Although historically digital tonometry has been recommended as a means of estimating intraocular pressure (IOP) in dogs and
cats, I find the method extremely unreliable. With digital tonometry, I have overestimated IOP in cats, brachycephalic dogs,
and dogs with rigid sclera, such as Boston terriers and Chihuahuas. I have also underestimated IOP in dolichocephalic animals
and animals with enophthalmos.
Rhea V. Morgan
The accuracy of estimating IOP with digital palpation is affected by the anatomy of the surrounding orbit, the position of
the globe within the orbit, and the status of the periocular soft tissues. I have found little correlation between the estimation
of IOP by using digital palpation and the actual measurement of IOP by using either an indentation (Schiøtz) or applanation
(Tono-Pen Vet—Medtronic Solan) tonometer. I highly recommend that small-animal veterinarians use either an indentation or
applanation tonometer to measure IOP and that equine practitioners consider adding applanation tonometers to their practices.
Although the indentation tonometer is being replaced by the applanation tonometer in many practices, it is still a reliable
tool, especially when used on a consistent basis.
Rhea V. Morgan, DVM, DACVIM, DACVO
Smoky Mountain Veterinary Services
1212 Sawtooth Ridge Way
Walland, TN 37886