Stiffness of the Natural Lens

(Funded by Leverhulme Trust and Wellcome Trust)

Dr Harvey Burd, Mr Geoffrey Wilde, Mr Chen-Ket Chai, Dr Stuart Judge

It is generally thought that the mechanical behaviour of the lens changes with age and that these age-related changes in lens stiffness are an important factor in the development of presbyopia. However, until relatively recently, remarkably few data on lens stiffness have been reported in the published academic literature.

The data on lens stiffness that are currently available in the research literature suggest that the lens stiffness increases substantially with age. However, there remains considerable inconsistency between stiffness data obtained by different researchers using different techniques. In particular, the classic data given by Fisher (1971) seems out-of-line with more recent measurements. Following an earlier pilot study (Burd, Wilde & Judge, 2006) we have developed a new form of spinning lens rig (which is a technique pioneered by Fisher) to make new measurements on the stiffness of the human lens.

The spinning lens test procedure that we are using involves spinning a de-capsulated lens about its optical axis. Images of the lens are collected while it is spinning and the deformations induced by the spinning process are used, via finite element inverse analysis, to infer data on lens stiffness.

lensspin

The recent spinning lens test program conducted by Geoffrey Wilde produced a substantial amount of data, some of which has not yet been analysed. In particular, there is a large set of data on the deformations in lenses with intact capsules. A future project is envisaged in which these data are investigated using a multiscale finite element model of the lens in which a structural model is used to represent the capsule.

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