Tonometer validation and intraocular pressure reference values in the normal chinchilla (Chinchilla lanigera).

Objectives: 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.
(© 2017 American College of Veterinary Ophthalmologists.)