A tonometry test measures the pressure
inside your eye, which is called intraocular pressure (IOP). This test is used
to check for
Normal eye pressure is
different for each person and is usually higher just after you wake up. IOP
changes more in people who have glaucoma. Women usually have a higher IOP than
men, and IOP normally gets higher as you get older.
A high IOP may mean that you have glaucoma or
that you are at high risk for developing glaucoma. People who have ongoing
pressures above 27 mm Hg usually develop glaucoma unless the pressure is
lowered with medicines.
People who have an ongoing IOP higher than
21 mm Hg but do not have
optic nerve damage have a condition called ocular
hypertension. These people may be at risk for developing glaucoma over
What Affects the Test
Reasons you may not be able to
have the test or why the results may not be helpful include:
Having a sore on your eye or an eye infection.
This increases your risk of an eye injury during the test.
nearsighted, having an irregularly shaped cornea, or
having had major eye surgery in the past.
Blinking or squeezing
your eyes shut during the test.
Having had laser refractive surgery
(such as LASIK).
What To Think About
Tonometry tests may be done over months or
years to check for glaucoma. Also, because intraocular pressure (IOP) can
change at different times of the day, tonometry is not the only test done to
check for glaucoma. If the IOP is high, more tests, such as ophthalmoscopy,
gonioscopy, and visual field testing, may be done.
ultrasound to measure the thickness of the cornea. The thickness of the cornea
can affect IOP measurement. Pachymetry is often done during a tonometry test.
It can help your doctor know your chance for developing glaucoma.
Normal IOP is different from person to person. About 40% to 50% of people who
have optic nerve damage caused by glaucoma have normal IOP.2, 3 In some cases of glaucoma there is
damage to the optic nerve even though the eye pressure is never above