Age-Related Changes in Lens Elasticity Contribute More to Accommodative Decline Than Shape Change.

Purpose: To determine whether lens biomechanical or geometric changes contribute to the decline in the accommodative capacity of the human eye, and to examine any differences in zonular function between different age groups. Methods: Eighteen finite element whole eye models were developed to simulate the accommodative process. Six models were constructed in each of the two age cohorts, from the fourth and the sixth decades of life using data from ex vivo human lenses. An additional six models combining the material properties of lenses from the fourth decade with the geometry of those from the sixth decade were included. Optical lens models developed based on the results of mechanical simulations were used to calculate the central optical power (COP). Results: The change in COP was significantly greater for both the fourth-decade models and the mixed models compared with the sixth-decade models. The rates of the change in geometric parameters relative to the increment of change in COP in the mixed models were greater than those in the fourth-decade models. The distribution of zonular force was consistent across all three groups. However, the sixth-decade models and mixed models exhibited similar distributions of zonular angles, both of which were greater than those in the fourth-decade models. Conclusions: Both biomechanical and geometric age-related changes contribute to the accommodative decline, with the material property manifesting a more substantial impact. Age-related changes in the lens do not influence the distribution of zonular tension, but do affect the angles that the zonule makes with the lens surface.