<p>Assessing the pupillary light reflex response among patients with neurological injuries is a cornerstone of early management and guides critical treatment decisions. Traditional manual assessments of this reflex using a flashlight have been shown in multiple studies to be inconsistent and unreliable. Substantial research evidence demonstrates improved accuracy of pupillary assessments when an automated pupillometer is used by clinical providers. Despite this evidence, anecdotal reports indicate routine use is fragmented and inconsistent. To effectively bridge this research to practice gap, an implementation science design was used to address the following aims: (1) Establish accurate estimates of routine use of evidence-supported automated pupillometry for patients after acute neurological injury; (2) Identify clinical determinants of routine use; (3) Identify clinician beliefs and perceptions of the acceptability, appropriateness, feasibility, and fidelity of pupillometer use. This multi-site, point prevalence observational implementation study took place at two academic ICU. Both sites recorded frequency of pupillometer use and acuity measures of patients receiving pupillometer use over a 2-week period to identify clinical determinants of routine use. Clinician perspectives on routine use were assessed using The Consolidated Framework for Implementation Research (CFIR), as well as measures for evaluating acceptability, appropriateness, and feasibility of this evidence-supported practice. Routine use of pupillometry was variable between sites. Site A had higher prevalence of pupillometer utilization than Site B. Multinomial logistic regression modeling indicated patient diagnosis, age, mechanical ventilation, and continuous electroencephalography were clinical determinants that influenced pupillometer use at Site B; however no association was evident at Site A. Clinician perspectives on the evidence and utility of pupillometer use were positive, suggesting characteristics of individuals and of the innovation were strong facilitators of routine use. Barriers included components of the inner setting for implementation, particularly resource availability and internal policies that influenced assessments. The majority of clinicians reported high acceptability and appropriateness of pupillometer use and felt this evidence-supported practice was feasible for routine use. Pupillometery is a useful tool for pupillary assessment, with a substantial evidence base to support routine use. Variation of this best practice persists, despite positive clinician perspectives in real world contexts. This study established baseline estimates of routine use, as well as factors influencing the frequency of pupillometer assessments. Additional research is needed to definitively determine optimal assessment frequency, role that clinical factors may play, as well as impact of pupillometery on patient outcomes.</p>