Correspondence: spatial variations of viscoelastic properties of porcine vitreous humors

Abstract

Using a microbubble-based acoustic radiation force approach, spatial variations of Young’s modulus and shear viscosity of the porcine vitreous humors in two groups— young pigs (6 months old) and mature pigs (2 to 3 years old)— were measured in situ. The measurements in these groups (4 specimens in each group) were performed in several positions along an anterior-to-posterior direction. At each position, microbubbles were generated by focusing a nanosecond pulsed laser beam and the displacement of each microbubble in response to an impulsive acoustic radiation force was measured every 10 μs using a custom-made high-pulse-repetition-frequency ultrasound system. Based on measured dynamics of the microbubble, Young’s modulus and shear viscosity at various locations of the vitreous were reconstructed. Young’s moduli of the young and mature porcine vitreous at anterior region were the highest, whereas the central region had the lowest values, indicating the clear spatial variations in the vitreous humor elasticity in both groups.

An evaluation of ocular elasticity using real-time ultrasound elastography in primary open-angle glaucoma

“…Other techniques for assessing vitreous elasticity include nuclear MRI for the liquefaction of the vitreous, 30 radiation force, 31 ultrasound image velocimetry, 32 and microbubble-based acoustic radiation force technique. 33 By using this last technique, Yoon et al 33 reported that the AV has a higher share of viscosity than the PV and central vitreous. Changes in the vitreous may be observed in glaucoma.…”

“…In our study, the elastographic measurements were shown to have relatively lower elasticity values in PV in both the glaucomatous and healthy eyes ( Figure 1). Yoon et al 33 found that the viscosity of AV and PV are different. This supports our results.…”

Macro- and Microscale Properties of the Vitreous Humor to Inform Substitute Design and Intravitreal Biotransport

“…While the vitreous humor is known to degrade with age, much less is known about its age-related changes in the mechanical properties of the vitreous humor, mostly due to the difficulty in obtaining human donor tissue at younger ages. Zimmerman (1980) reported the in vivo modulus of the vitreous from patients aged 18,26,28,38,47, and 50 years old and found no discernible differences due to age, potentially due to the unreliable measurements primarily based on patient compliance. 45 Weber et al (1982) calculated the spring constant and damping factor of human vitreous from donors aged 44 to 73 years but did not report any significant age-related changes.…”

“…Ideally, the mechanical properties of the intact vitreous humor should be tested in vivo. Non-invasive techniques used to study the material properties of the vitreous include MRI, 12,19,30,36,42 light scattering, 35,45 microbubble-based acoustic radiation force 28 , ultrasound, 29,39,47 and Brillouin spectroscopy. 160 With the advantageous ability of nondestructive in vivo vitreous assessment, the disadvantage of these methods is that they do not provide data (storage modulus and loss modulus) that are comparable to the current rheological data on the vitreous humor or reported experimental hydrogel vitreous substitutes.…”

Measurements of acoustic radiation force of ultrahigh frequency ultrasonic transducers using model-based approach

“…Theoretical model of the motion of a solid sphere in a viscoelastic medium was developed and experimentally validated in our lab [21][22][23][24] . In our previous study, we developed a theoretical model of a gas bubble under ARF and measured the mechanical properties of the crystalline lens and the vitreous humor of bovine and porcine eyes using a 3 MHz transducer for pushing and a 25 MHz transducer for tracking [25][26][27][28] . In this study, we used a 130 MHz PUT to displace a solid sphere in a gelatin phantom and a 45 MHz tracking ultrasonic transducer (TUT) to track the displacement of the sphere.…”