The Truair Tonometer

I have designed a novel and improved tonometer, the Truair.
Tonometers are instruments for measuring intraocular pressure (IOP) which is pressure of the fluid that fills the eyeball, and there are a few types. A tonometer is used routinely in clinical examination of the eyes, principally because abnormal IOP can seriously damage the sight. This damage, glaucoma, occurs to one person in about fifty. Glaucoma is usually gradual and insidious, and can be difficult to diagnose.

Tonometers normally operate by measuring the force that produces a given mechanical deformation of the eye's surface shape, generally at the central cornea as measurement is most reliable if made there. Designs of tonometer in current use have several significant inherent sources of error. These include the variation in physical characteristics of different corneae, forces within the eye surface's film of moisture, operator skill, and operator bias.

The need for more credible tonometry has increased since gradual acceptance that glaucoma often occurs with apparently normal tonometry results yet may not occur in eyes where tonometry gives abnormally high results. Another reason is the growth in popularity of surgery to alter corneal shape (to adjust the focus of the cornea so as to reduce the need for spectacles) which increases the variation in physical parameters of different corneae, impairing the diagnosis and treatment of glaucoma.

The operating principle of the Truair tonometer is to flatten ("applanate") a small area of the cornea before air, at varying and electronically monitored pressure, can escape from the instrument only through a small vent in the applanated interface. The air pressure that just allows the fluid to escape is the IOP.

This design would appear to have many advantages over those in use. It would give more accurate and comfortable measurement of IOP. Measurement would be unaffected by variations in physical characteristics of the cornea, its tear film, ocular rigidity, periocular stability, or differences between operators. It features easy internal alignment enabling patients to use it with little instruction.

Furthermore it would be fully objective, simple to use by lay personnel, easily portable, operate in any orientation, usefully monitor short-term variations in IOP, and require no staining eyedrops. There would be less opacity approaching the eye than for existing tonometers causing apprehension which also causes errors. Peripheral corneal measurement, which is more tolerable, would be more reliable than with existing methods. It would cost less to produce than its best competitor.

A UK patent, number GB2308462, was granted in December 1999 for the Truair tonometer. Prototyping and clinical trials are to be done. Authoritative clinical interest has been expressed in a reliable prototype ready for independent large-scale population trials with comparison to existing methods of tonometry.

Keen commercial interest would follow and the inventor would seek to license the technology for production. The market is for one tonometer per approx 6000 population in the developed world.

Please contact me if you would be interested in helping to prototype, test and produce the Truair tonometer.

Dr David Burns
119 High Road, East Finchley, London N2 8AG