What to do with incurable adult amblyopia?

In a new study, neuroscientists from the Massachusetts Institute of Technology (MIT) and Dalhousie University (Dalhousie University) proved that by temporarily anesthetizing the retina of a good eye, they can lastingly improve the amblyopia of two different mammals Vision, even after a critical period
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Mark Bear said these encouraging results support further preclinical testing of this new treatment, in which injection of tetrodotoxin (TTX) can temporarily and reversibly silence the retina of non-amblyopic eyes
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Mark Bear, professor of neuroscience at The Picower Institute for Learning and Memory at MIT, is the corresponding author of the study published in the journal eLife

Professor Bear from the Department of Brain and Cognitive Sciences at MIT said: "We have observed that every animal has recovered
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We have done better than anyone expected

Kevin Duffy, a professor in the Department of Psychology and Neuroscience at Dalhousie University, added that the results of the study provide hope that this method will eventually be applied to humans
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"These noteworthy data show an unparalleled recovery status," said Duffy, who co-led the study with Ming-fai Fong, a postdoctoral fellow in Bear's Picall Institute laboratory
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"I am hopeful and optimistic that this research can provide a new and more effective way to treat amblyopia

A new way to treat amblyopia

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This new method is based on decades of basic neuroscience findings led by Bear, which reveal the development of amblyopia
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When the input signal of the amblyopic eye becomes weak, the key connections or "synapses" in the neural circuits from the eyes to the visual cortex of the brain will shrink.

In 2016, Bear, Duffy, Fong and colleagues demonstrated that they can temporarily inactivate two retinas with TTX to restore vision in amblyopic mice
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But in the new study, they are trying to determine whether vision can be restored by temporarily suspending retinal activity in non-amblyopic eyes in older animals, Fong said

"These differences may seem small, but for several reasons, they are a big problem," she said
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"First of all, the inactivation of these two types of retina effectively eliminates vision; even if it is temporary, this brings some practical challenges

The researchers also tried to confirm their results in multiple species to ensure that this effect also applies to mammalian brains
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We have good reasons to think so

Therefore, in this new study, the research team tested whether the administration of TTX in a non-amblyopic animal model can completely restore the visual response of the amblyopic eye after a critical period
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Not only was this true in every animal tested, but the visual response of the eyes that received TTX always returned to normal levels

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Bear said: "This is a very clear proof that understanding the principles of synaptic plasticity can lead to a new treatment strategy
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Researchers even show that in the visual cortex, which is atrophy due to amblyopia, neurons that transmit visual input can return to normal size
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Bear said the effect of this treatment is stronger and more consistent than clinical cases of human non-amblyopic blindness, because once the synaptic connections of the amblyopic eye are restarted and the retinal activity of the non-amblyopic eye is restored, they will strengthen each other
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This result supports that the temporary inactivation of non-amblyopic eyes lays the foundation for the permanent enhancement of synapses in amblyopic eyes
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The theory believes that when the non-amblyopic eye is completely inactive, the input level of the amblyopic eye is sufficient to trigger synaptic enhancement, or "long-term enhancement
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Ming-fai Fong, Kevin R Duffy, Madison P Leet, Christian T Candler, Mark F Bear.
Correction of amblyopia in cats and mice after the critical period .
ELife , 2021; 10 DOI: 10.
7554/eLife.
70023