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Cornea is one of the most highly innervated tissues in the organism. Opioid receptors have already been detected in cornea; so the topical use of opioids is presented as an analgesic alternative in treatment of ulcerated corneas, with no damage in cicatrization. This research aimed to evaluate the corneal sensitivity of the 1% morphine sulfate solution in the intact cornea of dogs. Ten dogs with no ocular lesions were treated with one drop of saline solution on right eye (GC), and one drop of 1% morphine sulfate solution with the pH corrected for 7.2 on left eye (GM). The parameters evaluated were: tonometry, esthesiometry, Schirmer lacrimation test, pupil diameter and the presence of conjunctival hyperemia and blepharospasm with and without light source. The evaluations happened before collyrium instillation and 10, 20, 30, 60 and 240 minutes after it. It was performed variance analysis (ANOVA) for the parametric tests, comparing the means by the Tukey-Kramer test. Hyperemia and blepharospasm were evaluated by the chi-square test. The conjunctival hyperemia observed in the GM group was significantly higher (7/10) than in the CG group, which did not present hyperemia (P<0.05). Two eyes from GM showed blepharospasm with light source at 10 minutes. There were no differences in corneal sensibility, pupil diameter and Schirmer lacrimation test. The intraocular pressure was lower in the GM group compared to the GC group at 240 minutes. Topical administration of 1% morphine sulfate solution does not cause analgesia in intact cornea and promote irritation in eye and annex after instillation. [ABSTRACT FROM AUTHOR]