Internal deformation of the human crystalline lens during accommodation.

To describe the internal deformations in the crystalline lens that occur during accommodation.A computer-based mechanical model of accommodation was created using the finite element method. The lens geometry of the model was based on in vivo measurements of human lenses in the accommodated state. The mechanical properties of the lens were based on ex vivo measurements of human lenses. To achieve a state of disaccommodation, the lens equator was stretched by 7%. The internal strains and displacements were calculated for a young accommodating lens, a lens of pre-presbyopic age and a lens of presbyopic age (20, 40 and 60 years old, respectively).The model showed that the radial strain was maximal in the nucleus for the young accommodating lens and minimal in the nucleus for the oldest non-accommodating lens. In the young lens the deformations occurred throughout the entire lens, whereas in the older non-accommodating lens the deformations were concentrated in the equatorial region.The model predicted that during accommodation, changes in lens thickness are mainly caused by deformation of the nucleus. In the older, non-accommodating lens, the deformations occur predominantly in the equatorial region and do not affect the central curvatures of the lens.