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Data show link between intraoperative cyclotorsion and age, gender, ablation duration
Am J Ophthalmol. 2010;149(2):229-237.
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Intraoperative cyclotorsion was associated with age, gender and duration of ablation in LASIK with iris registration and dynamic rotational eye tracking, according to a study.
"Femtosecond flaps do not seem to have a disadvantage over microkeratome flaps as far as iris recognition and success of intraoperative dynamic rotational tracking is concerned," the study authors said.
The prospective interventional cases series included 275 eyes of 142 patients who underwent LASIK with attempted iris recognition and dynamic rotational tracking. Ablation was performed with the Technolas 217z100 excimer laser (Bausch + Lomb); 136 procedures had femtosecond laser flaps, 96 had microkeratome-assisted flaps and 43 had epi-LASIK flaps.
Wavefront-guided LASIK was performed on 160 eyes and non-wavefront-guided ablation was performed on 115 eyes.
Study data showed that pre-ablation static iris registration was successful in 247 eyes (89.8%); the success rate was not strongly correlated with flap creation method. Age, number of laser pulses delivered and gender correlated significantly with amount of intraoperative cyclodeviation.
Femtosecond-assisted flaps and amount of intraoperative cyclotorsion most strongly correlated with tracking difficulties that required linking the ablation to a new intraoperatively captured iris image. However, the three flap creation methods had similar numbers of cases involving non-resolvable failure of intraoperative rotational tracking.
Value of absolute intraoperative cyclotorsion was 2.99° (range: 0° to 9.3°), the authors reported.
This study shows very nicely that cyclotorsion must not be underestimated in corneal refractive surgery. The static as well as the dynamic component can negatively influence the exactness of the correction. Rotational eye tracking is, therefore, preferable. This is already true for “standard” correction algorithms; all the more so, for wavefront guided corrections in their not-rotationally symmetric components.
The wide variability between individual cases demonstrated in this study clearly show that individual cases need to be considered and that averaged result data are meaningless in this context.
– Thomas F. Neuhann, MD
OSN Refractive
Surgery Board Member
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