Optic nerve stimulation offers hope for visually impaire
Scientists are
developing a technology for the visually-impaired people that bypasses
the eyeball entirely and sends messages to the brain, paving the way for
a new visual aid for daily living.
Researchers from Swiss Federal
Institute of Technology Lausanne (EPFL) and Scuola Superiore Sant'Anna
in Italy use a new type of intraneural electrode called OpticSELINE to
stimulate the optic nerve. The technology, described in the journal , has been successfully tested in rabbits.
"We believe that
intraneural stimulation can be a valuable solution for several
neuroprosthetic devices for sensory and motor function restoration. The
translational potentials of this approach are indeed extremely
promising," said a professor. Researchers noted that blindness affects an estimated 39
million people in the world. Many factors can induce blindness, like
genetics, retinal detachment, trauma, stroke in the visual cortex,
glaucoma, cataract, inflammation or infection. Some blindness is
temporary and can be treated medically, researchers said.
The idea is to produce
phosphenes, the sensation of seeing light in the form of white patterns,
without seeing light directly. Retinal implants, a prosthetic device
for helping the blind, suffer from exclusion criteria. For example, half
a million people worldwide are blind due to Retinitis pigmentosa, a
genetic disorder, but only a few hundred patients qualify for retinal
implants for clinical reasons. A brain implant that stimulates the
visual cortex directly is another strategy albeit risky.
A priori, the new
intraneural solution minimises exclusion criteria since the optic nerve
and the pathway to the brain are often intact. Previous attempts to
stimulate the optic nerve in the 1990s provided inconclusive results.
Intraneural electrodes may be the answer for providing rich visual
information to the subjects. They are also stable and less likely to
move around once implanted in a subject, according to the scientists.
"Cuff electrodes are surgically placed around the nerve, whereas
intraneural electrodes pierce through the nerve," said Diego Ghezzi from
EPFL.
Together, Ghezzi, Micera and their teams engineered the
OpticSELINE, an electrode array of 12 electrodes. In order to understand
how effective these electrodes are at stimulating the various nerve
fibres within the optic nerve, the scientists delivered electric current
to the optic nerve via OpticSELINE and measured the brain's activity in
the visual cortex.
They developed an elaborate algorithm to decode the
cortical signals. The researchers showed that each stimulating electrode
induces a specific and unique pattern of cortical activation,
suggesting that intraneural stimulation of the optic nerve is selective
and informative. As a preliminary study, the visual perception behind
these cortical patterns remains unknown.
"For now, we know that
intraneural stimulation has the potential to provide informative visual
patterns," Ghezzi said. "It will take feedback from patients in future
clinical trials in order to fine-tune those patterns. From a purely
technological perspective, we could do clinical trials tomorrow," he
said.