The retina contains five different cell types, organized in laminar fashion. At the back of the retina are the photoreceptors, which are the only cells in the retina that detect light. Signals are relayed from the photoreceptors through the bipolar cells to the ganglion cells. The ganglion cells project to the brain. Horizontal cells also receive input from the photoreceptor cells and modulate bipolar cell activity.
Amacrine cells receive input from bipolar cells and modulate ganglion cell activity.
Light passes through the retina, and through the ganglion and bipolar cells before it reaches the photoreceptors. The inner nuclear layer contains the cell bodies of the bipolar, amacrine and horizontal cells and the outer nuclear layer contains the cell bodies of the photoreceptors. The inner plexiform layer contains the connections between the bipolar, amacrine and ganglion cells. The outer plexiform layer contains the connections between the photoreceptors, horizontal cells and bipolar cells. The outer segments of the photoreceptor cells border on the pigmented epithelium, which absorbs excess light at the back of the retina.