refractive indices

[mma]

There was a previous post about what refractive index should be used for different power ranges. I can't seem to find it. Could someone be kind enough to give an approximate guide (assuming average bridge, A and B measurements, etc).

Thanks!

[finefocus]

Please get a collection of samples (you'll need at least a dozen, 20 would be better) of stock lenses cut in half to show the thickness of various powers, both spherical and aspheric. Learn, if you don't already know, how to demonstrate the effect of eyesize reduction on thickness by drawing on the samples. This is easy on minus lenses, trickier on plus lenses. Then allow the patient to choose the thinnest one that fits their budget. This is an economic question, not an optical question (exception: aspheric for higher plus). I don't mind a bit having the patient buy 1.70 for a 2.00 diopter correction, as long as they know exactly what their options are, and they aren't lied to about how their vision will, or will not, be affected. If the lens samples are beyond your budget, many a lens company can provide a thickness comparison chart. Don't be roped into thinking that certain powers get certain indices; there is more to it than that.

[renee1111]

There was a previous post about what refractive index should be used for different power ranges. I can't seem to find it. Could someone be kind enough to give an approximate guide (assuming average bridge, A and B measurements, etc).

Thanks!

I would say that a good guide to follow would be

pl to + -2.00, use CR39
+ -2.00 to + -4.00, use either 1.56, Trivex, or poly
+ - 4.00 to + -6.00, use 1.6
+ -6.00 and over, use 1.67 or 1.74

I didn't include glass...well, because I hardly ever use it. Of course other factors such as semi-rimless frames could also play a part in lens selection, but this seems to work well for me.
Hope this helps! :o

[finefocus]

I would say that a good guide to follow would be

pl to + -2.00, use CR39
+ -2.00 to + -4.00, use either 1.56, Trivex, or poly
+ - 4.00 to + -6.00, use 1.6
+ -6.00 and over, use 1.67 or 1.74

I didn't include glass...well, because I hardly ever use it. Of course other factors such as semi-rimless frames could also play a part in lens selection, but this seems to work well for me.
Hope this helps! :o

I'm a -4.00; if you "gave" me a mid-index material like those listed above, I'd resent it. I want the best I can get. If offered 1.70 aspheric, I'd want it. I might choose to be content with 1.6 or 1.67 (after I knew the price), but I insist on making the decision myself. I further insist on seeing, really seeing, just what difference it makes to upgrade. I think that many customers are just like me: they want info and context, but not prejudgement of their desires.

[renee1111]

I'm a -4.00; if you "gave" me a mid-index material like those listed above, I'd resent it. I want the best I can get. If offered 1.70 aspheric, I'd want it. I might choose to be content with 1.6 or 1.67 (after I knew the price), but I insist on making the decision myself. I further insist on seeing, really seeing, just what difference it makes to upgrade. I think that many customers are just like me: they want info and context, but not prejudgement of their desires.

Well sooorrrryyyy. Oh, but you think it's "okay" to put a 2.ooD correction in a 1.74, give me a break! I was only trying to help mma come up with an "approximate guide", which clearly you weren't tying to do.

[Jacqui]

I run a small wholesale lab and this is what I tell my customers as a rule of thumb,this does not take into consideration higher cylinders, prism or frame size:

PL to +/- 3.00 use CR-39, Trivex or maybe 1.56

+/- 3.00 to +/- 6.00 use 1.60 or Trivex

+/- 6.00 and higher use 1.67 or 1.70

I never use Poly for any Rx and won't use 1.74 because the US version is only made by the Evil Empire.

[finefocus]

Well sooorrrryyyy. Oh, but you think it's "okay" to put a 2.ooD correction in a 1.74, give me a break! I was only trying to help mma come up with an "approximate guide", which clearly you weren't tying to do.

(1) Sorry if I was strident.
(2) You're right, I wasn't trying for an approximate guide.
(3) My point is that customers rarely fall into catagories in a chart:
each case is different, each case has not a few factors, but many; and many of those are subjective.
(4) LET THEM CHOOSE.

