A research team from the Italian Institute of Technology has developed a prosthetic optical implant with hopes of saving people afflicted by macular degeneration from losing their vision.
Macular degeneration is the most common cause of blindness, affecting over 10 million people in the United States. Exacerbated by old age, it occurs when fatty deposits accumulate beneath the retina, causing retinal deterioration. This renders the retinal photoreceptors incapable of receiving light and properly focusing images. Medication can slow down disease progression, but a cure has not yet been developed.
The research team has developed a thin, implantable prosthetic made from a silk-based substrate coated in a layer of semiconducting polymer.
The polymer material is photovoltaic: it transforms light into electric current. This electricity can bypass the damaged retinal photoreceptors and directly stimulate the retinal neurons, thereby circumnavigating the main barrier to treating the disease.
Alternative proposals to treat macular degeneration have been made, including gene editing to target a mutation, made possible by CRISPR technology. This has not been tested in humans due to ethical concerns. Strides have also been made in bionic eye construction, but safety concerns have delayed human testing.
A photo of a patient with macular degeneration. Image credit: Ralf Roletschek
A type of rat, dubbed “the Royal College of Surgeons” rat, is the first known rat to have inherited macular degeneration and thus has served as the primary test subject for the prosthesis. Rats with significant vision impairments were surgically implanted with the device.
After 30 days of healing, their pupillary reflexes were tested to demonstrate how sensitive each was to light. Exposed to a light with brightness equivalent to a sky at twilight, the rats’ reflexes were identical to those of healthy rats. This change persisted 10 months after surgery when the rats were retested, though the rats had sustained more vision impairments in the interim.
During the reflex testing, researchers identified increased brain activity in the primary visual cortex, detected by PET imaging. This region is responsible for visual processing, and verified the activation of the retinal neurons. Aside from this, the researchers are still largely unclear on the exact biological phenomena caused by the implant.
Nonetheless, the researchers call this observed increase in brain activity a sign of a “rescue of the visual function” in their paper, stating that “[their] results highlight the possibility of developing a new generation of fully organic, highly biocompatible and functionally autonomous photovoltaic prostheses for subretinal implants to treat degenerative blindness.”
The research team plans the first human trials in the second half of this year and will gather results in 2018. They further add that their device “could be a turning point in the treatment of extremely debilitating retinal diseases."
Two hundred eighty eight million people are predicted to have macular degeneration by the year 2040. If the implant succeeds, potentially hundreds of millions of people could be “rescued” from going blind.
Source: Nature Materials. A fully organic retinal prosthesis restores vision in a rat model of degenerative blindness. March 6, 2017.