Effect of suction angle on zonular fibers during residual cortex removal in phacoemulsification using finite element modeling

Purpose: The suction of the eye lens cortex is an integral step of cataract surgery. Two conventional angles of cortex removal, including suction in the tangential or normal direction to the cortex surface, have different resulting stress and the risk of failure. However, there is no study about the effect of suction angle on the risk of zonules failure. So, this investigation aimed to evaluate the effect of suction direction on zonules' mechanical behavior using finite element modeling. Setting: In-silico Study Design: 3D finite element model experimental study Methods: A 3D finite element model was developed, including nucleus covered by cortex and capsule. Similar to cataract surgery, a circular rapture was considered at the top of the capsule to apply suction pressure. Finally, Zonular fibers were modeled as a continuum body using 3D solid elements (C3D8R). A custom FORTRAN subroutine was implemented to enforce tension-only behavior, mimicking the physiological characteristics of the zonules, which are resistant to tensile but not compressive loads. This method allows for a realistic simulation of zonular mechanics during cortical aspiration. Results: The suction processes in tangential and normal angles were simulated; The resulting relative displacements between the cortex and capsule, as a criterion of cortex separation, versus the resulting maximum zonule displacements, were recorded in each model. The cortex-capsule relative displacement versus maximum zonule displacement indicated a diagram slope of 0.09 for tangential applying pressure and 0.02 in the case of applying normal pressure. Conclusion: The results illustrated that zonules were less tensile in a specific magnitude of cortex-capsule relative displacement under tangential applying pressure, which means eye zonules have a lower risk of failure until the separation of the lens cortex.