Tonometry

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Tonometry is a diagnostic test to measure the pressure inside your eye or also known as intraocular pressure (IOP). This measurement can help your doctor determine if you are at risk of glaucoma.

Apart from tonometry, there are other methods that can be used for eye pressure testing, including an alternative tonometry test called pneumotonometry, as well as the use of a Tono-Pen.

A commonly used tonometry is applanation (Goldmann) tonometry which uses a small probe to flatten part of your cornea so that eye pressure can be measured through a microscope called a  slit lamp. This type of tonometry is highly accurate and has been considered the international gold standard for eye examinations.

Pneumotonometry involves applying air pressure to your eye through a device that resembles an air piston. This instrument blows short breaths of air into your cornea and measures your eye pressure. If the results are abnormal, your doctor may usually order other tests to confirm the diagnosis.

Meanwhile, a tono-Pen is a handheld device that is shaped like a large marker. This device provides a digital readout of eye pressure. Although useful in most cases, the Tono-Pen is considered less accurate than the tonometer.

Alternative names for tonometric testing: 

  • Intraocular pressure (IOP) measurement,
  • Glaucoma test,
  • Goldmann applanation tonometry (GAT).

How Tonometry Works

Tonometry is a standard eye examination, particularly for glaucoma — an eye disease that can cause blindness by damaging the nerve at the back of the eye (optic nerve). Optic nerve damage can be caused by a fluid buildup that does not drain properly out of your eye.

Tonometry is able to provide a complete picture of your eye health and is used as a reference for treating diseases, such as:

  • Cataract,
  • Macular degeneration,
  • Xerophthalmia,
  • Retinal detachment,
  • Corneal ulcers,
  • Retinoblastoma, and
  • various other eye diseases.

A tonometer is an instrument that determines IOP by measuring the resistance of your cornea to indentation.

Cost Estimation for Tonometry

The cost for a tonometry test may vary — depending on your choice of hospital. For more details regarding the cost of a tonometry test procedure, contact Smarter Health.

Pre-Tonometry

Before your tonometry exam, you should remove your contact lenses first. If you have a history of corneal ulcers or eye infections or a family history of glaucoma, you should report to the doctor who performs the exam.

During Tonometry 

In general, tonometry is performed upon an anesthetized ocular surface. A topical anaesthetic is usually given, such as proparacaine (Alcaine) or tetracaine (Pontocaine).

There are three main methods of measuring eye pressure:

Goldmann Applanation 

This type of tonometry exam can only be done by an ophthalmologist. Your ophthalmologist will give you anesthetic eye drops that will numb the surface of the eye. Then, a fine strip of paper stained with orange dye is held to the side of the eye. Sometimes the dye is already in the numbing drops. This dye makes it easier for your ophthalmologist to examine your cornea thoroughly 

Next, your ophthalmologist will ask you to rest your chin on soft support and look directly at the microscope (slit lamp). Then, the lamp is moved forward until the tip of the tonometer just touches the cornea.

Blue light is used so that the orange dye will glow green. This will help your doctor see through the eye lens at the slit lamp. Then, your doctor adjusts a dial on the machine to provide a pressure reading. Then, your tension will be checked on the tonometer and your eye pressure will be measured through the IOP.

You should avoid rubbing your eyes for 30 minutes until the anaesthetic effects completely disappear. 

Electronic Indentation Tonometry

Electronic tonometry may be performed by an ophthalmologist or a general practitioner. You will be given eye drops to prevent discomfort and numb the surface of the eye.

As per your doctor’s instructions, you will look straight ahead or sometimes down. Meanwhile, the device will touch the surface of the cornea and instantly measure the eye pressure. You will hear a clicking sound each time a reading is obtained. Your doctor gently places the rounded tip of a tool that looks like a pen directly on your cornea. The IOP reading shows on a small computer panel.

You should avoid rubbing your eyes for 30 minutes until the anaesthetic effects completely disappear.

Non-contact (or air-puff) Method

This type of tonometry is performed by a general practitioner or ophthalmologist and you will not be given anesthetic drops. In this method, you rest your chin on the device while looking straight ahead. When you are at the correct distance from the device, a small beam of light reflects your cornea to the device

This test uses a puff of air to flatten your cornea; how much it average depends on eye pressure. This causes the small beam of light to travel to different places on the instrument. The instrument also measures eye pressure by looking at how far the small beam of light travels. The test may be performed several times for each eye.

Post-Tonometry

Some people may experience a sight sting or tingling on the cornea after the procedure. However, it will disappear within 24 hours. Be sure you do not rub your eyes after the exam. Talk with your doctor immediately if you feel any pain in your eye during the test or 48 hours after the test. Your doctor will conduct further treatment and exam. 

Understanding Your Tonometry Test Results 

When reading the tonometry, it may be necessary to take the test again to ensure the readings’ consistency. If you question the accuracy of the readings or the device, alternative tonometric methods may be used to help confirm or refute the readings.

It should be noted that eye pressure is different from person to person. However, the normal eye pressure is ranging from 12 to 22 mmHg, while abnormal eye pressure is 20 mmHg. The majority of glaucoma sufferers have eye pressures above 20 mmHg.

If you have higher eye pressure than normal yet the optic nerve appears normal, you may have something called ocular hypertension. Ocular hypertension does not show any specific symptoms but may cause glaucoma over time. Your doctor will continue to monitor your eye condition through routine testing. Or, your doctor may decide to lower the pressure by prescribing eye drops that you will have to apply daily. The eye drops will help protect your optic nerve from any potential future damage and, in the long term, help save your vision.

Therefore, tonometry is required to examine your eye. The tonometry results, along with other vision exams, can help your doctor diagnose your eye health. Then, your doctor will also review your eye health history and symptoms experienced.

Side Effects of Tonometry

In general, tonometry has a low risk of complications. However, if performed continuously, it may cause several side effects, such as corneal abrasion (corneal abrasions), swollen eyeball, infections, and reactions to eye medications. However, the percentage of these complications is very low, around 1% to 2%.

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