Validation of the TonoVet rebound tonometer in normal and glaucomatous cats

OBJECTIVE:  To validate intraocular pressure (IOP) readings obtained in cats with the TonoVet tonometer. Animals studied  IOP readings obtained with the TonoVet were compared to IOP readings determined by manometry and by the Tono-Pen XL in 1 normal cat and two glaucomatous cats. TonoVet and Tono-Pen XL readings were also compared in a further six normal and nine glaucomatous cats.

PROCEDURES: The anterior chambers of both eyes of three anesthetized cats were cannulated and IOP was varied manometrically, first increasing from 5 to 70 mmHg in 5 mmHg increments, then decreasing from 70 to 10 mmHg in 10 mmHg decrements. At each point, two observers obtained three readings each from both eyes, with both the TonoVet and Tono-Pen XL. IOP was measured weekly for 8 weeks with both tonometers in six normal and nine glaucomatous unsedated cats. Data were analyzed by linear regression. Comparisons between tonometers and observers were made by paired student t-test.

RESULTS:  The TonoVet was significantly more accurate than the Tono-Pen XL (P=0.001), correlating much more strongly with manometric IOP. In the clinical setting, the Tono-Pen XL underestimated IOP when compared with the TonoVet .

CONCLUSION: Both the TonoVet and Tono-Pen XL provide reproducible IOP measurements in cats; however, the TonoVet provides readings much closer to the true IOP than the Tono-Pen XL. The TonoVet is superior in accuracy to the Tono-Pen XL for the detection of ocular hypertension and/or glaucoma in cats in a clinical setting.