There is nothing terrifying about taking an applanation tonometry test, although it can certainly seem like that when you are first going to have one. These tests are taken by using specially fitted slit lamps or other similar devices and they are useful in measuring the fluid pressure inside the eye (intraocular pressure). This field of ophthalmology is also known as ocular tonometry and is one of the best ways of checking for severe eye problems that need to be identified quickly in order to be able to treat them effectively.
What are the conditions it is used to test for?
Glaucoma is the main condition that applanation tonometry is used to test for. This eye disease can cause blindness through damage to the optic nerve in the back of the eye and one of the causes of this damage can be a build up of excess fluid in the eye which refuses to drain properly. There are a variety of methods to measure intraocular pressure, which can give a good indication if there is any fluid buildup in the eye that might be an early precursor to glaucoma.
Various tonometry methods
Applanation tonometry is only the main method of detecting fluid buildup and excess intraocular pressure. It is also the most reliable of all the tests and is considered the benchmark in ophthalmology. A small probe attached to slit lampsis used to look at the eye and the pressure is measured by the amount of pressure needed to flatten the cornea.
This benchmark test can be stressful though, especially for children and other patients who are not cooperative, so there are other tests designed which are less effective, but can still give a good indication.
Electronic indentation tonometry
This is a small electronic device to which a sterilized head is attached and then it is placed against your cornea. The intraocular pressure is displayed in digital form on the pen like device. Readings can be different to applanation tonometry though and it is useful to do more than one test.
Pneumotonometry (non contact; with air)
This type of tonometry is done without contacting the actual cornea of the eye and is the most useful for testing groups of people who will not cooperate, such as children. A small puff of air is blasted at the eye in order to flatten the cornea. If the cornea cannot be flattened, the process is repeated with more air pressure and eventually the amount can be determined. This is most often used to check if there is a high intraocular pressure and is probably the best way to test children, as they will often not really cooperate with applanation tonometry methods.
Indentation tonometry
This uses a mechanical plunger to push down on the cornea and measures how much weight is needed to flatten the cornea. It is not very accurate and not used a lot by optometrists any more, but it is still in common use in some places where access to portable electronic devices and applanation tonometryis limited.

















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