Customised system reduces aberrations
Cheryl Guttman
in Munich
THE Allegretto Wave excimer laser system (WaveLight Laser Technologie) used in conjunction with the M2 microkeratome (Moria) significantly reduces higher-order aberrations in patients with myopic astigmatism, suggest the early results of an ongoing prospective clinical trial.
The study is being conducted by A. John Kanellopoulos MD, in Athens, Greece. Paul Hughes MD presented the data on behalf of Dr. Kanellopoulos at the XXI Congress of the European Society of Cataract and Refractive Surgeons.
He reviewed the three-month postoperative results in 122 eyes that underwent LASIK with the WaveLight system. The mean preoperative sphere and cylinder values were -4.85 D and -1.25 D, respectively. Mean preoperative UCVA was 20/200.
The Wavelight Tserning analyzer projects 169 laser beams onto the retina. Analysis of the displacement of the spots provides the aberration data
At the three-month visit, mean UCVA had improved to 20/18 and 92% of eyes were seeing 20/20 or better uncorrected. Rates of patients achieving even better levels of uncorrected vision were also high. In 57% of eyes, UCVA was 20/15 or better, while 34% were seeing 20/10 or better uncorrected. All of the eyes were corrected to within 0.5 D of intended SE.
The mean higher-order aberration RMS was 0.25 microns preoperatively. Postoperatively, all but four eyes demonstrated a reduction in total higher order aberrations, and the mean RMS for the study group decreased to 0.15 microns. Safety was outstanding with no cases of loss of BSCVA. Rather, more than half of the eyes gained at least one line of BSCVA and about one-fourth gained two or more lines. "The study population is relatively small and follow-up still early, but the results even on the first day after surgery were extraordinary. Those impressive outcomes may derive from use of the M2 microkeratome, which produces a very smooth pass, and/or from the wavefront-guided treatment with this flying-spot laser that creates a very smooth ablation of the corneal stroma bed," said Dr. Hughes.
The analyser uses triangulation to insure centration of the wavefront measurement. Decenterations of more than 10 microns are not acceotable for measuring data
Spherical error for the study eyes ranged from -0.5 D to -6.75 D preoperatively. Pre-op astigmatism ranged up to -3.75 D. The surgeons used the Tscherning-type WaveLight Wavefront Analyser. Each eye underwent four scans with the pupil dilated to 7.0 mm by instillation of tropicamide (Mydriacyl) 1.0 %. Only patients with four reproducible aberration measurements were eligible for the wavefront-guided procedure. Patients also underwent measurement of scotopic and mesopic pupil sizes, and those data were used to calculate the wavefront-guided optical zone.
"Wavefront is the buzzword in refractive surgery today, but it is also a necessary tool in clinical practice. Wavefront monitoring is essential because patients are expecting it, and so it is critical that the surgeon and staff understand the technology. Furthermore, there are certain patients who can really benefit from a wavefront-guided procedure, including patients with large pupils, especially those with light-coloured irides, as well as individuals with high astigmatism, and those seeking enhancements because of unsatisfactory quality of vision or to enhance monovision," said Dr. Hughes.
Translationof the captured retinal image to a wavefront map
The Allegretto Wave laser system received FDA approval in October 2003. The system uses a 0.9 mm flying spot beam with a Gaussian-profile at a frequency of 200 Hz. It also has an active eyetracking system using an infrared camera and three individual illumination modules that sense ocular movement by fixing on the pupillary reflex. The tracker operates at a detection frequency of 250 Hz and has a reaction time of 6 to 8 msec.
A. John Kanellopoulos MD
NYU Medical School
Laservision.gr Eye Institute, Athens laservision@internet.gr
Customised
