Tonometry

Eye pressure measurement, glaucoma screening

Overview

Tonometry is the measurement of intraocular pressure, the fluid pressure inside the eye, and is a key part of assessing glaucoma risk and managing the disease. Goldmann applanation tonometry, introduced in the 1950s and long regarded as the reference standard, uses a small prism mounted on a slit lamp to measure the force needed to flatten a fixed area of the numbed cornea. Noncontact air puff tonometers estimate pressure from the corneal response to a jet of air and are often used for screening. Rebound tonometers, which bounce a tiny probe off the cornea, are handheld and require no anesthetic, and some versions are designed for use at home. Pressure is reported in millimeters of mercury, and the statistically normal range is commonly given as roughly 10 to 21. Readings are influenced by central corneal thickness, so pachymetry is often performed as well. Intraocular pressure varies throughout the day, and normal tension glaucoma and ocular hypertension illustrate that pressure alone does not determine whether optic nerve damage occurs.