Annals of B-Pod: Mastering Minor Care
/Under Pressure: A Tonopen Tutorial
Prepare
1. Find your Tonopen. At our shop the Tonopen lives in the cabinet in the attending office.
2. Adequate corneal analgesia is key. Instill tetracaine in both eyes prior to using the Tonopen.
3. If you are assessing the patient for corneal abrasions, perform the fluorescein exam prior to using the Tonopen as the Tonopen may inadvertently cause small abrasions.
4. Place a cover over the tip. It slides on like a condom and then roll the ridge into the grove.
Calibrate
1. The Tonopen should be calibrated before each and every use.
2. With a cover on the tip of the instrument, hold the instrument in a vertical position with the tip down.
The steps required for proper calibration of the tonopen. If after completing this sequence the tonopen reads "Bad" instead of "GOOD", as shown above, the tonopen requires recalibration.
3. Press the on button quickly twice.
4. The display will show CAL.
5. Wait 30-60 seconds until the instrument displays UP.
6. Immediately turn the instrument 180 degrees so that the tip is pointing toward the ceiling.
7. The instrument should display GOOD, and if it does, it is ready for use.
Measuring Intraocular Pressure (IOP)
An example of the double rows of dashes indicating the tonopen is properly calibrated and ready to measure iop.
1. Having the patient laying flat or against a headrest facilitates measurement; however, the pressure can be measured in any position.
2. Hold the eyelids open but make sure that you do not put any pressure on the eye.
3. Push the button once and you should see double rows of dashes. Careful not to push twice as it will cause the instrument to go back into calibration mode.
An example of a Tonopen averaged IOP Measurement.
4. Tap gently and quickly on the cornea. You should hear beeps as each measurement is taken. After 4 valid readings are obtained, a final beep will sound and the averaged measurement will appear on the LCD along with the single bar denoting statistical reliability (you want them all to be less than 5% difference or you need to repeat the measurement). You do not (contrary to local urban legend) need to measure three different times. You only need to tap quickly until it gives the final beep. That gives you four valid readings.
Trouble Shooting Q&A With our minor care gurus Drs. Alexander Trott and Edmond Hooker
I cannot get the instrument to calibrate and give two rows of dashes. What is wrong!?
“If you try repeatedly and cannot get the instrument to calibrate, it may need new batteries. You can replace them yourself, or you can just email Dr. Hooker, and he will fix it as quickly as possible. Batteries should be kept in the same cabinet as the instrument in the attending office.”
I’m getting very high measurements, but clinically there is low suspicion for elevated IOP. What’s going on?
“The most common cause of a falsely elevated reading is that the operator has inadvertently put pressure on the eye. When holding the eye open with your finger and thumb, make sure that there is no pressure being put on the eye. You can always check the other eye. If both are elevated, it is likely operator error.”
The instrument calibrates fine, but when I go to measure the IOP, it does not beep.
“The instrument must have two rows of dashes (not one) in order for it to take measurements. Make sure that it has two rows of dashes.”
I’ve provided adequate analgesia but the patient is still squinting.
“Ask the patient to keep both eyes open during the procedure. If they shut the good eye, they are more likely to squint and reject the Tonopen. ”
Authored by: Benjamin Ostro, MD
Edited & Posted by Grace LaGasse, MD
