This is pretty wild. In her latest Brain Science podcast, Ginger Campbell interviews Stephen Macknik on his work to develop a visual replacement implant for blind people. For a quick overview, check out this short video.
One question Campbell asks, that I was wondering myself: how does the light reach the neurons in the LGN nucleus of the thalamus deep in the center of the brain? Macknik points out that the gene therapy causes the protein receptor genes to develop in the whole neuron, including the axon terminals that reach into the visual cortex, so the implant doesn’t need to project to the thalamus, just to the end of their axons in the visual cortex.
For more details, check out the podcast itself (it’s about 69 minutes). It gets a bit technical, but it’s a fascinating interview, and a powerful demonstration about how neuroscientific knowledge can be used.