Environmental Toxicology and Pharmacology 21 (2006) 215–221 A focus on the human lens in vitro I. Michael Wormstone ∗ , David J. Collison, Simon P. Hansom, George Duncan The Humane Research Trust, School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK Available online 22 August 2005 Abstract The lens is a unique organ in that it is avascular and non-innervated, obtaining all nutrients from the aqueous and vitreous humours that bathe the lens. All lenses attempt to achieve the same goal, namely to maintain transparency and focus light on to the retina. However, the mechanisms by which these processes are maintained, or disrupted leading to a loss of transparency, are likely to differ in some cases between animals and humans. To allow comparison to take place, human in vitro models have been developed, ranging from whole organ culture to the generation of human lens cell lines. All have their merits and limitations, but as a whole, they permit extensive studies of lens cell behaviour and function to be carried out. Together, these in vitro methods allow the biological events of the lens to be further understood. Moreover, they could help identify the mechanisms that give rise to cataract and posterior capsule opacification, a problem that occurs following surgery, providing therapeutic targets for their prevention. © 2005 Published by Elsevier B.V. Keywords: Lens; Human; Cataract; Posterior capsule opacification; In vitro; Culture 1. Introduction At first glance, the lens is a simple organ but its apparent simplicity disguises a wealth of cell biological sophistication and ingenuity. The level of complexity in our understanding of this organ is, however, increased when we consider species variation. All lenses attempt to achieve the same goal, namely to maintain transparency and focus light on to the retina. However, the mechanisms by which these processes are maintained, or disrupted leading to a loss of transparency, are likely to differ in some cases between animals and humans (Vrensen, 1994; Fougerousse et al., 2000; Rhodes et al., 2002). It is, therefore, important to identify the similarities and differences between human and animal species, such that meaningful advances in human biomedicine can be achieved. For comparison to be made, it is important to identify the different mechanisms driving similar cell biological events in the human lens. The review that follows will consider some of the techniques currently employed to study human lens cells in vitro. ∗ Corresponding author. Tel.: +44 1603 591319; fax: +44 1603 592250. E-mail address: i.m.wormstone@uea.ac.uk (I.M. Wormstone). 2. The lens The lens is a unique organ in that it is avascular and non- innervated, obtaining all nutrients from the aqueous and vitreous humours that bathe the anterior and posterior regions of the lens, respectively (Davson, 1984). All cells within the lens are derived from epithelial cells and the region where cell division and fibre differentiation take place is highly localised (Fig. 1). In the nor- mal lens, these events only take place at the equatorial region while the central epithelium is in effect a non-dividing popula- tion. Identifying the processes controlling normal cell function is of great importance as modification of these highly regu- lated mechanisms can result in lenticular pathologies, namely cataract. 3. Cataract Cataract is one of the major causes of blindness in the world and is a disease largely associated with the elderly (Thylefors et al., 1995). The incidence of cataract on a global scale is not uniformly distributed, with developing countries showing a far greater frequency than developed countries. Cataract is the term used to describe any opacification of the lens and this may be restricted to a localised region or can involve the entire lens 1382-6689/$ – see front matter © 2005 Published by Elsevier B.V. doi:10.1016/j.etap.2005.07.012