Comparison of pupil size measurement: Repeatability and agreement across four devices with different measurement principles under varied lighting conditions.

Abstract

Aim: To evaluate the repeatability of pupil size measurements obtained with four different devices under varying lighting conditions and to assess the agreement between them.

Methods: This prospective study included 80 healthy participants with a mean age of 27.5 ± 8.8 years (range 19-58). Pupil size was measured under mesopic (4 lux) and low photopic (50 lux) conditions using two open-field devices (tabletop and handheld PowerRefractors) and two closed-field devices (MS-39 and NIDEK Tonoref III). Three consecutive measurements were taken per eye for each device. Repeatability was analysed using the repeatability limit (R Limit), while the agreement was assessed with Bland-Altman analysis.

Results: All devices demonstrated R Limits lower than 1 mm under both low photopic and mesopic conditions. The NIDEK Tonoref III had the best repeatability under low photopic conditions (R Limit = 0.52 mm), while the tabletop PowerRefractor had the best R Limit under mesopic conditions (0.68 mm). The agreement analysis under mesopic conditions revealed smaller mean differences and narrower limits of agreement (LoA) (approximately 2 mm) among devices with similar designs (tabletop with handheld PowerRefractor and MS-39 with NIDEK Tonoref III), while combinations of designs exhibited wider variability. Mesopic conditions yielded more consistent LoA across all device pairs.

Conclusions: All devices showed excellent repeatability. Instruments with similar measurement designs demonstrated better agreement, particularly under low photopic conditions. Significant variability existed when comparing open- and closed-field devices. These findings underscore the importance of selecting appropriate instruments for clinical and research applications, and highlight the need for further validation of pupillometry devices.