Rhodopsin protein molecule. Computer model of a molecule of the protein opsin that forms part of the rhodopsin complex. Rhodopsin is found in the rod photoreceptor cells in the retina of the human eye, where it absorbs light falling on the retina. The rhodopsin complex consists of opsin bound to a non-protein component, retinal (not seen). The retinal molecule absorbs light, which causes it to change shape and separate from the opsin. This initiates the transmission of nerve impulses to the brain, leading to the sensation of vision. The great sensitivity of rhodopsin (also called visual purple) is what allows vision in dim light.