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 intraocular pressure of aqueous humor, the liquid found inside the eye. 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 an air-puff tonometer. This machine provides a quick and forceful blast of air onto the surface of the eyes, which flattens the cornea. The instrument measures the time it takes for the portion of the cornea to completely flatten. The air-puff 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. One 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 can be quite expensive, so they are not always used by eye care professionals for basic screenings. A newer version of the Tono-Pen is the Diaton Tonometer, which looks much like a cross between a pen and a digital thermometer.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 widely considered the most accurate tonometer on the market. The Goldman Tonometer is used mainly for patients who are suspected to have or who have already been diagnosed with glaucoma or other eye problems. 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.
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