Tonometry frequently asked questions

You will find below a broad range of queries about subjects such as; sterilization processes for reusable tonometry prisms, the benefits of applanation tonometry and how to get your tonometer serviced, repaired and calibrated.

If you have a query which is not answered on this page then please call our customer services team on 01279 883720 or you can contact us via the button below.

Expand the questions below to find out more


HS-UK is the only approved Haag-Streit tonometer service centre in the UK. We have been servicing tonometers for 50 years. Our engineers are fully-trained, ensuring your tonometer is serviced to the highest standards. We can service both Perkins and Goldmann tonometers. Contact our service team to book your tonometer service on 01279 883720 or email service.uk@haag-streit-uk.com.


Historical data shows that Goldmann applanation tonometry is more accurate than non-contact tonometry. It offers low intra and inter-observer variability, giving more reliable results. Further information on this is covered in the Haag-Streit Academy Slit Lamp Advance Skills Course.


You can buy a calibration check rod/control weight from the HS-UK eshop


You will find information on how to connect a Goldmann tonometer to a slit lamp on page 9 of the Goldmann tonometer IFU, which can be found on the HS-UK website.


Yes, the shelf life of Tonosafe disposable prisms is 5 years. You can find the expiry date on the label of the box and also on the side of each individual tray.


Tonosafe comes in a box of 100 prisms. Tonosafe is available to purchase on the HS-UK eshop.


You can perform a calibration check on your Goldmann tonometer using weights. Information on this can be found in the service tonometry manual


Goldmann applanation tonometry is considered the reference standard for IOP measurement in current clinical practice due to its historical use in most clinical research studies and the extensive publications on its validity, reliability, and reproducibility.


The instructions for the cleaning and disinfection of tonometry prisms can be found on the HS-UK website here.


The Perkins Mk 3 uses LED illumination which significantly reduces the power consumption. Once charged, the battery can last for up to 24 hours continuously. The battery pack for a Perkins Mk 3 is expected to last for a minimum of six years.


Tonosafe disposable prisms are both clinically safe and highly accurate. You can find information and clinical studies which provide further information on this in the studies & publications section on the Tonosafe webpage.


Tonosafe is available to purchase on the HS-UK eshop. If you are looking at purchasing multiple boxes, then please contact our customer services team on 01279 883720 or at sales.uk@haag-streit.com.


The Perkins Mk3 tonometer is compatible with both Haag-Streit Goldmann reusable prisms and Tonosafe disposable prisms.


The HS-UK Service Division is the only UK service provider that uses genuine Haag-Streit tonometer parts and test jigs calibrated to Haag-Streit standards, as it is the only Haag-Streit authorised applanation tonometer service agent in the country.

You can rest assured we use state-of-the-art testing and calibration equipment and genuine parts and materials, all manufacturer-supplied. At our purpose-built, fully equipped workshop facility, your tonometer will be fully inspected, its worn or broken parts will be replaced, including cone arms and bearings, and its calibration will be checked, all before it is thoroughly decontaminated and returned to your clinic. Click here to find out more about the HS-UK Service Division and taking out a service contract.