The effects of ingestion of 60 mg pyridostigmine bromide on contrast sensitivity in man.

The effects on vision of ingestion of the anticholinesterase pyridostigmine bromide (60 mg), assessed from pharmacokinetic data to provide at least 20% inhibition of blood cholinesterase over the 1 1/2-4 1/2 h experimental period, was compared with 60 mg lactose in a double-blind crossover protocol. Contrast sensitivity to stationary oscilloscope-generated gratings of 3-40 c/deg showed a small but significant increase of 7% which was consistent with a small reduction in pupil diameter, surmised to cause a small improvement in optical quality. This reduction in pupil diameter was, however, overshadowed by a larger though still non-significant reduction on the second visit to the laboratory compared with the first. Contrast sensitivities to laser interference fringes observed in the Maxwellian view, by which the effects of the optical media are essentially bypassed, thus providing an entirely neural assessment, were unchanged after pyridostigmine. It is concluded that pyridostigmine may be given as a prophylactic in anticipation of exposure to an organophosphorus anticholinesterase without a deleterious effect on stationary visual function.