The Mydriatic Effect of a Mixture of Ephedrine and Homatropine.

Abstract

The use of a mixture of ephedrine and homatropine as a mydriatic for diagnostic purposes has been recommended by Geppert and Groenouw. 1 They found that a small amount of homatropine enhances the mydriatic effect of ephedrine, and the time at which mydriasis passes off is practically equal to ephedrine. Later this observation was repeated by many clinicians 2 using “Mydrin”, which is a mixture of ephedrine and homatropine. By comparative experiments with ephedrine and homatropine we have further observed the mydriatic effect of this mixture.

White rabbits were used. The horizontal diameter of the pupil was measured in a dark-room, the source of light being at a constant distance. The change of pupil in strong light was also observed at a constant distance from a lamp. The drugs were applied to the conjunctival sac. A great number of preliminary experiments showed that the pupil on both sides responded to the drugs at practically the same rate and strength. The mixture of ephedrine and homatropine was in the proportion of one hundredth part of the latter to one part of the former substance.

In 6 experiments the mydriatic effect of a small dose of ephedrine on the homatropinized eye was observed. A small amount of homatropine such as one drop of 0.001% to 0.005% solution was applied to the eye on one side (which would produce a dilatation of 1 to 2.5 mm.) and half an hour later one drop of 0.1% to 1% ephedrine solution was applied to the homatropinized eye and also to the eye of the other side. In one case ephedrine (7 mg. per kilo) was injected intravenously. The homatropinized pupil was further dilated by ephedrine but its dilatation was simply due to an additional effect of the mydriatic action of ephedrine and homatropine and was not an augmentation of the homatropine effect.