Tonometry through the ages.

The definition of glaucoma has changed over the decades from a simple ocular pressure disease to a systemic disorder of multivariate etiology. Glaucoma may be defined for the individual eye as a chronic ocular disease with various underlying pathophysiologic disorders. However, elevated intraocular pressure (IOP) is still the most important risk factor for an untreated glaucomatous eye to progress to a more severe stage of the disease. As the main risk factor within therapeutic reach, IOP and its appropriate measurement deserve our ongoing interest. Not only has our understanding of glaucoma changed but also our approach to the measurement of the IOP. In this article we focus our attention on the various developments in tonometry from the simple force-tonometers of the late 19th century to the high-technology pressure tonometers that were recently introduced for clinical use.