Evaluation of three hand-held tonometers in normal canine eyes.

Tonometry, an indirect measurement of intraocular pressure (IOP), is important for the diagnosis and management of glaucoma and uveitis. The aim of this study was to compare the performance of three hand-held tonometers in normal canine eyes. Eyes from cadavers of dogs without observable ocular disease were used to compare tonometric measurements with direct manometry over a range of 7.4-65mmHg. In vivo measurements using the three tonometers in both eyes of 12 healthy dogs were compared. All tonometers significantly underestimated manometric values both ex vivo and in vivo. One tonometer showed a small fixed bias over the range of IOP, whilst the other two tonometers had a negative proportional bias. The results of this study show that differences exist between handheld tonometers across the clinically relevant range of IOP, and that all underestimate manometric measurements.