Objective composite score synthesising pupil size, latency, and constriction velocity.
Optical Response Probe
Input the NPi value from the automated pupillometer to objectively interpret the current state of neuro-pupillary mechanics.
Guidelines & Evidence
Clinical Details
Section 1
When to Use
When to Use
Objective monitoring of comatose patients in the ICU (TBI, ICH, Stroke).
Early detection of increasing intracranial pressure (ICP).
Standardizing pupil assessment to eliminate inter-observer variability.
Identifying transtentorial herniation risks before clinical signs appear.
Section 2
Formula & Logic
Automated Pupillometry
The NPi is a proprietary composite score (0–4.9) derived from seven biometric variables: Size, Latency, Constriction Velocity, Maximum Constriction, Dilatation Velocity, and Percent Change.
Interpretation
NPi Range
Status
Clinical Significance
3.0 – 4.9
Brisk (Normal)
Intact neuro-mechanical pathway.
0.1 – 2.9
Sluggish (Abnormal)
Potential brainstem compression or rising ICP.
0
Non-Reactive
Fixed pupil; likely midbrain/CN III failure.
Section 3
Pearls/Pitfalls
Herniation Warning Time
The NPi can detect sluggishness caused by early uncal compression—due to increased ICP—up to 4–12 hours before the human eye can perceive a change in pupil reactivity. A trend from 4.5 down to 2.8 is an indication for immediate repeat CT or neurosurgical intervention.
Section 4
Evidence Appraisal
Primary Reference
Pupillary reactivity as an early indicator of increased intracranial pressure: The introduction of the Neurological Pupil index
