Tonometry

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How is the Test 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.