The mammalian lens consists of two cell types, lens fiber cells which form the bulk of the lens, and a monolayer of epithelial cells that cover the anterior surface of the fibers. Lens epithelial cells are responsible for homeostasis regulation of the lens, including electrolyte and fluid transport. Under normal development, lens epithelial cells progressively differentiate and mature. Lens epithelial cells then migrate from the equatorial region into the interior of the lens to produce transparent crystallins, elongate to form lens fiber cells, and eventually lose their nuclei and other organelles. Studies have shown that lens epithelial cell differentiation and lens polarization are regulated by growth factors present in the ocular fluids, such as epidermal growth factor, basic fibroblast growth factor, insulin growth factor, and insulin.