[Magdalen] Random facts of the day

[Sally Davies]

Supposed to be on a study day and getting distracted by random facts.

Did you know...

- the nerve cells in the eye (retinal ganglion cells) do not have any
myelin around them until after they pass beyond the back of the eye?

After that, they do. Myelin would speed them up BUT it's opaque to light
and would affect our vision.

Then it gets really random...

- some species, e.g. chicken and rabbit, do have myelinated retinas. So
their eyes would react very fast but not see very well? Might that explain
why these animals sometimes seem to take fright at silly things?

I tried to find out which other animals have myelinated retinas but Google
has not been my friend there.

- some humans have a mostly benign condition with white or grey patches on
their retina under opthalmoscope. This is because when their eyes were
forming, the physical barrier that is supposed to stop the myelin-forming
cells from getting inside the eye, didn't do its job and let a couple of
them in. Not enough to cause visual impairment in most cases so it's only
found when you're been examined for something else.

By about eight months' gestation, a baby has myelin most of the way down
its optic nerves, but when it is born the eyes aren't quite ready to work
and the brain still has to figure out what to do with visual information.
So the eyes wander around, at first only fixing onto faces - because the
human face is already pre-wired into their brain as something they can
recognise and like.

As always with neuroscience, this stuff about myelin in the eye was
mostly discovered by doing nasty things to animals.

But it is an example of how wonderfully and remarkably we are made!

Sally D