title: Circadian rhythm of intraocular pressure in cats.
abstract: OBJECTIVE
  To evaluate the rhythm of intraocular pressure (IOP) in healthy domestic cats with no evidence of ocular disease and to analyze the influence of photoperiod, age, gender and ocular diseases on diurnal-nocturnal variations of cat IOP.
  
  
  METHODS
  All animals were Domestic Short-haired cats; 30 were without systemic or ocular diseases, classified as follows: 12 male intact adult cats, five intact adult female, five adult spayed female, and eight male cats; the latter were less than 1 year of age. In addition, five adult cats with uveitis and three adult cats with secondary glaucoma were included.
  
  
  METHODS
  IOP was assessed with a Tono-Pen XL at 3-h intervals over a 24-h period in 12 healthy adult male cats kept under a photoperiod of 12-h light/12-h darkness for 2 weeks. Eight animals from the same group were then kept under constant darkness for 48 h, and IOP was measured at 3-h intervals for the following 24 h. In addition, IOP was assessed at 3 p.m. and 9 p.m. in five intact females, five spayed females, and in eight young cats, as well as in five adult cats with uveitis and three glaucomatous cats.
  
  
  RESULTS
  Consistent, daily variations in IOP were observed in animals exposed to a light-dark cycle, with maximal values during the night. In cats exposed to constant darkness, maximal values of IOP were observed at subjective night. Differences of IOP values between 3 p.m. and 9 p.m. (diurnal-nocturnal variations) persisted in intact females, spayed females, and young animals, as well as in uveitic and glaucomatous eyes.
  
  
  CONCLUSIONS
  The present results indicate a daily rhythm of cat IOP, which appears to persist in constant darkness, suggesting some level of endogenous circadian control. In addition, daily variations of cat IOP seem to be independent of gender, age, or ocular diseases (particularly uveitis and glaucoma).
authors: Laboratorio de Fisiología del Sistema Nervioso y Endocrinología, Departamento de Fisiopatología, Facultad de Ciencias Veterinarias, Universidad Nacional del Centro de la Provincia de Buenos Aires, Tandil, Argentina.
authors: María J
authors: MJ
authors: Del Sole
authors: Pablo H
authors: PH
authors: Sande
authors: José M
authors: JM
authors: Bernades
authors: Marcelo A
authors: MA
authors: Aba
authors: Ruth E
authors: RE
authors: Rosenstein
mesh_terms: D000818:Animals; D002371:Cat Diseases / Q000503:physiopathology; D002415:Cats / Q000502:physiology*; D002940:Circadian Rhythm; D005260:Female; D005901:Glaucoma / Q000503:physiopathology / Q000662:veterinary; D007429:Intraocular Pressure / Q000502:physiology*; D008297:Male; D012016:Reference Values; D014065:Tonometry, Ocular / Q000662:veterinary