Eye structure. Coloured light micrograph of a section through the inner surface of a human eye. This slice shows the vitreous humour (transparent liquid in the eye, top), the retina (pink), the choroid (black layer) and the sclera (white external surface, bottom). The eye works by allowing light to be focused by the lens onto the retina. The retina contains photoreceptor cells (small purple dots), which allow the eye to distinguish between colours (cone cells) and to see at night (rod cells). The choroid layer lines the inside of the eye underneath the retina and is pigmented to prevent light reflecting inside the eye and distorting the image. Magnification: x160 when printed at 10cm wide.