Seeing the light : different photoreceptor classes work together to drive adaptation in the mammalian retina

Environmental illuminance can vary in intensity by up to 11 log units. The retina must adapt to these light conditions to allow stable image recognition under vastly different light conditions. The same object can generally be recognised both under twilight and bright sunshine. The retina adapts to the presenting light conditions by changing the relative sensitivity of the photoreceptive systems, however, do these adapting systems regulate themselves or does an independent photoreceptor set the absolute light intensity of the system? Three main photoreceptor classes have been widely characterised in the retina: rods, cones and intrinsically photoresponsive retinal ganglion cells (ipRGCs). We present here a discussion of recent literature that has identified the contribution of all three of these photoreceptor classes to aspects of light adaptation in the retina.