How do you do tonometry

You will be asked to place your chin and forehead at the slit lamp for IOP measurement. The tonometer blue tip will be moved forward till it gently touches the cornea and the lever is adjusted to gauge the eye pressure. Examination What are the tests done to diagnose glaucoma? How is gonioscopy done?

How is the optic nerve examined? How is the visual field examined? Clin Ophthalmol. Aziz K, Friedman DS. Tonometers-which one should I use? Eye Lond. J Glaucoma. Your Privacy Rights. To change or withdraw your consent choices for VerywellHealth. At any time, you can update your settings through the "EU Privacy" link at the bottom of any page. These choices will be signaled globally to our partners and will not affect browsing data.

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Physical properties of the ocular surface—particularly corneal resistance and surface tension of the tears—have a practical influence on applanation measurements. The method involves contacting an anesthetized cornea with a tonometer tip approximately 3. The size of the tonometer tip is deliberate to minimize the impact of the corneal resistance and the surface tension of the tear film.

The examiner turns the tension knob that alters the force applied to the cornea, and the IOP is determined in mm HG when the internal aspect of the two semicircles are in contact with each other. The force used to flatten the cornea is detected by sensors, recorded and converted to mm Hg.

The benefit to NCT is that no anesthetic is required since the cornea is not contacted during the procedure. The device is easily portable and is most advantageous when used on scarred or edematous corneas. However, it uses a disposable latex tip and is contraindicated if the patient has a latex allergy. Rebound tonometry assumes that harder eyes those with a high IOP will induce a more rapid deceleration of a probe than a softer eye those with a low IOP.

The rebounding velocity is then converted into mm Hg. Avoid applying pressure to the globe when holding the lids open, and make sure the contact area is free of eyelashes.

Lift the upper lid with your index or middle finger without pinning the eyelid against the eyeball. Alternatively, use a cotton-tip swab to roll or hold the upper eyelid against the superior orbital bone. Be sure to obtain the pressure reading on the central cornea with the eye in primary gaze. Instruct patients to keep both eyes open and concentrate on a distant target such as a fixation light or a point past your ear. Lastly, patients may find it easier to keep their eyes open if they concurrently open their mouth.

This may not be practical in the slit lamp, but it can be helpful when using handheld devices like the Tono-Pen or Icare. DO use the appropriate amount of fluorescein. During GAT and Perkins tonometry, it is important to instill the correct amount of fluorescein in the eye, using either Fluress fluorescein sodium and benoxinate hydrochloride, Akorn or fluorescein strips with a topical anesthetic. Placing too much fluorescein into the eye will make the mires too thick, causing the IOP reading to be overestimated.

Have the patient blink and wipe his or her eyes if too much fluorescein is present. Instill additional fluorescein if an inadequate amount is in the tear film; otherwise, the mires will appear thin and the measurement will be underestimated.

When measuring the IOP, the light source is also important. The cobalt blue light source should be bright, diffuse and obliquely directed toward the tonometer tip. Use non-contact methods, like Tono-Pen, Icare or NCT, on patients with active corneal infections or corneal epithelial defects. Also, take care with patients who have recently suffered from an ocular chemical burn or have a history of recurrent epithelial erosions.

It is important the instrument of choice is clean and disinfected. If it shows abnormal results, your doctor will usually perform other tests to confirm your diagnosis. Your doctor can touch this device to your eye to measure the pressure.

The iCare tonometer is also a handheld device that gently taps the front of the eye to obtain a pressure reading. Your eye doctor may order the Goldman applanation tonometry test if they suspect that you may be at risk of glaucoma.

They may also order the applanation tonometry test to confirm or rule out glaucoma if another eye test has indicated a potential problem. According to the AAO , you may be at heightened risk of glaucoma if you:. Once your eye is numb, your doctor may touch a small strip of paper that contains orange dye to the surface of your eye to stain it. This helps increase the accuracy of the test. By flattening your cornea just a bit, the tonometer can detect the pressure in your eye.

Your eye doctor will adjust the tension until they get a proper reading. Tonometry is extremely safe. However, even if this happens, your eye will normally heal itself within a few days. According to the Glaucoma Research Foundation , the normal eye pressure range is 12 to 22 mm Hg. High eye pressure is just one symptom of glaucoma and your doctor will do additional testing to confirm the diagnosis.

Your doctor will discuss treatment options with you if they diagnose you with glaucoma or pre-glaucoma. Does your child have an unusually large eye?