Estimation of Accommodative Forces in Aging Human Eye

Changes in mechanical properties of the human crystalline lens over the years result in loss of accommodation amplitude and eventually in presbyopia, a condition in which the focus-shifting ability of the eye diminishes. Some material property changes of aging human crystalline lenses have already been mapped over human life. 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 focus shifts has been limited to a few age groups. The purpose of this thesis was to create a complete map of accommodative forces for aging human crystalline lenses. We used mechanical properties available in the literature to develop a mechanical model of the crystalline lens for age groups between 10-70 years. Then, a detailed finite element modeling of the lens and optical power calculations obtained from changing lens shape during simulated accommodation were used to create a complete map of accommodative forces over human life. We found that an S-curve-shaped decrease of total outwards equatorial forces was required on the capsule to achieve previously reported accommodative amplitudes. The total force ranged from 0.5 Newtons for 10-year-olds to near zero Newtons for 70-year-olds, with a steep decrease happening between the ages of 30 and 50 years old. The aging human eye’s estimated accommodative force map reported in this study could benefit future efforts for accommodation restoration and artificial lens replacement studies.