Viscoelastic properties of fresh human lenses under 40 years of age: Implications for the aetiology of presbyopia

Aim: To determine the viscoelastic properties of fresh human lenses obtained from cadavers under 40 years of age. Methods: 52 intact clear, human lenses were obtained from 26 donors (mean age of 27.5±9.2 years) within 9±4 h of death. The viscoelastic properties of the lens nuclei and 16 of the lens cortices were quantified within 42±10 h of death using a controlled-strain, linear, simple-shear rheometer. Results: The means (±SD) of the viscoelastic properties of the lens nuclei at a frequency of 75 Hz were: elastic shear modulus, G′=11.00±4.67 Pa, viscous shear modulus, G′′=24.91±10.98 Pa, magnitude of the complex shear modulus, |G*|=27.23 Pa, dynamic viscosity, η′=0.33 Pa.s, damping ratio, ζ=2.26 and phase shift, δ=66.17°. There was no statistical difference in these measures between the lens cortices and their respective lens nuclei. There was a small age-related statistically significant increase in G′, p=0.003, but not G′′ or |G*|. Conclusions: The observed age-related increase in tissue stiffness of the lens nucleus, ∼0.4 Pa/year, is too small to account for the 10 dioptre decline in accommodative amplitude in this age group.