Purpose:
As the choice of adequate means for intravital observation and quantitative evaluation of accommodation physiology is limited, its biomechanical modeling is advisable. Purpose: numerical modeling of accommodation within the deformation model of human eye; a study of the impact of biomechanical parameters of certain tissues of the eye on its accommodative ability.
Methods:
The finite element method (ANSYS) has been applied. A nonlinear 3D problem was solved which took account of the liquid, which was being modeled statically. The parameters that determined accommodative ability of the eye included accommodation volume as well as energy used to shift the gaze from the near to the distant target and vice versa.
Results:
The numerical biomechanical model of the eye includes the crystalline lens (containing the nucleus and the capsule), ciliary body, zonular fibers, iris, limb, cornea, sclera, extraocular muscles (including the eye string), optic nerve, vitreous, choroid, retina. A series of analyses have been performed to observe processes of accommodation and eyeball rotation in the eye socket with various values of mechanical properties of eye tissues. Optical power and energy required for crystalline lens deformation under the simulated processes have been evaluated (Fig.1,2).
Conclusions:
Accommodation volume and energy used depend on the value of the force created by active contraction of the ciliary muscles, mechanical properties (rigidity) of the crystalline lens content, the rigidity ratios of lens capsule/cortex and cortex/nucleus, as well as biomechanical properties of the sclera and extraocular muscles. It is shown that the anterio-posterior axis of the eye may increase by up to 0.5 mm with the contraction of the extraocular muscles. Numerical modeling of accommodation within the complete biomechanical model of human eye shows that it agrees with Helmholtz accommodation theory.
Keywords: accommodation • ciliary muscle • optical properties