====== 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.

===== Related Pages =====
  * [[glasgow_coma_scale]]
  * [[cranial_nerve_examination]]
  * [[brain_herniation_syndromes]]

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The [[Neurological Pupil index]], or NPi, is an [[algorithm]] developed by NeurOptics, Inc., that removes subjectivity from the [[pupil]]lary [[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.