Pupil Reactivity

Pupil Reactivity

Pupil reactivity refers to the change in pupil size in response to light stimulus. It is a fundamental component of the neurological examination and provides key insights into brainstem function and intracranial dynamics.

Assessment

Use a penlight to shine light into each eye from the side.
Observe for:
- Direct response: constriction of the illuminated pupil.
- Consensual response: simultaneous constriction of the opposite pupil.
Evaluate the speed and symmetry of the response.

Normal Response

Pupils constrict briskly and equally to light.
Indicates intact cranial nerves II (optic) and III (oculomotor), and midbrain integrity.

Abnormal Findings

Pattern	Description	Possible Causes
Fixed and dilated	No response to light	Uncal herniation, CN III palsy, brain death
Bilateral dilated, non-reactive	No response in both pupils	Severe hypoxia, anticholinergic overdose
Pinpoint, non-reactive	Very small, fixed pupils	Pontine hemorrhage, opioid toxicity
Sluggish reactivity	Slow constriction to light	Raised ICP, early herniation

Clinical Relevance

Early detection of neurological deterioration (e.g. herniation syndrome).
Monitoring in ICU and neurocritical care settings.
Prognostic value in traumatic brain injury and coma.

The Neurological Pupil index, or NPi, is an algorithm developed by NeurOptics, Inc., that removes subjectivity from the pupillary evaluation. A patient's pupil measurement (including variables such as size, latency, constriction velocity, dilation velocity, etc.) is obtained using a pupillometer, and the measurement is compared against a normative model of pupil reaction to light and automatically graded by the NPi on a scale of 0 to 5. Pupil reactivity is express numerically so that changes in both pupil size and reactivity can be trended over time, just like other vital signs.

Table of Contents

Pupil Reactivity

Assessment

Normal Response

Abnormal Findings

Clinical Relevance

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