Accommodative forces in aging human eye

Changes in the mechanical properties of the human crystalline lens over the years result in a loss of accommodation amplitude and eventually in presbyopia. While some material property changes of the aging human crystalline lens have been mapped, challenges remain in their in vivo characterization. Conflicting findings in the literature highlight the complexity of accurately defining lens biomechanics. Young's modulus, anterior and posterior lens curvatures, lens thickness, and refractive index are examples of these well-studied properties. However, knowledge of forces applied to the crystalline lens for generating corresponding accommodative amplitudes has been limited to a few age groups. A full mapping of these accommodative forces over decades for the aging human eye remains incomplete. We used mechanical properties available in the literature to develop a mechanical model of the crystalline lens for age groups between 10 and 70 years. Then, finite element modeling and optical power calculations obtained from lens deformation during simulated accommodation were used to create a map of accommodative forces over the human lifespan. We found an S-curve-shaped decline in total equatorial forces required on the capsule to achieve reported accommodative amplitudes. This decline does not indicate increased lens compliance but reflects the possibility of age-related weakening of the applied force. The total force ranged from 0.5 N at age 10 to near zero at age 70, with a steep drop between ages 30 and 50.