Today, we are going to start talking about prism.

(upbeat music)

Yesterday, not such a good day in some ways.

I shot this opening sequence, I think 15 times in about

six different ways, and I just couldn't get it right.

So, I set it to the side, shot the white board lesson,

came back out here this morning

and I'm gonna give it another try.

And I think I got it.

Insteada talkin' and talkin' and talkin',

I think I'm gonna let this sum up this way.

You will learn as much about prism

that you need to in order to be good about your job.

Why would I say that?

In my 20-plus years as an optician,

working daily, hands on, busy practices,

busy stores, I saw a prism maybe 100 times

and that is out of thousands and thousands

of jobs that I've seen over those years.

I don't know where I fall on the scale.

You may work at a doctor's office

that does prism 9 out of 10 jobs, I don't know.

You may be at a doctor's office or a store

that never does it.

Wherever you fall along that scale,

is going to be what you need to get out of this.

And I'm gonna let it just settle right there.

We are gonna look at prism.

They are wicked cool things.

And we are gonna spend some time

at the bench, just briefly.

Then, we're gonna hop over

to our very good white board lesson.

Remember, I shot it yesterday, so I already know that.

This is a 35 diopter ophthalmic prism.

You can buy these online from a company called Burnell.

There is their address right there for you.

They're not very expensive.

If you could, I would get maybe a 10, a 20 and a 30.

If you're struggling with this, it certainly may help

you grasp the concepts a little better.

And they're just plain kind of fun to play with.

Everything that we do from this point forward

is gonna work on one basic principle.

And that is an image when viewed through a prism

is shifted towards the apex.

Remember that our prism has a base and it has an apex.

Here is a black line.

No magic here.

If I move this prism over my object, or my black line,

you will see that it shifts in appearance towards

the apex of the lens.

This 35 diopter prism is quite strong, it's why

the effect is pretty dramatic.

That's it.

That's really about all we needed to cover here

on the bench.

I want you to be the best darn optician that you can.

And I want you to truly understand what it is

that you're doing and why it is that you're doing it.

So for those of you that are with me and want to

take the baby steps and build the foundation

that you need to be the best optician that you can,

then just bear with me for the next ten minutes.

And we're gonna get through it.

This is how I think about this stuff.

Everybody learns in a different way.

That's one of the keys to education.

This stuff may work for you.

It may not.

If it does, fantastic.

Let's give it a try.

In the perfect world, perfect scenario,

this is how things work.

You've got the sun and the sun is pouring billions

of rays of light down, and it's hitting objects

like our little fire plug or fire hydrant,

whatever you want to call it there.

The rays of light reflect off objects

and they hit somebody's eye.

Could be your eye, could be mine.

And it ends up in your brain.

Those rays of light, because this eye is perfectly healthy,

a great clear cornea, crystalline lens, good vitreous humor,

healthy retina, great optic nerve,

no interpretation problems in the brain.

All those reflect rays give you everything that you need

to understand that the object that you're looking at

is in fact a fire hydrant.

It's in the right place, it's red, it's about two feet tall,

it has one, two, three, four openings.

Everything looks great.

There's no visual acuity problem,

there's no refractive errors.

Everything that I'm going to be talking about

for the next few minutes is all based on the idea

that we've got a healthy eye, healthy brain,

everything's working just fine.

What happens when I put a prism, that one

that we were talking about just a few moments ago

over on the bench, and I place it between

my healthy normal eye, my perfectly working brain,

and my object?

What happens to that object as it's perceived by my

brain over here, is that it will appear to shift position

towards the apex of my prism.

What we just did on the bench just a minute ago.

If I call this a one diopter prism, I can predict

with pure and perfect mathematical accuracy

that my object, my viewing point is going to shift

from where it is to one.

If I make that prism a little bit stronger,

and I say it's a two, I can predict with pure accuracy,

predictability, that my object will now shift that far.

Let's take it one step further of course,

you can kind of see where this is going.

If I make it a great big fat prism wedge,

and I say it's a three, I can predict

that it will shift from here to here.

It is the predictability of that shift in relationship

to viewing through the prism, that shift towards the apex,

that lets us move object around

in the brain through the eye for people that don't

have this perfect scenario going on.

Now let's talk about what happens when

we have a problem between here and here.

We no longer have the perfect situation.

Our cornea is misshapen in some way,

maybe too shallow, maybe too steep,

maybe it's astigmatic, maybe it has two curves on it.

Maybe our crystalline lens is getting clouded over.

Maybe our vitreous humor is a little bit cloudy.

Maybe there's a problem, a compromise somewhere

in the fovea, the macula, the retina.

Or perhaps our poor little brain up here,

which has got so much going on,

there's so much between here, and here, and here,

and here, that can go wrong here.

Sometimes I always wonder how we see at all.

But anyway.

When I have a problem here, and I'm looking at my object,

my fire hydrant may appear blurry, or fuzzy.

It may seem distorted in some way.

It may seem misshapen, particularly if

I have a high astigmatism issue.

To correct for that, so I have this looking correct

to my eye and my brain, obviously,

we start using prescription lenses.

The difference between the prescription lens

and these simple prism lenses, is that we start

playing with the shape, the size, and the position.

Remember our old friend here, that very first

lens that we looked at together?

Remember that I can move this around in front of my eye?

I can place the power where I need it to be.

In order to get this sharp, I start playing with the

shape of the prisms, the size of them, the position of them.

These could become anything.

If you stop and think about it, it's almost mind boggling.

In sphere powers, you run in normal range,

let's say about plain O to 20 in both plus and minus.

That's about 40 times quarter diopter steps.

Cylinder you got about zero to 10.

And you've got 180 possible degrees of position.

It's mind boggling the variability that we could have here.

Plus lenses, astigmatic, a little bit weaker in one part,

a little bit stronger in that part.

I could rotate the lens around in front of the eye.

I can fine tune this, I can fine tune that,

I can fine tune position, and I can put in front of my eye,

I can work my eye and my brain in concert,

and I can get this to look beautiful, sharp,

crisp, clear, by using prescription lenses.

Now, what happens when it's blurry,

and it's a little misshapen, and oh man, it's up here,

when it shoulda been down here.

Or worse, it's down here and shoulda been up here.

What happens then?

Prism.

Astigmatism.

I have two different powers on the lens.

This one's a little bit weaker than this one.

This one's a little bit stronger.

I can move my lens around, I can fine tune,

I can get it looking beautiful, perfect, sharp, clear.

But in order to move it back up to where it belongs,

I'm gonna add additional prism.

That additional prism wedge in the correct place,

the correct power, will allow me to also move it

back to where I need it to be.

So the combination of these three, if you will,

lets me fine tune this to be in any position

that I need it to so that my eye sees it and my brain

sees it in the right place, looking the right way.

Badump-bump-pa.

Basic prism theory.