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Li Chen, Dimitri Chernyak; Pupil Non-circularity of the Human Eye in a Large Patient Population. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2112.
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Pupil non-circularity can affect the accuracy of pupil-based eye tracker in LASIK surgery. In this paper, we investigate the pupil non-circularity of the human eye in a large LASIK patient population.
962 eyes from an Optical Express preoperative LASIK clinical datasets were included in this study. Scotopic and photopic eye images were captured using the pupillometer of the iDesign Advanced WaveScan Studio (AMO Development, LLC). The pupillometer captures a pair of images of the eye illuminated by a combination of IR and NIR LEDs for scotopic illumination and a pair of green LEDs for photopic illumination. The scotopic and photopic eye images were analyzed to locate the pupil boundary. The boundary was fitted with a best-fitting circle to locate the pupil center and calculate the pupil diameter. The pupil boundary was also fitted with a best-fitting ellipse. The pupil non-circularity was calculated from the major diameter (a) and minor diameter (b) of the best-fitting ellipse as, Non-circularity=2(a-b)/(a+b).
The mean age of this LASIK patient population was 36.96±12.42 (SD) (range 18 to 68 years). The mean pupil diameter in the photopic eyes was 5.62mm ± 1.06 (SD) (range 2.95 to 8.86 mm), and the mean pupil diameter in the scotopic eyes was 6.68mm ± 1.00 (SD) (range 4.08 to 9.00 mm). On average, the orientation of the best-fitting ellipses showed mirror symmetry for both the left and right eyes. There was no significant difference in pupil non-circularity between the photopic and scotopic eyes (P-Value=0.09). The average pupil non-circularity was 3.75% ± 2.27% (SD) (range 0 to 16.07%) in the photopic eyes and 3.93%± 2.33% (SD) (range 0 to 15.86%) in the scotopic eyes. There were 56.04% of photopic eyes and 58.72% of scotopic eyes with non-circularity larger than 2%. There was a tendency that non-circularity increased with age both in photopic eyes and scotopic eyes.
In this LASIK patient population, there was no difference in pupil non-circularity between the photopic and scotopic eyes. More than one half of photopic and scotopic eyes showed noticeable elliptical pupil boundaries. Pupil non-circularity increased with age both in the photopic eyes and the scotopic eyes. Wavefront measurement and eye tracking during LASIK procedures need to consider the effect of pupil non-circularity because large ranges of pupil non-circularity are observed in the clinical data.
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