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H.A. Weeber, G.L. van der Heijde; Strain Distribution Within the Crystalline Lens During Accommodation and Disaccommodation . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5857.
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© ARVO (1962-2015); The Authors (2016-present)
To define the local deformations within the crystalline lens during accommodation and disaccommodation.
The local mechanical properties of crystalline lenses of different ages were measured using Dynamic Mechanical Analysis. The measurement results were used as input in a mechanical model of accommodation. The model determined the local strains and displacements within the lens. The results were compared to in vivo observations.
The lens measurements resulted in the stiffness gradient within the lens as a function of age. The ratio between nuclear and cortical shear modulus ranged from 0.15 for the youngest (19Y) lens to 32 for the oldest (78Y) lens. When the stiffness gradient was implemented into the mechanical model of accommodation, the model showed that for a young and well–accommodating lens, the axial strain is maximal in the center of the lens (strain=0.175) and minimal in the lens cortex (strain=0.066). For the older near–presbyopic lens, the strain in the center of the lens is 0.019 and was maximal near the anterior and posterior poles (0.084 and 0.146, respectively).For the young well–accommodating lens, the internal displacements are high and occur all throughout the lens volume. For the older, near–presbyopic lens, the internal displacements were relatively small and occur almost entirely near the lens equator, even when the lens was heavily stretched by the zonular fibers.
The internal axial strains within the lens during accommodation occur mainly in the center of the lens. This is in good agreement with known in vivo observations made with Scheimpflug imaging. The older near–presbyopic lens does not change its lens power even when it is heavily stretched, because any lens deformations occur only at the lens equator and do not carry on to the optical center of the lens.
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