Pachymeter

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Ultrasonic pachymeter

A pachymeter (sometimes also called pachometer; from ancient Greek παχύς pachýs "thick" and μέτρον métron "tool for measuring") is a measuring device for measuring the corneal thickness on the human eye .

The corneal thickness is relevant for the correct determination of the intraocular pressure using tonometry , since the measured value is influenced by the corneal thickness in all common methods. The standard corneal thickness is 550 µm.

Furthermore, the reduced thickness of the central cornea is the second most important risk factor for glaucoma. Conversely, an above-average corneal thickness appears to reduce the risk of glaucoma. In addition to the above-mentioned direct influence on the pressure measurement, it is assumed that the cause is that people with a thick cornea have a more stable structure of the lamina cribrosa sclerae, so that the optic nerve head reacts less sensitively to pressure increases.

Pachymetry also plays an important role in preparation for various eye operations . In addition, values ​​of the corneal thickness measurement at different locations can show manifest form anomalies of the cornea such as keratoconus and keratoglobus and even detect early forms (Belin-Ambrosio method). This plays an important role in refractive laser surgery in order to avoid postoperative complications such as keratectasia .

Two different methods are used:

  • the non-contact optical measurement (optical coherence pachymeter, English OCP ) and
  • the determination by means of ultrasound , in which a small ultrasound head is placed on the cornea.
  • Using modern Scheimpflug imaging (e.g. Pentacam), thickness values ​​can be determined over the entire cornea.

Both methods allow the corneal thickness to be determined with an accuracy of a few micrometers. The former procedure is offered or advertised by many ophthalmologists as an individual health service ("IGeL service").

literature

  • Tamara Myers: Mosby's Medical Dictionary. 8th edition. Mosby Elsevier, St. Louis MO 2009, ISBN 978-0-323-05290-0 .

Individual evidence

  1. ^ Wilhelm Gemoll : Greek-German school and hand dictionary. 9th edition, reviewed and expanded by Karl Vretska . Freytag u. a., Munich a. a. 1965.
  2. ↑ Josefine Haak: Comparative measurement of the central corneal thickness and testing of reliability using ultrasound and laser interference pachymetry. (PDF; 2.4 MB) Greifswald 2008, p. 10 (Dissertation, Greifswald, Ernst-Moritz-Arndt-Universität, Medical Faculty, 2009, accessed on June 12, 2013).
  3. ^ Ocular Hypertension Treatment Study. Retrieved May 22, 2017 (English).
  4. ↑ Oculus Pentacam Interpretation Guide. Oculus, accessed December 18, 2018 .