Lasers & photonics
Even the most successful existing devices only have a very tiny view field.
Based on where their implant is placed, Yang’s team believe that it stimulates bipolar cells. In rats, they’ve shown that their device can cause changes in brain activity that indicate the visual pathway has been activated. But, notes Yang, that doesn’t tell us what the rats are actually seeing. In a few years’ time, the team hopes to trial their device in human patients.
Proton-pumping protein
Another school of thought focuses on using light- activated proteins, like bacteriorhodopsin, to mimic the light-absorbing properties of photoreceptors. Biotech company LambaVision is developing one such implant: a scaffold coated with bacteriorhodopsin. Bacteriorhodopsin is a proton pump: that is, it captures light energy and uses it to transport protons from one side of the protein to the other. In response to light stimulation, “the protein pumps protons, so hydrogen ions, to the bipolar and ganglion cells. With hydrogen ions, you’re changing the pH around those cells that’s going to be picked up by receptors,” explains LambaVision’s CEO, Nicole Wagner. “That’s what sends a signal to the bipolar cells, the ganglion cells and eventually the brain.”
The scaffold itself is a lattice that has alternating layers of the protein and a polymer deposited on top – a process that’s done 200 times. “Think about painting a wall: the more layers, the more light you absorb,” Wagner says. “And the greater the signal that you get to send to the back of the eye.”
The team expects that this will bring on better results than solutions currently on the market. With some of the electrode-based prosthetics out there, patients are able to sort high-contrast socks or walk along a large black line, Wagner says. “We’re expecting higher resolutions than that… we would expect a
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patient to be able to do the daily activities of life.” Like watching a baseball game on television, for instance. Plus, this strategy doesn’t rely on singular connections between an electrode and neuron, as if plugging an electrical cable into a wall socket. Instead, it aims to mediate the ion environment, Wagner shares. This would allow for a wider range of signals to be collected and passed on. “The analogy is Wi-Fi… you’re actually changing that whole environment so you don’t need a one-to-one connection. You’re actually getting a greater reach than some of those electrode-based prosthetics.”
Studies on rats with retinitis pigmentosa showed that the implant could stimulate ganglion cells, though we don’t yet know what sort of visual resolution this could bring on – nor how wide the field of vision would be.
Human trials on the horizon There’s a lot of activity and different approaches within this field, notes Wagner – after all, we still don’t have a cure for blindness. But soon, we’ll hopefully see some artificial retinas in human trials: Chichilnisky aims to do it within four years, while Wagner hopes to get there in three. For Yang, it’s the real-world impact these devices could have that keep her team motivated. She shares an anecdote: when in Paris to visit their collaborator lab, Yang and her colleagues were having lunch in a small, cosy restaurant. A group of blind people entered, but because the space was too narrow for them to use their canes, they walked in single file with their hands touching the person in front of them. “I think that was a moment for the entire team,” she says. “The patients that, hopefully, we will be able to help in future are sitting right next to you.” ●
Medical Device Developments /
www.medicaldevice-developments.com
Natali _ Mis/
Shutterstock.com
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