TITLE: COMPARISON OF THE ANALGESIC EFFICACY OF TOPICAL MORPHINE AND A TOPICAL LOCAL ANESTHETIC FOR CORNEAL ABRASIONS

AUTHORS: Thomas Burns, MD¹, B. Patel, MD², W. Soscia, MD², A. Crandall, MD², A. Peters, RN¹, M. Jensen, RPh²
AFFILIATION: ¹Dept. of Anesthesiology, Univ. of Utah, Salt Lake City, UT; ²Dept. of Ophthalmology, Univ. of Utah, Salt Lake City, UT.

INTRODUCTION: Topical local anesthetics such as tetracaine, bupivicaine and benoxinate are the current therapy for ophthalmic analgesia. Application of local anesthetics has been associated with deleterious effects on the corneal epithelium. In addition, the loss of corneal sensitivity is profound, so that some patients may further injure their corneas without being aware of the self-injury. For these reasons, development of a safer yet effective topical analgesic is warranted. One smaller study showed the dramatic analgesic effect of topical morphine 0.5% applied to the eye for corneal abrasions after vitrectomy (1). This supports the premise that peripheral opioid receptors are present in the corneal epithelium and mediate antinociception during inflammation. The current study compared and contrasted the effects of topical morphine versus standard topical benoxinate in patients with corneal abrasion.
METHODS: After IRB approval, eligible, consenting patients with corneal abrasions entering the University's outpatient clinic were enrolled and randomized to the preservative-free topical morphine 0.1%, or the topical benoxinate 0.4% group. Twenty- two patients, 11 in each group, were enrolled in this double blind study. Each group received two drops of solution with fluores- cein and were examined. The topical morphine dose was 0.05mg. Before treatment, at ten minutes and 24 hours after treatment, patients were questioned regarding their level of pain and side effects. Pain was assessed by a blinded investigator using a 0-10- point visual-pain scale. Corneal healing was assessed by slit lamp examination.
RESULTS: The mean pain score for the 11 patients in the benoxinate group was 3.5 before medication and 1.91 ten minutes later. Mean pain score for the 11 patients in the topical morphine group was 4.23 at presentation and 2.35 ten minutes later. Mean pain in the benoxinate group 24 hours later was 1.19. Mean pain for the topical morphine group at 24 hours was 1.45. Analysis of the data showed no statistically significant difference between the two solutions in regards to pain relief or side effects at alpha=05, using the Mann Whitney test. Time of onset for analgesia and duration of action were the same in both groups.
DISCUSSION: The analgesic effect of topical morphine was equivalent to topical benoxinate. There was no difference in side effects or healing. Topical morphine acts directly on the disrupted corneal epithelium and is effective and safe in treating inflammatory eye pain.
REFERENCES:

1) Br J Opth 1994; 78: 138-41.