A group of 18 researchers from several Chinese universities has developed a tiny retinal prosthesis that restores vision in blind mice and monkeys. Their study, published this summer in Science, concluded that the implant not only restored the animals' sight, but also allowed them to perceive the infrared spectrum, which is invisible to the human eye. The authors refer to this as "enhanced vision" and hailed the implant's ability to expand perception of vision in low light and the general range of visual sensibility. However, the road to human trials is still long, and developers say that it would not be ethical to apply the nanoprosthesis to people with healthy eyes.
The study's objective was to restore vision in cases of blindness caused by degenerative retinal diseases, such as retinitis pigmentosa and age-related macular degeneration. The tiny implant, measuring two millimeters in width and height, with a width of 0.1 millimeters, replaces damaged photoreceptors by mimicking their functions. It differs from other prostheses of the same membrane because it is constructed from tellurium nanowires, a conductive material with high light sensitivity that allows it to absorb both visible and low-energy photons, which are impossible for humans to detect.
Such is the explanation of the scientist Jiayi Zhang from Fudan University in Shanghai, who participated in the study. "By converting that light into spontaneous electrical signs transmitted by the brain, the prosthesis imitates and amplifies the function of the natural photoreceptors, managing to restore vision in cases of retinal degeneration and extend the range of visual sensitivity beyond the norm."
The blind rats and macaques who were implanted with the nanoprosthesis recovered pupil reflexes and recognized geometric patterns. In addition, they showed neural activity in the visual cortex when exposed to light with wavelengths of up to 1,550 nanometers. In comparison, human photoreceptors are only sensitive up to approximately 700 nanometers.
"Theoretically, the ability to perceive the infrared spectrum can allow for access to a wider range of environmental signals, such as night vision, heat detection and even visual applications via obstacles," says Zhang. Results among monkeys whose eyes were not damaged were even more surprising to scientists. The "extended vision" proved to be compatible with natural vision, and the animals were able to perceive objects at even lower light levels than the rodents.
The study notes that another advantage of tellurium is its biocompatibility, as the primates survived with the implant for more than three months. "The device has favorable physical properties, including its passive design, small size and ultra-thin profile, which significantly reduces surgical complexity and minimizes damage to the surrounding retinal tissue during application," says Zhang.
The horizon looks bright for the implant's clinical use on humans who have photoreceptor cells that have been damaged by degenerative illnesses in their advanced stages, though its authors do call for caution. "Our immediate goal is to continue with development and testing in the academic field, although we are open to other avenues of entrepreneurship if opportunities arise," says Zhang.
It also presents an ethical dilemma, as it has been proven that, at least in primates with physiology similar to humans, not only did the implant restore vision, but it is also expanded it to new spectral ranges. "Are we simply treating blindness or also enhancing human capabilities? That tension will likely influence how this technology evolves," says Zhang. This dilemma becomes even more complex when considering possible uses beyond medicine, such as technological or even military applications.
The study refers to a type of "pseudo-scotopic near-infrared vision" equivalent to night vision, which provides better contrast and object detection in difficult environments, along with a remarkable ability to identify heat sources. Therefore, implanting the prosthesis in people with normal vision "is not ethically permissible," says Zhang. "Furthermore, for those with intact vision, infrared detection can be easily achieved with external devices, so surgery is not necessary."
Such discretion does not hide the team's optimism regarding its implant's future applications. This is the first study to use tellurium nanowires in a retinal prosthesis, which allow for more natural contact with the layers of the retina, reducing inflammation, and improving signal transmission. In addition to its level of compatibility with the human body, it is noteworthy that it does not require an external power source like other models, as energy comes directly from absorbed light, without the need for bulky auxiliary equipment.
Zhang's enthusiasm does not waver when asked about the cost of the prosthetic and its potential for use by public health systems, saying that, "currently, the cost of manufacturing the tellurium-based prosthesis is relatively low due to the simplicity of the materials and the scalable nature of the production process." However, several tasks remain before moving onto clinical trials, such as optimizing manufacturing, ensuring regulatory compliance, and validating long-term efficacy. The team's aspirations are clear: "If we succeed in transferring it to clinical production, we anticipate that the cost could remain significantly lower than that of many existing visual prosthetic systems," says Zhang.