September 20, 2012
Vision Research Links Color Blindness To Eye Cells, Not Brain
Alan McStravick for redOrbit.com - Your Universe Online
Over the past few years, several advances have been made in the field of ocular health. Much of the research in color vision deficiencies has been conducted in Australia by researchers at The Vision Centre and The University of Sydney.
Only a few months back, a major leap forward was achieved in the area of cortical color blindness caused by a traumatic brain injury. That study, like most others, focused on searching the vision centers of the brain for possible ways to improve or eradicate color blindness. While the findings for that study still remain valid, a recent study led by Professor Paul Martin of The Vision Centre and The University of Sydney has determined that in congenital or inherited color blindness, the vision cells, or cone cells, are responsible for the condition rather than unusual biological wiring that exists between the eye and brain.
The implications of these findings are far-reaching since color vision deficiency is the most common genetic disorder in humans. It has been determined that this disorder is most often inherited as a direct result of recessive mutations affecting the X-chromosome. For this reason, color vision deficiency is far more prevalent amongst males, affecting an estimated 1 in 8 men. Females have a far lower incidence of color blindness, at approximately 1 in 200. It is estimated that there are 13.5 million color blind people the U.S. alone and more than 200 million worldwide.
With this most recent study, researchers feel they have taken a significant step forward in being able to restore the full range of chromatic vision for people who have been born color blind. Additionally, they are confident that they will be able to use these current findings to address age-related macular degeneration (AMD), which accounts for a high percentage of individuals who are termed ℠legally blind´.
Professor Martin explains, “There are millions of cones in our eyes - vision cells that pick up bright light and allow us to see colour. They are nicknamed red, green and blue cones because they are sensitive to different wavelengths of light."
“We now know that in the macular region of the eye, each cone has its own ℠private line´ into the optic nerve and the brain. Just as a painter can mix from three tubes of paint to produce a wide and vivid palette, our brain uses the ℠private lines´ from the three cone types to create thousands of colour sensations,” Martin explained
“Scientists previously thought that full colour vision depends on specialised nerve wiring in the eye and brain, but animal studies show that the wiring is identical for monkeys whether they have normal or abnormal colour vision.”
These findings led Professor Martin and his team to realize that there was nothing wrong in the brain. The information traveling the ℠private lines´ he referred to was uninterrupted and processed normally. The problem, they determined, must be in the first stage of sight. This is how they refocused on the cone receptor cells in the eye itself.
“Now that we know faulty wiring isn´t the cause, we can concentrate on fixing the cones, which are controlled by genes — and thus prone to mutation or mistakes during cell replication. There are already promising results from gene therapy as a way to restore full colour vision in colour blind monkeys. While we still have some way to go,” continued Professor Martin.
“The benefits of this gene therapy — if successful — can potentially extend beyond providing complete colour vision.”
In the pathology of AMD, explained professor Martin, “energy supplies to the macula can´t keep up with demand. So the ℠private line´ system must be very energy-intensive. Gene therapy could be used to turn down the cones´ energy demand, or to increase energy supply from supporting cells to cone cells.”
His research team, along with clinical researchers at the Save Sight Institute, are trying now to determine just how many of these ℠private lines´ exist in the human brain. They are hoping that with that information, they will learn where energy demand is highest, allowing them to target gene therapies in the correct locations.
Professor Martin and his team hail the initial animal research on ℠private lines´ for color vision, stating that it directly provided a new path towards understanding and possibly eradicating one of the more important visual diseases in humans.
Funding for these studies, via The Vision Centre, is provided by the Australian Research Council as the ARC Centre of Excellence in Vision Science.