(applause)
- Are you ready to play America's hottest new game show?
Name That Condition!
That's right, here is your chance to play along
with our studio contestants and see how you do naming
these seven refractive errors of the human eye.
You'll have seven seconds for each one.
Let's get going.
(upbeat instrumental music)
Hello, and welcome to the Laramy-K Optician Works
training center where today we are going to talk about
seven of the eight refractive errors of the human eye.
We will leave Presbyopia for another day.
Now, I can remember my first full semester in college
for becoming an optician, and there's something that's
always haunted me.
We did optics, and we did math, and we did Snell's Law,
and we did theory, and for an entire semester.
We came back second semester and somebody finally put the
refractive errors on the board.
It was like a light bulb went on for me, an epiphany moment.
It was like, "Oh, there's a why to the how."
And I just think it's so important.
I don't know about you, but I think it's time that we put
things right.
There, that's better.
We will begin with Simple Myopia.
Remember, super important we are studying the why here,
not the how.
The how is when we put a lens in front of this to correct
the error that's back here.
So, today although I put a prescription note up there,
we are not going to talk about that.
Simple Myopia and what's, again, nice is the simple flat
one-dimensional drawing, the eye stays the same,
the incoming rays stay the same, the cornea stays the same,
nothing changes.
Simple Myopia, the light enters the eye, all the rays coming
into the eye converge on one single point, that's why it's
called Simple, however, that point is a place ahead of where
we want it.
We want it on the retina, the macula, the fovea,
the place of perfect vision around the optic nerve that
let's our brain see what we need to see.
Simple Myopia, rays coming in gather at a single point,
unfortunately, it's the wrong point, it's a little shy
of where it needs to be.
Why is it a little shy?
A couple of possible scenarios, one is the eyeball itself
is a little bit long in shape, the rays want to be here
but the retina is back here.
The cornea is a little steep, it does have a somewhat
plus shape, pluses converge, if it converges them a little
bit too quickly, they fail to reach the back of the eye.
Obviously, you could also have a combination of those two
things, it doesn't change anything.
You still have refractive error number one, Simple Myopia.
Next would be Simple Hyperopia.
Same eyeball, same cornea, same shape, same rays of light
coming in, hitting the cornea, passing through the eye
and instead of falling short, they are falling on an
imaginary place beyond where we want them.
We want them here, they are trying to hit
out here someplace.
Obviously, putting them not where we want them, but to the
side of where they actually need to be.
Why does this occur?
Kinda the opposite of the myopia situation.
Our cornea might be a little shallow, so it's not bringing
them in, converging them early enough so that they hit where
they need to be, our eyeball may be a little bit short,
the retina, the fovea in relationship to where the light
enters the eye is a little bit closer, or of course,
a combination of those, too.
There is Simple Hyperopia.
Refractive error number three, Simple Myopic Astigmatism.
In this case, same eyeball, same situation, same rays
of light, same cornea, rays of light enter the eye,
some of the rays hit exactly where we need them to be,
perfect, spot on, perfect vision in that meridian.
The other set of rays entering the eye, they fall short,
they don't reach where they need to be.
Why?
The cornea is misshapen in that football shape, it has
Astigmatism, some of the rays of light pour through,
they do not require any correction at all, which is where
our zero comes from, the other meridian they need a little
bit of help going from here to back there,
Simple Myopic Astigmatism.
Next up, number four, Simple Hyperopic Astigmatism,
just the reverse of Simple Myopic Astigmatism.
Same eyeball, same cornea, say rays of light hitting,
enter the eyeball, some of the rays end up exactly where
they need to be, another set falling on that imaginary
point beyond the eye.
These rays of light require no correction, hence zero in
the prescription, the other rays of light need a little bit
of help being drawn from here back to that point on
the fovea, the macula, the retina to get
that perfect vision.
Why does this happen?
Because the cornea is misshapen, it has two instead of
one curve, hence bending the light in two different ways
with two different focal points within it.
Yes, this is far more complex and
if I had the perfect scenario it would be
a three-dimensional model, but we've been teaching this
stuff this way for a couple hundred years now,
it certainly works.
Conceptually, it's actually a really good model, and
I think the three-dimensional piece of how this works
and how it gathers light in all the different ways
and circle around when going through a lens
is actually better to conceptualize through the lens,
which is what you're all about anyways, designing that lens
to correct this.
So, these drawings work pretty darn good.
Number five in our list, Compound Myopic Astigmatism.
It's a variation of the Simple and in this case we have our
same eye, our same cornea, our same rays of light coming in,
strike, enter the eye, and none of them reach where they
need to be, some get closer than others.
These rays are gonna need more power to go from here to here
where we need them, than this set of rays.
That's why we have power in all meridians and why we have
two different strengths in our lens order
or our prescription values.
So that is Compound Myopic Astigmatism and of course,
caused by that misshapen cornea.
Next up would be Compound Hyperopic Astigmatism and that
looks like this, same eyeball, same cornea, same rays
of light hit, enter the eye, and they fall on an imaginary
point past where they need to be.
We want 'em here and they're ending up out here somewhere,
the actual rays are missing that central point.
Some of the rays miss a little bit, some of the rays miss
by a whole lot.
We need to bring that set of rays from here to here,
so we're gonna use some power to do that.
These rays need less power than these do in order to bring
them to where we need them, hence, the different power
and the different values.
Compound Hyperopic Astigmatism.
Last, but certainly not least, is Mixed Astigmatism,
which you might figure would look like this.
Some of the rays are failing to meet the back of the eye,
some are falling behind.
We've got our same eye, our same cornea, our same rays
of light, we need to take these and bring them to here.
We need to take these and bring them back to here.
Our cornea is misshapen, it's misshapen in such a way
that we have some rays that are beyond, some rays that
are not close enough, so we are going to have a prescription
and we'll learn this in later lessons that has both
plus power and minus power within the same lens.
Those are seven of the eight refractive errors of the human
eye, we will get to Presbyopia soon.
As they say, it's not really an error it is more of
a condition.
(applause)
Are you ready to play America's hottest new game show?
Name That Condition!
That's right, here is your chance to play along with our
studio contestants and see how you do naming these seven
refractive errors of the human eye.
You'll have seven seconds for each one.
Let's get going.
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I do hope you found that useful.
If you did, please hit the like button.
Please leave me a comment, I love getting them.
I'm actually kinda sad I don't get more.
I will see you again next week.
(applause)
(upbeat instrumental music)