Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Researchers discover mechanism that helps humans see in bright and low light

15.10.2009
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 Kefalov, 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 Müller cells, these cells support and interact with rods and cones. The researchers treated mouse retinas with a chemical that destroyed the Müller cells, then exposed the retina to bright light, followed by darkness.

"When we blocked the function of Müller 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 Müller 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.

Wang JS, Kefalov VJ. An alternative pathway mediates the mouse and human cone visual cycle. Current Biology vol. 19 (19), Oct. 13, 2009.

(related paper)

Wang JS, Estevez ME, Cornwall MC Kefalov VJ. Intra-retinal visual cycle required for rapid and complete cone dark adaptation. Nature Neuroscience, vol. 12, pp. 295-302, online Feb. 1, 2009

This study was supported by the National Eye Institute of the National Institutes of Health and by Research to Prevent Blindness.

Washington University School of Medicine's 2,100 employed and volunteer faculty physicians also are the medical staff of Barnes-Jewish and St. Louis Children's hospitals. The School of Medicine is one of the leading medical research, teaching and patient care institutions in the nation, currently ranked third in the nation by U.S. News & World Report. Through its affiliations with Barnes-Jewish and St. Louis Children's hospitals, the School of Medicine is linked to BJC HealthCare.

Jim Dryden | EurekAlert!
Further information:
http://www.wustl.edu

More articles from Life Sciences:

nachricht A new technique isolates neuronal activity during memory consolidation
22.06.2017 | Spanish National Research Council (CSIC)

nachricht CWRU researchers find a chemical solution to shrink digital data storage
22.06.2017 | Case Western Reserve University

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

Im Focus: Optoelectronic Inline Measurement – Accurate to the Nanometer

Germany counts high-precision manufacturing processes among its advantages as a location. It’s not just the aerospace and automotive industries that require almost waste-free, high-precision manufacturing to provide an efficient way of testing the shape and orientation tolerances of products. Since current inline measurement technology not yet provides the required accuracy, the Fraunhofer Institute for Laser Technology ILT is collaborating with four renowned industry partners in the INSPIRE project to develop inline sensors with a new accuracy class. Funded by the German Federal Ministry of Education and Research (BMBF), the project is scheduled to run until the end of 2019.

New Manufacturing Technologies for New Products

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

A new technique isolates neuronal activity during memory consolidation

22.06.2017 | Life Sciences

Plant inspiration could lead to flexible electronics

22.06.2017 | Materials Sciences

A rhodium-based catalyst for making organosilicon using less precious metal

22.06.2017 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>