title: Determination of tear break-up time reference values and ocular tolerance of tetracaine hydrochloride eyedops in healthy horses.
abstract: BACKGROUND
  Tetracaine hydrochloride (THCl) has been reported to cause irritation in dogs. In man, some topical anaesthetics have been shown to disrupt the tear film. Tear break-up time (TBUT) is a useful test allowing an assessment of the quality of the precorneal tear film. Only one TBUT value has been reported in horses with no information on the technique used.
  
  
  OBJECTIVE
  To provide a method for performing the TBUT in horses and to report any side effects of a single application of THCl in clinically normal horses, particularly on the stability of the tear film.
  
  
  METHODS
  In Study 1, one drop of 0.5 or 1% THCl was applied to one eye of 20 horses divided in 2 groups. Treated eyes were assessed for the development of side effects 2.5 and 5 min after treatment. In Study 2, the TBUT was measured in both eyes of 2 groups of 10 horses, before and 2.5 and 5 min after, instillation of one drop of either 0.5 or 1% THCl.
  
  
  RESULTS
  No animals developed any ocular side effect after instillation. Basal TBUT was 8.3±1.3 s. TBUT decreased from baseline 5 and 2.5 min after application of one drop of 0.5% THCl and one drop of 1% THCl, respectively.
  
  
  CONCLUSIONS
  A technique to measure the TBUT in healthy horses is described and normal range values that could be used as a reference were obtained.
  
  
  CONCLUSIONS
  THCl is well tolerated in horses but lowers the TBUT.
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 / Q000009:adverse effects*; D000818:Animals; D005260:Female; D006736:Horses; D008297:Male; D009883:Ophthalmic Solutions; D013666:Tears / Q000737:chemistry*; D013748:Tetracaine / Q000009:adverse effects*
chemical_list: D000779:Anesthetics, Local; D009883:Ophthalmic Solutions; D013748:Tetracaine