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J Porter, G Yoon, C Kwon, S MacRae, IG Cox, DR Williams; Effect of Corneal Decentration on Refractive Surgery Outcome . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2031.
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Purpose: To understand the effect of corneal decentrations on the outcome of laser refractive surgery and to evaluate how fast an eye tracker is needed to minimize decentration effects from a customized laser ablation. Methods: A pupil camera operating at 30Hz was used to monitor corneal decentration during a conventional laser refractive surgery procedure without an eye tracker. The measurement accuracy was 0.11 mm in both the horizontal and vertical directions. From these data, we computed the temporal power spectrum for 5 patients (9 eyes). The temporal power spectrum succinctly quantifies the amount of eye movement that occurs at different frequencies. The mean laser treatment was -3.95D sph, -0.66D cyl. A Shack-Hartmann wavefront sensor (B&L Zywave) and corneal topographer (B&L Orbscan II) were used to measure changes in the eye's total wave aberration and corneal shape. Results: The mean of the pupil decentrations from the ablation axis was -0.003 mm and 0.047 mm in the horizontal and vertical directions, respectively. The standard deviation in both the horizontal and vertical directions, respectively, was 0.247 mm and 0.193 mm. The temporal power spectra in both directions are similar. The power of the decentration up to 1 Hz included approximately 96% of the total power of the decentration, on average, in both directions. Conclusion: The most problematic corneal decentrations during LASIK are relatively slow drifts in eye position. An implication of these measurements is that an eye tracking system with a 1 Hz closed-loop bandwidth could compensate for most corneal decentrations in a conventional or customized ablation. These eye movement data can also be used to estimate the aberrations induced by decentration and their influence on retinal image quality.
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