Comparison of three methodologies for measuring intraocular pressure in healthy cats

Measuring intraocular pressure (IOP) is crucial for identifying potentially damaging changes in the eyes, including diseases as glaucoma and uveitis. This study compared intraocular pressure (IOP) measurements in cats using the Tonovet and Tonovet Plus (rebound), Tono-Pen Avia Vet (applanation), and Kowa HA-2 (Goldman's methodology applanation) tonometers.

55 healthy cats (108 eyes) were assessed through three distinct studies: An ex vivo experiment (10 eyes of five cats) to correlate IOP manometry and tonometry values and ascertain the correlation coefficient (r2); an in vivo study (10 eyes of five sedated cats) to contrast manometer and tonometer readings; and an outpatient clinical trial (80 eyes of 45 cats) to analyze only tonometer measurements.

The r ² values observed in the ex vivo study were Tonovet (0.923), Tonovet Plus (0.925), Tono-Pen Avia Vet (0.877), and Kowa HA-2 (0.901). The IOP values in mmHg in the in vivo study were as follows: Manometer (16.1 ± 2.7), Tonovet (21.1 ± 3.6), Tonovet Plus (19.7 ± 7.2), Tono-Pen Avia Vet (17.6 ± 7.9), and Kowa HA-2 (16.8 ± 2.0). In the outpatient clinical study, the IOP values in mmHg were as follows: Tonovet (19.7 ± 6.6), Tonovet Plus (17.1 ± 5.4), Tono-Pen Avia Vet (16.3 ± 4.3), and Kowa HA-2 (14.5 ± 2.2).

IOP and manometry readings were strongly correlated by all tonometers. In the clinical setting, the most and least IOP measurements were recorded using Tonovet and Kowa HA-2, respectively, stressing the importance of an IOP reference table for each tonometer in feline practice.