Comparison of the effects of topical and systemic atropine sulfate on intraocular pressure and pupil diameter in the normal canine eye

ObjectiveTo compare the effects of topical 1% atropine sulfate and systemic 0.1% atropine sulfate on the intraocular pressure (IOP) and horizontal pupil diameter (HPD) in the canine eye. ProceduresFour groups, each containing 10 dogs of varying age, breed, and sex were treated as follows: (i) One 30L drop of topical 1% atropine sulfate was applied unilaterally in each dog, (ii) A control group, one drop of 0.9% saline was used, (iii) 0.06mg/kg atropine sulfate was given by intramuscular injection, and (iv) Control with saline injected intramuscularly. In all groups, IOP and HPD were measured every 5min over 60min. ResultsTopical atropine significantly increased IOP in the treated eye with no change in the untreated eye. A maximum increase in IOP from 17.73.1 to 20.3 +/- 3.1mmHg (14.7% increase) was obtained 23.0 +/- 14.3min post-treatment. Maximal HPD of 12.1 +/- 1.7mm in the treated eye occurred 46.5 +/- 6.3min after treatment, with no increase in the untreated eye. Systemic atropine caused an increase in IOP in both eyes, showing a maximum at 15.5 +/- 10.6min post-treatment with an IOP of 17.3 +/- 4.6mmHg in the right eye and 17.1 +/- 5.2mmHg in the left eye (21.8% increase in the right eye and 21.6% in the left eye). Maximal HPD was noted in both eyes 30.0 +/- 11.6min after treatment. ConclusionsAtropine sulfate causes a significant increase in IOP when given both topically and by intramuscular injection. It should be used with caution, or indeed avoided entirely, in dogs with glaucoma or in those with a predisposition to the condition.