Automated Pupillometry Value Differences Serve as a Prognostic Indicator Even When They are Within Normal Range

Introduction. The pupillary light reflex (PLR) is an integral aspect of the neurologic exam. With the enhancement of automated infrared pupillometry (AIP), the Neurological Pupil index (NPi) is being increasingly used when performing a neurological examination. NPi difference (the absolute difference between paired NPi readings from the left and right eye) is a relatively unexplored variable in AIP assessment.Aim. This study evaluates the association between Glasgow Coma Scale (GCS) scores and NPi differences between the left and right eyes, when the NPi is normal, in patients enrolled in a multi-center prospective database.Material and Methods. Restricting observations to only include NPi values ≥ 3 (normal), there were 2,572 qualifying patients with 3,519 pupillometer readings linked to GCS values. Linear regression and ANOVA models were developed to investigate the relationship between GCS and NPi difference.Results. Subject mean age was 55.88 (16.95) years and 54.5% were female. Mean NPi difference was 0.36 and mean GCS was 12.06. Regression analysis indicated a slight negative association between NPi difference and GCS (r2 = 0.0696, P < .0001). When observations were dichotomized as either NPi difference ≥ 0.7 (large) or < 0.7 (small), there was a statistically significant difference in the mean GCS (10.76 [3.90]) for large NPi difference vs. small NPi difference (13.15 [2.68]; P < .0001).Conclusions. Even among patients with normal PLR, a large NPi difference is associated with lower GCS scores. Trending and evaluating the NPi difference may become an important aspect of patient assessment. (JNNN 2021;10(4):168–174)