Homo sapiens, visual creatures, with reasonably good acuity and remarkable colour vision.
Heh. Don't be fooled - our eyes are full of flaws, and these are just four of them!
[INTRO by Caro Waro & Cristina de Manuel]
Number One - our Lens
The lens is a very important part of the eye, after the cornea has bent the light into our
eyeball, it is the lens' job to focus on the objects of interest. However, our lens will
only work for about half of our lives, and that is down to the way they develop.
The lens forms during pregnancy by layering concentric layers of crystalline cells, and
during development they receive their nutrients straight from some special capillaries that
go straight to the lens. After birth, these capillaries atrophy, and the lens receives
its nutrients via diffusion from the aqueous humour, which is the liquid inside our eyeball.
The trouble is, these concentric layers do continue to add themselves during our lives, and
eventually it does hit a point at around 40-50 years where the cells in the centre of the
lens can no longer receive the nutrients from the outside, so they die, and when they die,
their physical properties change so the lens as a whole is no longer as pliable as it used
to be, which means that we then need reading glasses.
Number two is eye growth
The size of our body parts when we are born is not the same as the size of our body parts
when we're adults, and it is very important that they all scale up whilst maintaining
function, and the eye is no different. Now, there are actually multiple factors that the
eyes use and feedback mechanisms to grow adequately, but the two main ones, are first of all, how
clear the image is. If we have an unclear image forming in our retina the eye tends
to take this as a signal that it has to grow more, and the other one is the amount of sunlight
we receive. Researchers have found that the more sunlight
we get, the slower our eyes grow. So when they say that kids that study a
lot tend to need glasses because they're shortsighted, it's not because of the strain of reading
but because they are doing it indoors and aren't getting enough daylight.
Now the last two flaws are actually related to the fact that our retinas are back to front. In
a future video I'm actually going to explain why this is a really good idea for our eyes,
but it does come with these two flaws.
Number three is the blind spot.
On top of our retina we have several layers of neurons that process our visual input,
however, these must deliver this information to the brain that's on the other side, so
they all gather together to form the optic nerve and they funnel through the retina.
And the trouble is that at that point we have no visual input. Now the brain does do a great
job at photoshopping this in, so most of the time you're never going to notice, but it does mean that
for certain professions such as pilots they must constantly scan the horizon to make sure
that there are no aircrafts incoming in the blind spot.
And last but not least is retinal vasculature
So in addition to those layers of neurons, we also have some blood vessels on the top.
Once again the brain does a great job at filtering it out and thank goodness they are translucent
so they can just colour correct, so we don't realise that we don't have these capillaries
on top. If you're interested there are actually two easy ways for you to be able to visualise
these capillaries. The first one is you can take a concentrated beam of light, like your phone torch, and
shine it onto the side of your eye. The light will enter the eye through the sclera and
will go through the blood vessels casting a shadow onto the other side which is what
you'll be able to see. Now, obviously be safe when doing this, don't use something silly like
a laser, make sure you're using something very safe like a torch or a phone torch.
And the other way is even easier, you can just look up at the sky and you'll probably notice a
lot of little white dots swimming around. This is known as the blue entoptic phenomenon
and what you're seeing are your white blood cells. The brain actually cancels out the
red blood cells that we see, but because the white blood cells are a different size and
shape and less common, the brain doesn't actually get rid of them, but they don't really interfere
with vision. Sometimes you'll notice some small black fringes,
and this is because there's sometimes a small space in between the red blood cells following those white blood
cells. It is completely harmless and most of the time you're never going to notice that they're even there
Anyway, so these were four flaws in our eye structure out of many that we most certainly
have, I'd love to know whether any of these are news to you or not. As always I have extra
stuff on the blogpost! Thanks so much for watching me and I'll see you in the next one.
[Music: THASTOR & CRYOSLEEPKITTEN] [Host, writer and editor: Inés Dawson]