---
title: 3.7 Anisocoria (Pupil Size Difference)
description: "Anisocoria is the difference in pupil size between the right and left eye, expressed as an absolute percentage difference in PI ratio. | Absolute difference | Severity | Clinical note | |--------------------|----------|--------------| | < 2% | ****None**** — within normal…"
url: "https://cnri.edu/docs/3-7-anisocoria-pupil-size-difference/"
updated: "2026-03-24"
category: Reading the Analysis Results
---

# 3.7 Anisocoria (Pupil Size Difference)

Anisocoria is the difference in pupil size between the right and left eye, expressed as an absolute percentage difference in PI ratio.

| Absolute difference | Severity | Clinical note |

|--------------------|----------|--------------|

| < 2% | ****None**** — within normal limits | Physiologically symmetric |

| 2–4% | ****Mild**** | May be physiological; monitor |

| 4–8% | ****Moderate**** | Notable asymmetry; flagged for observation |

| > 8% | ****Severe**** | Significant asymmetry; research observation flagged |

Moderate and severe anisocoria activates a TBI (Traumatic Brain Injury) indicator flag, which is noted in the results and PDF report. This flag is a research observation reference, not a diagnostic finding.

The larger pupil (OD or OS) and the absolute difference are displayed in the bilateral comparison card.