Graduate Thesis Or Dissertation
 

Evaluation of Topical Application of 1% Morphine Sulfate Solution as an Analgesic on the Healthy Equine Eye

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  • Corneal ulcers are one of the most common eye conditions of the horse, with potentially serious complications such as loss of vision or the eye itself. They are extremely painful due to the large number of sensory nerve endings found in the cornea. Horses frequently show signs of ophthalmic pain despite systemic analgesics, which have side effects including renal and gastrointestinal toxicity, and CNS excitement. Morphine applied topically to the eye has been shown to have a rapid onset of action in rabbits, dogs and humans and provides effective analgesia without deleterious side effects on corneal healing. Despite investigation of topical ophthalmic morphine in other species, there are no published reports for its use in horses. In the first study detailed here, we evaluated whether or not short term administration of 1% morphine sulfate was safe to use on the equine cornea and whether this morphine would be absorbed into the serum, aqueous, or vitreous. Morphine was applied topically to one eye of six horses every four hours for 72 hours before euthanasia. Serum samples were collected at varying time points during the study and ocular fluid collected immediately after euthanasia. Treated and control corneas were sent for histopathology. Horses showed no systemic or ocular adverse effects. Corneal histopathology confirmed there was no difference in microscopic appearance between morphine treated and control corneas. Morphine was detected by ELISA in aqueous humor of the treated eye for all 6 horses with a mean ± standard deviation of 165.18 ng/ml ± 87.69 ng/ml. Morphine was also detected in vitreous humor of the treated eye of 5/6 horse with a mean ± standard deviation of 4.87 ± 4.46 ng/ml. Morphine was detected in the serum of 5/6 horses at varying time points. There was significant variability in serum morphine concentrations between horses. In general, topical morphine sulfate applied to the eye every four hours can be expected to result in systemic absorption, with peak systemic concentrations occurring approximately 5-10 minutes after administration. In addition, morphine concentrations were more consistently detected on day two and three, than day one of administration. Maximum systemic concentration reached in a single horse was 6.98 ng/ml. The objective of the second study was to test the hypothesis that topical 1% morphine sulfate applied to the equine cornea will result in decreased corneal sensitivity compared to a control eye as measured by corneal aesthesiometer. Mean baseline corneal touch threshold of both control eye and treated eye was 21.8mm. Corneal touch threshold was not significantly different between morphine treated and control eyes at any time point. In conclusion, these studies determined 1% morphine to be safe for short term use on the equine eye and showed that 1% morphine does not provide an anesthetic effect on the intact cornea. Further studies to evaluate a possible analgesic effect are warranted.
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file details GordonEmma2016.pdf 2017-08-04 Pubblico Scaricare