Modelling the human accommodation system using finite element analysis

Abstract

The human accommodation system has been extensively examined for over a century, with a particular
focus on trying to understand the mechanisms that lead to the loss of accommodative ability with age
(Presbyopia). The accommodative process, along with the potential causes of presbyopia, are disputed;
hindering efforts to develop methods of restoring accommodation in the presbyopic eye. One method that can be used to provide insight into this complex area is Finite Element Analysis (FEA).
The effectiveness of FEA in modelling the accommodative process has been illustrated by a number of accommodative FEA models developed to date. However, there have been limitations to these previous
models; principally due to the variation in data on the geometry of the accommodative components, combined with sparse measurements of their material properties. Despite advances in available data, continued
oversimplification has occurred in the modelling of the crystalline lens structure and the zonular fibres that
surround the lens. A new accommodation model was proposed by the author that aims to eliminate these limitations. A novel representation of the zonular structure was developed, combined with updated lens and capsule modelling methods. The model has been designed to be adaptable so that a range of different age accommodation
systems can be modelled, allowing the age related changes that occur to be simulated. The new modelling methods were validated by comparing the changes induced within the model to available
in vivo data, leading to the definition of three different age models. These were used in an extended sensitivity study on age related changes, where individual parameters were altered to investigate their effect on the accommodative process. The material properties were found to have the largest impact on the
decline in accommodative ability, in particular compared to changes in ciliary body movement or zonular
structure. Novel data on the importance of the capsule stiffness and thickness was also established.
The new model detailed within this thesis provides further insight into the accommodation mechanism, as
well as a foundation for future, more detailed investigations into accommodation, presbyopia and accommodative restoration techniques.

Date of Award	19 Nov 2013
Original language	English
Supervisor	John G Swadener (Supervisor) & Leon Davies (Supervisor)