Finite Element Implementation, Validation, and Interpretation of a Solitary Wave Tonometer Using Hyper-Viscoelastic Corneal Models

Glaucoma is an age-related disease whose progression can be slowed by managing intraocular pressure (IOP). While Goldmann applanation remains the gold standard for IOP measurement, it provides only single-point readings that may fail to capture circadian fluctuations and sporadic pressure surges. This limitation can be addressed with a patient-operated device capable of continuous monitoring or frequent measurements anywhere, anytime. Our group has recently proposed a new tonometer based on the propagation of highly nonlinear solitary waves within a chain of particles. An incident solitary wave (ISW) is induced at one end of the chain. Once the ISW reaches the opposite end and in dry contact with the eye to be evaluated, a primary and a secondary solitary wave (PSW and SSW) rebound. The waves are detected by a sensing coil along the chain. The hypothesis behind the proposed solution and proved already experimentally on proxy and ex-vivo corneas is that the travel time of the waves is monotonically dependent to the IOP. This paper examines the effect of IOP and central corneal thickness (CCT) on the propagating waves using advanced finite element analysis with a hyper-viscoelastic model of artificial corneas. These numerical simulations validate previous experimental findings while demonstrating that the hyper-viscoelastic model provides superior accuracy when compared to an earlier linear model developed by the group, in capturing the relationships between time-of-flight, IOP, and CCT. These results advance the theoretical foundation of a new portable device that could improve glaucoma care.