A new measuring method of non-contact-tonometry

Background The measuring value of intraocular pressure (IOP) in non-contact -tonometry (NCT) depends on IOP and is additionally highly influenced by th e biomechanical parameters of the cornea. These parameters (especially corn eal thickness) differ among several patiens. It is desirable to characteriz e this influence and to correct the measuring value during the IOP measurem ent. The new tonometer consists of an air pulse applicator generating an ai r pulse with a ramp-shaped rising and a sharp decay after switching off and a Michelson-type laserinterferometer for detecting the corneal movement du ring the air pulse application and the oscillation after switching off the air pulse. Method The method was tested with a mechanical phantom eye. The pressure in side the chamber of the phantom is adjustable. Measuring surfaces, which ha ve to simulate the shape and the elastic properties of the cornea, are made of soft silicon rubber and fabricated with different thicknesses. Results Measurement results show that both the rise of the corneal deformat ion and the damped oscillation (frequency and damping) depend from material thickness and internal pressure of the phantom eye. Conclusion Thus a characterization of the influence of the mechanical prope rties and a determination of a corrected IOP-value are possible. The task a t present is the investigation and formulation of the mathematical dependen ces.