Eye lens. Coloured scanning electron micrograph (SEM) of a freeze-fractured lens (crystalline lens) of an eye. The fracture plane has revealed the stacked linear arrangement of the fibre-like cells (grey). The transparency of the lens is thought to arise from this regular interlocking arrangement, as well as the absence of cell nuclei and the cells mainly containing the protein crystallin. The lens (found at the front of the eye) focuses light onto the light- sensitive cells in the retina at the back of the eye. The adult lens has no blood supply. It is sustained by the humours, fluids found inside the eyeball. Magnification: x3000 when printed 10 centimetres wide.