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.