TONOMETER-BASIC CLINICAL SCIENCES

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WHAT IS TONOMETER?

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In order to ensure a person’s optic nerves are healthy, optometrists check the pressure placed on them by the fluid in the eyes. This pressure is called intraocular pressure and should measure between 10 mmHg and 21 mmHg. Measurements that are higher than normal can be a sign of early glaucoma or retinal detachment.

The tool used to measure intraocular pressure is called a tonometer. A tonometer is used to measure the production of aqueous humor, the liquid found inside the eye, and the rate at which it drains into the tissue surrounding the cornea. Usually, the tests performed by a tonometer are simple and require only a short span of time to complete.

The most basic type of tonometer is called an Air Jet Tonometer. This machine provides a quick and forceful blast of air onto the surface of the eyes, which flattens the cornea. The instrument then measures the rate at which the eye fluids rebound and fill the space where the liquid has just been pushed aside by the blast of air. The Air Jet Tonometer does not require eye drops, and the results are available within seconds. This type of tonometer is also reasonably priced, making it the most commonly used type of tonometer for optometrists.

An alternative type of tonometer is a pen shaped object called a Tono-Pen, which barely touches the eye’s surface. Numbing drops are first placed onto the eye. Then, this tonometer gently rests on the surface of the eye in order to get an accurate pressure reading.

Tono-Pens sell for well over 2,000 US dollars (USD), so they are not always used by eye care professionals. A newer version of the Tono-Pen is the Diaton Tonometer, which looks much like a cross between a pen and a digital thermometer. The Diaton Tonometer works within seconds, does not require eye drops and never touches the cornea, yet gives extremely accurate readings.

The Goldman Tonometer is the most accurate tonometer on the market, but also the most expensive. Priced in the high thousands of USD, the Goldman Tonometer is unaffordable for many eye care professionals and used mainly for patients who have already been diagnosed with glaucoma. The Goldman Tonometer utilizes a small cone that is gently placed against the eye’s surface in order to measure the intraocular pressure, making it necessary to first apply numbing drops.