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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


Normal values

Pupil constriction to light

Diameter (mm)

<0.5 mm

Asymmetry (mm)

<0.5 mm

% Pupillary constriction to light (%PLR)


Latency (s)


Constriction velocity (mm/s)

1.5 mm/s (<1 mm/s: pathological)

Dilation velocity (mm/s)


Neurological pupillary index (NPi)


Pupil dilation to pain

Pupillary dilation reflex (%)


Pupillary pain index

Depends on intensity of stimulation [16,17,18,19]

  1. PLR pupillary light reflex