Modeling and analysis of the mechanical parameters and effect of relative humidity on porcine eye lens
The mechanism of accommodation and the progressive, age-related loss of accommodation with age---called presbyopia---are still debated. These mechanisms have not yet been rigorously established due to a paucity of reliable experimental data regarding the mechanical and geometric properties of all tissues involved. Thus, there exists a need for the development of a mechanical model of the eye lens that can help in the development of a bio-material which mimics the geometric, optical, and mechanical properties of the natural lens.
To this end, 32 young, fresh porcine eyes were mechanically tested by mounting them on a lens spinning rig placed in an environmental control chamber. Photographs were taken using an automated imaging system at different angular velocities. An inverse mechanical model was then developed to estimate the mechanical properties. Parameters for various constitutive models were determined using an optimization algorithm which matches the model-predicted lens shape to that observed during experiments. The effects of relative humidity on these mechanical properties were also considered.
An isotropic, non-homogeneous, nearly-incompressible, neo-Hookean constitutive model was found to best describe the experimental data. The shear modulus was found to significantly in-crease as relative humidity decreased. Additional analysis suggested the presence of adhesion or cross linking between lens fiber cells. Shear modulus data was comparable to literature values for the young porcine lens and middle-aged human lenses.