Relationship between pupil size and acetylcholinesterase activity in patients exposed to sarin vapor

Objective: To elucidate the effect of sarin vapor on pupil size and erythrocyte acetylcholinesterase activity (AchE). Design: Retrospective observational survey. Setting: Emergency department of an urban teaching hospital. Patients: 80 patients who were exposed to sarin in a terrorist attack in Tokyo subways. Measurements and results: Pupil size and AchE activity on the day of exposure were measured. Among the 8O patients, the pupils were miotic ( < 3 mm) in 50 patients (62.5%), while AchE activity was below the normal range ( < 1.2 U) in 34 patients (42.5%). AchE was significantly lower in the miotic group than in the group with normal pupils (1.0 ± 0.5 U vs 1.5 ± 0.3 U, p < 0.01). In the miotic group, AchE activity was lower than normal in 32 patients (64.0%) but was decreased in only 2 patients in the normal pupil group (6.7%) (p < 0.01). Conclusions: Miosis is a more sensitive index of exposure to sarin vapor than erythrocyte AchE. Systemic poisoning is apparently less likely to develop if the patient's pupil size is normal on arrival at the hospital.