Growth of the lens: in vitro observations.

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.