Navigation Links
Researchers discover mechanism that helps humans see in bright and low light
Date:10/13/2009

Oct. 13, 2009 -- Ever wonder how your eyes adjust during a blackout? When we go from light to near total darkness, cells in the retina must quickly adjust. Vision scientists at Washington University School of Medicine in St. Louis have identified an intricate process that allows the human eye to adapt to darkness very quickly. The same process also allows the eye to function in bright light.

The discovery could contribute to better understanding of human diseases that affect the retina, including age-related macular degeneration, the leading cause of blindness in Americans over 50. That's because the disease and the pathway the researchers have identified both involve cells called cone cells.

Age-related macular degeneration may be modulated, perhaps, through this pathway we've identified in the retina, says principal investigator Vladimir J. Kefalov, Ph.D. Deficiencies in this pathway affect cone cells, and so does macular degeneration, so it's possible that if we could enhance activity in this pathway, we could prevent or reverse some of that damage to cone cells.

The retina's main light-sensing cells are called rods and cones. Both use similar mechanisms to convert light into vision, but they function differently. Rods are highly sensitive and work well in dim light, but they can quickly become saturated with light and stop responding. They don't sense color either, which is why we rarely see colors in dim light. Cones, on the other hand, allow us to see colors and can adapt quickly to stark changes in light intensity.

The researchers began with studies of salamanders because their cone cells are abundant and easy to identify. Cones rely on light-sensing molecules that bind together to make up visual pigments. The pigments get destroyed when they absorb light and must be rebuilt, or recycled, for the cone cells to continue sensing light. After exposure to light, key components of pigments called chromophores can leave the cells and travel to the nearby pigment epithelium near the retina. There the chromophore is restored and returned to the photoreceptor cells.

Earlier this year, the research team removed the pigment epithelium layer in salamander retinas, so that pigment molecules could not be recycled that way. Then they exposed retinal cells both to bright light and to darkness. The rods no longer worked, but the cones continued to function properly, even without the eye's pigment epithelium.

Exposure to bright light destroyed visual pigments in rods, and those cells could not recycle chromophores, says principal investigator Vladimir J. Kefalov, Ph.D., assistant professor of ophthalmology and visual sciences. Pigments in cones, by contrast, quickly regenerated and continued to detect light even without the pigment epithelium, so it was clear a second pathway was involved.

In the new study, Kefalov did the same experiments in cells from mice, primates and humans with the same result.

To learn how cones were able to recycle pigments without pigment epithelium, Kefalov's team has focused on a particular type of cell in the retina. Called Mller cells, these cells support and interact with rods and cones. The researchers treated mouse retinas with a chemical that destroyed the Mller cells, then exposed the retina to bright light, followed by darkness.

When we blocked the function of Mller cells, the retinal visual pathway could not function because cones ran out of photopigment and could not adapt to dark, Kefalov says.

The new paper, published in the journal Current Biology, suggests Mller cells are key to this pathway in mammals, including humans.

When those cells function properly, cones in the mouse, primate and human retinas are able to function in bright light and adapt to darkness, independently of the pigment epithelium, Kefalov says.

He says this discovery means it may one day be possible to manipulate this pathway in the retina to improve vision when the other pathway, involving pigment epithelium, has been interrupted by injury or disease, such as age-related macular degeneration.


'/>"/>

Contact: Jim Dryden
jdryden@wustl.edu
314-286-0110
Washington University School of Medicine
Source:Eurekalert

Related medicine news :

1. New effort to battle antibiotic resistance rallies researchers throughout Harvard University
2. Researchers report benefits of new standard treatment study for rare pediatric brain cancer
3. Researchers identify genes associated with onset age of Parkinsons disease
4. BUSM researchers identify better laser for treating facial spider veins
5. Toronto researchers discover novel circulation in human eye, new glaucoma treatment target
6. Researchers find demand for cosmetic and surgical procedures in dermatologic surgery rising rapidly
7. Using synthetic evolution to study the brain: Researchers model key part of neurons
8. Researchers at Boston University School of Medicine incorporate multisite geriatric clerkship
9. Researchers use computational models to study fear
10. Researchers develop an integrated treatment for veterans with chronic pain and posttraumatic stress
11. UT Houston, Jamaica researchers launch autism study
Post Your Comments:
*Name:
*Comment:
*Email:
(Date:6/25/2016)... , ... June 25, 2016 , ... On Friday, June ... a Bronze Wellness at Work award to iHire in recognition of their exemplary accomplishments ... of the 7th annual Maryland Workplace Health & Wellness Symposium at the BWI Marriott ...
(Date:6/24/2016)... ... 24, 2016 , ... June 19, 2016 is World Sickle Cell Observance Day. ... the benefits of holistic treatments, Serenity Recovery Center of Marne, Michigan, has ... , Sickle Cell Disease (SCD) is a disorder of the red blood cells, which ...
(Date:6/24/2016)... ... June 24, 2016 , ... ... for accelerated orthodontic treatment. Dr. Cheng has extensive experience with all areas of ... AcceleDent, and accelerated osteogenic orthodontics. , Micro-osteoperforation is a revolutionary adjunct to ...
(Date:6/24/2016)... , ... June 24, 2016 , ... ... at the Clinical Decision Making in Emergency Medicine conference in Ponte Vedra Beach, ... journal articles published in Emergency Medicine Practice and Pediatric Emergency Medicine ...
(Date:6/24/2016)... ... ... National recruitment firm Slone Partners is pleased to announce the ... as Vice President of North American Capital Sales at HTG Molecular . ... team in the commercialization of the HTG EdgeSeq system and associated reagents in North ...
Breaking Medicine News(10 mins):
(Date:6/24/2016)... , Belgium , June 24, ... VNRX), today announced the appointment of Dr. ... Directors as a Non-Executive Director, effective June 23, ... Audit, Compensation and Nominations and Governance Committees.  As ... Futcher will provide independent expertise and strategic counsel ...
(Date:6/23/2016)... 23, 2016 Any dentist who has made an ... current process. Many of them do not even offer this ... and high laboratory costs involved. And those who ARE able ... such a high cost that the majority of today,s patients ... Parsa Zadeh , founder of Dental Evolutions Inc. and ...
(Date:6/23/2016)... , June 23, 2016 Research and ... Devices Medical Market Analysis 2016 - Forecast to 2022" ... The report contains up to date financial data derived ... Assessment of major trends with potential impact on the market ... of market segmentation which comprises of sub markets, regional and ...
Breaking Medicine Technology: