EXPERIMENTAL USE OF TETRODOTOXIN FOR CORNEAL PAIN AFTER EXCIMER-LASERKERATECTOMY

Purpose. To determine the duration of anesthesia, effect on corneal re epithelialization, and systemic toxicity of topical tetrodotoxin (TTX) administered after excimer laser keratectomy. Methods, Two groups of six rabbits each underwent excimer laser keratectomy in the right eye to create a 5-mm-diameter wound, 75 mm in depth. One group then receiv ed a 40-mu l aliquot of topical 1 mM TTX into the injured eye, whereas the other group received 40 mu l of the sodium citrate vehicle as a c ontrol. The rabbits were treated with TTX or vehicle again at 6, 12, 1 8, and 24 h. Corneal sensation was tested at 3, 6, 9, 12, 15, 18, 21, 24, 30, 32, and 40 h. To determine whether TTX inhibited corneal reepi thelialization, compared with vehicle-treated control eyes, the healin g rate of the epithelial defect was measured. Results, Administration of TTX every 6 h for 24 h produced nearly complete anesthesia for grea ter than or equal to 30 h. At 32 h, 8 h after the final application of TTX, there was still significant anesthesia of the TTX-treated cornea s (p = 0.0325, Wilcoxon test). Normal corneal sensation in all TTX-tre ated animals returned at 40 h, or 16 h after the final dose. in contra st, vehicle-treated eyes all had normal sensation for nearly the entir e duration of the experiment. At 40 h, the TTX-treated eyes had slight ly lar er defects than vehicle-treated eyes, 7.85+/-1.74 versus 4.54+/ -1.31 mm(2) (p < 0.025, t test). However, at 39 h and thereafter, both groups were equally healed (p > 0.05, t test). No systemic toxicity w as observed in any of the rabbits. Conclusion. Topical TTX is a long-a cting and nontoxic local anesthetic in a rabbit model of excimer laser keratectomy.