Daytime Variations in Pupil Size Under Photopic Conditions

PURPOSE: To assess the daytime variations in pupil size when far and near targets are viewed under photopic conditions. METHODS: We prospectively examined 20 eyes of 20 healthy subjects [27.3 years ± 4.1 (SD)]. Using an open view-type infrared video pupillometer, pupil sizes were measured in subjects looking at targets 5 m or 1/3 m away under photopic conditions (400 lux). The first measurement was performed at 8.00 h, with following measurements at 3-h intervals until 20.00 h. The average pupil size for 5 s consecutive measurements was used for analysis. RESULTS: The respective pupil sizes during far and near viewing were 3.80 ± 0.72 and 3.15 ± 0.62 (mean ± SD); 3.73 ± 0.78 and 3.08 ± 0.70; 3.74 ± 0.82 and 3.06 ± 0.68; 3.79 ± 0.67 and 3.17 ± 0.71; and 3.91 ± 0.76 and 3.13 ± 0.70 mm, at 8.00, 11.00, 14.00, 17.00, and 20.00 h. The pupil sizes did not differ significantly with time over the course of the day [far (p 0.94) and near (p 0.98) (one-way analysis of variance)]. The daytime variations of pupil size were 0.64 ± 0.33, and 0.41 ± 0.29 mm, respectively. Two eyes (10%) and one eye (5%) showed differences of more than 1.0 mm during daytime hours in pupil sizes while viewing far and near target, respectively. CONCLUSIONS: In this study, young adults show no significant variations in photopic pupil size throughout daytime hours. However, a single pupil size measurement appears to be insufficient for clinical use in some eyes.