The aging human lens: structure, growth, and physiological behaviour

The aging human lens has been the subject of intense research over the past 20 years, for a number of quite disparate reasons. The fact that the incidence of cataract rises exponentially with age after 50 years1 provides the driving influence for much of the effort, but the unique accessibility, homogeneity, and basic simplicity of structure of the organ itself makes it a fruitful system for fundamental studies of tissue growth, development, and differentiation.2-4

Images of the whole human lens in vivo have been available for detailed analysis since the introduction of the quantitative slit lamp (or Scheimpflug) camera (Fig 1). This has been invaluable in providing an understanding of the changes in shape and optical properties both of the ‘normal’ and cataractous aging lens.5-7 The lens is also accessible as an in vitro system of study through the provision of donor eyes for corneal transplant and general research. Since the lens has no direct blood supply, it survives well both in the globe itself and in organ culture media.8-10 Whole cataractous lenses were also once routinely available before the advent of extracapsular cataract extraction (ECCE) with intraocular lens implantation and in the past there have been combined slit lamp and in vitro studies which have correlated changes in light scatter and absorbance with specific alterations in ion and protein levels (Fig 1 and Marcantonio et al11 and Hockwin et al12).