Tonometer


A tonometer is an instrument used by eye care professionals to measure the pressure inside the eyeball. This is known as the intra-occular pressure and can be an indicator of certain diseases.

There are a variety of tonometers used by opticians. Applanation or Goldmann tonometry is the so called ‘gold standard’ test, meaning it is the best and most widely used. This method uses a sterilised prism to measure the force required to flatten part of the front of the eye called the cornea. It is a relatively quick and painless procedure, however due to the eye contact, some local anaesthetic eye drops are used to prevent any pain.

Another method is Dynamic Contour Tonometry, which is used less widely than Goldmann tonometry. The optician places a disk shaped like the front of the eye onto the cornea. A constant pressure is passed through the disk onto the eye, and changes in the intra-occular pressure can be measured, for example when the heart beats. This is a fast procedure, lasting approximately 10 seconds per eye. Again, anaesthetic drops are used to prevent any pain.

Transpalpebral tonometry measures the intra-occular pressure through the eyelid, and requires no anaesthetic drops or sterilisation prior to the test. It involves dropping a tiny rod onto the eyelid, at which point the instrument measures how far it bounces back. This allows an indirect measure of the intra-occular pressure.

Non-contact tonometry uses a jet of air to flatten the cornea. This can be measured and used to calculate the intra-occular pressure. This is mainly used to measure high intra-occular pressures and is useful as it requires no sterilisation or anaesthetic.

There are a wide variety of other tonometers available. Rebound tonmeters are particularly helpful as they are portable, which allows you to examine children and eldery patients who are not mobile.

The main use of tonometers is to detect a condition known as glaucoma. This is a raised intra-occular pressure, which if not treated can lead to vision problems.


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