Doctor of Philosophy
University of Wollongong. School of Chemistry
Heys, Karl Robert, Changes to stiffness and water in the human lens with aging and cataract, Doctor of Philosophy thesis, University of Wollongong. School of Chemistry, University of Wollongong, 2010. https://ro.uow.edu.au/theses/3330
Presbyopia is the loss of ability of the human lens to undergo accommodation and thus focus on near objects. This disorder is characterised by an increase in focal point resulting in a need for reading glasses by middle age. It had been suggested that this may be due to the progressive increase in lens stiffness with age but up until this point, the data to support this has been very limited.
To investigate lens stiffness change, a DMA (Dynamic Mechanical Analyser) was used together with a small probe to gain measurements across the lens surface. Total water was analysed using TGA (Thermogravimetric analysis), and free and bound water data was obtained using a DSC (Differential Scannning Calorimeter).
Analysis of both fresh human lenses and frozen lenses revealed dramatic alterations in stiffness with age, with a 500‐1000 fold increase being observed (between 10 and 70 years of age). A change with age was observed in the distribution of water between free and bound components. In young lenses the ratio was around 1:1 (free:bound); this ratio increased to 2:1in older lenses. The stiffness of cataract lenses was found to be dependent both on the age of the lens, and the stage of cataract.
Such dramatic changes in the stiffness of the lens nucleus must have an effect on lens functioning. Although establishing that large lens stiffness changes occur with age, these studies did not identify the cause. A change in the distribution of water that was found with age could possibly be responsible. It becomes apparent that care needs to be used when interpreting data from animal models, as the human lens is unique.