Air Puff Tonometers

The first air puff type tonometer was the American Optical NCT Mk 1 introduced in about 1975. The principle of operation is a piston which fires a small jet of air towards the centre of the eye at a distance of approximately 5mm and a sensor which detects the time taken from the moment of firing the piston to applanate or flatten the cornea. This time factor corresponds to the IOP and is calculated in software and shown on a display in mmHg.

There are many manufacturers including AO/Reichert, Nidek, Topcon, Kowa and Canon which all use this same basic arrangement.

The other type of air puff tonometer is the Keeler Pulsair introduced in around 1988. This uses an entirely different principle from all other puff tonometers in that it has a compressor which pumps an air cylinder to a known pressure. The compressed air is released by a valve and the IOP is calculated from the time taken to applanate the cornea.

With all makes and models of Air Puff Tonometer, it is important to keep the glass around to puff tube clean. This glass gets dirty very quickly due to splashes from the patient's eye and this affects the accuracy of the readings and ease of use. Clean the glass with a soft lens cloth. Do not use any alcohol as quite often the glass is held in with glue which may melt allowing the glass to fall out.

Please use the links below to find more specific help for your Tonometer:

• American Optical NCT
• Reichert Xpert and Xpert Plus
• Nidek NT series
• Topcon CT-10/CT-20
• Topcon CT-60/CT-80