---
title: What causes small pupils (miosis)?
description: "Miosis means abnormally small pupils. It can arise from eye conditions, medications, or neurological problems. ## Common causes of constricted pupils Certain drops and systemic drugs cause pupillary constriction. Bright light also naturally makes pupils smaller. - Pilocarpine and other…"
url: "https://bluefinvision.com/knowledge-base/topics/symptoms-signs/what-causes-small-pupils-miosis/"
updated: "2025-12-31"
category: "Symptoms & Signs"
---

# What causes small pupils (miosis)?

Miosis means abnormally small pupils. It can arise from eye conditions, medications, or neurological problems.

## Common causes of constricted pupils

Certain drops and systemic drugs cause pupillary constriction. Bright light also naturally makes pupils smaller.

- Pilocarpine and other glaucoma medications
- Opioid painkillers such as morphine
- Normal response to strong light or close focusing
- Horner syndrome can cause one small pupil

## Serious neurological causes

Very small pupils with reduced responsiveness can accompany brainstem problems or toxic exposure. Prompt medical review is essential.

- Pontine haemorrhage or stroke
- Organophosphate or nerve-agent poisoning
- Other brain injuries affecting autonomic control
- Emergency assessment is required if miosis appears suddenly with other symptoms