January 21, 2011
January 21, 2011
Fast, powerful, precise and safe, the SCHWIND AMARIS represents an important advance in laser-assisted in situ keratomileusis (LASIK). It combines a high ablation speed with a turbo eye tracker for monitoring pupil and limbus tracking, rotational balance and advanced cyclotorsion control. These factors ensure the perfect balance between extremely high speed and accuracy. With its repetition rate of 500Hz, minimum spot size of 0.54mm (full width at half maximum, FWHM) and its super-Gaussian beam profile, the SCHWIND AMARIS ensures very high ablation accuracy; this results in exceptionally smooth treatment surfaces and an extremely accurate reproduction of ablation volumes, allowing successful treatment.
In our trial, all LASIK procedures were performed using the SCHWIND AMARIS, and all patients were corrected using the SCHWIND-CAM ‘aberration-free’ treatment. All evaluated eyes were healthy and untreated. All flaps were created using the Carriazo-Pendular microkeratome (superior hinge), and the optical zone was set to 6.0, 6.5 or 7mm. Pre-operatively, spherical equivalent refraction (SEQ) was -0.50 to -8.25D, the sphere was 0.00 to -8.25D and the cylinder was up to -5D. All data from the 364 eyes were analysed for a post-operative period of three months.
A scattergram is the best way to show the predictability of the refractive outcome. Figure 1 shows attempted refraction versus achieved refractive change for each eye three months post-operatively. The narrow scatter between laser settings and achieved SEQ at three months is obvious. The mean post-operative SEQ was -0.17±0.24D.
Figures 2a and 2b show the refractive outcome in terms of SEQ and defocus equivalent. An impressive 75% of the 364 evaluated eyes were in the range of ±0.25D of SEQ, and 89% were within ±0.5D in terms of defocus equivalent.
Change in Best Spectacle-corrected Visual Acuity – Safety
Safety is described by the change in best spectacle-corrected visual acuity (BSCVA), which is measured by the number of Snellen lines that change post-operatively. At three months, 44% of the evaluated eyes gained one or more Snellen lines, and no patient lost more than one Snellen line (see Figure 3).
Pre-operative Best Spectacle-corrected Visual Acuity versus Post-operative Uncorrected Visual Acuity
Figure 4 displays the pre-operative BSCVA compared with postoperative uncorrected visual acuity (UCVA) at three months. Fifty-five per cent of all treated eyes had a UCVA of 20/16 or better. In summary, a significant change towards improved visual acuity even for these early results is obvious.
Figures 5a and 5b show the double-angle scatter plot of the cylindrical value, with a good post-operative scatter after three months. Mean post-operative cylinder was 0.06±0.23D.
Achieved Correction Over Time – Stability
The stability of the results for the one-week, one-month and three-month follow-up examinations (see Figure 6) shows the high success rate. Discussion and Comments by Dr Francesco Carones The new AMARIS platform from SCHWIND incorporates some significant technological improvements, such as the 500Hz repetition rate, the dualenergy fluency output, the 5D 1,050Hz eye-tracking device and the super-Gaussian 0.54mm beam profile, making this device the state of the art in excimer laser technology. Our multicentre study presents the preliminary results of LASIK for correcting myopia and myopic astigmatism using standardised, aberration-free ablation profiles, with a three-month follow-up period. This time-frame is obviously too short to allow us to draw conclusions on medium- and long-term stability and results. However, the following comments can be made.
The technological improvements had a positive impact on the results achieved three months after LASIK. The accuracy proved to be very high given the range of attempted correction. The scattergram in Figure 1 shows very small deviations from target (no eyes outside the ±1.00D range), while Figure 2 presents very precise outcomes, proving the accuracy of the original algorithm as no nomogram adjustments were made in this study. It is also interesting to note the very low variability of results among the investigation sites, meaning that the environment – i.e. humidity, temperature and altitude – plays only a secondary role. Figures 5a and 5b show by vector analysis that not only was the cylinder component dramatically reduced, but also that there was no induction of astigmatism at all. The visual acuity results reflect the high accuracy. The treatments were not customised and targeted at reducing high-order aberrations, but rather were optimised with the aim of not inducing spherical aberrations. Nevertheless, there was an overall UCVA gain compared with pre-operative BSCVA and an overall BSCVA gain compared with pre-operative values. These improvements may be related to the high quality of the ablation pattern, which produces very smooth ablated surfaces and allows optimal visual performance to be achieved. Long-term follow-up on these patients will provide more indications about the stability of the results. In the meantime, our meta-analysis indicates that the SCHWIND AMARIS platform is more accurate, precise, reliable and safe in the correction of myopia and myopic astigmatism. In addition, all of the investigators indicated that the laser station is very comfortable for both the surgeon and the patient, with improved ergonomics and efficiency. In particular, ablation times are significantly reduced, allowing a much faster flow of patients in the surgical room.