May 27, 2015
Today in optometry, much emphasis is put on correctly measuring a patient’s IOP to the exact mm Hg. With attention being placed on corneal pachymetry and hysteresis, there is another simple – yet important – step you can do to ensure proper IOP reading. It has to do with that red line on your Goldmann tonometer.
When Dr. Goldmann developed his tonometer, he calibrated it to produce a specific area of flattened cornea: 7.354 mm2. This is derived from the equation to find the area of a circle: area = 3.14 x radius2. In our situation, the radius of the Goldmann probe is 1.53 mm. When measuring spherical corneas, measurements can be made on any meridian. We use 0 and 180 for convenience.