Four freshly enucleated normal porcine eyes were cannulated with two 25-gauge needles; one connected via tubing to a mercury manometer calibrated continuous physiologic recorder and the other connected to a reservoir of lactated Ringer`s solution on an adjustable stand.
Triplicate IOP readings were taken with the TonoVet and then the Tono-Pen Vet at 5, 10, 15, 20, 25, 30, 35, 40, 50, 60, 70, 80 mmHg.
Linear regression showed strong linear trends for both the TonoVet (r2 = 0.969) and Tono-Pen Vet (r2 = 0.983).
The TonoVet slightly underestimated IOP at lower pressures and slightly overestimated IOP at higher pressures (y = 1.092x − 4.0, where y = tonometer reading, x = manometer reading, and 4.0 = intercept).
The Tono-Pen Vet consistently underestimated IOP (y = 0.773x − 2.1).
These differences were statistically significant (P = <0.001, one-way repeated-measures ANOVA).
As in other species, both the TonoVet and Tono-Pen Vet tonometers do not measure true IOP in the porcine eye; however, the TonoVet more closely approximated true IOP in the normal porcine eye than the Tono-Pen Vet and may be the tonometer of choice for this species.
Source: Lewin, A. C. and Miller, P. E. (2016), Calibration of the TonoVet and Tono-Pen Vet tonometers in the porcine eye. Veterinary Ophthalmology. doi: 10.1111/vop.12445
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