Regulating the body clock – The unrecognised role of the eye

Abstract

AbstractLittle more than a decade ago discussion that the eye might contain another photoreceptor, different from the rods and cones, generated either polite amusement or a hostile rebuttal. The dogma was that all light detection took place by these photoreceptors whilst the other cells of the retina act only to process visual signals. However, several lines of research led to the discovery that the vertebrate eye, including humans, contains another class of photoreceptor based upon a small number of photosensitive retinal ganglion cells (pRGCs). These specialised neurons detect environmental irradiance and regulate a wide range of physiology and behaviour including the regulation of 24h body clocks, sleep, alertness, mood and even pupil size. Furthermore, the pRGCs have been shown to utilize a novel light signalling pathway based upon the photopigment melanopsin. Collectively these findings have transformed our understanding of how the eye detects light and are redefining our assessment, treatment and care of individuals with eye disease. The discovery and current understanding of this “third” class of ocular photoreceptor will be reviewed in this presentation.