Intraocular pressure measurement can be done in several ways. Many people are familiar with the air puff. This method was popular when optometrists were not allowed to place anesthetic eye drops in the patients eyes. Theanesthetic drops are necessary to applanate (flatten) the central cornea thereby measuring the resistance over a certain known area and deducing the pressure. The measurement assumes a standard rigidity and thickness of the cornea. These assumptions are not always correct and a thin cornea will lead to a falsy low reading and underestimate the actual pressure. The converse is true of a thick cornea.