[bob_f_aboc]

(1) Sorry if I was strident.
(2) You're right, I wasn't trying for an approximate guide.
(3) My point is that customers rarely fall into catagories in a chart:
each case is different, each case has not a few factors, but many; and many of those are subjective.
(4) LET THEM CHOOSE.

We are the professionals. It is our responsibility to make sure the patient is in the proper lens taking into account Rx, lifestyle, hobbies, frame, etc...

I make Trivex my standard lens. I will order CR-39 or poly if the patient insists on "only what the insurance covers." I fit Trivex lenses up to ~
±5.00 depending on the frame fit. Above that I will move into 1.6 or 1.7 all the while explaining to the patient what the added benefit is to each material. If they then choose to downgrade in material, they have been warned and it is noted in the chart.

[mma]

Thanks for all the responses. Very insightful viewpoints!

[finefocus]

We are the professionals. It is our responsibility to make sure the patient is in the proper lens taking into account Rx, lifestyle, hobbies, frame, etc...

I make Trivex my standard lens. I will order CR-39 or poly if the patient insists on "only what the insurance covers." I fit Trivex lenses up to ~
±5.00 depending on the frame fit. Above that I will move into 1.6 or 1.7 all the while explaining to the patient what the added benefit is to each material. If they then choose to downgrade in material, they have been warned and it is noted in the chart.

My Rx is (OD) -3.00 -1.50 x 103 (OS) -2.25 -1.00 x 57 add (OU) +2.50
My frame is 50/19, PD 30.5/30.
I am an Optician, do not use my glasses in hazardous situations (I have safety glasses), wear PAL's, play a bit of golf, read a lot, work out 4 days a week, chase grandchildren around; I enjoy long hot bubble baths and long walks by the sea, and want World Peace. Pray tell then, what is the perfect lens material for me? Trivex? Why not 1.67 or 1.7? It's not a vision issue, it's a thickness vs. cost issue; no professional is better suited than I am myself to make that choice for me. And when I want sunglasses in PAL polaroid, in a 60 eye, must I use CR39? Kinda thick, can't I have poly for that pair? Or 1.67? As a professional, you should be able to educate me, not decide for me.

[bob_f_aboc]

My Rx is (OD) -3.00 -1.50 x 103 (OS) -2.25 -1.00 x 57 add (OU) +2.50
My frame is 50/19, PD 30.5/30.
I am an Optician, do not use my glasses in hazardous situations (I have safety glasses), wear PAL's, play a bit of golf, read a lot, work out 4 days a week, chase grandchildren around; I enjoy long hot bubble baths and long walks by the sea, and want World Peace. Pray tell then, what is the perfect lens material for me? Trivex? Why not 1.67 or 1.7? It's not a vision issue, it's a thickness vs. cost issue; no professional is better suited than I am myself to make that choice for me. And when I want sunglasses in PAL polaroid, in a 60 eye, must I use CR39? Kinda thick, can't I have poly for that pair? Or 1.67? As a professional, you should be able to educate me, not decide for me.

With the information you presented, the difference between Trivex and 1.7 would be ~1mm at the thickest edge. If you are comfortable paying that much for something most people not in this profession would never notice, then so be it.

I will fit 1.67 polarized lenses and also poly polarized. Sun lenses are a different story than dress. The polarization will mask some of the abberration caused by polycarbonate. That is up until there is a useful supply of Trivex polarized lenses.

If a patient comes into my office and demands the absolute thinnest lens, I will quote the price and let them decide. Otherwise, I will fit the lens that I feel is the best blend of cosmetics and function and explain exactly why to the patient.

I must be doing something right. Repeat patients in this office in the last 2 years that I have been here are up over 150% from before I took over as the optician.

