search retinal implants for vision res-
toration, and my own master’s the-
sis revolving around restoring vision
through optogenetics was conducted
in the laboratory of Thomas Münch.
While all of these methodologies hold
merit, including them all is beyond the
scope of this article, and therefore the
following will focus solely on the op-
togenetic approach.
The main idea of the optogenetics ap-
proach to vision restoration is to re-
store the light-transducing element
of the visual system by introducing
light-sensitive proteins into the ret-
ina. One of the first and most widely
used proteins is channelrhodopsin-2
(ChR2), which was discovered in the
unicellular algae Chlamydomonas
reinhardtii (13). These algae primar-
ily use this light-sensitive protein as
a means to increase photosynthesis:
by sensing where light is coming from
they can orient and move toward it.
relatively precisely expressed into cells
in different environments, such as
in the retina. This is exactly what the
optogenetic method for visual resto-
ration strives to do. The concept is to
take a biologically derived light-sensi-
tive protein and circumvent the failing
natural system to activate the remains
of the intact visual architecture. At the
moment, the optogenetic proteins we
have in hand do not afford all the de-
tailed responses photoreceptors do,
but they do at least grant the ability to
catch light once again.
Eric James McDermott
Catch me a rainbow. Image source: Rachel
Andrew (flickr.com)
ChR2 is not the only optogenetic pro-
tein, for example, Wyk and Kleinlogel
(2) developed a novel optogenetic tool
called Opto-mGluR6 which report-
edly (and supported by my own data)
is more light-sensitive than ChR2.
Reports show that ChR2 is respon-
sive to 1 order of magnitude, or only
the uppermost 8.33% intensity levels
of the normal dynamic range of hu-
mans (11), while Opto-mGluR6 is re-
portedly responsive to 4.3 orders of
magnitude, or the uppermost 35.8%
intensity levels of the normal dynamic
range (2). This is important because
this expanded range of Opto-mGluR6
allows the retina to respond to lower
light levels and not only to the ex-
tremely high, rare, and photo-toxic
light levels needed to activate ChR2.
These light-sensitive proteins can be
extracted, replicated, and now can be
graduated from the Neural and
Behavioural Sciences master’s
program in 2016. He is cur-
rently a neuroscience PhD
candidate in Tübingen.
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