Halo 194 (Jan 2019)
Different methods for measuring intraocular pressure
Abstract
Tonometry is a method for measuring intraocular pressure (IOP). Goldmann applanation tonometry (GAT) represents a golden standard for measuring IOP. The measurement is conducted by measuring the force needed to straighten out a certain area of the cornea. Errors do occur when using the GAT method: inadequate shape and arrangement of fluorescent pictures, bulbar pressure, wrong calibration, astigmatism, corneal pathology (edema, distortion, central corneal thickness), body posture, obesity, the Valsalva maneuver. Modifications of Goldmann's applanation tonometry are methods by Dreger, Perkins and Halberg. Alternative ways to measure IOP are: the digital method and the impression method using Schiotz tonometer. The dynamic contact tonometry(DCT, PASCAL) uses contact, but is a non-applanation method of measuring IOP. It is based on the matching shapes of the head of the tonometer and the cornea, enabling the head of the tonometer to take on the role of the bulbar sheath. Therefore, it directly measures the force transferred onto the bulbar sheath, which is the result of IOP. DCT is an ophthalmology device available commercially since 2004 that measures IOP directly by measuring dynamic pulsatile fluctuations in IOP using a piezoelectric sensor embedded into the tip that touches the cornea. Other tonometry methods are: a) pneumotonometry, b) Ocular Blood flow (OBF), c) non contact tonometry: Grolman's air tonometer, Air-puff tonometer, Ocular Response Analyser (ORA), d) Mackay-Marg electric tonometer, Tono-Pen, Proview Phosphene tonometer, Rebound tonometar. Goldmann applanation tonometry continues to be the golden standard in measuring IOP. It is exact, but not too precise. If more precise measurements are needed other methods of measuring IOP are available.