[finefocus]

With the information you presented, the difference between Trivex and 1.7 would be ~1mm at the thickest edge. If you are comfortable paying that much for something most people not in this profession would never notice, then so be it.

I will fit 1.67 polarized lenses and also poly polarized. Sun lenses are a different story than dress. The polarization will mask some of the abberration caused by polycarbonate. That is up until there is a useful supply of Trivex polarized lenses.

If a patient comes into my office and demands the absolute thinnest lens, I will quote the price and let them decide. Otherwise, I will fit the lens that I feel is the best blend of cosmetics and function and explain exactly why to the patient.

I must be doing something right. Repeat patients in this office in the last 2 years that I have been here are up over 150% from before I took over as the optician.

Bob, I'm sure you're doing well. I didn't doubt your ability, and I agree that upgrading relatively low powers to higher indices might not be cost-effective. I disagree that we in the business are more aware of thickness-I have patients who bring their own micrometers!

[Jacqui]

I have patients who bring their own micrometers!

Must be engineers from Silicon Valley

[chip anderson]

I notice in some post we seem to be equating the "best" to be the thinnest, or highest index, or newest, or highest tech, or most expensive.
This seems to be a odd syndrome in our society. Newer doesn't mean better. A -2.00 in CR-39 or glass might actually allow one to see better than a 174. It might be just as light in the right configuration.
Never confuse "New" with better. It might be in some situations it might be highly inferior in others.
Somewhat like "antibacterial soap" being a new fad, slightly more expensive but leaving exactly the same bacteria count after washing as regular soap. Sometimes at the expense of forgetting the purpose of soap= The stuff's purpose is to mix oil and water.

Chip

[Fezz]

Welcome back Friend!


I hope this is a permanent adventure!

Here is to you!

:cheers::cheers::cheers:

[Ocular Dexter]

There was a previous post about what refractive index should be used for different power ranges. I can't seem to find it. Could someone be kind enough to give an approximate guide (assuming average bridge, A and B measurements, etc).

Thanks!

This is a great study covering RX ranges and done by Ed De Gennaro. It not only looks at indices but also abbe and weight! http://www.youngeroptics.com/pdf/tri..._Monograph.pdf

[Chris Ryser]

.

I notice in some post we seem to be equating the "best" to be the thinnest, or highest index, or newest, or highest tech, or most expensive.
Chip

Well, well, well ..............................welcome back Chip and thanks to Steve for arranging it.

To come back to this thread..............I observe that you posted my opinion too before I had the chance to ro do it.

It is still a fact that glass is the best material, but too labor intensive these days,.............however CR39 is the still the closest and next best choice to glass.

But CR39 according to a majority of post's has become the neglected orphan of OptiBoard's younger members who must have been well and effectively brainwashed by the lens manufacturers to use higher index lenses for just about everything.

High index will never provide the same clear vision as glass or CR39 and it only real reason to be on the market is for est ethics reasons of making thinner lenses due to flatter curves and vision, that does not equal the visual aid of the latter.

The insurance patients who can not afford more and get the CR39 lens ,actually get the best material and the ones that can afford it will pay more for a less effective material.

[Darryl Meister]

Certainly, prescription ranges are important to thickness considerations. But also keep in mind that the size of the frame can actually influence lens thickness even more than the prescription for the same amount of change. Even a pair of -2.00 D spheres can look like "coke bottles" in a large enough frame. I wonder if "thinner, lighter" lenses shouldn't at least be offered to any patient who might enjoy a potential benefit from them. The ideal lens thickness for most patients is inevitably "zero," and many are willing to pay to get as close as possible to that number.

Some very astute comments have been made by Chip and Chris regarding the balance between cosmetics and optics. Fortunately, there are mid- and high-index lens materials available now that offer relatively high Abbe values (in the 40+ range), so eyeglass wearers no longer necessarily need to settle on a compromise between either, if these high-performance lens materials are within their budget.

