BIOMECHANICAL MODELLING OF THE PSEUDOEXFOLIATION SYNDROME IMPACT IN THE LENTICULAR SYSTEM'S ACCOMMODATIVE

The study of the crystalline lens complex and its disorders in the context of the scarcity of available clinical and experimental data demands the need for finite element (FE) method studies. The present work has the objective of portraying the relevant features that can lead to the worsening of an individual's visual capacity due to the pseudoexfoliation syndrome. The accommodative capacity of the human lens, when subjected to pseudoexfoliative conditions, is of extreme importance when evaluating the clinical visual capability of the lens.

IDMEC, Instituto Superior Técnico, University of Lisbon; Hospital da Luz Lisbon, Lisbon

Finite element models for a lens complex were developed, composed by the capsule, cortex and nucleus, and anterior, equatorial and posterior zonular fibers. The stretching of the zonules was simulated, from an accommodated to a relaxed state, following Helmholtz's theory of accommodation. Pseudoexfoliative conditions were assessed and analyzed for each individual and group zonular sets. The zonulopathy origin was examined, as well as its extension throughout the composition of the zonular structures. Among other metrics, the amplitude of accommodation of the models was measured by means of dioptric power computation resorting to the Central Optical Power quantity.

With the progression of the disease in the anterio-posterior direction, the accommodative capability becomes more deficient, reaching cases where there is a complete loss of the accommodative capacity. The impact on the amplitude of accommodation was compared between inferior and superior dialysis for the different zonular evaluations. The superior dialysis presents optimal conditions to further the disruption of the fibers and reduce the accommodative amplitude of the lens, when compared with the inferior dialysis location.

This work presents a realistic model of the healthy lenticular system, whilst providing a quantification of the visual accommodative capacity of the lens in healthy conditions and throughout the progression of the pseudoexfoliation disease. The accommodation amplitude of the affected eye becomes an asset when estimating the severity of the syndrome in a patient, given that this quantity can be obtained in a clinical setup. Additionally, the analysis of the severity of the pseudoexfoliation syndrome provides data in the context of the locations that present a greater risk to crystalline lens surgery.