Feasibility of cavitation nucleation 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 its flexibility. Here, we present early results on the feasibility of the technique. First, the cavitation threshold was determined: the focus of a 4-elements transducer was placed in the lens nucleus in a porcine eye, and signals emitted in the focal area were acquired using an imaging array and reconstructed using frequency-domain passive cavitation imaging (PCI) with Richardson-Lucy deconvolution. Inharmonic emissions inside the lens were calculated, and we evidenced two distinct populations: low and high amount of signal inside the lens, when cavitation was absent or present, respectively. Peak negative pressure of 23 MPa for 20 μs pulses at 1.1 MHz provided a clear chance of nucleating cavitation with our system. Exposures were performed after 10 s of cavitation using a PRF of 250 Hz. Cavitation clouds were clearly visible in B-mode images for both 6-months old and 3-years old porcine eyes. The absence of cataract was confirmed on transparency images, and histology revealed no damages to the lens structure. These preliminary results are encouraging towards the application of cavitation in the crystalline lens.