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L. Chen, D. A. Chernyak; Pupil Size Changes During Refractive Surgery. Invest. Ophthalmol. Vis. Sci. 2009;50(13):572.
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The accuracy of ablation during laser refractive surgery often relies on precise detection of the pupil center to align the laser to the eye being treated. During surgery, varying light conditions, various sensory and emotional conditions and the different accommodative states of eye can greatly affect pupil size. With pupil contractions and dilations, the pupil center can shift relative to the cornea thus contributing to potential sub-optimal outcomes. This paper investigates the changes of pupil size during refractive surgery.
12 surgical eyes had undergone LASIK refractive surgery. All procedures were performed on a single laser system by the same surgeon. Pupil illumination was held constant during the procedure. Dynamic changes of the pupil were recorded from each surgical eye by collecting digital images at 30 frames per second through the surgical infrared camera. Eye tracking simulations were conducted with these offline surgical image sequences recording the pupil size for each frame.
6 of the 12 surgical eyes had significant pupil diameter changes during LASIK refractive surgery. From all 12 surgical eyes, the average of pupil size changes was 11.2% of the eye’s initial pupil size and the standard deviation of pupil size changing was 16%. Changes of pupil size varied individually. Both pupil contractions and dilations were observed during surgery. Asymmetrical pupil dilation was observed from one surgical eye. Significant distortion of iris features was also observed. Such iris distortion may lead to potential sub-optimal performance of a torsional tracking system that relies on tracking such features. In one case, the pupil center shifted up to 0.11mm relative to the cornea with the pupil size changing.
Surgical eyes showed significant pupil size changes during LASIK refractive surgery under the same pupil illumination. Pupil size changes, accompanied by relative shifts in the pupil center position, can decrease ablation centration accuracy. Iris distortions can lead to a decrease in performance of iris-based torsional tracking systems. Therefore, without taking any technological compensational steps, it is important to keep the pupil size stable during surgery with conventional and custom refractive surgery.
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