Things are looking up for people with failing eyesight. Scientists have come up with a completely organic retinal prosthesis that has passed preliminary animal tests, restoring vision to the blind. The new implant converts light into an electrical signal that stimulates nerve cells in the retina.
The retina is where vision starts. Light entering the eyeball passes through the transparent lens and focusing cornea to strike the retina, a sensory membrane that lines the inner surface of the back of the eyeball. The retina is composed of several layers. Specialized cells called photoreceptors lie within one of the retinal layers.
Photoreceptors in the retina convert light into signals that are transmitted to the brain. When these light sensors are damaged, vision becomes impaired. In some cases, the damage to the retina can’t be reversed, resulting in blindness.
There are two types of photoreceptor cells responsible for color vision and night vision – rods and cones.
Rods are located throughout the retina and:
- Detect motion
- Provide black-and-white vision
- Function well in low light
Cones are concentrated in a small central area of the retina called the macula and:
- Provide central vision
- Provide color vision
- Function best in medium and bright light
A small depression at the center of the macula (called the fovea) contains only cone photoreceptors. Maximum visual acuity and color vision are focused at the macula point.
More than 9 million Americans suffer from age-related macular degeneration (AMD), the most common, serious eye disease related to aging. AMD affects one in 14 Americans over age 40 and more than 30 percent of seniors over age 75.
That’s why the promise of a totally organic artificial retina implant is good news for millions of people worldwide. An international team led by the Italian Institute of Technology has come up with a new, alternative approach to restoring sight to a damaged retina.
The implant is composed of a thin layer of conductive polymer over a silk-based substrate and covered with a semiconducting photovoltaic polymer. The semiconducting polymer absorbs photons when light enters the lens of the eye, electrically stimulating retinal neurons and filling gaps in the eye’s natural, damaged photoreceptors.
Prior scientific studies proposed treating retinitis pigmentosa (a genetic disorder of the eyes that causes vision loss) with biologically-engineered eye devices to stimulate the malfunctioning neurons with lights. Another technique used CRISPR gene editing to repair the cellular mutations that cause blindness.
The study authors experimented on Royal College of Surgeons (RCS) rats, the first identified animal with inherited retinal degeneration. They surgically placed a fully organic prosthesis in the genetically defective eyes of the rats and tracked the subretinal implantations over a long term in vivo (in the living body of a plant or animal).
The research team tested how sensitive the rats were to light (the pupillary reflex) 30 days post-op, as compared to healthy rats and untreated RCS rats.
The implanted rats responded at low light levels of 1 lux (somewhat brighter than the light from a full moon) about the same as untreated RCS rats.
When the light intensity increased to between 4–5 lux (about the same as a dark twilight sky), the pupillary reflex of the treated rats was almost the same as healthy animals.
Retesting the rats at six and 10 months after surgery showed that the implant was still effective.
The researchers reported that their completely organic prosthesis demonstrated electrophysiological and behavioral changes in long-term live-animal subretinal eye implantation. The artificial device restored light sensitivity and visual acuity for up to 6–10 months after surgery.
Positron emission tomography (PET) imaging confirmed an increase in the basal metabolic activity of the primary visual cortex that processes visual information.
The scientists share a clear vision of the future of their invention even though “the detailed principle of operation of the prosthesis remains uncertain” – they aren’t sure how it works.
Ophthalmologist Grazia Pertile from the Sacred Heart Don Calabria in Negrar, Italy, spoke for the innovative group when she said:
“We hope to replicate in humans the excellent results obtained in animal models. We plan to carry out the first human trials in the second half of this year and gather preliminary results during 2018. This [implant] could be a turning point in the treatment of extremely debilitating retinal diseases.”
Keep an eye on this exciting new technology that could restore sight to the blind – organically.