3D BIOMECHANICAL MODELLING OF THE LENTICULAR SYSTEM UNDER CATARACT SURGERY

After cataract surgery, various complications can occur, most notably posterior chamber IOL dislocation. This complication often arises from zonular weakness, with pseudoexfoliation being reported as a predisposing factor of in-the-bag IOL dislocation cases. The aim of the present computational work is to comprehend the biomechanical behaviour of the human eye lens complex before and after cataract surgery, identifying potential factors contributing to late in-the bag IOL dislocation.

A Finite Element (FE) analysis of the human eye in healthy, cataract and pseudophakic states is proposed, under intact and pseudoexfoliative conditions. Several 3D models were developed, composed by the nucleus, cortex, capsular bag and zonules, with the IOL replacing the crystalline in the pseudophakic model. The postcataract capsular bag was considered to be collapsed, both in the anterior and posterior portions of the structure. The stretching of the zonules was simulated, from an accommodated to a relaxed state, following Helmholt’z accommodation theory. The pseudoexfoliation was modelled by progressively reducing zonular thickness. The pseudophakic model was subjected to gravity load conditions and different IOL positions to assess their impact on zonular failure.

Results indicate minimal gravity load impact on the pseudophakic complex, with the horizontal IOL position yielding the least amount of stress in the represented ocular structures. Pseudoexfoliation heightened zonular stress in the affected areas, potentially contributing to disease progression and late in-the-bag IOL dislocation in pseudophakic eyes. The analysis of pre- and post-surgery conditions revealed increased capsular stresses in the pseudophakic eye, potentially offering insights into phenomena like the observed dead bag syndrome  in specific postoperative cases.

This work led to the collection of novel data concerning the pseudophakic complex configuration, as well as the notion of cataract development within the lens complex. The insights obtained related to the impact of IOL insertion in the human eye, particularly by considering pre-existent degenerative scenarios, become of clinical importance, as it could lead to optimal configurations to be tested in a surgical environment.