The effects of 0.025% hyoscine hydrobromide eyedrops on visual function in man

Abstract

Instillation of three drops of 0.025% hyoscine hydrobromide into one eye at 5 min intervals caused a mydriasis and cycloplegia of rapid onset and of 4-6 days' duration; this was similar to the previously reported actions of concentrations of up to 0.5%. After refraction for the working distance of the experiments, contrast sensitivity to stationary oscilloscope-generated grating patterns of 10 and 20 c/deg was unaffected despite the mydriasis. Also, contrast sensitivity to laser interference fringes of 10 and 20 c/deg observed in the Maxwellian view, in which the effects of the ocular media are bypassed, was unaffected. Contrast sensitivity to a 3 c/deg phase-reversed grating pattern was, however, transiently reduced by 40% after hyoscine. A second series of experiments showed a deleterious effect of hyoscine on contrast sensitivity to both stationary and phase-reversed grating patterns of 2, 3 and 5 c/deg while contrast sensitivity at 10 c/deg was not consistently affected. These results were explained by a direct deleterious action of hyoscine at the level of the retina, specific to channels that detect low spatial frequencies.

Pharmacokinetic–pharmacodynamic relationships of central nervous system effects of scopolamine in healthy subjects

“…Average observed (with SD error bars) and predicted (two-compartment model) scopolamine plasma concentrations The very long duration of pupil dilation, in line with the prolonged cycloplegic effects of anticholinergic ocular mydriatics [49], could possibly be explained by an element of retention of the drug in the anterior chamber of the eye and/or a high sensitivity of the iris to cholinergic inhibition. This could not be examined any further, because the effect lasted much longer than the observation period of this study, which refuted PK-PD analyses.…”