Comparison of TonoLab , TonoVet Plus, and Tono‐Pen AVIA Vet Tonometers for Measuring Intraocular Pressure in Rats

OBJECTIVES: To assess the agreement between intraocular pressure (IOP) measurements in rats using different animal-adapted tonometers and to evaluate the relation among the devices. METHODS: IOP was measured using the TonoLab tonometer, followed by the TonoVet Plus and finally, the Tono-Pen AVIA Vet. A total of 24 eyes were studied from 12 healthy Wistar rats anesthetized with sevoflurane. Agreement analysis was performed between the TonoLab tonometer and the TonoVet Plus, and the TonoLab and Tono-Pen AVIA Vet using the intraclass correlation coefficient (ICC). For the tested pairs, Bland-Altman graphs were also performed. The relation of TonoVet Plus and Tono-Pen AVIA Vet tonometers to TonoLab was also evaluated using a simple linear regression. RESULTS: The agreement between the TonoLab tonometers and the TonoVet Plus was weak (ICC = 0.173, 95% CI [-0.129; 0.489], p = 0.130) and not statistically significant. The agreement between the TonoLab and the Tono-Pen AVIA Vet tonometers was negligible (ICC = 0.011, 95% CI [-0.117; 0.218], p = 0.448). Linear regression analysis between the TonoLab and the TonoVet Plus (p = 0.256), as well as between the TonoLab and the Tono-Pen AVIA Vet (p = 0.897), was not statistically significant. CONCLUSIONS: The measurements revealed a consistent pattern in which the Tono-Pen AVIA Vet showed the highest mean IOP values, followed by the TonoVet Plus and the TonoLab. Knowing the normal values of indirect IOP in rats for each of these tonometers, as well as the differences between them, is fundamental for the proper interpretation of the measurements obtained and for allowing reliable comparisons between the devices.