Acoustic tonometry: feasibility study of a new principle of intraocular pressure measurement.
OBJECTIVE
An accurate measurement of intraocular pressure (IOP) is still essential for detecting, following-up, and treating glaucoma. The objective of the interdisciplinary project GlauPhon was to prove a new noncontact tonometry principle that analyzes the acoustic oscillation of the eye.


METHODS
Three enucleated porcine eyes were infused via the optic nerve with a saline solution. The IOP was adjusted by varying the height of the infusion bottle. A speaker closed one end of a cylindrical pressure chamber and an eye was fixed to the other side. A PC sound card induced the speaker to oscillate by generating a rectangular signal (20 Hz). A pressure sensor recorded the oscillating pressure within the chamber. For each IOP a calculation was performed that characterizes the attenuation profile.


RESULTS
Each series of measurements revealed an evident dependency between the amplitude difference and the IOP. The highest signal belonged to low IOP levels and it decreased with increasing IOP. The correlation of the mean acoustical signal with the given IOP showed a highly significant correlation coefficient (r=-0.98). As a result, the measured oscillation parameters are strongly dependent on the exerted IOPs.


CONCLUSIONS
The experiments verified the presumed relation between the acoustic oscillation of the eye and the IOP. Nevertheless, further developments are necessary for converting the oscillation parameters into reliable IOP values, to construct a tonometry device for clinical trials.
von Freyberg
Axel
A
Bremen Institute for Metrology, Automation and Quality Science (BIMAQ), University of Bremen.
Sorg
Michael
M
Fuhrmann
Martina
M
Kreiner
Christine F
CF
Pfannkuche
Jens
J
Klink
Thomas
T
Hensler
Dina
D
Grehn
Franz
F
Goch
Gert
G
D000162:Acoustics; D000818:Animals; D004867:Equipment Design; D005240:Feasibility Studies; D007429:Intraocular Pressure / Q000502:physiology*; D013552:Swine; D014065:Tonometry, Ocular / Q000295:instrumentation*