title: Daytime profile of the intraocular pressure and tear production in normal dog.
abstract: OBJECTIVE
  To evaluate the circadian rhythms of intraocular pressure (IOP) and tear production in dog exposed to a natural photoperiod.
  
  
  METHODS
  We used 12 clinically healthy Beagles dog housed under natural photoperiod at indoor temperature and humidity.
  
  
  METHODS
  Intraocular pressure and Schirmer tear test (STT) I were measured every 4 h over a 48-h period in both eyes in each animal. Statistical analysis of the data was performed by one-way repeated-measures anova, Student's t-test, and single cosinor method.
  
  
  RESULTS
  On each day, there was a highly significant effect of time on both parameters. A statistically significant difference of STT I values was observed comparing left and right eyes (P < 0.0001). Robust daily rhythms were observed for both parameters, IOP values showed diurnal acrophase (left eye: 09:33 +/- 00:50 h; right eye: 09:25 +/- 00:22 h), while STT I values showed nocturnal acrophase (left eye: 20:27 +/- 00:46 h; right eye: 20:00 +/- 00:05 h).
  
  
  CONCLUSIONS
  This study has demonstrated circadian rhythms in both IOP and STT I.
authors.affiliation: Department of Experimental Sciences and Applied Biotechnology, Laboratory of Veterinary Chronophysiology, Faculty of Veterinary Medicine, University of Messina, Polo Universitario dell'Annunziata, 98168 Messina, Italy.
authors.forename: Claudia
authors.initials: C
authors.lastname: Giannetto
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Piccione
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Giudice
mesh_terms: D000818:Animals; D002940:Circadian Rhythm / Q000502:physiology; D004285:Dogs / Q000502:physiology*; D005260:Female; D007429:Intraocular Pressure / Q000502:physiology*; D008297:Male; D013666:Tears / Q000378:metabolism*