title: Effect of age, gender, weight, and time of day on tear production in normal dogs.
abstract: OBJECTIVE
  To investigate the effects of age, weight, gender, and of time of day on tear production in normal dogs.
  
  
  METHODS
  studied One hundred ophthalmoscopically and systemically unremarkable dogs.
  
  
  METHODS
  Schirmer tear tests (STT) were performed every 2 h during the day on one randomly chosen eye of each of 100 dogs.
  
  
  RESULTS
  There was a statistically significant effect of time of day and age on the STT measurement. The mean STT decreased by 0.4 mm for every 1 year that age increased (P=0.007). Mean STT values taken at 10:00 am were 0.7 mm lower than values taken at 4:00 pm (P=0.04).
  
  
  CONCLUSIONS
  Tear production decreases with age in the normal dog. In this population of dogs the largest difference was between the 10:00 am and the 4:00 pm STT measurements, but this still only amounted to 0.7 mm. This value is unlikely to be of clinical significance in the diagnosis of keratoconjunctivitis sicca (KCS).
authors.affiliation: The Queens Veterinary School Hospital, University of Cambridge, Madingley Road, Cambridge CB3 OES, UK. claudia.hartley@aht.org.uk
authors.forename: Claudia
authors.initials: C
authors.lastname: Hartley
authors.forename: David L
authors.initials: DL
authors.lastname: Williams
authors.forename: Vicki J
authors.initials: VJ
authors.lastname: Adams
mesh_terms: D000367:Age Factors; D000818:Animals; D001835:Body Weight / Q000502:physiology; D002940:Circadian Rhythm; D004283:Dog Diseases / Q000175:diagnosis; D004285:Dogs; D005260:Female; D007638:Keratoconjunctivitis Sicca / Q000175:diagnosis / Q000662:veterinary; D008297:Male; D012737:Sex Factors; D013666:Tears / Q000378:metabolism*