The effect of age on human natural lens growth and biometry

The human lens is a continuously growing organ. Knowledge of how this continuous growth generates the function and properties of a lens is essential for understanding the development of age-related disorders such as cataract and presbyopia. This project aimed to gather information on the growth and physical properties of the human lens by measuring wet and dry weights, dimensions, optical and mechanical properties. Of particular interest were the data on dry weights and the data on young lenses which do not currently exist in literature.Lenses were obtained from eye bank eyes. Their dimensions were measured with a newly built digital mini shadowgraph imaging system constructed especially for this purpose. Their opto-mechanical properties were obtained using a custom designed lens stretcher system. Then, after measuring their wet weights, the lenses were subjected to formalin fixation (one week) and incubation in hot air oven (80°C for two weeks) until a constant dry weight was achieved. Measured lens parameters were analysed as a function of age using linear and non-linear regression methods.Data on lens weights were obtained for 502 lenses aged 20 weeks of gestation to 93 years; probably the largest series over a wide age range. The results suggest that the human lens grows in two phases: an asymptotic phase that starts prenatally and continues postnatally into the first three years of life and then a linear phase thereafter. Shadowgraph experiments were performed on 141 lenses (aged 29 days to 88 years) and the data were analysed for biometric information such as equatorial diameter, axial thickness, anterior thickness, posterior thickness and volume for all lenses. The results on the dimensions of the in vitro lenses gave more insights into the remodeling process that occurs in the human crystalline lens unlike the other species. Stretching experiments were performed on 91 lenses (aged 1 day to 78 years). The age-related changes in the optical and mechanical properties of the lenses were within the physiologically relevant range and agree with the classical Helmholtz theory of accommodation. The scientific information obtained will be invaluable in the development of biomechanical modeling and therapies for presbyopia