Daytime variations in pupil size under photopic conditions

To assess the daytime variations in pupil size when far and near targets are viewed under photopic conditions.

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.

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.

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.