Intraocular pressure in American Bullfrogs (Rana catesbeiana) measured with rebound and applanation tonometry

Objective To measure the intraocular pressure (IOP) in normal American Bullfrogs (Rana catesbeiana) with rebound and applanation tonometry and to create calibration curves for both tonometers to determine the actual IOP of bullfrogs. Procedures Twenty bullfrogs were evaluated with slip-lamp biomicroscopy, indirect ophthalmoscopy, rebound tonometry, and applanation tonometry. Axial globe length and corneal thickness were measured in the three largest and the three smallest frogs with ultrasonography and optical coherence tomography, respectively. Two frogs were euthanized for direct manometry. Results The median IOP was 4 mmHg with the rebound tonometer and 16 mmHg with the applanation tonometer. The correlation coefficient (r(2)) between the manometry measurements and the tonometers was 0.95 and 0.91 for the rebound and applanation tonometers, respectively. The corresponding equations were y = 0.331x + 0.558 for the rebound tonometer and y = 0.675x + 1.907 for the applanation tonometer. The median axial globe length was 0.94 cm. The median corneal thickness was 0.093 mm. Conclusions The rebound tonometer is the preferable tonometer for American Bullfrogs. Neither tonometer produced IOP readings that matched the manometer. The rebound tonometer was more precise and it was faster and easier to use.