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. The photoreceptors convert incoming photons into neurochemical signals. Rod photoreceptors have a long, cylindrically shaped outer segment with membranous disks that are stacked with photopigment.
Cone cells have a shorter, more tapered outer segment with fewer membranous disks.
The rods are much more sensitive to light than cones and mediate most vision at night or in low light. In contrast, the cones are differentially sensitive to varying wavelengths, and mediate color vision. At the peripheral retina, there are more rods than cones, and more photoreceptors per ganglion cell. The peripheral retina is designed to detect minute levels of light. They contain seven transmembrane domains and interact with heterotrimeric G proteins, called transducin, or Gt.