Is quantitative pupillometry affected by ambient light? A prospective crossover study

Pupillary examination is a central part of the neurological assessment. While quantitative pupillometry (QP) improves reliability, the impact of ambient light, particularly on the Neurological Pupil index (NPi), remains unclear. This study aimed to clarify the effects of ambient light on QP parameters in a critical care setting.

We performed a prospective crossover study, including 20 adult patients requiring invasive ventilation. Pupillometry was performed during bright condition (BC1), then dark condition (DC), then bright condition again (BC2). In our primary analysis we compared NPi values across conditions (DC1 vs. BC, BC vs. DC2, DC1 vs. DC2). In the secondary analysis, we compared all other QP parameters.

All QP values except constriction velocity and dilation velocity were non-normal. The median NPi was significantly lower in BC compared to dark conditions DC1 in both eyes. In 25% of participants the NPi decreased by 0.6 or more. Conversely, a significant increase in median NPi of both eyes was observed when switching from bright conditions back to dark (BC vs. DC2). No significant difference was found between the two dark condition measurements (DC1 and DC2). The secondary analysis showed that the differences in NPi were driven by differences in most, but not all, QP parameters included in NPi.

We corroborate previous findings that the level of ambient light affects QP parameters in critically ill patients. This needs to be considered for accurate interpretation of QP parameters. Future studies may explore potential automated light correction methods for wider clinical applicability.