Toward ultrasound-mediated elasticity modulation and monitoring in the crystalline lens

Abstract

Presbyopia is the age-related stiffening of the crystalline lens, reducing near vision. We propose ultrasonic cavitation to interact with the lens structure and restore flexibility by disrupting the disulfide bonds responsible for lens stiffening. Peak negative pressure of 25MPa for 6-μs pulses at 2 MHz with a 100 Hz pulse repetition frequency allowed cavitation nucleation in the lens nucleus of both 6-months and 3-years old porcine eyes. Disulfide bonds disruption was evaluated in both ovoalbumin gels and ex vivo lens using Raman spectroscopy. We explored the measurement of surface wave dispersion over a 0.1 to 2 kHz frequency range to evaluate viscoelastic properties of the lens samples. We identified two regions in the dispersion curves: a sharp decline at low frequency due to guided waves and a gradual slope at high frequency, attributed to viscoelastic dispersion of a Scholte wave. By fitting the dispersion curves with a Kelvin–Voigt model, we found that while the impact of ultrasound remained uncertain, elastography allowed appreciating the age-dependentshear and viscosity moduli.