Intraocular pressure measurements with the Tono-Pen XL® and Perkins® applanation tonometers in horses and cattle

Abstract

The objective of this study was to compare the accuracy between two applanation tonometers, Tono-Pen XL® and Perkins®, in horses and cattle. The eyes of 20 horses and 20 cattle conscious and healthy were evaluated for the in vivo study and both eyes of 5 horses and 5 cattle were used as controls for the postmortem study. In conscious animals, the tonometry was performed with auriculopalpebral nerve block and then topical anesthesia for both tonometers and 1% fluorescein eye drops only for the Perkins tonometer. Readings of intraocular pressure (IOP) in the postmortem study were taken using manometry and tonometry by Tono-Pen XL® and Perkins®. The correlation coefficient (r²) between manometry and applanation tonometers Tono-Pen XL® and Perkins®, in horses, were 0.845 and 0.989, respectively, and in cattle, were 0.772 and 0.988, respectively. The mean IOP values in conscious horses with Tono-Pen XL® and Perkins® were 20.1±3.9mmHg and 20.9±3.2mmHg, respectively, and in conscious cattle, these values were 17.2±2.4mmHg and 17.9±1.4mmHg, respectively. There was a strong correlation between the IOP values obtained by direct ocular manometry and the Tono-Pen XL® and Perkins® tonometers in horses and cattle. There was no statistically significant difference between the mean IOPs obtained with both tonometers in conscious animals; however, there was a difference between the minimum values, which were on average 2-3 mmHg lower with the Tono-Pen XL® tonometer than with the Perkins® tonometer, which justifies a table of normal values differentiated for each tonometer.O objetivo deste estudo foi comparar a acurácia entre dois tonômetros de aplanação, Tono-Pen XL® e Perkins®, em equinos e bovinos. Os olhos de 20 equinos e 20 bovinos conscientes e saudáveis foram avaliados para o estudo in vivo e ambos os olhos de 5 equinos e 5 bovinos foram usados como controle para o estudo post-mortem. Nos animais conscientes, a tonometria foi realizada com bloqueio do nervo auriculopalpebral e depois anestesia tópica para ambos os tonômetros e colírio de fluoresceína a 1% somente para o tonômetro de Perkins. Leituras da pressão intraocular (PIO) no estudo post-mortem foram realizadas utilizando manometria e tonometria pelo Tono-Pen XL® e Perkins®. O coeficiente de correlação (r²) entre a manometria e os tonômetros de aplanação Tono-Pen XL® e Perkins®, em equinos, foi de 0,845 e 0,989, respectivamente, e, em bovinos, foi de 0,772 e 0,988, respectivamente. Os valores médios de PIO nos equinos conscientes com Tono-Pen XL® e Perkins® foram 20,1±3,9mmHg e 20,9±3,2mmHg e, em bovinos conscientes, os valores foram de 17,2±2,4mmHg e 17,9±1.4mmHg, respectivamente. Houve uma forte correlação entre os valores obtidos de PIO pela manometria ocular direta e os tonômetros Tono-Pen XL® e Perkins® em equinos e bovinos. Entretanto, houve uma diferença entre os valores mínimos, em média 2-3mmHg menor com o tonômetro Tono-Pen XL® do que o tonômetro de Perkins®, o que justifica uma tabela de valores diferenciada para cada tonômetro.