Measuring intraocular pressure by different methods

Tonometry is the measurement of intraocular pressure (IOP). Normal IOP values range from 10 to 21 mmHg (15.5 mmHg +/- 2 SD). They are influenced by various factors, including the patient's position during measurement, central corneal thickness, corneal diameter and curvature, rigidity of the cornea, and the cornea's state of hydration. Until now, Goldmann applanation tonometry has been seen as the gold standard for intraocular pressure measurement. But many new techniques and devices for determining IOP have been developed, such as noncontact tonometry, the To-no-Pen, the ICare tonometer, dynamic con-tour tonometry, TGDc-01 tonometry, and the ocular response analyzer. The aim of these techniques is to minimize distorting influences to obtain the "true IOP." Several of these methods show advantages in specific situations; however, limitations exist that should be considered when interpreting the obtained IOP results. This article describes the individual methods of measurement and discusses their advantages and disadvantages.