Separate from rods and cones, a novel system in the eye is used to manage sleep/wake cycle and detect an awareness of light
BOSTON - December 14, 2007 - Much like the ear serves two functions; both hearing and balance, researchers at Brigham and Women’s Hospital (BWH) and Harvard Medical School have found more evidence that confirms that the human eye is used not only for vision, but also for maintaining responses to light to regulate the sleep/wake cycle and other daily rhythms. The results of these studies, which were conducted in collaboration with the University of Oxford, Imperial College and City University in the UK, and Thomas Jefferson University in the US, are available online in the December 13, 2007 edition of Current Biology.
“This research confirms the recent finding that a novel photoreceptor system in the eye exists that regulates the human sleep/wake cycle and the brain activating effects of light which is different from the system used for vision,” said Dr. Steven Lockley, senior author of the study and a researcher in the Division of Sleep Medicine at BWH. “We also showed that rudimentary visual responses also use this new photoreceptor system, questioning the traditional view that rods and cones are responsible for all visual responses to light,” he added.
Researchers collected data on two blind subjects, who, when exposed to bright light, exhibited biological responses in circadian rhythm, hormone levels, pupil constriction and changes in brain function. They also found that at certain wavelengths, one subject indicated a visual awareness of light, suggesting that a photoreceptor in the eye recognizes and responds to certain wavelengths of light independently of the system of rods and cones used for vision. Researchers attribute these responses primarily to stimulation of photosensitive retinal ganglion cells found in the eye that are most sensitive to short-wavelength, blue light.
“These results are the final step in confirming that a novel non-rod, non-cone photoreceptor system is present in the human eye. More research is now needed to determine the pathways and structures in the brain which respond to light and control these “nonvisual” biological responses to light in all of us” Lockley concluded.
This research was funded by the Wellcome Trust and the National Institutes of Health.
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Brigham and Women’s Hospital (BWH) is a 747-bed nonprofit teaching affiliate of Harvard Medical School and a founding member of Partners HealthCare System, an integrated health care delivery network. BWH is committed to excellence in patient care with expertise in virtually every specialty of medicine and surgery. The BWH medical preeminence dates back to 1832, and today that rich history in clinical care is coupled with its national leadership in quality improvement and patient safety initiatives and its dedication to educating and training the next generation of health care professionals. Through investigation and discovery conducted at its Biomedical Research Institute (BRI), BWH is an international leader in basic, clinical and translational research on human diseases, involving more than 800 physician-investigators and renowned biomedical scientists and faculty supported by more than $400M in funding. BWH is also home to major landmark epidemiologic population studies, including the Nurses' and Physicians' Health Studies and the Women's Health Initiative.