0:13
Okay, so how is it that light comes to be focused just perfectly on the, the retina?
And when I say just perfectly, what I mean is that a,
a spot out here needs to not only to hit the retina but
it needs to be focused right there so
that everything from that, from that point, oops,
everything from this point gets focused not just close to here,
but actually at a specific level in the, in the retina.
If we, if we just blew this up, and here's the back of the eye, and
then here is the retina.
0:58
We need to get light focused to be right there at the back of the retina.
Not anywhere in the retina, but right there.
And so, that's a, that's a difficult task.
And the major, determinant of where light is focused is the length of the eye.
The cornea makes a contribution, but it only can work with the length of the eye.
And so if we look at, for instance, far vision, what you see is
that people are, have either, and this is grossly exaggerated.
They can have eyes that are too long, and they can have eyes that are too short,
and if they have eyes that are too long and they're looking far off,
now light gets focused and it's not even at the retina, or it's not at the right
place at the retina, it's in the vitreous humor or too superficial in the retina.
1:57
Whereas if the eye is short, the light will be focused behind the retina.
Behind the point where we need to get to.
So the process of making the eye just the right length is called emmetropization.
And the and the, a person who has the perfectly
2:20
eyes are of perfect length is, has emmetropia.
Now there is a epidemic in particular
of myopia, and to understand a little bit why this is called myopia.
Or short-sightedness.
Remember that the, that during the near triad is going to change the,
the focus of light, change the depth, so in a long eye,
the near triad is able to to
3:01
Okay. So
people that have a long eye are nearsighted.
They can see near.
They can't see far.
That's, that's what I have.
That's what the majority of people with refractive errors,
refractive errors just means that the light's not getting to the right spot.
3:25
Where as this it, in a hyperopic or
too short eye, this doesn't work as well and
these people are what's called farsighted they're, we won't go into why that is.
But it, the very important point, which is that myopia is at
3:48
epidemic proportions in many populations.
So there are populations in Asia,
where over 50%, well over 50% of the people, have myopia.
And myopia is,
is you may think it's just, it's no problem because you can get glasses.
Well that is true.
But it also puts, a person at risk for,
for other issues such as retinal detachment.
4:17
Now, the interesting thing about emmetropization is that this is
a process that depends on an interaction between the retina and the sclera.
This outer portion of the eye.
In, in experiments, people have actually cut the optic nerve and
it's it's clear that emmetropization still happens.
So it does not in any way depend on seeing.
It doesn't depre, depend on the brain at all.
This is a process that takes place out here.
And. Interestingly enough, there, the,
one of the reasons that myopia, is, is at epidemic proportions is that
there are populations, that are susceptible to myopia, for
genetic reasons that are un, unknown, undescribed, as of, as of now.
But adding on to a genetics susceptibility is
a another risk factor amongst genetically
susceptible populations is early reading and early education.
Because there's so much near vision.
The idea being that in order to make the, the eye, the right length.
There has to be sufficient distant vision at an early age.
And so you know, curiously, there is,
there's something that education's not doing a, a great job for us.
It's actually promoting eye
lengthening in in, in young, young individuals.
From at risks populations.
5:59
So, the idea is go look far, and and
minimize your risk of developing myopia.
Okay, so in the next section, we're going to talk about the retina.
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Peggy MasonProfessor
