Dark adaptation of the eye during carbon monoxide exposure in smokers and nonsmokers.

Smoking and engine exhaust fumes are the most common sources of unnoticed carbon monoxide (CO) poisoning. In the military environment, incomplete burning of gun powder or flying at altitude may be additional hazards, especially at night, since the eye is very sensitive to any lack of oxygen supply. Dark adaptation time and light sensitivity of the dark adapted eye was measured in five young healthy smokers and nonsmokers during CO exposure. Breathing 70 and 100 ppm CO in the inspired air after a prime dose of 5,000 ppm for 5 or 8 min resulted in an almost linear increase of carboxyhemoglobin (HbCO) saturation up to 19.1 +/- 1.0% HbCO in smokers as compared to 17.5 +/- 1.9% in nonsmokers. Dark adaptation time was longer and light sensitivity of the dark adapted eye was reduced in smokers as compared to nonsmokers at comparable levels of both inspired CO and HbCO. The cause for this may be the chronic poisoning with CO, stemming from cigarette smoking.