How is Tonometry Performed?
There are two methods of measuring IOP in animals: indentation tonometry and applanation tonometry. With indentation tonometry, the measuring instrument applies a rod of a certain weight to the surface of the cornea. The distance that the rod indents the cornea is inversely related to the pressure within the eye. In other words, the softer the eye, the more the rod indents the cornea. The harder the eye and higher the IOP, the less indentation occurs. The primary tool used for indentation tonometry is the Schiotz tonometer. When using the Schiotz tonometer, the distance the rod moves is reflected in the movement of a small metal tone arm across a number scale on the top of the instrument. This number is then converted to mmHg through the use of two conversion scales specifically established for the dog and the cat. In order to get an accurate reading, the animal’s nose is pointed toward the ceiling so the Shiotz can utilize the effects of gravity to indent the cornea. With applanation
