A rapid pupillometry protocol for clinical use: Effect of age and test-retest repeatability

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.

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 sec before flash onset), maximum pupil constriction (MPC) following the flash, and post-illumination pupillary response (PIPR; median size 6 - 8 sec after flash offset) were quantified.

Experiment I showed that from 1 - 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.

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 minutes including DA), this approach has promising clinical utility.