Tonometry

Tonometry:  How to check intraocular pressure.

I recently had to check intraocular pressure in a patient, and it had been awhile since I had done that.  Hence a good time for a review.

Tonometry is used to estimate intraocular pressure (IOP).  Elevated IOP is important to recognize because if unrecognized and untreated, it can cause visual field loss and blindness.  Sudden elevation of IOP can be seen after trauma and with primary angle closure glaucoma.

Tonometry is indicated:

1.  To confirm a diagnosis of acute angle closure glaucoma.  Patients typically complains of acute aching pain in one eye, blurry vision, red eye, "steamy cornea."  May also present with headache, nausea, vomiting, which can mislead the clinician to search for non-ophthalmologic causes of symptoms.

2.  After trauma.  Retrobulbar hematoma and hyphema can lead to elevated IOP.

3.  To determine baseline IOP in patient with iritis (this can be deferred to ophthalmology follow-up unless that patient has signs of elevated IOP).

Absolute contrindication to tonometry:  suspected globe perforation
Relative contraindication:  corneal defects

Technique for using Tono-pen XL
1.  Apply topical anesthetic to eye
2.  Calibrate Tono-pen and apply sterile latex cover
3.  Position can be sitting upright or supine; Tono-pen just needs to be perpendicular to corneal surface
4.  Hold the probe like a pen and lightly touch to cornea.  You will hear a click and see a reading on the screen.  After 4 valid readings a final beep will sound and the screen will display the average measurement.


Normal eye pressures range from 10-21 mm Hg.


[Clinical Procedres in Emergency Medicine, 4th Ed. Roberts and Hedges, Eds. Philadelphia: Elsevier, 2004]