Miosis is a sign of exposure to which group of agents?

• A. Vesicant
• B. Radiologic
• C. Nerve agent
• D. Blood agent

Answer: (C)

Miosis, or pinpoint pupils, reflects excess acetylcholine acting on muscarinic receptors, which is a hallmark of nerve-agent exposure. Nerve agents are cholinesterase inhibitors; they block the enzyme that breaks down acetylcholine, causing a buildup at muscarinic sites. In the eye, this leads to contraction of the iris sphincter muscle and a very constricted pupil. You’ll often see other muscarinic effects as well—excessive salivation and sweating, tearing, bronchorrhea, bradycardia, and abdominal cramping—creating a distinctive pattern of symptoms that points to nerve-agent exposure.

Vesicants mainly cause delayed skin and eye injury, not pupil constriction. Radiologic exposure produces radiation sickness symptoms such as nausea, vomiting, and fatigue. Blood agents cause rapid systemic hypoxia symptoms rather than pinpoint pupils. When miosis is observed in a suspected chemical exposure, treat it as nerve-agent exposure with decontamination and supportive care, including ready access to atropine and pralidoxime.