Figure 1. Structure of the eye and cellular lens; organization of vertebrate lenses. Small cuboidal epithelial cells cover the anterior surface. At the anterior/posterior equator, these cells exit the cell cycle and begin to elongate as they move into the interior. A few hundred microns into the lens, fiber cells undergo a final stage of terminal differentiation where they lose cell nuclei and organelles. At right is a histological section of an adult mouse eye.