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Tonometry is an examination, in which the intraocular pressure is measured. The intraocular pressure is a specific pressure on the eyeball. An excessively high intraocular pressure may cause damage to the retina or optic nerve. Tonometry is part of the standard examination done in case of eye problems.
Tonometry is widely used by the ophthalmologist and optician. Measuring the intraocular pressure is of particularly interest when glaucoma is suspected. An excessively high intraocular pressure may cause glaucoma. In the worst case, glaucoma leads to visual impairment or blindness.
The doctor measures with the aid of an instrument whether the intraocular pressure is too high.
There are several ways and instruments to measure the intraocular pressure:
- Applanation tonometry. This is the most reliable and accurate way to measure the intraocular pressure. Prior to the tonometry, anesthetic eye drops and a light-reflecting substance are administered. Then, the device (the tonometer) is placed directly onto the eyes. By means of blue light, the pressure in the eyes is measured. Most ophthalmologists and optometrists in hospitals use applanation tonometry to measure the intraocular pressure.
- Non-contact tonometry. Here, the patient gets a puff of air into the eye to measure the intraocular pressure. There is no direct contact with the eye. Many opticians use non-contact tonometry. However, this method is less reliable and less accurate than applanation tonometry.
- Tono-pen. This is a portable pen, which is tapped a few times against the eye to measure the intraocular pressure. The tono-pen is primarily intended for bedridden patients or those with abnormal corneas, for example after a cornea transplant.
The result of a tonometry is immediately known after measuring the intraocular pressure.
- The term ‘tonometry’ is derived from the Latin word tonus (pressure). The suffix -metry indicates that it is a measurement.