A study published in Nature Neuroscience explains how scientists managed to coax optic nerves of mice so they could regenerate their vision even if nerves were entirely disconnected. The optic nerve cables can follow their former shapes and routes as they reconnect through each cell.
This finding shows that, in a near future, it will be possible to restore eyesight to blind people. The team, led by Andrew Huberman from Stanford University, purposely damaged the optic nerve in one eye of mice. The remaining connections between the optic nerve and the brain tend to decay, and the mouse becomes blind. But if the nerve becomes stimulated with specialized chemicals, the relationships can recover and attach themselves to their places of origin. The recovery process took three weeks.
Curing blind mice could eventually lead to curing blind people
Cells known as ganglions lie in the retina. They pick up visual information and send it through the optic nerve. Ganglions are connected to axons, which comprise the optic nerve as they reach the brain. Retinal ganglion cells are unique since they are the only link between the brain and the eye.
The process of damaging the optic nerve of mice was to resemble the effects of glaucoma, the leading cause of blindness without a known cure. Just like in the experiment, glaucoma puts pressure on the optic nerve, but this pathology is also caused by some strains of cancer and physical injuries.
The mice were subjected to either molecular reactivation to allow nerve regeneration, stimulation through high-contrast images, or both. The team found out that if the optic nerve axons receive constant stimulation alongside molecular reactivation, they can regenerate 500 times faster.
One of the most interesting tests was to show the mice a picture of a black circle as it grew bigger with each second. This test replicates the perception of a bird of prey as it approaches. When the mice were put to this test, they looked for shelter, led by their natural instinct.
Without the specialized treatment and stimulation, axons in mammals cannot regenerate by themselves, unless they are located outside the central nervous system. Researchers did not understand why the axons managed to restore in the same configuration that they had when the optic nerve was damaged.
“For the longest time people in the field wondered if neurons could regenerate and form the correct patterns to connect to the brain, and we found that they did,” Huberman stated.
But even if the mice were able to undergo optical nerve restoration, they still failed some tests regarding their ability of differentiating objects. Huberman said that, although they could prove that the axons were able to reach both the brain and the eye, some important molecular indicators are still missing, which do not allow the eye to determine which subtype of ganglion cell is linked to a particular axon.
Huberman expects that related findings beneficial for humans should take no longer than five years to appear. Since the culprit behind blindness tends to be significant damage to the optic nerve, it may not be as far-fetched to think that human blindness could be completely eradicated in the following century.
— Kevin Mitchell (@WiringTheBrain) January 7, 2016