Effect of Sarin on Dark Adaptation in Man: Mechanism of Action

¹ From the Psychology Branch, Clinical Research Division and Special Evaluations Branch, Biological Assessment Division, Chemical Warfare Laboratories, Army Chemical Center, Maryland

Adult human male subjects exposed for 2-minute periods to isopropyl methylphosphono-fluoridate (Sarin) vapor in concentrations of approximately 2 mg per cubic meter of air, producing only a moderate miosis with no other significant obvious sign of anticholinesterase action, exhibit a significant elevation of absolute visual threshold in the dark-adapted eye. It was found that instillation of Sarin in aqueous solution into the conjunctival sac does not elevate the threshold despite considerable miosis, and protecting both eyes from direct contact with Sarin vapor sufficient to prevent miosis does not prevent the action upon the absolute visual threshold; also in a subject in which miosis was similarly prevented in one eye alone, the visual threshold was elevated in both eyes. It is concluded that Sarin brings about its effect upon the visual threshold through an extraocular action, probably in the central nervous system.