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Li Chen, Dimitri Chernyak; Pupil Changes under Scotopic and Photopic illumination. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1524.
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To investigate changes in pupil and iris diameter, location of pupil center and non-circularity of pupil under scotopic and photopic illumination.
Scotopic and photopic eye images of 98 eyes from 49 subjects (age range, 26 to 75 years) with normal eyes were captured using the pupillometer of iDesign Wavefront Studio (AMO Development, LLC). The pupillometer operated by capturing 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 scotopic illumination. The scotopic image was captured first, then the green LEDs were turned on and the photopic image was captured. The scotopic and photopic eye images were then analyzed to locate pupil and iris limbus boundary. Pupil boundary and iris boundary were fitted with a best-fitting circle to locate the center and diameter. The shift in pupil position relative to the cornea was calculated from the pupil center and iris center from scotopic and photopic images. Pupil boundary was also fitted with a best-fitting ellipse and the non-circularity of pupil was calculated from the major diameter and minor diameter of the best-fitting ellipse.
Under photopic illumination, the mean pupil diameter was 4.26 mm ± 0.95 (SD) (range 2.08 to 7.13 mm), and the mean iris diameter was 12.03 mm ± 0.31 (SD) (range 11.22 to 12.67 mm); Under scotopic illumination, the mean pupil diameter was 6.09mm ± 1.00 (SD) (range 3.43 to 8.13 mm), and the mean iris diameter was 12.03 mm ± 0.32 (SD) (range 11.45 to 12.69 mm). Pupil diameter decreased as a function of age was observed both in photopic and scotopic conditions. Iris diameter also showed a 0.24 mm average decrease in aged eyes of the over 60s (unpaired t-test, p=0.002) both under photopic and scotopic illumination. With changes of pupil diameter from photopic and scotopic illumination, the mean pupil center shifting toward temporal to cornea center was 0.064 mm ± 0.045 (SD) (range 0.004 to 0.293 mm). On average, the pupil non-circularity was 0.037 from the 98 photopic eyes and 0.046 from the 98 scotopic eyes.
This study not only confirmed pupil diameter decrease with aged eyes, but also observed decreased iris diameter in aged eyes. Pupil center shifted temporally from the cornea center with changes of pupil diameter under scotopic illumination. Non-circularity of pupil increased on average with the increased pupil diameters under scotopic illumination.
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