|
Restoring vision might sometimes be as simple as
turning out the lights. That's according to a study
reported on February 14 in Current Biology, a Cell
Press publication, in which researchers examined
kittens with a visual impairment known as amblyopia
before and after they spent 10 days in complete
darkness.
Depriving normal visual experience in one eye early
in life produces a reduction in visual acuity (amblyopia)
for that eye (blue circles) while the acuity of the
other eye is normal (red). The visual acuity of the
amblyopic eye remains low compared to the fellow eye,
but after immersion in complete darkness the
amblyopic eye very quickly recovers to match the
visual acuity attained by the normal eye. Credit:
Current Biology, Duffy et al.
Researchers Kevin Duffy and Donald Mitchell of
Dalhousie University in Canada believe that exposure
to darkness causes some parts of the visual system
to revert to an early stage in development, when
there is greater flexibility.
"There may be ways to increase brain plasticity and
recover from disorders such as amblyopia without
drug intervention," Duffy says. "Immersion in total
darkness seems to reset the visual brain to enable
remarkable recovery."
Amblyopia affects about four percent of the general
population and is thought to develop when the two
eyes do not see equally well in early life, as the
connections from the eyes to visual areas in the
brain are still being refined. Left untreated, that
imbalance of vision can lead to permanent vision
loss.
In the new study, the researchers examined kittens
with amblyopia induced by experimentally depriving
them of visual input to one eye. After those animals
were plunged into darkness, their vision made a
profound and rapid recovery. Further examination
suggested that the restoration of vision depends on
the loss of neurofilaments that hold the visual
system in place. With those stabilizing elements
gone, the visual system becomes free to correct
itself.
Darkness therapy holds promise for the treatment of
children with amblyopia, the researchers say, but
don't try this at home. They think that the darkness
must be absolute to work, with no stray light at any
time. It is also important to address the original
cause of the amblyopia first, and to ensure that a
period of darkness will not harm an individual's
good eye.
The researchers are still working out just how much
darkness is required, and for how long. Regardless,
they say it is unlikely that a drug could ever
adequately mimic the effects of darkness that they've
seen.
"The advantage of a simple nonpharmacological
sensory manipulation, such as a period of darkness,
is that it may initiate changes in a constellation
of molecules in a beneficial temporal order and in
appropriate brain regions," they write.
For more information
Current Biology, Duffy et al.: "Darkness alters
maturation of visual cortex and promotes fast
recovery from monocular deprivation."
http://www.cell.com/current-biology/abstract/S0960-9822%2813%2900020-1
(MDN)
|
