[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 the biomechanical parameters of the cornea. These parameters (especially corneal thickness) differ among several patients. It is desirable to characterize this influence and to correct the measuring value during the IOP measurement. The new tonometer consists of an air pulse applicator generating an air pulse with a rampshaped rising and a sharp decay after switching off and a Michelson-type laserinterferometer for detecting the corneal movement during the air pulse application and the oscillation after switching off the air pulse.


METHODS
The method was tested with a mechanical phantom eye. The pressure inside the chamber of the phanton is adjustable. Measuring surfaces, which have 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 deformation and the damped oscillation (frequency and damping) depend from material thickness and internal pressure of the phantom eye.


CONCLUSIONS
Thus a characterization of the influence of the mechanical properties and a determination of a corrected IOP-value are possible. The task at present is the investigation and formulation of the mathematical dependences.
Plagwitz
K U
KU
Institut für Biomedizinische Technik und Medizinische Informatik, Technische Universität Ilmenau.
Lemke
K
K
D003316:Corneal Diseases / Q000175:diagnosis; D007429:Intraocular Pressure / Q000502:physiology; D019047:Phantoms, Imaging; D014065:Tonometry, Ocular / Q000295:instrumentation* / Q000379:methods*