Calibration of the Alcon applanation pneumatonograph and Perkins tonometer for use in rabbits and cats.

The Alcon pneumatonograph (PTG) and Perkins tonometer were calibrated for use on rabbits and cats by connecting the eyes of the anaesthetised animal to a pressure manometer and performing tonometry at varying known pressures. The slope of the calibration graph obtained for the PTG was steeper when the stopcock was closed just before tonometry, whereas open and closed stopcock curves were identical using the Perkins tonometer. When using the PTG on rabbits it was found that tonometer readings could exaggerate changes in intraocular pressure unless converted to mmHg using a relevant calibration curve.