AN EVALUATION OF THE EFFECTIVENESS OF INTRAMUSCULAR ATROPINE OR HOMATROPINE EYEDROPS IN PREVENTING THE EFFECTS OF PHYSOSTIGMINE EYEDROPS ON HUMAN VISION

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Abstract
An intramuscular injection of 2 mg atropine sulphate was given at either 8 or 120 min prior to instillation of 0.25% physostigmine sulphate eyedrops. In this way, the maximum accommodative change and the concomitant reduction in contrast sensitivity caused by physostigmine coicided with, respectively, the peak plasma atropine concentration or the fully developed mydriasis and reduction of near-point accommodation caused by atropine. Atropine at both times did not affect the miosis, the reduction in near-point, the increase in acccommodation or the reduction in contrast sensitivity caused by physostigmine. Contrast sensitivity to a phase-reversed grating pattern was actually diminished by atropine, though this was ot statistically significant. By contrast, 2% homatropine hydrobromide eyedrops did effectively antagonize physostigmine''s actions. This indicates that the rate of delivery of atropine from the intramuscular injection was insufficient to compete against the ocular effects of physostigmine.