- They say that Alessandro della Spina

may well have started it all.

Snow was so certain of his calculations,

he called his thoughts a law.

Newton gave us white light as appearing as a rainbow.

We all know that Fernel was a whiz with lenses in a row.

Prentice knew his prism pretty well.

While Abby knew his value,

we can tell.

We know that Franklin made an executive decision

when the bifocal he did create.

Now here's another optical gem,

I think you'll find quite great.

It's the Seeger's Rule of the optical business.

And it even pertains to this week's topic,

thickness.

The rule my dear friend,

it goes like this:

when dealing with optics you always give up something

to get something.

And that ends our poetry reading for today.

(intense music)

What do I mean by that?

Particularly when I'm talking about lenses to fill

higher prescriptions.

Let's just say minus five and up,

plus three and up.

Everything you do is a compromise.

If you want the thinnest lens possible,

maybe you'll choose a high-index lens.

But then you may suffer for some weight,

you may suffer from some chromatic aberration.

Let's say you want the lightest lens.

Maybe you'll choose poly,

and your optics won't be so good.

Let's say you want the greatest optics possible.

Might choose glass,

suffer the the weight,

the danger of wearing glass.

Everything is a trade-off.

But what I'm here to talk about today

are some things that you can do kinda before the sale,

kinda during the sale,

and then when you're working with your lab.

In order to make your life easier,

get a much better quality lens,

and of course ultimately make your customer

that much happier with their pair of glasses.

I wrote stuff up there just so I could say more shtuff.

If I were to take all of this information,

everything that you need to know,

everything you need to think about

when dealing with higher power lenses,

it boils down to the golden rule.

Not even millimeters matter.

Tenths of a millimeter matter.

Super super important.

We are gonna talk about the high prescription

wheel of terror.

(shrieking violins)

Yeah okay I just made that up.

Decentration.

Any decentrationer lens leads to issues with cutout.

Cutout means that we're gonna increase the size of the lens,

which leads to thickness.

The never-ending cycle.

The high prescription wheel of terror.

Related to that,

we'll talk about how blank size and thickness

are related to each other.

We are going to talk about small is good,

and simple is good.

And if you look closely,

you can actually read between the lines.

Where it says "fashion be damned".

I don't care if the girl on the front cover

of the "Height" magazine has glasses that are this big.

That's horrible okay?

Small is good,

simple is good.

We'll talk about that.

We will talk about cribbing.

(horse neighs)

No not a horse cribbing.

It's something different.

I'll show ya.

And we are not going to be talking about Taylor Swift,

so we are not going to shake shake shake shake shake.

Instead we're gonna be talking about Janet Benjamin,

and her need for the shape shape shape shape shape.

And then we will talk a little bit about

working with the lab.

So you get the best high prescription lenses possible.

Let's start with the high prescription wheel of terror.

(scary music)

(woman screams in terror)

(loud power saw)

What do I mean when I talk about decentration?

You should know this already,

and there's tons of this stuff on the website.

So if you're not sure look at it.

But here's a drawing to illustrate it.

If my frame PD and my patient PD do not match,

eventually as I move that lens over

to allow for decentration I am gonna end up with a gap

between the lens and the eye wire.

Obviously that is not okay.

It doesn't matter if it is plus or if it's a minus.

If I have a large eye wire,

and a narrow PD,

eventually I am gonna run out of lens

to fill the eye wire opening.

So you can see how decentration leads to cutout problems.

Cutout problems mean that we have to increase

the size of the blank that we're going to cut down

to fit the eye wire.

Any time that we have decentration,

we have cutout,

we have thickness issues.

And here's why:

You can see all of these lenses are the same.

They're all plus three,

they all have roughly the same curves on the back

and on the front.

As I increase the blank size necessary

to cut out for that eye wire,

that blank is going to become thicker.

Remember I said tenths of a millimeter matter here.

If you don't take anything else away from this video,

I want you to always remember,

every customer you look at.

Keep this in the back of your mind.

