With far more than 100 million nerve cells, the retina is the first stage of our visual system and our window to the outside world. The process includes detection of light impulses (photons) by different light receptors, in general called rods (120 million cells) and cones (6 million cells), and the fast and continuous translation, filtration and post-procession into electrical signals (or nerve impulses). These signals are then passed through the optical nerve’s 1.5 million fibres to the visual centre of the brain and reinterpreted into a cohesive image.
The flexibility and economy with which retinal cells work together remains beyond our powers of imagination: the eye reports numerous signals to the brain at once, including separate detection of light (light on) and dark (light off), general patterns and finest details, movements and different hues (including: red, green and blue). This literally makes the eye a camera with 10 to 15 different films and despite it appears so naturally to us, the perception of an image is the result of a most complex interaction process involving millions of cells and the electrical signals they produce and pass on to the brain.
What you can see on this image is the (1) rods and cones layer. It is located below the pigment epithelia which has been cut away during the preparation and is not visible on this image (black space on top). Below the rods and cones layer you can find the (2) outer nuclear layer (ONL) which contains the nuclei of the rods and cones. The adjacent (3) outer plexiform layer (OPL) is followed by the (4) inner plexiform layer (IPL), which contains numerous cell types, including horizontal cells, bipolar cells and amacrine cells. At the very bottom you can see the (5) inner nuclear layer (INL), followed by the (6) ganglion cell layer with two (7) blood vessels shown at left and (8) nerve fibers (which form the optical nerve).