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Table 1 Parameters provided by manufacturers of two automated infrared pupillometry devices: Neuroptics NPi-200 and NeuroLight-Algiscan

From: Essential Noninvasive Multimodality Neuromonitoring for the Critically Ill Patient

Type of stimulation Parameters Normal values
Pupil constriction to light Diameter (mm) <0.5 mm
Asymmetry (mm) <0.5 mm
% Pupillary constriction to light (%PLR) 35–40%
Latency (s)  
Constriction velocity (mm/s) 1.5 mm/s (<1 mm/s: pathological)
Dilation velocity (mm/s) 2.83
Neurological pupillary index (NPi) ≥3
Pupil dilation to pain Pupillary dilation reflex (%) 33
Pupillary pain index Depends on intensity of stimulation [16,17,18,19]
  1. PLR pupillary light reflex