Tonometry is a test that measures the intraocular pressure (IOP) insides the patient's eyes with the aim of determining whether or not they are at risk for glaucoma. Glaucoma is a set of diseases that can lead to progressive and irreversible vision loss.
The link between ocular pressure and the results of glaucoma was identified as far back as the 10th century AD by an Arabian surgeon, and in the 1600s the use of fingers by the practitioner were used to manually test for pressure.
Today, of course, fingers are no longer necessary thanks to the development of applanation tonometry.
Also known as Goldmann tonometry, this test utilizes a small probe that applies soft pressure to gently flatten an area of 3.07mm of the patient's cornea. An attached microscope known as a slit lamp is traditionally used to look into the eye while a calibrated dial measures how much pressure is used.
More recently, technology has allowed tonometers to be shrunken down from a bulky device that has to be anchored down, to a small and portable handheld device—all while retaining high levels of accuracy and consistency…
…And it’s this type of handheld tonometer that I’ll be discussing in today’s article:
How To Use A Handheld Tonometer
While traditional equipment required several separate mechanisms, handheld applanation tonometry tools like AccuPen have synthesized much of this into one easy device. For the test, you'll simply need to gather:
AccuPen or other handheld tonometer
2 wrapped tonometer tip covers
Next, you'll have to set up the handheld tonometer for the recording of the new patient's pressure.
Use the manufacturer's instructions of your device to reset all measurements so that IOP measurements, averages, CCT entries, and Calculations are all set to zero. Ensure that you have a new cover fit snugly at the tip of the handheld device.
Step-By-Step Guide: How To Take The Measurement
- Instill the local anesthetic drops into the patient's eye. This will ensure that they won't feel the sensor tip touch their eye to help reduce erratic movement and flight responses.
- Once he or she has blinked a few times to ready the anesthetic effect, ask the patient to look straight ahead with both of their eyes wide open, and to remain as perfectly still as possible.
- Ready the handheld tonometer by pressing and releasing the Action control button. The device should respond with two high pitched beeps and a rotating line that indicates the device is ready to take the new patient's reading.
- Use one of your thumbs to gently hold up the patient's top eyelid. It's important to take care and not put any pressure on the eye.
- With your other hand, steadily move the tonometer forward and tap the sensor tip against the patient's eye.
- The handheld tonometer will automatically record the measurement and proceed to the next measurement if required.
- The device will emit another high pitched beep to indicate every successful measurement.
- Handheld tonometers will be set up to take an automatic 6-9 measurements (as directed by the practitioner) before emitting a final three beeps to indicate that all the requested measurements have been taken.
- Remove the tonometer from the patient's eye and review the measurements by pressing the up and down control buttons.
- You can choose to delete any measurement and the tonometer will automatically recalculate the average of the remaining measurements.
- Record the measurements on the patient's chart.
- Replace the tonometer's covering.
- Repeat the entire procedure on the patient's other eye.
Analyzing The Results
Normal eye pressure can differ from person to person and is generally at its highest just after a person wakes up. In general, women tend to have higher average intraocular pressures then men and for everyone normal levels go up with age.
As a whole, normal intraocular pressure should be between 10 and 21 millimeters of mercury (mm Hg).
Abnormal pressures are anything higher than 21 mm Hg. These abnormal high levels generally indicate that a patient either has glaucoma or is at a heightened risk for developing the disease.
Patients with ongoing pressure readings over 27 mm HG will usually develop glaucoma unless the pressure can be quickly lowered with medication.
While this is the preferred test, on some people and in some situations the results may not be accurate. Such reasons include:
Patients with eye infections or sores.
Patients who are extremely nearsighted or have an irregularly shaped cornea.
Patients who have had laser refractive surgery, i.e. LASIK
Patients who consistently blinked or shut their eyes during the test.
Applanation tonometry tests should be done over months or years, with higher frequency for older patients, to check for the potentiality of glaucoma.
If there are high measurements, it's recommended for the patient to undergo other testing such as ophthalmoscopy to determine risk levels and to craft a treatment plan. But handheld tonometers like the AccuPen are best for initial testing.