Eye lens. Coloured scanning electron micrograph (SEM) of a freeze-fractured lens (crystalline lens) of an eye. The fracture plane has revealed the fibre-like cells (vertical rows) of the lens. The transparency of the lens is thought to arise from the regular arrangement of these cells, the absence of cell nuclei and the main constituent of the cells, the protein crystallin. The lens (found at the front of the eye) precisely 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 aqueous (fluid) and vitreous (jelly) humours inside the eyeball. Magnification: x500 at 6x7cm size.