Changes in Focal Length and Spherical Aberration of the Human Crystalline Lens with Ageing

Abstract

The human lens undergoes many changes during ageing that compromise vision. Many of these changes are relatively poorly characterized due to the difficulties of measuring optical properties of the human lens in vivo. We have undertaken a study of human eye bank eyes to better understand some of the effects of aging on the human lens which may help to understand presbyopia and the lens paradox. The lens continues to grow throughout life resulting in an increase in axial thickness1 and increased curvatures2. This would be expected to result in an increasing lens power that, without compensatory changes in the eye, would cause a myopic shift with ageing. However, presbyopia results in exactly the opposite effect, namely a loss of near vision. Changes in the refractive index distribution in the lens have been suggested to account for this ‘lens paradox’3,4. Previous studies have attempted to model changes in the refractive index distribution with ageing, but these models are in part based on assumptions that have not been verified for the human lens. In addition, in order to completely understand how the lens contributes to visual function in the eye it is necessary to consider the interaction of the lens optics with the cornea and the comeal-lens separation.