I am David Burns, an optometrist in London, UK. Please read about the tonometer that I have designed.
Tonometers are for measuring intraocular pressure (IOP) which is pressure of the fluid that fills the eyeball. There are a few types. They are routinely used in clinically examining 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 without warning until it is too late to save the sight.
Tonometers normally operate by measuring the force that produces a given mechanical deformation of the eye's surface shape. The measurement is generally made on the central cornea because it is the least fluid area of the eye.
Existing tonometers 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 been heightened by two trends. The first is the gradual acceptance that glaucoma often occurs with apparently normal tonometry results yet it may not occur in eyes where tonometry gives abnormally high results. The second is the growth in popularity of surgery to alter corneal shape. This surgery is done to adjust the focus of the cornea so as to reduce the need for spectacles, but it greatly increases the variation in physical parameters of different corneae, confounding the diagnosis and treatment of glaucoma.
The operating principle of the proposed tonometer is to flaten a small area of the cornea. Air, at varying and electronically monitored pressure, can escape from the instrument only through one small exit in the applanating surface. The pressure that just allows the fluid to escape is the IOP.
The new tonometer's design would 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 to enable patients to use it alone with little instruction.
Furthermore it would be fully objective, simple to use by lay personnel, easily portable, operate in any orientation, useful monitor variations in intraocular pressure over several seconds, and require no staining eyedrops. Opacity approaching the eye, causing apprehension which also causes errors would be reduced. Peripheral corneal measurement, generally less disturbing, would be more reliable than with existing methods. Finally, it would cost less to make than its best existing competitor.
A UK patent, number GB2308462, was granted in December 1999 for the proposed tonometer. Prototyping and clinical trials are to be done. Authoriative 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 produce this tonometer.
David Burns, Optometrist