CALIBRATION OF TONOMETER

Checking the calibration of a tonometer

To ensure an accurate measurement of intraocular pressure, a tonometer needs accurate calibration. 

To check if the calibration is correct, a calibration bar is used. 

Tonometer and a calibration bar. 

The following steps show how the calibration is checked: 

1. Attach the calibration bar to the body of the tonometer as shown. 

2. The bar has five markings, the central one is used to check if the tonometer has been calibrated accurately for 0 mmHg, the next markings on either side of the centre are used to check for accurate calibration for 20 mmHg. The last markings nearest to the end are used to check for 60 mmHg.

3. To check if the tonometer has been correctly calibrated for 60 mmHg, line up the marking on the bar furthest from the centre with the marking on the knob that hold up the bar (as shown in the video; to check for 0 and 20 mmHg line up the  bar as described in 2 and repeat steps 3 and 4).

4. Now move the knob on the tonometer and note the pressure at which the tonometer  tip tilt forward. If the tilt occurs when the pressure is at 60 the tonometer is calibrated  correctly. If the tilt occurs below or above 60, the tonometer should be sent for re-calibration.

Checking the calibration for 60 mm Hg. The end point occurs  when the tip of the tonometer tilts forward and the bar moves to  horizontal position. If the reading is 60 at this point, the tonometer is correctly calibrated.