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Mon July 30, 2012
How an experiment on blind mice could help blind humans see
A potential new cure for blindness is showing promise in an experiment at the University of Washington and University of California. The study shows that losing your eyesight as you grow older may someday be reversible.
The experiment used mice – blind mice.
Researchers showed that you can inject a certain compound, called AAQ, into the eyes of a blind mouse – whose photoreceptors have actually died – and it will behave like it can see. It reacts to bright light, its pupils dilate and shrink, and it tries to navigate using its eyes.
For example, a normal mouse cringes and hides when exposed to bright light. Blind mice don't. But the blind mice that were treated with AAQ fled from a light.
From mouse to human
How would it look through the eyes of a human?
“If you take an individual who has no light perception … my best guess is that this compound would give such a person a good sense of what their environment looks like,” says U.W. ophthalmology professor Russ Van Gelder, one of the principal investigators. "That is, where the walls are, and where the ground is, and where large structures are."
It’ll take years of testing, in dogs and monkeys, before they can tell if the person would get sharp vision, enough to allow them to read or drive, or if they’d just see blurry outlines.
The type of blindness in the mice is similar to what happens to people with macular degeneration, and retinitis pigmentosa, which causes younger people to go blind.
Research started with hijacking brain cells
The experiment derives from earlier research at U.C. Berkeley, where Richard Kramer and Dirk Trauner developed the AAQ compound. They were looking for ways to re-program brain cells. The compound allows them to "hijack" cells, and control when a neuron cell "fires" or sends a message to neighboring cells.
(Video: Mice with a genetic disease that causes blindness regained some sight after injection with a chemical “photoswitch.” The eye of the untreated mouse on the left shows no response to light, while the pupil of the mouse on the right, which was injected with the chemical, contracts in light. Credit: Richard Kramer, UC Berkeley, courtesy of Neuron.)
The compound attaches to a cell, and when a certain color of light hits the compound it either activates the cell or shuts it off. In this case, they used a violet light to turn cells on, and a green light to quiet those cells.
Next step -- using the compound to restore vision
In macular degeneration and retinitis pigmentosa, you lose the light-sensing cells in the back of the eye. These are the rod and cone cells that act like pixels in your camera. Instead of 10 megapixels in your camera, the eye's retina has more than 100 megapixels. And in these diseases, all of those pixels go dark.
For the most common type of macular degeneration, there are currently no treatments. A Seattle company called Acucela is testing a drug that would slow down the vision loss. But nothing can restore eyesight once its lost.
Van Gelder and Kramer believe AAQ could change that.
This new chemical doesn’t bring the dead cells back to life. Instead, it hijacks nearby cells that normally help relay messages from the cones and rods in the back of the eye to the brain. The chemical allows those cells to detect light.
Star Trek goggles?
If it does make it to humans, Van Gelder says they’ll probably need to wear special glasses or goggles to help those cells detect the full spectrum of light. For example, the current experimental mice would not be able to see anything red.
The chemical would also have to be delivered through a time-release drug capsule, implanted into the eye a few times per year. Otherwise, it wears off quickly.
The research was published in the July 26th issue of the journal Neuron.
Elsewhere, other researchers are tackling the same problem by attempting to use stem cells to reprogram cells in the retina, while others are injecting genetic material into cells to do the same thing.
“The advantage of this approach is that it is a simple chemical, which means that you can change the dosage, you can use it in combination with other therapies, or you can discontinue the therapy if you don’t like the results. As improved chemicals become available, you could offer them to patients. You can’t do that when you surgically implant a chip or after you genetically modify somebody,” Kramer said, in a news release.
Kramer has co-founded a company attempting to commercialize a viable drug.
Video: Below is a CBS television station's report on the research:
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