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.