Tonometry is a test to measure the pressure inside your eyes. The test is used to screen for glaucoma.
Intraocular pressure (IOP) measurement; Glaucoma test; Goldmann applanation tonometry (GAT)
How the Test is Performed
There are many methods of testing for glaucoma.
The most accurate method measures the force needed to flatten an area of the cornea.
- The surface of the eye is numbed with eye drops. A fine strip of paper stained with orange dye is held to the side of the eye. The dye stains the front of the eye to help with the exam.
- The slit-lamp is placed in front of you. You will rest your chin and forehead on a support that keeps your head steady. The lamp is moved forward until the tip of the tonometer just touches the cornea.
- Blue light is used so that the orange dye will glow green. The health care provider looks through the eyepiece on the slit-lamp and adjusts a dial on the machine to give the pressure reading.
- There is no discomfort with the test.
A different method uses a handheld device shaped like a pencil. You are given numbing eye drops to prevent any discomfort. The device touches the outside of the eye and instantly records eye pressure.
The last method is the noncontact method (air puff). In this method, your chin rests on a padded stand.
- You stare straight into the examining device. The eye doctor shines a light into your eye to properly line up the instrument, and then delivers a brief puff of air at your eye.
- The machine measures eye pressure by looking at how the light reflections change as the air hits the eye.