How to Measure Intraocular Pressure With a Tonometer
Eye pressure is created by the internal flow and drainage of eye fluid, called aqueous humor. When this intraocular pressure is hindered by conditions such as glaucoma, abnormally high eye pressure may occur. To measure eye pressure, the eye doctor may use an instrument called a tonometer. Because the head of the instrument touches the eye, the doctor and his assistant must know how use the tonometer.
- Direct the patient to sit in front of the slit lamp. This is an instrument to which the tonometer prism is attached. It allows you to look in the eye using various magnifications and also illuminates the eye.
- Place a drop of an orange dye, called fluorescein, in the eye to be tested. This drop anesthetizes the eye and stains it orange for the test. Warn the patient that this might sting slightly or feel unusual.
- Move the slit lamp in front of the patient and instruct him to place his chin on the chin rest.
- Instruct the patient to keep both eyes open wide and to look straight ahead. Allow him to blink several times before he attempts to hold them open for you.
- Lower the arm holding the tonometer and angle the slit lamp's blue light so that it hits the tonometer prism.
- Move the instrument slowly towards the patient's anesthetized eye.
- Look through the eyepiece of the instrument. When the prism just touches the eye there will be two green semi-circles visible. Stop moving forward.
- Adjust the measuring knob so that the two semi-circles just touch. An accurate measurement will look like the green semi-circles are linked perfectly together without any overlap or space between them.
- Move the instrument away from the patient. Anesthetize the opposite eye and repeat.
- Write down the number that appears on the instrument's knob.