Ocular Tonometry Through Sonic Excitation and Laser Doppler Velocimetry

Abstract

Glaucoma is an insidious eye disease which must be detected in its early stages for there to be successful treatment. Primary detection of glaucoma and evaluation of therapy have depended upon tonometric methods which require applanation of the cornea. A new method of IOP determination which is noncontacting and nonapplanating has been devised. The technique utilizes low-level sonic excitation of the eye and detection of the resulting cornea vibrations by laser Doppler velocimetry. Studies of a laboratory model and of freshly excised lambs’ eyes show that there is a measurable shift of corneal response frequencies with changing IOP. An empirical relationship between IOP and response frequency for in-vitro lamb’s eyes was found to be f = 233.65 + 6.9 (In IOP in mm Hg)1/2. Standard deviation of all data obtained in the physiological range of IOP’s was approximately 2.5 mm Hg for the experiment which was devised to test the idea. The results provide the basis of design for a procedure to be used in vivo.