The larger the eye wire,

the bigger the lens blank you're gonna need

to cut out to fill that prescription,

and the thicker that lens will be.

This isn't a one dimensional pretty drawing,

this is the way it is.

Increase that blank size,

you're gonna get a thicker lens.

Thicker lens,

never a good thing.

Now let's take that a step further,

and look at that lens within the eye wire opening.

If my brown lines are my frame,

and my frame PD and my patient PD are the same,

at least I'll have the same thickness on each side.

But when I begin to de-center the lens,

look what happens.

On the minus lens,

I get a thick edge temporally,

and a slightly thinner lens nasally.

In a plus I get a thick edge nasally,

and a slightly thinner lens temporally.

Alright I know you're now,

you're saying,

"hey you're just telling me problems problems,

give me some solutions".

So let's talk about how you make

your life a little bit better when dealing

with those higher plus and minus prescriptions.

One of the most important things

that you can do during the sale,

when you're helping your customer

pick out a pair of glasses,

is to try to get your frame PD

as close as your patient PD as possible.

'Course I know that's not always possible,

and it's gonna very rarely be perfect.

But remember those tenths of a millimeter matter.

If you're patient's right on the edge,

they got that 49 and a 47,

go with the 47 when your script is high.

I don't care if there's a little touch

or it's not textbook perfect.

If you have a high script,

smaller is better.

Keep that frame PD,

patient PD as close as possible.

You're gonna get a much better lens as a result.

What does that look like?

It looks like these three drawings.

This is what you're after.

You want a frame PD that is equal or close

to your patient PD.

Notice how nicely centered their eyes are.

Here, frame PD is too wide.

Eyes are way way in close and tight.

You're gonna get a whole lot of edge thickness

out towards the temporal end of that frame.

Here we have a frame PD that's too narrow.

Frame is in,

eyes are out.

You're gonna have thickness issues in the nasal area.

So always strive for that perfect balance

of frame PD, patient PD.

Being as close as possible.

I just touched on this,

these two are of course very closely related.

But the other thing you're gonna want to do

is always choose, again,

that smallest eye wire.

And here's why.

You can see why small is good.

Look at the drawing.

We have a blue frame,

a brown frame,

and red frame to choose from.

Let's say those frame sizes are only one millimeter

difference in size.

That's half a millimeter on each side of the lens,

each side of the frame.

Even that half a millimeter is going to make a difference

in that finished-edge thickness.

Cribbing means to chew.

And with modern surfacing equipment,

if you provide us with all the information that we need,

that I'm about to show you,

we can crib the lens.

It means we can chew away material around the outside

so it is roughly the shape of the frame

that you're going to put them in.

It has a whole lot of advantages.

Greatly reduces wear and tear on equipment,

particularly your edger obviously.

Reduces the chance of lens spin on the block.

Reduces the change of warping the lens from heat

generated in the process of edging.

And obviously just overall reduces finishing time.

Alright let's talk about our shape,

which is related to our comment that simple is good.

Let's take a look at this drawing.

Sharp corners, unique shapes, straight edges.

Try to avoid them.

As you see,

as I move my lens blanks which are always going to be

either a rounder or oval shape.

Choosing a frame that is not a rounder and oval

is greatly going to increase the chance that you're

gonna have cutout problems.

You saw that first oval or round lens over a round frame,

how much I could move it over before I got the gap.

Well if you look at something with sharp corners,

squares, odd shapes.

it takes very little movement to start creating that gap.

The gap means that I'm gonna have cutout problems,

cutout problems mean I have to increase my blank size,

increasing my blank size means

I'm gonna have additional thickness.

Which of course is not what you're after.

That is why we're asking you to give us the shape.

Remember that tenths of a millimeter matter

when we're working with higher prescriptions.

Remember of course it's never perfect,

but try your best to match your frame PD

and your customer PD.

Always choose the smallest size and shape that will work

for your customer's needs.

Remember that with enough information we can crib the lens.