Quantitative Pupillometry Values Are Similar in Bright Light and Dim Light Conditions

BACKGROUND: The recommendations to leave the lights on or turn the lights off before testing the pupillary light reflex (PLR) are primarily based on historical precedent. There is a lack of evidence to determine the best practice regarding adjusting ambient light when obtaining pupil measurements using a quantitative pupillometer (QP). OBJECTIVES: To examine the difference in QP measurements taken from the same subject in bright light versus in a darkened room. METHOD: Before the human subject study, light readings were obtained with a lux meter to identify the range and central tendency for light in an intensive care unit. A set of 4, paired-sample within-subjects QP measurements was obtained in alternating bright and dark rooms. RESULTS: Among 32 healthy volunteers, we found neither statistical nor clinically relevant differences in the neurological pupil index score in paired observations (P = .12) taken in bright light [mean = 561.5 (37.3) lux] or dark conditions [mean = 0.9 (0.3) lux]. This remained true in a mixed model controlling for repeated observations (P = .25). DISCUSSION: Pupil size was larger in dark conditions. But the finding that the pupillary light reflex functions normally despite fluctuating light levels is not unexpected. CONCLUSION: The evidence does not support a need for nurses to adjust light levels before measuring the PLR with a pupillometer.