of the patients treated with waveguided ablation achieved 20/10, compared to only 5% of standard LASIK patients; 45% were between 20/16 and 20/12, compared to 30% of LASIK patients; and 30% achieved 20/20 compared to 50% with LASIK alone. Thus 80% achieved 20/20 or better with wavefront, while 85% got that correction with standard LASIK. Dr. Seiler reiterated that, at least at this stage in its development, wavefront guided ablation is best used to clean up previous bad results, that it has not yet achieved its potential but correlates well with BCVA, and supernormal vision may yet be achievable.

The road to super vision

Dr. Holladay led off the RSIG meeting discussions with his “prolate is best” speech. He said LaserSight plans to use its stereographic AstraMax analyzer to achieve prolate customized ablations. Michael Knorz, MD, next described the Bausch & Lomb approach using its ZyWave and Technolas 217Z system. Marc Odrich, MD, then discussed Visx’s CAP (topographic — using the Zeiss MasterVue topographer) method, comparing it with wavefront, with only limited experience. Dr. McDonald then presented her previously reported results, which showed that PRK waveguided results appear to be better than those achieved with LASIK. And finally, Scott MacRae, MD, discussed Nidek’s OPD Scan approach, which combines topography with a scanning slit autorefractor/retinoscopy to give wavefront-like results.

Panel discussion

But the best was left for last; a round table discussion where five leading refractive surgeons, Rubens Belfort, MD, Daniel Epstein, MD, Jose Guell, MD, Ronald Krueger, MD, and Michael Lawless, MD, debated the merits of wavefront versus traditional corneal topography. Some of the panelists thought that topographical analysis was more relevant and easier to understand, while others thought that wavefront was the future, with topography as an adjunct. Most agreed that wavefront presented more information, but the question was, could this information be used with today’s laser systems to provide better refractive solutions?

Some of the comments:

On the subject of wavefront versus topography:

• topography may be valuable for planning ablation;
• gather the topography, but treat with the wavefront;
• wavefront doesn’t give the location of the aberration, we need the topography to find out where it is;
• topography is probably quite good, but wavefront is the future and will be done.

Can wavefront be used to create new contact lenses to compensate for higher order aberrations?

• possibly, but topographic analysis is good too;
• we could make a wavefront contact lens, but it would ride and move on the corneal surface;
• it is easy to make the lens (both Visx and Asclepion are making trial lenses) but the problem is keeping it centered on the eye.

What about Hartman-Schack aberrometers versus Tschenring?

• clinical evidence isn’t in yet;
• there is no comparative data yet as to which provides better information;
• Hartman-Schack has been used for gathering astronomical data with excellent results.

Some of the more creative panel members gave thought to the possible use of wavefront in the future for tracking cataract formation, diagnosing dry eye and other systemic problems of the visual system.

All in all it was a very interesting and productive 2 days of discussion about the future of customized refractive surgery.