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MILAN — Clinical experience is helping surgeons understand which patients would benefit most from wavefront-guided LASIK using the Zyoptix (Bausch & Lomb) system, according to Stephen Slade MD, Houston, Texas.

Dr Slade reviewed clinical experience with the Zyoptix system in a presentation at the Video Refractiva conference here. He is the Medical Director for TLC (The Laser Centre) and serves as Chair of the Refractive Surgery Section of the American Society of Cataract and Refractive Surgery (ASCRS). He is also the Medical Monitor for the Bausch and Lomb/Technolas Excimer Laser.

The Zyoptix system combines the Zywave wavefront aberrometer, Obrscan II corneal diagnostics and the Technolas 217 excimer laser to create customised corneal ablations.

Early clinical experience with the system suggests that the theoretical advantages of such a system, including better outcomes in larger pupils and fewer problems with halos and glare, are becoming manifest, he reported.

Dr Slade presented data from several studies, including a trial that compared Zyoptix-guided outcomes with conventional Planoscan LASIK in 91 eyes. The initial mean manifest sphere was –3.56 D in the Zyoptix group and -3.69 D in the Planoscan group.
At one week, Zyoptix-treated eyes improved to 0.07 D and traditionally treated eyes improved to -0.03 D. Little change was seen at the one and three month follow-ups.

The mean preoperative manifest cylinder was -0.67 D for Zyoptix group and
-0.60 D for the Planoscan eyes. At one week this had improved to -0.31 D for the Zyoptix patients and -0.34 for the controls. Again, results were stable for both groups at three months.

In terms of manifest sphere, 77% of the Zyoptix-treated eyes were within 0.5 D of the intended target after three months. A similar proportion, 75%, of those in Planoscan group was also within 0.5 D of target refraction. A total 96% of the Zyoptix group and 98% of the Planoscan group were within 1 D of target.

Both groups did well in terms of best-corrected visual acuity. Nearly 100% of patients in both groups achieved at least 20/25. A total 95% of each group was at 20/20 at the three-month follow-up. A third of patients in the Zyoptix group attained 20/15 at three months, as did 42% of the Planoscan patients. A handful of patients in each group attained 20/10.

Differences between the treatments became apparent when comparing higher order aberrations over time. While little difference was seen in lower orders (preoperative values ranged from 0 um to 0.49 um), higher order Planoscan patients were statistically more likely to have higher order aberrations following treatment, Dr Slade reported.

He also reviewed the results of a second study involving 193 eyes operated with the Zyoptix system at one of three sites. Preoperative mean sphere was –3.50 D (range –7.0 D to 0.50 D) and the mean cylinder value was 0.059 D (range –2.25 D – 0 D). The analysis was performed for a 6.0 mm pupil size.

After one week 67% of the eyes were within 0.5 D of the expected outcome. Some 91% of eyes were within 1.0 D after three months, while 65% were within 0.5 D. All eyes attained uncorrected visual acuity of at least 20/30, with 92% achieving 20/20. A quarter of the eyes reached 20/13 and a small percentage reached 20/10 or better. Moreover, 70% of the eyes showed improvements in third order aberrations, he reported.

Patients respond in the affirmative
Dr Slade also presented the results of a qualitative vision quality questionnaire that was administered to 365 patients that had undergone standard LASIK and 114 who had received a Zyoptix procedure. The poll compared patients’ responses preoperatively and one-month postoperatively.

Patients reported consistently better satisfaction with Zyoptix. One quarter of Zyoptix patients reported that vision had improved in bright light conditions compared to preoperative vision, as did 10% of standard LASIK patients.

A total 7% of Zyoptix patients reported worsening of vision in bright light compared to 13% of Planoscan patients. In dim light, 27% of Zyoptic patients reported improved vision after treatment compared to 13% of Planoscan patients. Some 11% reported decreased visual acuity in dim lighting conditions after Zyoptix treatment compared 23% of Planoscan patients.
Zyoptix-treated patients also reported better results in night driving. Nearly one third of patients reported improvement in night driving vision with Zyoptix treatment, compared to 18% of those in the Planoscan group. These differences were statistically significant, he noted.

One theoretical advantage of the Zyoptix approach is reduced ablation of tissue. A random sample of cases appears to confirm the theory in practice. In another study, researchers chose five cases from each dioptre range from the complete Zyoptix cohort. The selection included 55 cases with spherical equivalents up to –12 D.

The study compared ablation depths achieved with Zyoptix with simulated values of standard LASIK software (Planoscan 2000). Zyoptix-guided treatment was associated with improved tissue preservation in most ranges. Significantly less tissue was ablated for –4 D, -6 D and higher ranges, but not for –2 D, -3 D or –5 D, he said.

Wide variability from surgeon to surgeon
Additional follow-up analyses highlight the role of the individual surgeon. Dr Slade presented data indicating considerable variability in the outcome of wavefront-guided surgery depending on the surgeon.

For example, an analysis of the results of one surgeon showed no worsening higher order aberrations with Zyoptix, compared to measurable differences seen Planoscan. In the hands of another surgeon, however, treatment with Z Zyoptix produced worse results than Planoscan did. This highlights the need for standardised procedures, Dr Slade stressed.

He noted that the available clinical data confirms the Zyoptix system does indeed reduce wavefront aberrations postoperatively compared to standard treatment. The stability of good visual acuity seen in patients who have undergone Zyoptix treatment, along with qualitative data suggesting fewer problems with glare also support the use of this approach.

Potential candidates who could expect visual benefits from Zyoptix would include the 55% of patients with preoperative higher order aberrations. Patients with larger pupils (>6.5 mm) might also be candidates as would those patients with higher orders of myopia and those with thin corneas, he said.

However, the clinical data also highlights the need for further steps in the development of wavefront-guided approaches. He stressed the need for developing standardised procedures, reducing sources of induced wavefront aberration, as well as the importance of learning to deduce optimum induced wavefront corrections.

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