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Tonometry
Table of Contents:
Alternative names
intraocular pressure
Definition
Tonometry is a procedure that measures the pressure inside the eyes. The test is used to screen for glaucoma, which is a disease in which the 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 3 methods of testing for glaucoma. In the Schiotz method, you will be lying on a table. Loosen any tight clothing around your neck (tightness may increase the pressure inside the eyes). You will be asked to look down as the upper eyelid is raised and a drop of anesthetic is placed in the eye. You then need to look at a spot on the ceiling. A tonometer (a small, smooth instrument) is lowered onto the surface of the eye for a few seconds. The procedure is then repeated for the other eye.

The applanation method measures the force required to flatten a certain area of the cornea. A fine strip of paper that is stained with an orange colored dye (fluorescein) is touched to the side of the eye. The dye stains the front part of the eye to help with the examination. The dye rinses out of the eye with tears. An anesthetic drop is also placed in the eye. The slit-lamp is swung in front of you and you rest your chin and forehead on the support that keeps your head steady. The lamp is moved forward until the tonometer touches the cornea. The health care provider looks through the eyepiece on the lamp and adjusts the tension on the tonometer.

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 aligned 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. 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.

Children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:


How the test will feel
There should be no pain with the Schiotz and applanation method because of the anesthetic. In the noncontact method, you may feel mild pressure on your eye.
Risks
If either the Schiotz or applanation method is used, there is a small chance the cornea may be scratched (corneal abrasion). This will normally heal itself within a few days.
How the test is performed
People over 40 years old, especially African Americans, are at the highest risk for developing glaucoma. If glaucoma is detected early, it can usually be treated, but it may go unrecognized for years because there usually are no symptoms.
Normal values
The eye pressure is within the normal range.
What abnormal results mean
Glaucoma may be detected.

Additional conditions under which the test may be performed:
  • hyphema
Special Considerations
Not applicable.
[Definition] [Alternative names] [How the test is performed] [How to prepare for the test] [How the test will feel] [Risks] [How the test is performed] [Normal values] [What abnormal results mean] [Special Considerations]

   

Disclaimer

The information contained above is intended for general reference purposes only. It is not a substitute for professional medical advice or a medical exam. Always seek the advice of your physician or other qualified health professional before starting any new treatment. Medical information changes rapidly and while NIO and its content providers make efforts to update the content on the site, some information may be out of date. No health information on NIO, including information about herbal therapies and other dietary supplements, is regulated or evaluated by the Health Ministry of the Government of India and therefore the information should not be used to diagnose, treat, cure or prevent any disease without the supervision of a medical doctor.