Agreement and repeatability of infrared pupillometry and the comparison method

Objective: To evaluate the accuracy and repeatability of the widely used co mparison method of measuring pupil size. Design: Cross-sectional study. Participants: Fourteen eyes of seven healthy myopic subjects were examined. Intervention: Two examiners made two repeated measures of pupil diameters o f 14 eyes using Rosenbaum card comparison pupillometry and infrared pupillo metry, Subjects fixated on a distant visual acuity chart, and pupils were m easured under three luminance conditions. The agreement and inter-rater rep eatability of both methods were determined. Main Outcome Measures: Outcomes were pupil diameters, limits of agreement, and coefficient of repeatability of two examiners. Results: The mean difference between the two techniques ranged from 0.3 to 0.5 mm, The limits of agreement within two standard deviations ranged from 2.4 to 2.8 mm, Coefficient of repeatability ranged from 0.6 to 1.4 mm for i nfrared pupillometry and 1.0 to 1.2 mm for Rosenbaum pupillometry, Inter-ra ter repeatability of Rosenbaum pupillometry was consistently pupil diameter biased. Pupil diameters measured with the Rosenbaum method were consistent ly larger than diameters measured with the infrared technique for both exam iners under all luminance conditions. Conclusions: Results indicate that although the mean difference in techniqu es was small, the range of the agreement between the Rosenbaum and the infr ared techniques was large. The Rosenbaum method consistently overestimated pupil diameters and was subject to inter-rater repeatability bias. Rosenbau m pupillometry may not be appropriate when accurate pupil measurements are required. The results have implications for many clinical trials in ophthal mology, including those evaluating refractive surgery that use Rosenbaum co mparison pupillometry.