‘In the transparent retina, glial cells
with a higher refractive index can
guide light like fibre-optic cables’
Even more interesting was the fact that the colours
that were best guided by the glial cells matched nicely
with the colours of the cones. The cones are not as
sensitive as the rods, so this extra light let them work
better – even under lower light levels.
Meanwhile, the bluer light, which was not captured
efficiently in the glial cells, was scattered on to the rods
in its vicinity.
These results mean that the retina has been optimised
so the sizes and densities of glial cells match the
colours to which the eye is sensitive (which is in itself
an optimisation process suited to our needs). This
optimisation is such that colour vision during the day
is enhanced, while night-time vision suffers very little.
The effect works best when the pupils are contracted
at high illumination, further adding to the clarity of
our colour vision.
l Erez Ribak is a researcher in physics at Technion -
Israel Institute of Technology
We take our ability to
differentiate colour for granted,
but it appears to be improved by
the curious behaviour of cells in