Intraocular Pressure Measurement by Rebound Tonometry (TonoVet) in Normal Pigeons (Columba livia)

Abstract

We evaluated the applicability of a rebound tonometer (TonoVet) in pigeon eyes and established normal reference intraocular pressure (IOP) values in healthy pigeons; 20 eyes of euthanized pigeons were used for calibration of the TonoVet and 48 eyes of 24 adult pigeons were used for measurement of reference IOP. First, IOP of pigeon eyes ex vivo were measured using the 'd' and the 'p' modes of the TonoVet and compared to manometric IOP values from 5 to 80 mm Hg. Then, to establish normal reference values, IOP was measured from clinically normal pigeons in vivo. The 'd' and the 'p' modes of the TonoVet showed a strong linear correlation with the manometric IOP (<i>R</i>² = .996 and .991, respectively). The obtained regression formulas were: <i>y</i>₁ = 0.439<i>x</i> + 2.059 and <i>y</i>₂ = 0.330<i>x</i> - 0.673, respectively (<i>y</i>₁, 'd' mode of TonoVet; <i>y</i>₂, 'p' mode of TonoVet; <i>x</i>, manometric IOP). The 'd' and the 'p' modes consistently measured one-half and one-third of the actual IOP, 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 mm Hg. The actual IOP could be calculated using the presented formula. Considering the limitations of the 'p' mode, use of the 'd' mode is more appropriate. Therefore, the TonoVet rebound tonometry under the 'd' mode is a reliable method for measuring IOP in pigeons.