title: Effects of action of proparacaine and tetracaine topical ophthalmic formulations on corneal sensitivity in horses.
abstract: OBJECTIVE
  To compare the corneal anesthetic effects and duration of action of 2 ophthalmic anesthetic agents in horses.
  
  
  METHODS
  Prospective, randomized masked crossover study.
  
  
  METHODS
  8 clinically normal adult horses.
  
  
  METHODS
  Corneal sensitivity was determined by measuring each eye's corneal touch threshold (CTT) with a Cochet-Bonnet esthesiometer. Each eye's baseline CTT was recorded prior to anesthetic instillation at 0 minutes and every 10 minutes thereafter for 60 minutes. Each eye was randomly assigned to receive 2 of 4 treatments: 0.5% aqueous proparacaine ophthalmic solution (aqueous proparacaine; 8 eyes); 0.5% aqueous tetracaine ophthalmic solution (aqueous tetracaine; 8 eyes); 0.5% viscous tetracaine ophthalmic solution (viscous tetracaine; 8 eyes); and saline (0.9% NaCl) eyewash solution (8 eyes) as a negative control. There was a 48-hour washout period. Every horse received all treatments.
  
  
  RESULTS
  Median baseline CTT of eyes was 4.5 cm (range, 0.5 to 6 cm). Median CTT for saline solution-treated eyes never differed significantly from baseline. The maximum anesthetic effect with the other 3 treatments occurred at 10 minutes. Median CTT of eyes at 10 minutes was 0.5 cm (range, 0 to 2.5 cm) with aqueous proparacaine treatment, 0.25 cm (range, 0 to 2.0 cm) with aqueous tetracaine treatment, and 0 cm (range, 0 to 0.5 cm) with viscous tetracaine treatment. Maximum anesthetic duration was 20 minutes with aqueous proparacaine and aqueous tetracaine treatments and 30 minutes with viscous tetracaine treatments.
  
  
  CONCLUSIONS
  Treatment of eyes with viscous tetracaine resulted in the greatest decrease in CTT and the longest duration of action, compared with treatment with aqueous proparacaine or aqueous tetracaine.
authors.affiliation: Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, 48823, USA.
authors.forename: Karen L
authors.initials: KL
authors.lastname: Sharrow-Reabe
authors.forename: Wendy M
authors.initials: WM
authors.lastname: Townsend
mesh_terms: D000287:Administration, Topical; D000772:Anesthesia, Local / Q000662:veterinary*; D000779:Anesthetics, Local / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D003315:Cornea / Q000187:drug effects*; D018592:Cross-Over Studies; D006734:Horse Diseases / Q000188:drug therapy*; D006736:Horses; D009883:Ophthalmic Solutions; D011430:Propoxycaine / Q000008:administration & dosage / Q000494:pharmacology*; D013748:Tetracaine / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D000779:Anesthetics, Local; D009883:Ophthalmic Solutions; D013748:Tetracaine; C005717:proxymetacaine; D011430:Propoxycaine