Faster femtosecond laser speeds may improve outcomes
The WaveLight FS200 femtosecond laser lets surgeons create flaps in as little time as 8 seconds.
Click Here to Manage Email Alerts
Our practice has used the Alcon WaveLight refractive suite through all of its iterations. We therefore have a unique perspective on the actual vs. theoretical advantages of different laser speeds — particularly the 200-Hz, 400-Hz and 500-Hz systems — and how that affects outcomes. The latest version combines a 500-Hz excimer laser and a 200-kHz femtosecond laser, making it the fastest laser on the market today.
The WaveLight EX500 laser features a 1050-Hz-type eye tracker with a latency of about 2 milliseconds. It has a closed-loop system that seals the path of the laser beam, ensuring consistent energy delivery throughout each ablation, irrespective of changes in temperature and humidity. The system’s dynamic pupil tracking ranges from 1.5 mm to 8 mm; an active pupil centroid shift correction and a means to compensate for cyclotorsion on the table are additional features (not yet available in the U.S.). Some of the patient-specific applications include wavefront-optimized, wavefront-guided and topography-guided treatment options.
One of the major benefits of the refractive suite is the ability to treat 1 D in 1.4 seconds, so a standard flap is created in as little time as 8 seconds, but there is very little energy delivered to the cornea. The total procedure duration for flap cutting with the FS200 in our hands is about 20 seconds from the time the suction is turned on until it is subsequently turned off. Because the laser fires so quickly, there is less energy required (which may enhance safety), flap lifting is easier, and there is minimal postoperative inflammation due to the flap compared with previous femtosecond lasers we have used.
A. John Kanellopoulos
I should note that for side cuts, rings and spots should be slightly denser to avoid epithelial damage and the possibility of postoperative epithelial ingrowth.
We have been so impressed with the increased speed and accuracy of the system that our current refractive surgery protocol is to perform all-LASIK femtosecond surgery with the FS200. For myopes, we create a flap that is 8 mm in diameter and 110 µm thick. About 70% of our myopic corrections are standard prolate-optimized treatments. If the higher-order aberrations are greater than 0.4 µm, we use wavefront-guided treatments; if the cylinder is more than 2 D, we use topography-guided treatments. All hyperopes undergo topo-guided treatments with asphericity value adjustments. Hyperopes also differ from myopes in that the flap thickness is about 130 µm and the flap diameter is 9.5 mm. If necessary, we can create flaps as large as 10 mm.
Initial outcomes
We evaluated 198 consecutive LASIK patients in our refractive surgery center in Athens, Greece, examining refractive error, best corrected visual acuity, uncorrected visual acuity, flap parameters and flap creation, and excimer laser creation, among other parameters. The average follow-up was 6.2 months (range: 4 to 10 months).
The 165 myopes had a mean refractive error of –4.5 D, which improved to –0.25 D; UCVA improved from 20/80 to 20/17, and achieved flap thickness was only slightly off the intended 107 ± 5 µm and 8.1 mm diameter. At 3 months, 99% had UCVA of 20/40 or better, 6.7% gained two Snellen lines, and 43.7% gained one line. We were within 0.5 D of emmetropia in 82.6% of the patients.
Similar results were found with the 33 hyperopes. Our 3-month results showed mean refractive error improved from +2.5 D to –0.25 D, with a UCVA of 20/60 improving to 20/15. Uncorrected distance visual acuity ranged from 91.3% achieving 20/32 or better to 73.9% achieving 20/20 or better to 35% achieving 20/16 or better. Mean flap depth was 132 µm and 9.4 mm. About one-third gained one line, and 4.5% gained two lines at 3 months. A total of 66.7% were within 0.5 D of emmetropia. Impressively, the refractive astigmatism was managed as well, with about 70% under 0.25 D of astigmatism at 3 months.
Overall, flap creation was 15 seconds in the myopic group and 19 seconds in the hyperopic group; excimer laser ablation took 28 seconds for the myopes and 32 seconds for the hyperopes. What I found impressive, however, was the predictability of the spherical error correction considering how fast the laser is.
Initial impressions
For me, one of the most intriguing features of the refractive suite is how both the excimer and femtosecond lasers communicate, which helps eliminate calculation and input errors, thereby resulting in improved laser refractive outcomes. In everyday clinical practice, this translates into easier surgery for both the patient and surgeon and outstanding outcomes.