The optic nerve is like a high-speed fiber-optic cable between your eyes and your brain. But once that cable is cut, whether through trauma or disease, the nerve cannot be repaired and vision cannot be restored.
Some engineers are working to change that.
Shadi Dayeh, a professor of electrical and computer engineering at UC San Diego, has been developing a technology that could electrically stimulate and regenerate the optic nerve. His work is part of a multidisciplinary initiative called VISION (Viability, Imaging, Surgical, Immunomodulation, Ocular preservation, and Neuroregeneration) Strategies for Whole-Eye Transplant. The project aims to make vision-restoring, whole-eye transplantation a reality.
While whole-eye transplantation was first achieved in 2023, the procedure cannot yet restore sight. Dayeh wants to make whole-eye transplantation “not only anatomically viable but also neurophysiologically useful,” he says. If he succeeds, transplant recipients will actually be able to see out of their new eye.
“The optic nerve is the main highway between the eye and the brain. It’s also one of the hardest pathways to repair,” Dayeh says. “So, from an engineering point of view, it’s a major challenge and a major opportunity.”
But before they can reconnect the optic nerve to the brain, Dayeh’s team first has to understand how these two parts of our bodies communicate. Recently, the team completed what Dayeh calls “a foundational step:” mapping how changes in light, color, and frequency affect the visual axis, from the retina to the optic nerve and the brain.
Learning a visual language
The optic nerve is small, but mighty.
An average adult’s optic nerve is only about 4.5 to 5 centimeters long and roughly 0.5 centimeter wide. But a cross-section of the optic nerve holds over a million axons, the threadlike projections of nerve cells that conduct electrical impulses.
“The optic nerve is very small and delicate,” Sayeh says. “It’s a densely packed cable that carries an enormous information bandwidth—probably the densest bandwidth cable in our nervous system.”
To understand exactly how this delicate cable transmits visual information, Dayeh’s team has developed biocompatible electrode arrays that wrap around the optic nerve and sit on the visual cortex (the part of the brain that processes visual information) in animal and cadaver studies.
The arrays send electrical pulses across the visual pathway, from the optic nerve to the brain, and record the eye’s and brain’s responses to electrical and visual stimulation. This means the team can see how the optic nerve reads certain visual signals—such as changes in light, color, and contrast—how the optic nerve sends these messages to the brain, and how the brain interprets them.
“It’s like a distributed set of sensors in a communication system,” Dayeh says.
As the technology collects high-resolution data, the team maps the optic nerve and visual cortex to understand what Dayeh calls “the language of the visual pathway”—how visual signals get encoded in the optic nerve and represented in the visual cortex. “The idea is not just to record, but to build a code book across the visual pathway.”
The optic nerve isn’t a straight, uniform cylinder. Its diameter varies along its curving structure. That’s why Dayeh’s team developed electrode arrays that are ultrathin and flexible, ensuring stable placement, “like an electronic skin on the surface of the neural tissue,” Dayeh says.
Adding to the difficulty is the very tricky matter of charging optic and brain tissue. “The visual system is not like a muscle that you can electrically shock and then see what happens,” Dayeh says.
To avoid heating the tissue, Dayeh’s system maintains careful control of the density and spatial spread of the electrical charges. “The thermal load is very important for safety,” he says. “Much of our earlier engineering work went into electrode materials and geometries that can inject charge effectively and safely.”
Regenerating the optic nerve
Understanding the visual pathway’s language is one piece of a larger puzzle. Now that they have successfully mapped optic nerve and visual cortex signals, Dayeh’s team is investigating how their technology can help a severed optic nerve regenerate.
To that end, the electrode interface technology very precisely applies and records controlled, localized electrical stimulations to the optic nerve in order to determine where and how much stimulation can spur regeneration.
“The stimulation is not a magic switch,” Dayeh explains. “It’s a precision tool that assists and accelerates the biological processes of regenerating the neural pathway.”
Dayeh’s work contributes to several efforts aimed at restoring sight, which he considers “one of the most ambitious challenges in regenerative medicine and neurotechnology.” While Dayeh’s team measures, maps, and potentially guides the reconnection between the eye and the brain, other approaches include neuroprotection, or preserving the vision cells and circuits before they’re lost, and visual prosthetics and neural byass systems, which restore sight by delivering information directly to the retina, optic nerve, or visual cortex when the natural pathway cannot function.
Dayeh cautions that optic nerve regeneration is a developing field, and much is as yet unknown. Still, research has shown that, when active, cells can survive longer and can better integrate with surrounding tissue. Dayeh’s technology activates cells electrically. “In a simple sense,” he says, “our goal is to activate the cells so they survive longer.”
For now, optic-nerve regeneration technology is being tested in animals to show that a cut optic nerve can grow axons to the brain and restore vision. Dayeh anticipates that in perhaps three years, after rigorous tests and studies on the technology’s efficacy and safety, studies of the novel technology could be conducted for the first time in humans.
