Effect of topical administration of 1% morphine sulfate solution on signs of pain and corneal wound healing in dogs

Objective - To evaluate the effect of topical application of a 1% morphine sulfate solution (MSS) on signs of pain and wound healing in dogs with corneal ulcers and examine normal corneas immunohistochemically for the presence of μ and δ opioid receptors. Animals - 12 dogs. Procedure - A 7-mm superficial corneal ulcer was surgically created in the right eye (OD) of 10 dogs, after which gentamicin solution and 1% MSS (n = 6) or saline solution (4) was administered topically OD 3 times daily. Blepharospasm, tearing, conjunctival hyperemia, aqueous flare, esthesiometer readings, and pupil size were recorded before and 30 minutes after treatment in all dogs. Ulcer size and days to completion of healing were recorded. Corneas from 4 treated and 3 control dogs were evaluated histologically. Normal canine corneas from 2 dogs not used in the study were evaluated immunohistochemically for the presence of μ and δ opioid receptors. Results - Dogs treated with MSS had significantly less blepharospasm and lower esthesiometer readings than did control dogs. Duration of ulcer healing and findings of histologic evaluation of corneas did not differ between groups. Numerous δ and infrequent μ opoid receptors were identified in the corneal epithelium and anterior stroma of normal corneas. Conclusions and Clinical Relevance - Topical use of 1% MSS in dogs with corneal ulcers provided analgesia and did not interfere with normal wound healing. Both μ and δ opioid receptors were identified in normal corneas of dogs, although the μ receptors were present only in small numbers.