title: Duration of corneal anaesthesia following multiple doses and two concentrations of tetracaine hydrochloride eyedrops on the normal equine cornea.
abstract: BACKGROUND
  There is a clinical impression that tetracaine hydrochloride (THCl) eyedrops is a suitable topical anaesthetic in horses.
  
  
  OBJECTIVE
  To determine the duration of corneal anaesthesia following instillation of multiple doses and 2 concentrations of THCl in 10 healthy horses.
  
  
  METHODS
  The corneal touch threshold (CTT) was determined, in both eyes, before (basal CTT) and after application of one drop of 0.5% THCl, 2 drops at a 1 min interval of 0.5% THCl or one drop of 1% THCl. CTT was measured in mm every 5 min until complete recovery of the basal CTT. Treatments were separated by an interval of at least one week.
  
  
  RESULTS
  Corneal sensitivity was significantly reduced from baseline values for 30, 60 and 50 min after application of one drop of 0.5% THCl, 2 drops of 0.5% THCl and one drop of 1% THCl, respectively. Mean maximal anaesthetic effects, corresponding to a CTT of 0 mm, lasted 5.5, 16 and 15.25 min and maximal anaesthetic effect was present in 55, 90 and 80% of eyes, 5 min after application of one drop of 0.5% THCl, 2 drops of 0.5% THCl and one drop of 1% THCl, respectively.
  
  
  CONCLUSIONS
  The application of a second drop or the use of more concentrated eyedrops significantly increases duration of both anaesthesia and maximal anaesthetic effect.
  
  
  CONCLUSIONS
  Duration of corneal anaesthesia following tetracaine instillation was established enabling a better use when performing diagnostic and therapeutic procedures. Comparison of tetracaine with other ocular anaesthetics needs to be published in the future.
authors.affiliation: Department of Clinical Sciences, Faculty of Veterinary Medicine, Liège University, Liège, Belgium. smonclin@hotmail.com
authors.forename: S J
authors.initials: SJ
authors.lastname: Monclin
authors.forename: F
authors.initials: F
authors.lastname: Farnir
authors.forename: M
authors.initials: M
authors.lastname: Grauwels
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*; D004334:Drug Administration Schedule; D005260:Female; D006734:Horse Diseases / Q000601:surgery*; D006736:Horses; D008297:Male; D009883:Ophthalmic Solutions; D013748:Tetracaine / Q000008:administration & dosage* / Q000494:pharmacology*
chemical_list: D000779:Anesthetics, Local; D009883:Ophthalmic Solutions; D013748:Tetracaine