[Clinical evaluation of the Tonovet® reboundtonometer in dogs and cats considering potential errors in handling]

To evaluate the Tonovet® rebound tonometer in a larger number of dogs and cats free of ocular disease and to examine the impact of handling errors of the tonometer.

In 100 ophthalmologically healthy dogs (n = 80) and cats (n = 20) of different breeds (beagle, dachshund, retriever, brachycephalic dogs, domestic shorthair cats), the intraocular pressure (IOP) was measured bilaterally using the Tonovet® according to the manufacturer's instructions. Subsequently, different aspects of handling/positioning were altered (localisation and angle of impact, distance of probe to corneal surface). Finally a comparative measurement was made using the Tonopen Vet® applanation tonometer.

Mean IOP ± standard deviation (SD) in the dogs (160 eyes) was 13,7 ± 2.9 mmHg for the Tonovet® and 12.9 ± 3.1 mmHg for the Tonopen Vet®. In the cats (40 eyes) a IOP value of 16.7 mmHg ± 3.0 mmHg was obtained with the Tonovet® and 17.4 mmHg ± 3.0 mmHg with the Tonopen Vet®. Deviation from the manufacturer's recommendations on handling the Tonovet® during the measurement significantly affected the results obtained. Compared to the reference measurement, directing the Tonovet® onto the peripheral cornea (approximately 1.5 mm from the limbus) as well as reducing the measuring distance to <4 mm resulted in slightly elevated IOP readings. Substantial underestimation of IOP occurred with angular deviation of the measuring axis.

The Tonovet® rebound tonometer proved to be a valuable alternative to conventional tonometers for clinical use in dogs and cats. It is well tolerated by both canine and feline patients. However, the use of the Tonovet® in a clinical setting requires the examiner to consider potential sources of error when handling the tonometer to avoid false IOP readings.