Accuracy of intraocular pressure measurements in dogs using two different tonometers and plano therapeutic soft contact lenses

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Abstract

Objective|

To compare and evaluate the accuracy of intraocular pressure (IOP) measured through a therapeutic contact lens, using applanation (TonoPen XL®) and rebound (TonoVet®) tonometers in enucleated dog eyes.

Animals studied|

A total of 30 enucleated eyes from 15 beagle dogs.

Procedures|

To measure accurate IOP, the anterior chamber of each enucleated eye was cannulated with two 26-gauge needles and two polyethylene tubes were connected vertically to an adjustable reservoir bag of normal saline and a pressure transducer. IOP was measured by the TonoPen XL® followed by the TonoVet® without a contact lens. After a contact lens was applied to the cornea, IOP was re-measured in the same order. Three consecutive IOP measurements were performed using both tonometers.

Results|

Without the contact lens, the IOP values obtained by both tonometers correlated well according to the regression analysis (TonoVet®: γ2 = 0.98, TonoPen XL®: γ2 = 0.97, P < 0.001). The TonoPen XL® consistently underestimated values as transducer IOP increased; however, IOP values measured with the TonoPen XL® were in close agreement and were less variable than those determined with the TonoVet® when a contact lens was applied to the cornea. Bland-Altman analysis was used to determine the lower and upper limits of agreement (TonoVet®: −29.7 and +21.1 mmHg, TonoPen XL®: −3.9 and +3.6 mmHg) between the two devices.

Conclusions|

This study suggests that the TonoPen XL® is a useful tonometer for dogs wearing therapeutic contact lenses, and importantly, contact lenses would not need to be removed prior to IOP measurement.

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