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Dynamic eye tracking compensates for cyclotorsion in myopic astigmatic LASIK
J Refract Surg. 2010;26(1):17-27.
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Rotational eye tracking enhanced refractive outcomes of myopic astigmatic LASIK, according to a study.
"To the best of our knowledge this is the first study demonstrating the clinical effect of static and dynamic eye tracking with the outcome parameter of astigmatism correction," the study authors said. "The results compare favorably to the reports on cylinder correction in the literature."
The retrospective case series included 828 eyes for which at least 3-month postoperative results were available. All eyes underwent LASIK for myopic astigmatism performed with the Technolas 217z100 excimer laser and Advanced Control Eye Tracker (Bausch & Lomb).
Only eyes that underwent myopic LASIK and attempted cylinder correction of more than 0.75 D were included. Mean preoperative values were manifest refraction spherical equivalent (MRSE) of –4.31 D, cylinder of –1.27 D and sphere of –3.68 D. Postoperative refraction was assessed at 1 day, 3 months and 12 months.
Mean static rotation was 3.96° and mean dynamic rotation was 1.32°.
Mean MRSE was –0.10 D and mean cylinder was –0.33 D at 3 months postop.
Also at 3 months, predictability of MRSE correction was 90.2% within 0.5 D and 98.2% within 1 D. Predictability of cylinder correction was 82.5% within 0.5 D and 96.9% within 1 D. Predictability of sphere was 91.3% within 0.5 D and 98.7% within 1 D.
The efficacy ratio was 0.99 at 3 months. In addition, 100% of eyes had uncorrected visual acuity of 20/40 or better and 92.4% of eyes had UCVA of 20/25 or better.
"Our study demonstrates that significant cyclotorsion occurs before and during treatment," the authors said. "By using the dynamic rotational eye tracker presented, the efficacy of cylinder correction can be improved compared to those studies not performing cyclotorsional correction."
This is a good study by Neuhann et al to remind us that static cyclotorsion (from an upright to supine position) is a significant finding in a majority of our patients. We published a 2005 study with 1,019 eyes that revealed nearly identical levels of static cyclotorsion. Also, range of dynamic cyclotorsion (during the ablation) was about 3°, which we know from previous research to be on the border of visual significance in our ablation profiles. I think the take-home message here is that average static cyclotorsion is reconfirmed to average about 4° in our patient population, and we should be aware of that, especially when treating high levels of cylinder. Meanwhile, dynamic cyclotorsion has been found to be the less significant of the two.
– Daniel S. Durrie, MD
OSN Refractive
Surgery Section Editor