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

Abstract

OBJECTIVE: To compare and evaluate the accuracy of intraocular pressure (IOP) measured through a therapeutic contact lens, using applanation (TonoPen XL(&#xae;)) and rebound (TonoVet(&#xae;)) 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(&#xae;) followed by the TonoVet(&#xae;) 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(&#xae;): &#x3b3;(2) = 0.98, TonoPen XL(&#xae;): &#x3b3;(2) = 0.97, P < 0.001). The TonoPen XL(&#xae;) consistently underestimated values as transducer IOP increased; however, IOP values measured with the TonoPen XL(&#xae;) were in close agreement and were less variable than those determined with the TonoVet(&#xae;) when a contact lens was applied to the cornea. Bland-Altman analysis was used to determine the lower and upper limits of agreement (TonoVet(&#xae;): -29.7 and +21.1 mmHg, TonoPen XL(&#xae;): -3.9 and +3.6 mmHg) between the two devices. CONCLUSIONS: This study suggests that the TonoPen XL(&#xae;) is a useful tonometer for dogs wearing therapeutic contact lenses, and importantly, contact lenses would not need to be removed prior to IOP measurement.