How does Tonometer work for Eye Pressure Measurement

In the U.S., an estimated 3 million people have the optic nerve disease known as glaucoma. The number of affected population is expected to grow with the aging of the population. While there is no cure, careful monitoring can prevent permanent vision loss.

Because the most important risk factor for glaucoma is high intraocular or eye pressure, monitoring eye pressure is vital in determining if and when treatment is needed, and how well it is working. And the most important tool is a device called Tonometer for eye pressure measurement.

Types of Tonometry Tests

An eye care provider uses a tonometer for the measurement of eye pressure. This instrument calculates how resistant your cornea which is the clear, outer layer of the eye, is to an attempt to flatten it. This is done in different ways depending on the kind of tonometry test is being used. Some are more accurate than others, but each has distinct advantages.

• The Goldmann applanation tonometer is the most common test. Your healthcare provider puts anesthetic eye drops and adds small amount of dye into your eyes. After a few minutes, you are asked to position yourself in front of a slit lamp, an instrument that allows the provider to shine light into your eye and examine its structures.
• With non-contact tonometry or NCT, a gentle puff of air flattens the cornea which is why it is also called the “air puff” test. Many prefer this test because it does not involve touching the eye with a probe. With NCT, you sit at a machine and position yourself so that your eyes are properly aligned.
• An electronic tonometer is a handheld, mobile device that looks like a writing pen. It can be gently applied to your cornea like the probe used in Goldmann tonometry, but it is much quicker to use. Typically, this test needs to be repeated a few times in order to produce an accurate eye pressure measurement. Overall, it’s not as reliable or accurate as Goldmann tonometry.

Why Do you Need This Test?

Your eyes are filled with various fluids that keep them healthy. New fluid is constantly being made along wirh old fluid being drained out. But if this drainage system gets plugged, the fluids build up. That causes the pressure inside your eyes to rise.

Sometimes the pressure can be caused by an eye injury or trauma. Once your eye heals, everything may go back to normal. But some people have a drainage system that does not work like it should.

Over time, high pressure inside your eye can damage your optic nerve, which is important as it sends images from your eyes to your brain.If left untreated, it can cause glaucoma.

Since the disease usually does not have symptoms, regular eye exams are a good idea. Your eye doctor will check your eye pressure by doing a test using a device called tonometer. They can also track any changes in pressure over time.

What happens during a tonometry test?

Before the Goldmann tonometry test, your eye doctor will put numbing eye drops in your eye so that you don’t feel anything touching it.

Once your eye is numb, your doctor touch a small strip of paper that contains orange dye to the surface of your eye to stain it. This helps in increasimg the accuracy of the test.

Your doctor will then put a machine called a “slit-lamp” in front of you. They will ask you to rest your chin and forehead on the supports provided, then move the lamp toward your eye until the tip of the tonometer probe touches your cornea.

By flattening your cornea just a bit, the tonometer can measure the pressure in your eye. Your eye doctor will adjust the tension until they get a proper reading. Because your eye is numb, you will feel no pain during this procedure.

Tonometry is an extremely safe procedure.

What Do the Results Mean?

Eye pressure varies from person to person. Normally, it lies somewhere between 12–22 mmHg. Most people diagnosed with glaucoma have an eye pressure above 20 mmHg.

If your eye pressure measurement is high but your optic nerve looks normal, you may have what’s called “ocular hypertension.” You might not have any symptoms, but this could lead to glaucoma with time.

Some people with ocular hypertension never end up with glaucoma. Others develop it even though their eye pressure falls within a normal range. Because of this situation being usual, tonometry is only part of a complete eye exam. These results, along with other vision tests, help your doctor get a better idea of your eye health. They will also talk to you about your health history and any symptoms you are having.

If the test shows you have high eye pressure, your doctor may keep a close watch on it by having you come in for regular testing. Or, they could decide to lower the pressure by prescribing eye drops that you are supposed take every day or as advised. They will help protect your optic nerve from future damage and, in the long run, could save your sight.

Conclusion

Glaucoma progresses slowly. The most common type has no symptoms in the early stages. If you wait to have a test using a Tonometer for eye pressure measurement until you have vision loss, it won’t be possible to reverse your eye damage. This is why it’s important to have this test done before you have glaucoma symptoms.