A rapid pupillometry protocol for clinical use: effect of age and test–retest repeatability

Purpose Pupillometry is most commonly performed in laboratory settings using specialized, non-portable instruments that require lengthy test protocols. The purpose of this study was to develop and evaluate a rapid, clinically-applicable pupillometry protocol using a commercially available, portable, handheld instrument. Methods Thirty-seven healthy individuals (ages 21–61 years) participated in three experiments. In each experiment, the pupillary light reflex (PLR) was elicited by full-field, 500 ms chromatic flashes (470 nm and 621 nm; 12,000 Td). Experiment I evaluated the minimum dark adaptation (DA) time needed to achieve maximum PLRs. Experiment II determined the effect of age. Experiment III estimated PLR test–retest repeatability. For all experiments, baseline pupil size (BL; 1 s before flash onset), maximum pupil constriction (MPC) following the flash, and post-illumination pupillary response (PIPR; median size 6–8 s after flash offset) were quantified. Results Experiment I showed that from 1 to 3 min of DA, BL and MPC increased slightly (0.27 mm and 5%, respectively), whereas the PIPR increased considerably (17%). The responses did not change appreciably after 3 min, therefore a 3 min DA period was used for Experiments II and III. Experiment II showed a trend for BL and MPC to decrease with age, but correlations with age were not statistically significant (all p > 0.05). PIPR was independent of age (r = − 0.01; p = 0.96). Experiment III showed test–retest repeatability of approximately 1 mm for BL, and 10% for MPC and PIPR, indicating good repeatability. Conclusion The proposed approach is useful for measuring the MPC and PIPR across a broad range of ages and baseline pupil sizes. Given the device portability and short test duration (approximately 5 min including DA), this approach has promising clinical utility.