Growth of the lens (original) (raw)

Understanding the normal functioning of the human lens and its role in the development of disorders of vision, such as presbyopia and cataract, requires a thorough knowledge of how the lens grows and how its properties change with age. Many of these properties can be obtained only by studying the isolated organ in vitro. In addition, because of the difficulties in obtaining human tissues, animal lenses are frequently used as models for the human lens. Information is needed for these as well. In this review, current knowledge of lens growth and factors that affect growth are examined in a variety of species. Topics covered include changes in lens weight, dimensions, stiffness and refractive index distribution with age and the influence of other factors such as gender, environment and body size. From these, it has become clear that lens growth is not greatly affected by external influences. Although there are many similarities in the growth of lenses from different species, humans (and probably all primates) have distinctly different growth patterns, with prenatal and postnatal growth having different regulatory mechanisms. As a result, human lens properties are different from those of other species. Unfortunately, many of the published data are unreliable, presumably because of post-mortem changes, making it difficult to extrapolate in vitro observations to the in vivo situation. Figure 7. The relationship between (A) lens diameter and (B) thickness and age. Data were obtained from Glasser and Campbell 19 ( ), Jones and colleagues 20 ( ), Larsen 21 (᭹), Moffatt, Atchison and Pope 22 ( ), Pierscionek and Augusteyn 23 ( ), Rosen and associates 24 ( ), Schacchar 25 , ( ) and Smith 26 ( ). Growth of the lens Augusteyn Figure 11. Refractive index gradients along (A) the equatorial and (B) the sagittal axes for a 27-year-old ( ) and a 63-year-old ( ) lens. The data, which were kindly supplied by Drs C Jones and J Pope, were obtained using MRI. 46