Injections of a recently discovered chemical into the eyes of blind lab mice has restored at least part of the rodents' vision.
The chemical, called AAQ -- short for acrylamide-azobenzene-quaternary ammonium -- was not tested in humans, nor is it a cure for blindness. But researchers who treated mice with the molecule, a type of light-sensitive "photoswitch," think their method represents an advance in the quest to help the blind see.
"The photoswitch is injected into the vitreous cavity of the eye, but unlike the other strategies, it does not require highly invasive surgical interventions and its actions are reversible," the authors of a new study about AAQ wrote July 26 study in Neuron.
"This is a major advance in the field of vision restoration," said opthamologist Dr. Russell Van Gelder at the University of Washington, Seattle, a co-author of the study.
In a healthy eye, light strikes rod- and cone-shaped photoreceptor cells lining the retina, which transmit the signal into a network of nerves below them. Those nerves ultimately usher visual information to the brain.
Retinitis pigmentosa and age-related macular degeneration kill off the rods and cones, eventually causing blindness, but the network of nerves behind often remains intact.
By taking advantage of the intact nerves, a few biomedical tricks can already partially restore vision. Electronic sensors implanted in a retina, for example, can stimulate the nerves to send visual information when struck by light. Likewise, engineered viruses can implant genes into retinal nerve cells that make them react to light.
But these and other techniques are irreversible and can trigger immune responses that destroy the rest of an eye.
Van Gelder and colleagues knew AAQ reacted to light by changing its shape, and that it could bind to some types of cells. To see if it could affect vision, they raised mice with a genetic tweak that caused rods and cones to perish at an early age. Then they injected AAQ into the rodents' eyes.
In a subsequent test, the researchers put mice into a tube lit at one end by an LED bulb and dark at the other. Untreated mice milled about randomly, regardless of whether the light was on. After an AAQ injection, light caused them to retreat to the tube's dark end -- a behavior typical of mice that can see.
The researchers think AAQ substitutes for dead rods and cones by attaching to nerve cells, then generates a nerve impulse by changing shape when exposed to light.
AAQ isn't known to be toxic, but it isn't perfect. For one, its ability to switch from "on" to "off" shape drops in dim light. And while reversibility can be advantageous, it's effective for just a few hours. Nobody wants painful eye injections several times a day. And while AAQ partially restored vision, it's unlikely the mice enjoy clear, crisp vision.
Still, techniques to administer the molecule in slow-release form already exist, and longer-lasting and more-responsive versions of AAQ may soon be developed.
"This is what we are really excited about," said neurobiologist and study leader Richard Kramer of the University of California, Berkeley, in a press release.
Top image: dullhunk/Flickr
