Melanopsin and the influence of inner retinal photoreception

Abstract

Almost all species exhibit daily cycles of physiology and behaviour driven by an endogenous rhythmicity. This clockwork only provides a selective advantage when synchronised (entrained) to external time, measured by the repetitive, daily rotation of the earth on its axis and its annual movement around the sun. Humans have been traditionally considered to be a diurnal species, active in daylight and inactive with night but with the advent of urban living and artificial sources of lighting these rhythms of evolutionarily adapted patterns of behaviour and metabolism are being disturbed and redistributed. The disharmony is strongly expressed with shift-workers having higher rates of obesity, diabetes, metabolic syndrome and possibly prostate and breast cancer. Can these changes in human behaviour also be reflected more subtly in increasing rates of disease and cancer throughout the community. As a skin cancer clinician see an increasing diagnosis of melanoma, particularly. Does this represent maladaptive patterns of sun exposure. This certainly seems to be the case with recreational, rather than occupational exposure patterns.

Gross changes in illumination at twilight, dawn and dusk, are the zeitgebers that entrain the endogenous clockwork, the circadian system. What percentage of the population regularly observe these changes of light and how influential is this on our well-being?