Finite element model and experimental validation of a solitary wave-based tonometer

Glaucoma is an age-related incurable disease and the second cause of blindness in the world. The risk of developing glaucoma increases in the presence of elevated intraocular pressure (IOP), a risk factor that can be modified through surgery. In clinical practice, IOP remains the cornerstone of the diagnosis and management of glaucoma, and Goldmann applanation tonometry (GAT) is considered the gold standard in IOP measurements. However, GAT, as any other commercial system, provides a single value that is unable to frame the circadian rhythm and sporadic surges of IOP. This capability is only possible with a portable device that patients can eventually self-administer anytime anywhere. To serve the purpose, the device must be easy-to-use and not requiring sterilization or topical anesthesia. Additional desirable features are low price and adaptability to patient's eyeball geometry. To address these needs, our group has conceptualized, assembled, and tested a new tonometer based on highly nonlinear solitary waves propagating along a chain of particles, the last of which is in dry contact with the eye to be evaluated. The hypothesis is that the travel time of the waves propagating within the chain is monotonically associated with the IOP. In this study, the effect of central corneal thickness (CCT) and IOP of artificial corneas made of polydimethylsiloxane was quantified experimentally, and modeled numerically using static and dynamic finite element analyses. The numerical and experimental results agreed in identifying a correlation between ToF and IOP and CCT. However, some quantitative discrepancies between numerical and experimental results warrant the improvement of the model.