A pilot study for intraocular pressure measurements based on vibroacoustic parameters

Abstract

The present study aimed to identify vibroacoustic properties associated with intraocular pressure (IOP) changes and to suggest a new way to measure the IOP based on these properties. Ten ex vivo porcine eyeballs were used in this study. Each eyeball was fixated in a central hole of a Styrofoam block, and vibration applied to the Styrofoam block was transmitted to the eyeball. An accelerometer directly attached to the eyeball measured the vibration response. Excitations and measurements were performed for 1 s, and the excitation magnitude was varied for the same signal in repeat measurements. A 30-gauge needle was inserted into the anterior chamber of the eyeball to inject a balanced salt solution, and the height of the bottle was adjusted to adjust the IOP. A tonometer was used under identical conditions to measure the IOP five times, and the mean value was determined for further analyses. The measurements showed that the parameters resonance frequency and change in the magnitude of the vibration response (CMVR) increased with rising IOP values. The CMVR was highly correlated with the IOP (p-value < 0.0001). A linear mixed effects model (LMM) was used as a statistical analysis method. We confirmed that vibroacoustic properties of the eyeball are correlated with IOP changes. It is expected that the CMVR will serve as a new parameter for IOP measurements. Thus, in the future, continuous IOP measurements would be easily performed using the CMVR.

Eye orbit effects on eyeball resonant frequencies and acoustic tonometer measurements

“…The development of the fluid-filled and prestressed spherical model 9 is based on the derivation of the Grinfeld’s soap bubble vibration theory 10 (the fourth model in Table II) and the stretched plate vibration theory obtained from Mason’s book 11 . It has been proven that the sensitive range of this model is 20–140 Hz, which is also the range reported by Kim et al 2 . In acoustic tonometry, an acoustic trigger signal vibrates the eyeball, and then the frequencies or amplitudes of the responses from the cornea are detected.…”

“…Amplitudes 19 , amplitude changes 3 in the time domain, or frequency shifts 20 in the frequency domain could be measured using this technique. The change in the magnitude of the vibration response, based on the root mean square acceleration over time, could also be correlated with IOP 2 . Considering this result, we studied the frequency shift 9 and expanded on this research to measure the amplitude changes in the frequency domain.…”

“…However, access to IOP measurements outside hospital settings could further improve patient outcomes and convenience. Unlike the air-puff tonometer, in an acoustic tonometer, electro-acoustic technique is applied to measure IOP through frequency detection 2 – 4 . Because this tonometer consists of electro-acoustic components and does not require a large air chamber, it could be small, lightweight, and even integrated into consumer electronics such as smartphones.…”

Co-axial acoustic-based optical coherence vibrometry probe for the quantification of resonance frequency modes in ocular tissue

“…However, other simulations showed that the resonance mode frequencies of whole eyes show a more moderate increase with IOP 46 , 48 . This relationship being further verified by experimental observation of ex vivo porcine whole eye globe vibrational resonance mode frequencies increasing with IOP and in vivo human air-puff tonometry measurements which showed a high positive correlation between the higher order frequencies induced by the air-puff and the IOP 49 , 50 . Comparing these findings with that of the current study, in particular the results of Figs.…”

“…A number of publications have reported via numerical methods, FEM simulations and experiments that the amplitude of resonance modes of the cornea and whole eye globes are sensitive to IOP, some of these purporting the use of corneal resonance mode measurements for use in tonometry 41 , 49 , 59 . Similarly, there has been research conducted which has shown development of amplitude-based vibration tonometry, not necessarily at the resonance frequency of the cornea/whole eye 60 .…”