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

Objective To 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. Procedures Four groups, each containing 10 dogs of varying age, breed, and sex were treated as follows: (i) One 30 μL 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) 0.06 mg/kg atropine sulfate was given by intramuscular injection, and (iv) Control with saline injected intramuscularly. In all groups, IOP and HPD were measured every 5 min over 60 min. Results Topical atropine significantly increased IOP in the treated eye with no change in the untreated eye. A maximum increase in IOP from 17.7 ± 3.1 to 20.3 ± 3.1 mmHg (14.7% increase) was obtained 23.0 ± 14.3 min post‐treatment. Maximal HPD of 12.1 ± 1.7 mm in the treated eye occurred 46.5 ± 6.3 min 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 ± 10.6 min post‐treatment with an IOP of 17.3 ± 4.6 mmHg in the right eye and 17.1 ± 5.2 mmHg 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 ± 11.6 min after treatment. Conclusions Atropine 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.