Diamond coatings on a retinal prosthesis have been shown to aid biocompatibility, stability, and resolution. |
Research
groups in several countries are making progress in retinal prosthesis
development. If they achieve their aims, patients who have gone blind,
due to loss of their photoreceptors, could recover a better simplified
form of vision than with available prostheses. One of the groups shows
that diamonds could lead the way. (Jun ’11)
An
artificial device in the form of a retinal prosthesis can replace dead
photoreceptor cells by electrically stimulating the remaining neurons.
Two examples of retinal prostheses are digital camera-type electrode
arrays and photodiode arrays. However, they have exhibited low output of
electric currents meaning external batteries are needed, low
sensitivity and poor biocompatibility.
Researchers
at Okayama University Graduate School of Medicine in Japan have tried
to improve the performance of prostheses through the development of thin
and soft photoelectric dye-based retinal prostheses, where the
photoelectric dye chosen was not toxic to cells. By using a behavior
test, they could see that the subretinal prototype implantation in rats
led to recovery of vision. These prostheses absorb light and transform
photon energy to produce electric potentials.
Scientists
at the University of Tübingen in Germany have recently developed
another subretinal prosthesis and tested it on patients. They have
managed to show, for the first time, that micro-electrode arrays
containing 1500 photodiodes can give previously blind patients a
meaningful and detailed visual perception. Through a corresponding
pattern of 38 x 40 pixels produced by the chip, one patients could for
example read large letters as complete words, localize and approach
persons freely and describe different sorts of fruit.
While
another team of researchers from Moorfields Eye Hospital, Manchester
Royal Eye Hospital, Quinze-Vingts, Second Sight, Retina Foundation
Southwest and Johns Hopkins University, has shown for the first time
that a large group of blind patients fitted with a retinal prosthesis
can identify letters successfully. The patients used the Argus II
Retinal Prosthesis System, but the researchers are working on the third
model, increasing the number of electrodes from 60 to 240.
Researchers
connected to the European Commission-funded project DREAMS are instead
working on new types of nanotransducers, electric devices converting
energy from one form to another, based on artificial nanocystalline
diamond. The reasons for using diamond to coat the prosthesis are that
this semiconductor show stability, biocompatibility and allow for
reduced stimulation currents to improve the resolution from 60 pixels,
where only shapes and colors can be seen, to 1000 pixels. The scientists
have tested the tiny prosthesis on retinal cells to see that it can
replace the photoreceptors and U.S. colleagues have shown that a similar
implant in humans can function. However, no clinical trials using the
nanodiamond approach have been conducted.
Much
more work is needed before any of these retinal prostheses can be
widely available to patients, but the achievements made so far mean that
thousands of people could be offered the possibility to recover an
improved simplified form of vision in a not too distant future.
