Tonometry is a diagnostic test that measures the pressure inside
your eye, which is called intraocular pressure (IOP). This measurement can help
your doctor determine whether or not you may be at risk of glaucoma. Glaucoma
is a serious eye disease in which there’s an increased fluid pressure within your
eye. This increased pressure can damage your optic nerve. According to NIH Senior
Health, glaucoma is most likely to occur in people over the age of 60 and is
a leading cause of blindness within that age group.
In most cases of glaucoma, the fluid that normally bathes and
nourishes the eye drains too slowly, causing pressure buildup. Without
treatment, that pressure can eventually harm your optic nerve, causing a loss
of vision. Because these changes within your eye are often painless, they can
progress for years without you noticing.
Since glaucoma can cause eventual blindness if it’s not treated,
a tonometry test is critical for detecting eye changes early. If your test
results come back abnormal, your eye doctor will begin the treatment process,
which can delay the progression of the disease.
Tonometry is an eye test that can detect changes in eye pressure
long before you may be aware of them. The most common type of tonometry test is
called the "Goldmann applanation tonometry test." For decades, it has
been considered the international gold standard for measuring IOP. There are
other methods of testing for eye pressure, including an alternative type of
tonometry called "pneumotonometry," as well as use of the Tono-Pen.
involves applying air pressure to your eye, using an instrument that resembles
an air piston. The instrument blows a brief puff of air at your cornea,
measuring the pressure in your eye. If it shows abnormal results, your doctor
will usually perform other tests to confirm your diagnosis. This test is
usually considered less accurate than the Goldmann applanation tonometry test.
The Tono-Pen is
a handheld device that’s shaped like a large marker. It provides a digital
readout of eye pressure. Your doctor can use it to touch your eye and measure
pressure. Though useful in many cases, the Tono-Pen is considered less accurate
than the Goldmann tonometer in people with normal corneas.
Needs a Tonometry Test?
Your eye doctor may order the Goldman applanation tonometry test
if they suspect you may be at risk of glaucoma. If the air puff test or other
eye tests indicate a potential problem, they may ask you to go through the
tonometry test to confirm or rule out glaucoma.
According to the Mayo
Clinic, you may be at higher risk of glaucoma if you’re African-American or
Hispanic. You may also be at higher risk if you:
- are over 60 years old
- have a family history of glaucoma
- have diabetes
- have hypothyroidism
- have other chronic eye conditions or injuries
- are nearsighted
- have used corticosteroid medications for
prolonged periods of time
You might also be tested if you’re experiencing symptoms, such as:
- a gradual loss of peripheral vision
- tunnel vision
- severe eye pain
- blurred vision
- halos around lights
- reddening of your eye
All of these symptoms may be signs of glaucoma.
Happens During a Tonometry Test?
Before the tonometry test, your eye doctor will put numbing eye drops
in your eyes so that you don’t feel anything touching them. Once your eye is
numb, your doctor may touch a tiny, thin strip of paper that contains orange
dye to the surface of your eye to stain it. This helps increase the accuracy of
Your doctor will then put a machine called a
"slit-lamp" in front of you. You will rest your chin and forehead on
the supports provided. The lamp will then be moved toward your eyes until just the
tip of the tonometer probe touches your cornea. By flattening your cornea just
a bit, the instrument can detect the pressure in your eye. Your eye doctor will
adjust the tension until they get a proper reading.
Because your eyes are numb, you will feel no pain during the
procedure. Tonometry is extremely safe. However, there’s a very minimal risk
that your cornea could be scratched when the tonometer touches your eye. Even
if this happens, however, it will normally heal itself within a few days.
Do the Test Results Mean?
A normal test result means that the pressure in your eye is
within the normal range and you don’t have glaucoma or other pressure-related
eye problems. According to the Glaucoma Research
Foundation, the normal pressure range is 12 to 22 mm Hg. The measurement
"mmHg" means "millimeters of mercury," which are the units
used to record eye pressure.
If your test comes back with a pressure reading exceeding 20 mm
Hg, you may have glaucoma or pre-glaucoma. This isn’t always the case. Your
test result can also show high pressure if you’ve had an eye injury, or if you
have bleeding in the front of your eye caused by blood vessel problems,
inflammation, or other issues.
Your doctor will discuss treatment options with you if they
diagnose you with glaucoma or pre-glaucoma.