What is applanation tonometry?
Applanation Tonometry test measures the amount of pressure it takes to flatten a part of the cornea. Pressure readings help your doctor diagnose and track glaucoma. He will give you drops to numb your eye, then press lightly with a tool called a tonometer.
Why is applanation tonometry done?
Your eyes are full of different fluids that keep them healthy. New fluid is constantly being produced and the old fluid is drained. But if this drainage system becomes clogged, fluids build up. This increases the pressure inside the eyes.
Sometimes the pressure is due to an eye injury or trauma. Once your eye heals, everything will return to normal. But some people have a drainage system that doesn’t work the way it should.
Over time, the high pressure inside your eye can damage your optic nerve, which sends images from your eyes to your brain. If left untreated, it can cause glaucoma.
Since the disease usually has no symptoms, it is a good idea to have regular eye exams. Your ophthalmologist will monitor your eye pressure using a tonometry test. You can also track pressure changes over time.
Anyone can get glaucoma, but your chances are higher if:
- You are over 40
- You have a family member with glaucoma
- Are African, Hispanic, or Asian
- You have had an eye injury
- You have hyperopia or myopia
- You have been told that your corneas are thin in the middle
- Do you have diabetes?
- You have migraines
- You have circulation problems (blood flow)
When applanation tonometry is done?
A normal test result means that the pressure in your eye is within the normal range and that you do not have glaucoma or other pressure-related eye problems. Conferring to the Glaucoma Research Substance, the normal pressure range is 12 to 22 mm Hg. The measurement “mmHg” stands for “millimetres of mercury”, which are the units used to record eye pressure.
If your test comes back with a pressure reading greater than 20 mm Hg, you may have glaucoma or pre-glaucoma. This is not always the case. Your test result may also show high blood pressure if you have had an eye injury or if you have bleeding in the front of the eye caused by blood vessel problems, inflammation, or other problems. Your doctor will discuss treatment options with you if you are diagnosed with glaucoma or pre-glaucoma.
Applanation tonometry procedure
Before the tonometry test, your ophthalmologist will put numbing drops in your eyes so you don’t feel like anything is touching them. Once your eye is numb, your doctor may touch the surface of the eye with a small, thin strip of paper that contains orange dye to tint it. This helps increase the accuracy of the test.
Then your doctor will place a machine called a “slit lamp” in front of you. It will support your chin and forehead on the supports provided. The lamp will then move towards your eyes until only the tip of the tonometer probe touches your cornea. By slightly flattening the cornea, the instrument can detect pressure in the eye. Your ophthalmologist will adjust the tension until you get an adequate reading.
Because your eyes are numb, you will not feel pain during the procedure. Tonometry is extremely safe. However, there is minimal risk that your cornea will be scratched when the tonometer touches your eye. However, even if this happens, it will usually heal in just a few days.
Complications of applanation tonometry
Corneal abrasion, aggravation of ocular globe rupture, the transmission of infections, and reaction to ocular drugs are possible complications of tonometry. The risk of these complications is considerably low (less than 1%).
Accurate and precise IOP readings are imperative to assess a patient’s risk of progressive optic nerve damage. Inaccurate or inconsistent IOP measurements prevent the clinician from making accurate decisions about treatment and management and can put the patient at risk for visual field loss.