The effect of anticholinergic drugs on the inner eye muscles

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Abstract
Using 12 healthy volunteers, we tested the parasympatholytic effects on the eye. In a randomized crossover double-blind trial, hyoscine-N-butylbromide was tested against saline. Before (20 or 40 mg IV) and up to 45 min after the injection, pupillar light reaction, accommodation, visual acuity, and nyctometer values were measured. The range of accommodation diminishes according to dosage: 9–15 min after the injection, the inhibition is maximum; 45 min after the injection, only a small effect remains, even using the 40 mg dosage. Pupillary reaction is little affected by either dosage, and the pupil diameters at the end of the reaction are only slightly greater after the injection of either dosage than after placebo injection. The time constant of the reaction remains unchanged. Visual acuity and nyctometer values remain unchanged under the influence of hyoscine-N-butylbromide. The results are discussed with respect to the potential ability of a patient to meet the requirements of modern traffic. According to our findings, there are no opthalmologically-based reasons for an emmetropic person to assume impaired driving abilities after a single injection of hyoscine-N-butylbromide of up to 40 mg. If the accommodative capacity of a patient is impaired whose hyperopia is not fully corrected, the ability to drive in modern traffic may be impaired. After a single dose of 20 mg hyoscine-N-butylbromide (i.e., 1 ampule Buscopan), the impairment of even these patients does not last longer than about 45 min.