Tonometry
Key points
- Tonometry is a procedure that measures the pressure inside the eyes.
- The applanation method measures the force required to flatten a certain area of the cornea.
- Inform the health care provider if you have corneal ulcers and infections, an eye infection, if you are taking any drugs, or if you have a history of glaucoma in your family.
- The preparation you can provide for this test depends on your child's age, previous experiences, and level of trust.
Alternative names
Intraocular pressure measurement (IOP)
Definition
Tonometry is a procedure that measures the pressure inside the eyes. The test is used to screen for glaucoma, a disease in which pressure inside the eyes increases to the point that it impairs vision and if left untreated, may cause Blindness.
How the test is performed
There are several methods of testing for glaucoma.
The applanation method measures the force required to flatten a certain area of the cornea. A fine strip of paper stained with orange dye (fluorescein) is touched to the side of the eye. The dye stains the front of the eye to help with the examination, then rinses out with tears. An anesthetic drop is also placed in the eye.
The slit-lamp is placed in front of you and you rest your chin and forehead on a support that keeps your head steady. The lamp is moved forward until the tonometer touches the cornea. The light is usually a blue circle. The health care provider looks through the eyepiece on the lamp and adjusts the tension on the tonometer. There is no discomfort associated with the test.
A slightly different method of applanation uses a portable object similar to pencil. Again, you are given anesthetic eye drops to prevent any discomfort. The device touches the outside of the eye and an instant digital measurement is recorded.
The last method is the noncontact method (air puff). In this method, your chin is resting on a padded stand. You will be asked to stare straight into the examining instrument. The examiner will shine a bright light into your eye to properly align the instrument. A brief puff of air is blown at your eye. The instrument calculates pressure from the change in the light reflected off the corneas as the air puff is blown.
How to prepare for the test
Remove contact lenses before the examination. The dye can permanently stain contact lenses.
Inform the health care provider if you have corneal ulcers and infections, an eye infection, if you are taking any drugs, or if you have a history of glaucoma in your family.
For children:
The preparation you can provide for this test depends on your child's age, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics:
- Preschooler test or procedure preparation (3 to 6 years)
Written and revised by
Andrey Nailor, M.D.
Our doctors write and review articles for accuracy and keep them up to date.
health.am provides general information, not medical advice. Always consult a qualified health professional about your own health.