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Preliminary investigations into the analgesic effects of topical ocular 1% morphine solution in dogs and cats




To perform preliminary evaluations into the ocular analgesic effect of topical 1% morphine in a clinical setting and to determine onset, duration and complications.

Study design

Prospective, randomised, blinded clinical study.


Twenty six dogs and seventeen cats, all client-owned.


Dogs and cats with corneal ulceration requiring medical treatment or corneal conditions requiring surgery were included and randomly assigned to receive one drop of topical morphine (group M) or base solution (group B). Recordings were made prior to application and at 5, 10, 20, 30, 40, 50 and 60 minutes, then 2, 3, 4, 5 and 6 hours. Corneal aesthesiometry, blink rates and scores for blepharospasm (BLEPH), conjunctival hyperaemia (CH) and lacrimation (LAC) were recorded. Statistical analyses used anova, t-tests and Mann–Whitney U tests as relevant.


No significant effect of treatment group on any recordings was found at any time point in either dogs or cats. Adverse effects of increased BLEPH, CH or blink rate were observed in six animals (three cats from group M and three dogs from group B), occurring within 5 minutes of drop application and lasting for between 10 minutes and 6 hours.

Conclusions and clinical relevance

Topical ocular morphine showed no measurable analgesic effect against corneal pain in dogs and cats.