New research published in the journal Nature Neuroscience shows that scientists have been able to restore partial vision in mice by regenerating previously severed optic-nerves. This success is a first in a long series of attempts to repair damaged nerves, and may lead to further breakthroughs.
The optic nerve is a thin string of cells called axons that transmit information from the eyes to the brain. Once light has entered the eyes and contacts the retina, it is converted into a series of signals that is then sent to the visual cortex, part of the occipital lobe of the brain. These signals are then processed and interpreted as vision. Even with perfectly healthy eyes, and a fully functional brain, if the connection between them is damaged then eyesight can be severely diminished or lost completely.
Axons, like the nerves found in the spinal cord, don’t repair themselves once damaged. Much like a person with a spinal cord injury that causes permanent paralysis, there is no known remedy for blindness caused by damaged optic nerves.
For the purposes of the experiment, laboratory mice were used that had a specific eye disorder very similar to human glaucoma. This condition causes higher than normal levels of interocular pressure, which damaged the retina and optic nerve tissue at the back of the eye. Glaucoma affects more than 70 million people around the world, and is the number two leading cause of blindness, second only to cataracts.
Mice that were only affected by the condition in just one eye were selected, and were given biochemical manipulations that stimulated the mTOR pathway within the ganglion cells. The intention was to stimulate regenerative growth in the axon cells that connect to the brain. Several different methods were used to do so, and each provided modest, but measurable results.
However, when used in conjunction with one another, much greater results were achieved, and partial vision was restored. This improved vision was confirmed by placing small linders over the mouse’s good eye, and forcing it to uses its once-blind eye to see.