- CIRCADIAN PHOTORECEPTION: MORE THAN MEETS THE EYE by Steven W. Lockley
CIRCADIAN PHOTORECEPTION: MORE THAN MEETS THE EYE by Steven W. Lockley
Steven W. Lockley
PhD, Assistant Professor of Medicine
Division of Sleep Medicine, Harvard Medical School, Associate Neuroscientist, Division of Sleep Medicine, Brigham and Women’s Hospital.
In addition to visual function, the mammalian eye detects light for a range of behavioral and physiological responses separate and apart from sight. In humans, ocular light exposure resets the endogenous circadian pacemaker, suppresses synthesis of the pineal hormone melatonin, enhances morning cortisol production, increases heart rate and core body temperature, induces pupillary constriction, and improves subjective and objective measures of alertness.
Recently, major advances have been made in understanding how light is detected by the eye to transduce the circadian, neuroendocrine and neurobehavioral effects of light. A novel photoreceptor system has been discovered in the mammalian eye, including humans, that is anatomically and functionally distinct from the visual system. A novel photopigment, melanopsin, primarily mediates these responses to light via a small number of intrinsically short photosensitive retinal ganglion cells. These cells, and therefore our ‘non-visual’ responses to light, are most sensitive to shortwavelength blue light (max ~460-480 nm).
Short-wavelength light has the potential to be developed for a range of therapeutic uses including treatment of sleep problems induced by circadian rhythm disorders (shift-work, jetlag, advanced and delayed sleep phase syndrome, aging) or entrainment of the circadian system to unusual day-lengths (e.g., long-duration space flight, submariners, Antarctica). Preliminary studies have also shown that it can be used to treat Seasonal Affective Disorder and may be useful for correcting rest-activity disruption in dementia. The alerting effects of short-wavelength light also suggest that it can be used as a non-pharmacological countermeasure for drowsiness across a range of occupational, medical, educational and military settings.
There is enormous potential for developing these basic findings into real-world clinical and occupational applications in order to provide lighting that improves human health, safety and performance. Given the different, and sometime competing, spectral sensitivities of the visual and circadian photoreception systems, optimizing these multiple effects of light may require complex ‘smart’ lighting systems. The challenge to architects and lighting designers is to incorporate these basic findings into lighting that optimizes both the visual and non-visual effects of light simultaneously and safely.
Steven W. Lockley, PhD, Assistant Professor of Medicine, Division of Sleep Medicine, Harvard Medical School, Associate Neuroscientist, Division of Sleep Medicine, Brigham and Women’s