Navigation Links
Blind humans lacking rods and cones retain normal responses to non-visual effects of light
Date:12/13/2007

In addition to allowing us to see, the mammalian eye also detects light for a number of non-visual phenomena. A prime example of this is the timing of the sleep/wake cycle, which is synchronized by the effects of light on the circadian pacemaker in the hypothalamus.

In a study published online on December 13th in Current Biology, researchers have identified two totally blind humans whose non-visual responses to light remain intact, suggesting that visual and non-visual responses to light are functionally distinct. Indeed, this separation was suggested by earlier studies in mice that demonstrated that circadian rhythms and other non-visual responses remain sensitive to light in the absence of rods and cones, the two photoreceptor types that are responsible for vision.

It turns out that mammals have an additional light-sensitive photoreceptor in the retinal ganglion cell layer (pRGCs) that is directly sensitive to light and is primarily responsible for mediating these responses. These cells are most sensitive to short-wavelength light with a peak sensitivity at ~480 nm, in the visible blue light range. While these studies and others in sighted subjects suggested that this non-rod, non-cone photoreceptor might play an important role in human photoreception, this had yet to demonstrated unequivocally until now.

To address whether the cells identified in rodents and primates also exist in humans, Zaidi and colleagues first had to find patients who lacked functional rods and cones, but retained pRGCsa formidable task, given that fewer than 5% of totally blind people are thought to retain this response.

This group of researchers was able to identify two such rare patients, allowing them to perform a series of complementary experiments to address whether non-visual responses are possible in the absence of rods and cones and to determine the most effective wavelength, or color, of light that induced a response. In the first patient, the effect of light on melatonin secretion was examined. Melatonin is a hormone produced at night that influences arousal and is secreted in a cyclic fashion. Just like sighted individuals, the blind patient exhibited acute suppression of melatonin in response to light and was most sensitive to blue-light exposure.

Furthermore, blue light also shifted the timing of the circadian pacemaker and improved alertness, as measured by subjective scales, auditory reaction time, and changes in brain activity. While a few rods and/or cones may remain, Zaidi and colleagues have strong evidence to show that they contribute little, if at all, to these effects. Thus the authors were able to show that the effects were maximal in response to wavelengths of light that the retinal ganglion cells respond best to, and not the wavelength that the visual system detects best.

In the second patient, a different a set of tests was administered to assess the effects of light. First, the pupil-constriction response to various wavelengths and intensities of light was examined. Consistent with the major role of the pRGCs in mediating this response, pupillary contriction was stimulated most by blue light (~480 nm), the wavelength that pRGCs are most stimulated by.

Given that the non-visual responses to light appeared to be intact in this patient, the researchers were prompted to ask whether some minimal awareness of light might still be retained despite the inability to detect any response to light by conventional measures and the patients inability to see light. Remarkably, the patient was able to tell that the blue light, but not any other color, was switched on, demonstrating that the pRGCs also contribute to our ability to see light.

These results have a number of important implications for human vision and vision-related diseases. First, they suggest humans possess light-sensitive cells, apart from rods and cones, that are important for non-visual light responses such as the entrainment of circadian rhythms and elevating arousal and brain activity. Second, this information may change how injuries to the eye are treated.

For example, surgeons might want to think twice about removing a damaged eye that still possesses functioning pRGCs, given the important physiological role that these cells play in maintaining normally timed sleep. We will now need to begin to think about these additional functions of the human eye, and consider not just vision, but also how light affects sleep, alertness, performance, and human health. The remarkable discovery of a novel photoreceptor in the mammalian eye has shed new light on an organ that has been studied for thousands of years.


'/>"/>

Contact: Cathleen Genova
cgenova@cell.com
617-397-2802
Cell Press
Source:Eurekalert

Related medicine news :

1. Can brain-injured, partially-blind stroke patients regain some of their lost vision?
2. New discovery may improve treatment of one of the worlds leading causes of blindness
3. Verizon Awards $1.5 Million Grant to Expand American Foundation for the Blinds Web Site for Seniors With Age-Related Vision Loss
4. Diabetes: A Top Cause of Blindness Among Adults
5. Blinded by the Light? Vision Problems and Visual Discomfort Make Driving in the Dark Difficult, Uncomfortable for Most Americans
6. Survey Confirms Americans Have a True Blind Spot Regarding Their Eye Health - and the Real Danger of UV Rays
7. STEP HIV vaccine study to be unblinded
8. Gene therapy safety trial for childhood blindness under way
9. National Federation of the Blind to Award $100,000
10. Investigational Agent Targeting Metabotropic Glutamate 2/3 Receptors Demonstrates Antipsychotic Activity in Humans, Study in Nature Medicine Finds
11. Toddler Study Proves Humans Outsmart Apes
Post Your Comments:
*Name:
*Comment:
*Email:
(Date:6/24/2016)... ... 2016 , ... Marcy was in a crisis. Her son James, eight, was out of control. ... and physically. , “When something upset him, he couldn’t control his emotions,” remembers Marcy. ... rocks at my other children and say he was going to kill them. If ...
(Date:6/24/2016)... ... ... Global law firm Greenberg Traurig, P.A. announced that 20 Florida attorneys are ... for this recognition are considered among the top 2 percent of lawyers practicing within ... of this year’s Legal Elite Hall of Fame: Miami Shareholders Mark D. Bloom, ...
(Date:6/24/2016)... ... June 24, 2016 , ... Comfort Keepers® of San ... Society and the Road To Recovery® program to drive cancer patients to and from ... adults to ensure the highest quality of life and ongoing independence. Getting to ...
(Date:6/24/2016)... Plano, TX (PRWEB) , ... June 24, 2016 , ... ... taking part in Genome magazine’s Code Talker Award, an essay contest in which patients ... for an award to be presented at the 2016 National Society of Genetic Counselors ...
(Date:6/24/2016)... New York, NY (PRWEB) , ... June 24, ... ... lifestyle publication Haute Living, is proud to recognize Dr. Barry M. Weintraub as ... believes that “the most beautiful women in the world, and the most handsome ...
Breaking Medicine News(10 mins):
(Date:6/24/2016)... DUBLIN , June 24, 2016 ... "The World Market for Companion Diagnostic Tests" report to ... World Market for Companion Diagnostics The World ... diagnostic and personalized medicine diagnostics. Market analysis in the report ... Diagnostics Test Market (In Vitro Diagnostic Kits) by Region (N. ...
(Date:6/23/2016)... 2016  MedSource announced today that it has ... solution of choice.  This latest decision demonstrates MedSource,s ... their clients by offering a state-of-the-art electronic data ... nowEDC as the EDC platform of choice in ... "nowEDC has long been a preferred EDC platform ...
(Date:6/23/2016)... INDIANAPOLIS , June 23, 2016 Roche ... received 510(k) clearance for its Elecsys BRAHMS PCT (procalcitonin) ... severe sepsis or septic shock. With this clearance, Roche ... provide a fully integrated solution for sepsis risk assessment ... associated with bacterial infection and PCT levels in blood ...
Breaking Medicine Technology: