Intraocular Pressure Measurement with a Rebound Tonometer (TonoVet®) in Normal Pigeons

Abstract

The purpose of this study was to evaluate the applicability of a rebound tonometer (TonoVet®) in pigeon eyes and to establish normal reference intraocular pressure (IOP) values in healthy pigeons. Twenty eyes of euthanized pigeons were used for the calibration of TonoVet® and 48 eyes of 24 adult pigeons for the reference IOP. First, IOP of pigeon eyes ex vivo were measured using the d and the p modes of the TonoVet® and compared with manometric IOP values from 5 to 80 mmHg. Then, to establish normal reference values, IOP was measured from clinically normal pigeons in vivo. Both the d and the p modes of the TonoVet® showed a strong linear correlation with the manometric IOP (R2 = 0.996 and 0.991, respectively). The obtained regression formulas were y = 0.431x1 + 2.154 and y = 0.330x2 - 0.673, respectively (x1, d mode of TonoVet®

x2, p mode of TonoVet®

y, manometric IOP). The d and the p modes steadily underestimated the actual IOP by approximately 1/2 and 1/3, respectively. Therefore, the formula obtained through the d mode was applied to obtain reference values. The calibrated IOP of normal pigeon eyes was 19.5 ± 4.4 mmHg. The actual IOP could be calculated using the presented formula. Considering the limitations of the p mode, it would be more appropriate to use the d mode. Therefore, the TonoVet® rebound tonometry under d mode is a reliable method for measuring IOP in pigeons.