Study On Assessing The Mechanical Properties Of The Crystalline Lens Using Arfi-Based Ultrasound Elastography

The crystalline lens is an important part of the eye refractive system,which is the only refractive organ with the ability to adjust.As the lens' s accommodation ability will degenerate with the aging and lead to presbyopia and cataracts which seriously affect the life quality of the elderly and also bring a huge public medical burden.Lacking of a clear understanding of the pathogenesis of the diseases,we have not found a definitive method that can delay or cure these diseases.The biomechanics of the lens plays an important role in the accommodation mechanism.Therefore,the techniques for accurately characterizing lens mechanical properties in vivo in a nondestructive fashion can help us to explain the pathogenesis of presbyopia and cataracts,monitor the progress of the diseases,and investigate the methods to prevent and treat them.This objective of the study was to propose a new method based on ultrasound elastography to assess age-related changes in biomechanical properties of rabbit crystalline lens.The acoustic radiation force from VerasonicsTM Vantage256 platform was used to remotely perturb the anterior surface of the crystalline lens and then the vibration of the lens was detected by plane wave imaging.The group velocity and phase velocity of the propagation of the vibration in the lens were measured after demodulating the acquired RF data.The Young's moduli were estimated from group velocities.The shear elasticity moduli in Voigt model were estimated from phase velocity.The study evaluated the effectiveness of this method by in-vitro and in-vivo experiment.The results of in vitro experiment showed that group velocities,Young's moduli and shear elasticity moduli of porcine lens were significant larger than those of bovine lens and the difference between them was significant,which is in agreement with the results of traditional compression test.The in-vivo experiments were carried out on 13 New Zealand rabbits with slightly different ages.The results showed that the maximum amplitude of displacement decreased while the velocity and Young's modulus increased with age.The differences between different groups was significant.The correlation coefficient between group velocity and days was 0.84(p<5e-8),The correlation coefficient between group velocity and weight was 0.83(p<8e-8),which means the mechanical properties of the lens was closely correlated to the age and weight.The results show that the rigidity of lens was significantly increased with aging and also demonstrate that this new method is able to distinguish the slight different in lens' rigidity.This study demonstrates a promising means to assess the biomechanical properties of lens in vivo based on ultrasonic system,which can effectively reflect the changes of mechanical properties of the lens.This method has great potential to be used for noninvasive quantification of lens biomechanical properties and promote the study on the pathogenesis and therapy of presbyopia.