Calibration of a novel rebound tonometer (Tono-Vera (R) vet) in the porcine eye

Objective Porcine models of ocular disease are becoming increasingly utilized. A recently commercialized ocular tonometer, the Reichert Tono-Vera (R) Vet, has not been evaluated for use in pigs. The purpose of this study was to calibrate this device for use in porcine eyes and to determine which settings are most appropriate for use in pigs.Procedure The anterior chambers of five freshly enucleated normal porcine eyes were cannulated then connected to a reservoir of balanced salt solution and a physiologic monitor. Triplicate measurements were obtained with the four available settings: dog, cat, horse, and rabbit at intraocular pressures ranging from 5- to 80 mmHg. Bland-Altman analysis was utilized to determine bias and 95% limits of agreement for each setting.Results There was a strong positive linear regression trend for all settings (dog r(2) = 0.986, horse r(2) = 0.947, cat r(2) = 0.977, and rabbit r(2) = 0.982). The linear regression equations for the dog, horse, cat, and rabbit setting were y = 1.0168x - 2.6128, y = 0.8743x - 3.4959, y = 0.9394x - 7.3188, and y = 1.1082x - 3.4077. The average bias and 95% limits of agreement for dog, horse, cat, and rabbit settings were - 2.00, -8.32, -9.58, and 0.57 mmHg, and (-7.52, 3.53), (-19.00, 2.37), (-16.66, -2.50), and (-7.79, 8.93), in mmHg.Conclusion The Tono-Vera (R) Vet dog setting was most accurate and precise setting compared to true intraocular pressures. This setting is likely to be appropriate for in vivo use in pigs, with the appropriate correction formula applied.