Figure 3.

The zone of active metabolism in the adult human lens. The dark band at the top represents the lens epithelium. The gray oval at the periphery of the fiber mass includes all the lens fiber cells with nuclei and other membrane-bound organelles. The epithelium and the outer fiber cells are responsible for nearly all the metabolism in the lens. The available data suggest that the lens center has little or no metabolic activity. Based on experimental data, the filled arrows indicate the major route of entry of metabolites at the germinative zone, adjacent to the lens equator.¹² The open arrows depict the direction of diffusion of critical metabolites such as glutathione, from the metabolically active superficial fiber cells where they are produced, to the deeper fiber cells.