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