title: Tonometer validation and intraocular pressure reference values in the normal chinchilla (Chinchilla lanigera).
abstract: OBJECTIVE
  To determine accuracy and precision of three commonly used tonometers (TonoVet®and TonoLab®(ICare Oy, Finland)-rebound tonometers, and Tono-Pen VET™ (Reichert, NY)-applanation tonometer) in normal chinchillas, and to establish a normal intraocular pressure (IOP) reference range in this species.
  
  
  METHODS
  The anterior chambers of three chinchilla eyes were cannulated ex vivo and readings obtained at manometric IOPs from 5 to 80 mmHg, using each of the three tonometers in random order. Data were analyzed by linear regression, ANOVA, and Bland-Altman plots. Tonometry was performed in both eyes of 60 chinchillas (age 8 weeks-16.2 years) using the TonoVet®and relationship between age and IOP analyzed using linear regression. For all statistical tests, P < 0.05 was significant.
  
  
  RESULTS
  Intraocular pressure values obtained using the Tono-Pen VET™ and TonoVet®(in dog calibration mode;'d') showed strong linear correlation with manometry within the physiologic and clinically relevant range of IOP (0-50 mmHg). The TonoVet®'d' setting displayed significantly greater precision over the full range of IOP evaluated than the Tono-Pen VET™, and both TonoVet and Tono-Pen VET™ were significantly more accurate than the TonoLab®tonometer. Mean ± SD IOP (TonoVet®'d') in chinchillas was 9.7 ± 2.5 mmHg, and the 95% reference interval was 4.7-14.7 mmHg.
  
  
  CONCLUSIONS
  Both the Tono-Pen VET™ and TonoVet®provided clinically acceptable estimates of IOP in chinchillas. The TonoVet®provides accurate and precise IOP values, while Tono-Pen VET™ derived measurements showed greater variability. Values obtained either with the TonoLab®or TonoVet®used in the 'unspecified' calibration setting were inaccurate in this species.
authors.affiliation: Department of Surgical Sciences, School of Veterinary Medicine, University of Wisconsin - Madison, Madison, WI, 53792, USA.|McPherson Eye Research Institute, University of Wisconsin - Madison, Madison, WI, 53792, USA.
authors.forename: Kevin C
authors.initials: KC
authors.lastname: Snyder
authors.affiliation: Department of Surgical Sciences, School of Veterinary Medicine, University of Wisconsin - Madison, Madison, WI, 53792, USA.|McPherson Eye Research Institute, University of Wisconsin - Madison, Madison, WI, 53792, USA.
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Lewin
authors.affiliation: Department of Surgical Sciences, School of Veterinary Medicine, University of Wisconsin - Madison, Madison, WI, 53792, USA.
authors.forename: Christoph
authors.initials: C
authors.lastname: Mans
authors.affiliation: Department of Surgical Sciences, School of Veterinary Medicine, University of Wisconsin - Madison, Madison, WI, 53792, USA.|McPherson Eye Research Institute, University of Wisconsin - Madison, Madison, WI, 53792, USA.|Department of Ophthalmology & Visual Sciences, University of Wisconsin - Madison, Madison, WI, 53792, USA.
authors.forename: Gillian J
authors.initials: GJ
authors.lastname: McLellan
mesh_terms: D000818:Animals; D002682:Chinchilla / Q000502:physiology*; D007429:Intraocular Pressure / Q000502:physiology*; D012016:Reference Values; D015203:Reproducibility of Results; D014065:Tonometry, Ocular / Q000592:standards / Q000662:veterinary*
keywords: Tono-Pen Vet; TonoLab; TonoVet; chinchilla; intraocular pressure; manometry