Attention lens geeks

[drk]

Can anyone remember (or link to the thread that discusses) the formula for p.d. outset for wrap frames?

The variable is the degree of wrap. So, something like:

outset per lens = [(frame wrap in degrees)(Robert Martellaro's golf score)]/Harry C's shoe size x Barry Santini's systolic blood pressure.

[optical24/7]

It's on my bulletin board here at work. Tangent the wrap angle x 2. I know I got it from Harry a while back, not sure of the accuracy but we've been using it for years with no complaints..

[drk]

Thanks, 24/7.

That must be a hell of a bulletin board.

[drk]

BTW, is it:

(tangent wrap angle) x 2

or

tangent (wrap angle x 2)?

I'm thinking the latter...

[optical24/7]

wrap angle 20;

20(tan) x 2

20 tan = .3639

.3639 x 2 = .727

comp each eye's PD extra .727mm ( or 3/4th mm) out.

[drk]

Nice!

If I were a real man, I'd draw a picture and try to figure it out.

But...no.

[Quince]

Educational AND entertaining!

[Pete Hanlin]

That's a nifty formula (and one I've not seen before), thanks for posting it! I'll have to jot that one into the margins of my Optical Formulas book (by Ellen Stoner- comes in really handy from time to time).

[optical24/7]

As I posted, Harry C deserves credit for this.

[drk]

Here's a brain-buster:

Question 1: Visualize a 20 degree lens wrap/tilt on a +3.00 lens. So you outset ~1/2mm per eye so the eye looks through the "apparent optical center". Does prism result? I think "No, that's the point, dummy".

Question 2: We know that--not directly-relatedly--you should add BI prism for positive face form, and it's a variable of lens tilt and thickness. But generally it's the same old/same old ~1/2^. But if you're moving the OC's out in step #1 above to avoid BI prism and then you add it back with...BI prism, is it an exercise in futility in higher plus power lenses? I think "Yes, but it's better to design your software to do both calculations, because...computers just don't care."

Question 3: Since at least 1/4 of our patients are hyperopes, maybe we can forget the whole thing for them?

Question 4: Since the pickiest people on the world are myopes, we need to worry about them. Wrap tilting causes BO and we need to offset that with outsetting pds then adding the BI, too. I guess this is not a question.

Question 5: This confuses me the most. What softwares do this wrap comp? We know that sophisticated, branded PAL paradigms exist (virtually any one that has POW! customization) but how many SV paradigms are there?

I know that a lab I use has a nice, inexpensive FFSV program but I think it has two levels; the original set up for standard ophthalmic-type frames, and a newer one that takes POW! into effect. I know that there are branded designs, too (again, Shamir).

Question 6: So, what do you do for your SV wrap sunglasses and SV wrap sportsglasses for the little munchers?

a. I don't even bother with this minutiae. You've been huffing the tint unit.

b. I do the calculations with Opticampus and certain defaults, and order my own compensated lenses. I am indeed a sexy lens geek.

c. I'm smart...I order branded wrap lenses and pass the cost on to the customer for the extra service involved.

[Robert Martellaro]

Question 2: 2 cups differential geometry, and a teaspoon of "Back to the Future".

Question 6: C.

[drk]

Ok, which one do you like?

[optical24/7]

Here's a brain-buster:

Question 1: Visualize a 20 degree lens wrap/tilt on a +3.00 lens. So you outset ~1/2mm per eye so the eye looks through the "apparent optical center". Does prism result? I think "No, that's the point, dummy".

That's why you're outsetting.

Question 2: We know that--not directly-relatedly--you should add BI prism for positive face form, and it's a variable of lens tilt and thickness. But generally it's the same old/same old ~1/2^. But if you're moving the OC's out in step #1 above to avoid BI prism and then you add it back with...BI prism, is it an exercise in futility in higher plus power lenses? I think "Yes, but it's better to design your software to do both calculations, because...computers just don't care."

Induced prism has to be accounted for in the given Rx/frame combo so, yea.

Question 3: Since at least 1/4 of our patients are hyperopes, maybe we can forget the whole thing for them?

Nope, for the reasons above.

Question 4: Since the pickiest people on the world are myopes, we need to worry about them. Wrap tilting causes BO and we need to offset that with outsetting pds then adding the BI, too. I guess this is not a question.

agree

Question 5: This confuses me the most. What softwares do this wrap comp? We know that sophisticated, branded PAL paradigms exist (virtually any one that has POW! customization) but how many SV paradigms are there?

Optics, like math has absolutes. Most any wrap program that takes the same variables into account are going to come up with relatively the same answer.

I know that a lab I use has a nice, inexpensive FFSV program but I think it has two levels; the original set up for standard ophthalmic-type frames, and a newer one that takes POW! into effect. I know that there are branded designs, too (again, Shamir).

Question 6: So, what do you do for your SV wrap sunglasses and SV wrap sportsglasses for the little munchers?

a. I don't even bother with this minutiae. You've been huffing the tint unit.

b. I do the calculations with Opticampus and certain defaults, and order my own compensated lenses. I am indeed a sexy lens geek.

c. I'm smart...I order branded wrap lenses and pass the cost on to the customer for the extra service involved.

For 6, I go with C with one caveat; I like the Attitude series of lenses, but the lab doesn't automatically add BI prism so I order it that way.

[Robert Martellaro]

Shamir Attitude for most RXs. Always measure for POW values and fit optimally.

[Robert Martellaro]

<I like the Attitude series of lenses>

We agree again. What a surprise!

[optical24/7]

We agree again. What a surprise!

Brothers from different mothers....