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Schieotz  Tonometer

AcknowledgmentWe thank Terry Omond OA, Curator of the Calvary Hospital Museum, for the loan of the instrument.

Increase of the intra-ocular pressure is a common condition. It is known as Glaucoma and untreated resulted in blindness. Early diagnosis and treatment are now available. Professor Schioetz demonstrated his instrument to the Norwegian Medical Society in 1905.

The tonometer measures the amount of indentation of the cornea when a small weight is placed on it. The result is inversely proportional to the intra-ocular pressure and tables are provided to obtain the pressure value in mm Hg. The indentation tonometer required the cornea to be anaesthetised. It was used world- wide for the next 60 years. Later, as always new technology provided many improvements which increased the comfort and accuracy.

A Schiotz tonometer as used in the past. Two calibrating weights (top center). sliding spindle and corneal contact piece (extreme left). Note the scale 0-20



A close –up of a similar instrument showing the indentation of the anaesthetised cornea .  From http://comps. photosearch.com.bibcomps.

TABLES Certificate of accuracy and scales to read the intra-occular pressure


Other methods avoid anaesthetising the cornea and the probe is applied to the eye-lid or the cornea is deformed by a jet of air. They are less reliable.

The slit lamp


Actual measurement

Currently most intra-ocular pressure measurements are still made using corneal contact and local anaesthesia. However the patient comfort is much improved by use of the slit lamp. This instrument is commonly called the Hoffmann tonometer.