Time to maximum pupil constriction is variable in neurocritical care patients

Quantitative pupillometry (QP) use has grown exponentially. Each QP scan captures images of the pupil before, during, and after light exposure to provide component measures of the pupillary light reflex (PLR). This study explores if the time to maximum constriction (tMC) is uniform among neuroscience intensive care unit (NSICU) patients. The study enrolled 50 NSICU patients with normal PLR values in a cross-sectional study and adhered to the standard of care for pupil assessments to collect data on tMC within (comparing left eye and right eye) and between patients. The mean tMC of 0.97 (0.17) s was normally distributed across all patients and ranged from 0.46 s to 1.35 s. The mean tMC was similar for the left pupil (0.98 [0.16]s) and right pupil (0.96 [0.18]s; P =.546). The within-subject mean difference (left versus right eye) tMC was 0.13 (0.12)s and ranged from 0.0 to 0.56 s. The between-subject mean tMC was 0.97 (0.17) s and ranged from 0.46 s to 1.35 s. The tMC does not occur at a fixed point in time. Clinical applications that seek to characterize pupil health should account for varied tMC and explore relationships to discrete outcomes to determine the clinical usefulness of tMC.