Also, setting Trivex aside for the moment, I would say that 1.6 high-index lens materials have become the new "mid-index" materials. Many of these lens materials now offer a similar Abbe value compared with earlier mid-index materials along with a significantly higher refractive index. The most popular 1.6 high-index materials also offer a relatively high tensile strength, which makes them a good choice for rimless eyewear.

[Metronome]

I run a small wholesale lab and this is what I tell my customers as a rule of thumb,this does not take into consideration higher cylinders, prism or frame size:

PL to +/- 3.00 use CR-39, Trivex or maybe 1.56

+/- 3.00 to +/- 6.00 use 1.60 or Trivex

+/- 6.00 and higher use 1.67 or 1.70

I never use Poly for any Rx and won't use 1.74 because the US version is only made by the Evil Empire.

Delete..

[Metronome]

Certainly, prescription ranges are important to thickness considerations. But also keep in mind that the size of the frame can actually influence lens thickness even more than the prescription for the same amount of change. Even a pair of -2.00 D spheres can look like "coke bottles" in a large enough frame. I wonder if "thinner, lighter" lenses shouldn't at least be offered to any patient who might enjoy a potential benefit from them. The ideal lens thickness for most patients is inevitably "zero," and many are willing to pay to get as close as possible to that number.

Some very astute comments have been made by Chip and Chris regarding the balance between cosmetics and optics. Fortunately, there are mid- and high-index lens materials available now that offer relatively high Abbe values (in the 40+ range), so eyeglass wearers no longer necessarily need to settle on a compromise between either, if these high-performance lens materials are within their budget.

Also, setting Trivex aside for the moment, I would say that 1.6 high-index lens materials have become the new "mid-index" materials. Many of these lens materials now offer a similar Abbe value compared with earlier mid-index materials along with a significantly higher refractive index. The most popular 1.6 high-index materials also offer a relatively high tensile strength, which makes them a good choice for rimless eyewear.

Delete.

[Metronome]

.

Well, well, well ..............................welcome back Chip and thanks to Steve for arranging it.

To come back to this thread..............I observe that you posted my opinion too before I had the chance to ro do it.

It is still a fact that glass is the best material, but too labor intensive these days,.............however CR39 is the still the closest and next best choice to glass.

But CR39 according to a majority of post's has become the neglected orphan of OptiBoard's younger members who must have been well and effectively brainwashed by the lens manufacturers to use higher index lenses for just about everything.

High index will never provide the same clear vision as glass or CR39 and it only real reason to be on the market is for est ethics reasons of making thinner lenses due to flatter curves and vision, that does not equal the visual aid of the latter.

The insurance patients who can not afford more and get the CR39 lens ,actually get the best material and the ones that can afford it will pay more for a less effective material.

Delete.

[Metronome]

My Rx is (OD) -3.00 -1.50 x 103 (OS) -2.25 -1.00 x 57 add (OU) +2.50
My frame is 50/19, PD 30.5/30.
I am an Optician, do not use my glasses in hazardous situations (I have safety glasses), wear PAL's, play a bit of golf, read a lot, work out 4 days a week, chase grandchildren around; I enjoy long hot bubble baths and long walks by the sea, and want World Peace. Pray tell then, what is the perfect lens material for me? Trivex? Why not 1.67 or 1.7? It's not a vision issue, it's a thickness vs. cost issue; no professional is better suited than I am myself to make that choice for me. And when I want sunglasses in PAL polaroid, in a 60 eye, must I use CR39? Kinda thick, can't I have poly for that pair? Or 1.67? As a professional, you should be able to educate me, not decide for me.

Delete.

[Metronome]

Delete.

[bob_f_aboc]

I have a patient who who's Rx is -9.00. He wears CR-39 in a an oval shaped 54 eye metal frame. He's tried every high and mid-index material and couldn't wear any of them due to the chromatic aberration, and he insists on a relatively large frame. Rare case, but food for thought.

1.7 glass?

[Metronome]

1.7 glass?

Delete.