Effect of Sarin on Dark Adaptation in Man: Threshold Changes

¹ From the Psychology Branch, Directorate of Medical Research, Army Chemical Center, Maryland

The Hecht-Shlaer adaptometer was used with an artificial pupil of 2 mm diameter to measure the course and absolute threshold of dark adaptation following pre-exposure to 3784 mL intensity for 2 minutes. Two subjects were given three familiarization trials prior to exposure to Sarin (isopropyl methylphosphono-fluoridate) in a specially constructed chamber. Following exposure, measurements were made at intervals of 1, 4 and 24 hours. Measurements of pupillary diameter and red blood cell cholinesterase inhibition were made prior to and after exposure. After total exposure to Sarin for 2 minutes at a concentration of 2.73 mg/m³, one subject manifested 23% RBC cholinesterare inhibition whereas a second subject, administered a total exposure of 2.02 mg/m³ for the same duration, showed no inhibition of cholinesterase activity. Following exposure to Sarin, pupillary constriction became manifest and remained constant over a 24-hour period within the limits of errors of measurement. The concentrations of Sarin employed raised the absolute scotopic threshold significantly as measured 1, 4 and 24 hours after exposure. The decreasing monotonic relationship between threshold and time after exposure did not reach the state of complete recovery. The rate of adaptation for the cone region of the dark adaptation curve was significantly depressed as measured 1 hour after exposure, and recovery was observed at 4 and 24 hours after exposure.