It seems that many refractive surgeons have a waiting list of "complicated" eyes, patients who were referred to them for help with complications related to their LASIK or PRK procedures, but for whom conventional technology isn't yet up to snuff. In this, the first in a series of "Refractive Surgery" columns on complicated eyes, Review looks at the ways the various laser manufacturers and their users are approaching these patients. This month, we'll look at preliminary results from WaveLight's topography-guided treatments and Visx's CustomVue.

WaveLight's Allegro Topolyzer

For several years, some surgeons have argued that, in order to treat complicated eyes such as those with decentered ablations after LASIK, the surgeon would need to use a topography-guided approach, since the problems are on the cornea itself. The German company WaveLight agrees, and has recently rolled out its Allegro Topolyzer system in a few practices to see how effective it can be with these cases. The Allegro Topolyzer isn't yet available in the United States.

The WaveLight Allegro Topolyzer bases its planned ablations of irregular corneas on the eyes' topographic features.

Two surgeons who have worked with the device are Raymond Stein, MD, of the Bochner Eye Institute in Toronto and David Lin, MD, of Vancouver's Pacific Laser Eye Centre. They are consultants for WaveLight.

Drs. Lin and Stein say the complex eyes that can be treated with the system fall into several categories:

• Previous laser vision correction or radial keratotomy patients with very small optical zones. "Many of the early lasers for years used very small optical zones for treatment," says Dr. Stein. The topography-guided treatment can expand the zone.
• Decentered ablations.
• Central islands (localized areas of central steepness) left behind by some broad-beam lasers.
• Irregular astigmatism after laser vision correction, an irregular microkeratome cut or corneal transplant.
• Patients with mild keratoconus. Dr. Stein says that these patients have irregular astigmatism, and usually can't see that well with spectacles, often needing a hard contact lens to see. A topography-guided treatment may be able to smooth the cornea and improve best-corrected vision.
• The treatment. Dr. Stein says to first wait until the refraction and topography are stable, usually four to six months after their initial procedure.

The protocol involves taking multiple images of the patient's eye with the Topolyzer placido-disk topographer, which captures  22,000 data points. Dr. Stein says he tries to capture at least four images that look similar.

Though the Topolyzer appears to do a good job of capturing images, there are patients for whom imaging could be difficult. "Occasionally, with totally distorted corneas, you can't use the Topolyzer," says Dr. Lin. "These can occur after very weird flaps or terrible surface problems such as massive basement membrane disease or Salzmann's nodular degeneration."

Once the surgeons get an image they feel comfortable with, they save the topography on a floppy disk, which they then insert into the laser's computer. It's at this point, when the laser is planning the ablation, that the surgeon faces another decision point.

"The other catch is how much tissue has to be removed in order to correct the irregular astigmatism," says Dr. Stein. "For example, if we have to remove so much tissue from one part of the cornea that there's a 20-D difference between it and the other parts, that's really too much." The program will also tell the surgeon what areas of the cornea the tissue will be removed from.

Once the surgeon approves of the ablation and how much tissue will be removed, he can perform the treatment.

Dr. Lin, who has been using the system for a year, says he gets the best Topolyzer results from decentrations and optical zone enlargements. He also has treated irregular astigmatism, which he defines as a difference of 2 D or more between the superior and inferior quadrants of the cornea, or either ends of an astigmatism with an oblique axis.

He has performed in-office studies of just over 500 eyes where he's treated one eye with the Allegro Topolyzer and one without, and he says the former shows a uniform ablation without residual central astigmatism while the latter still has a kind of inferior curvature increase in comparison to the superior quadrant.

He's currently preparing his data from the irregular astigmatism treatments for presentation at the upcoming meeting of the American Society of Cataract and Refractive Surgery. Some of the data shows that, though the visual results of topography-guided treatment and conventional were similar in terms of postop uncorrected acuities, none of the topography-guided eyes lost a line of vision, compared to a small number of the conventional eyes. More of the topography-guided eyes gained at least a line of vision, as well. His retreatment rate for complex Topolyzer patients is less than 10 percent.

CustomVue and Aberrated Eyes

Stanford University's Director of Cornea and Refractive Surgery, Edward Manche, MD, recently completed a retrospective analysis of 120 eyes of 102 patients who had visual complaints postop and were subsequently treated with Visx's CustomVue wavefront-guided procedure.

"Of the patients, 119 were previous LASIK surgeries, and the remaining one was a PRK," says Dr. Manche. "The vast majority of them had poor quality of vision. A lot had night vision issues such as starbursts, glaring, halos, and some had distortion of their vision. Some of the corrections we did were fairly mild; they might have had 0.5 D of residual myopia or astigmatism, but their symptoms were disproportionate to their refractive error."

The preoperative workup for the treatment is similar to that of the Allegro Topolyzer in that the surgeon needs several reliable images, in this case wavefront maps, before proceeding. Dr. Manche shoots for three to six scans that are similar in terms of their data measurements, especially sphere and cylinder. He then makes sure the wavefront refraction matches the manifest refraction. If these disagree too much, such as one showing a cylindrical axis that's 90 degrees away from where it is in the other refraction, he won't do the case.

"When you do the actual treatment, I've found that you have to use a significant offset," says Dr. Manche. "We back off significantly on all the treatments. For instance, if someone were -1.5 +1.00 axis 90 and the WaveScan came out to -1.32 +1.1 axis 97, which would be pretty good agreement in terms of cylinder, we'd end up backing down to something like -1.1 +1.1 on the WaveScan. We'd find that, on average, we'd end up close to emmetropia or even slightly plus in such a patient by doing that correction."

Dr. Manche says the CustomVue results have been very good in certain patients. In his study, the average preop spherical equivalent was
-0.91, ranging from -0.13 to -2.4 D. At three months, the average SE refraction is -0.22 D, and 99 percent of the patients see 20/20 or better. Thirty-eight percent gained a line of vision, 57 percent stayed the same, and 5 percent lost a line.

As for optical aberrations, the problems the patients originally came to have treated, the mean higher-order root mean square value (RMS) dropped from 0.40 to 0.34. There was a reduction in coma and trefoil, but by three months spherical aberration returned to pre-enhancement levels. Overall, Dr. Manche says the "vast majority" of patients noted a resolution of their visual symptoms, however.

• Bad candidates. Dr. Manche says that custom ablation isn't for all patients with irregularities, though.

"Basically, I try to avoid doing [patients with] decentrations that are significant, 2 to 3 mm," he says. "I've tried that in the past with wavefront ablations and have been underwhelmed by the results. I don't think a wavefront ablation is that effective in recentering the ablation in significant decentrations."