Spectral analysis of viscoelasticity of the human lens.
OBJECTIVE
In the aging lens, two different structural changes become progressively apparent: loss of accommodation and formation of cataract. These changes are due to different alterations in lens structure taking place on a molecular scale.


METHODS
For the characterization of liquids, gels, elastic bodies and solids, dynamic mechanical analysis (DMA) represents a non-destructive macroscopic analysis method with considerable sensitivity to microscopic structural changes. Spectra of the shear compliance (reciprocal shear modulus) of human lenses at different ages were measured in a wide frequency range (1 mHz to 1 kHz). By means of computer analysis, the parameters of the involved relaxation processes and the viscous flow were determined.


RESULTS
The increase in cross-linking density was correlated with the disappearance of viscous flow in the measured spectra. The accumulation of high-molecular-weight aggregates was held responsible for the shift of the lower frequency relaxation process to lower frequencies with increasing stiffness, which is likely to be correlated with a prolonged accommodation time.


CONCLUSIONS
Dynamic mechanical analysis represents a useful method for the spectroscopic characterization and quantification of the changes in the macroscopic viscoelastic properties caused by molecular changes in cataract formation and loss of accommodation.
Soergel
F
F
Institute for Dynamic Materials Testing and Department of Applied Physics, University of Ulm, Germany.
Meyer
C
C
Eckert
G
G
Abele
B
B
Pechhold
W
W
D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D002386:Cataract / Q000473:pathology / Q000503:physiopathology*; D004548:Elasticity; D006801:Humans; D007908:Lens, Crystalline / Q000033:anatomy & histology / Q000502:physiology*; D008875:Middle Aged