Actual corridor lengths

[lensguy]

Anyone have a list of "ACTUAL" corridor lengths for progressives.
I have found this being a moving target from lens vendors (min fitting ht).
3 lenses in particular are driving me nuts

1. min fit ht 14..............actual corridor length unknown (disp guide states 9.5mm to 85% WHO CARES where's 100%):angry:
2. min fit ht 15..............corridor length 13mm............... 2mm of full near ??:finger:
3. min fit ht 16..............corridor length 12mm............... 4mm full near ++++:)


I am at the point to decide for myself min fit ht's, most companys seem to let the marketing depatment decide min fit ht's:confused:

sorry if this seem like a rant!!!

[Attitude]

Dr. Sheedy will be publishing results of his independent study soon in an upcoming Optometry Journal article. This year it will include some information you may find very useful, and insightful!

[vikramg]

Can any one tell me how to get hold of Sheedys report ?

I believe he has done a number of papers on how to evaluate and differentiate a progressive lens .

[Karlen McLean]

I don't have corridor lengths, but I have a current list of minimum recommended fitting heights. Would that help?

[Lewy]

It would be useful information to have. Also for a relative newbie to this board
where can I get a copy of Dr Sheedy's report, having trwaled the web for it already.

Lewy

[rinselberg]

Where can I get a copy of Dr Sheedy's report?You can find links to two of Dr. Sheedy's publications on this web page:
http://optometry.osu.edu/COOR/4059.cfm

Thanks to OptiBoarder Robert Martellaro
http://www.optiboard.com/forums/showpost.php?p=101391&postcount=14

[lensguy]

I don't have corridor lengths, but I have a current list of minimum recommended fitting heights. Would that help?

Thanks Karen,

But no, thats what is in doubt (in my mind). The min fit hight should be determined by the corridor length (as opposed to the marketing dept).
I am looking for this so I can establish some rules through 4 offices and 12 dispensers who cant agree on min fit hts. "The book say's ___mm" vs "the rep says___mm".

We do however agree that we should have 4mm @ 100% of near power to give the patient a fair chance (in most cases).

[rbaker]

First of all you have to define the term “corridor length.” Then you have to get all of the lens manufacturers to agree on the definition. That being done, you could possibly get some comparative numbers that might accurately represent actual lens geometry. I don’t think that this will ever happen.

Fortunately, an individual such as Dr. Sheedy will take on this process and provide you with some metrics.

[lensguy]

First of all you have to define the term “corridor length.” Then you have to get all of the lens manufacturers to agree on the definition. That being done, you could possibly get some comparative numbers that might accurately represent actual lens geometry. I don’t think that this will ever happen.

Fortunately, an individual such as Dr. Sheedy will take on this process and provide you with some metrics.


Corridor length: The distance from the fitting cross to 100% of add power.

I think this is a "standard" measurement, they MUST know this in order to not totally chop off all reading in the "how low can we go without redesigning our lens race"

[Bobie]

1. Varilux Comfort
1.1 Perfect fitting height 22 mm
1.2 Standard fitting height 20 mm
1.3 Recommended Minimum fitting height 18 mm
1.4 Minimum fitting height 17 mm

85% of Addition at 12 mm
100% of Addition at 18 mm

2. Varilux Ellipse
2.1 Perfect fitting height 16 mm
2.2 Standard fitting height 15 mm
2.3 Recommended Minimum fitting height 14 mm
2.4 Minimum fitting height 13 mm

85% of Addition at 9.5 mm
100% of Addition at 12 mm
85% of Addition is very important for PALs, because this is the first power that wear can start to read at near for few second.

Many of PALs have 100% of Addition at 18 mm like Varilux Comfort. But , have 85% of Addition at 14 mm ( deeper than Comfort 2 mm ). This 2 mm is very big difference when wearer sit down and open newspaper to read.
The wearer of Varilux Comfort can read like instant but the wearers of other PALs have to focus and up their neck for fews second before they can read.

The very strong point of Varilux Comfort is instant read like short corridor PALs , but much better comfort vision than short corridor PALs.

I ever fit fews hundreded of Varilux Comfort at fitting height 17 mm on wearer who get used to short corridor PALs and all of them was very happy even for near vision.

" Life is too short to see the world with short corridor PALs "

[NavyChief]

Actually looks like some lenses are listed on page three of this article. Doesn't include all, but will help.
http://optometry.osu.edu/COOR/pdfs/OptomVisSciArticle.pdf

[NavyChief]

Sorry, page 2

[Laurie]

Hi Lens Guy,

Great question.

Although there is no mandatory standardization of this parameter yet, here's a rule of thumb that I use:

I will assume a nearpoint area, at least 4 to 5mm vertically, at 100 percent of the add powers (no exceptions).

If the nearpoint is, say 5mm for example (which is a good quality amount...similar to the size of our pupil...) , then I would take the manufacturers recommonded fittting height, and subract 5mm. This will give you a fairly accurate number.

Now...do all lenses yield 4 to 5 mm of vertical area with 100 percent of the reading power? We wish! You can actually neutralize at different plots and measure for yourself.

If you receive 100 percent of the add (and, at least 4 to 5 mm of it), then subtract the 4 or 5 from the recommended fitting height and this will give you the corridor length.

If you do not receive 100 percent of the add (and, at least 4 to 5 mm of it), then send it back for redo. If it is impossible to reach at least 4 to 5 mm of 100 percent add power with your PAL of choice, then you may want to reconsider your PAL of choice and pick one that will consistently give you that criteria.


: )

Laurie

[Bobie]

Hi ,Laurie

70% of Addition is good enough for computer screen at 60 cm.

85% of Addition is good enough for read at 45 cm.

100% of Addition is good for read at 40 cm.

But many of PALs is 125% of Addition below 18 mm of fitting point like Summit pro , Hoyalux GP Wide , SolaMax.

And many of short corridor PALs is more than 125% of Addition below 18 mm of fitting point like Summit CD , Kodak Concise.

" Life is too short to read with 125% of Addition "

[Laurie]

Hi Bobie,



I agree...a working distance of 60 cm will require less than 100 percent of the add. Knowing that we need +2.50 D to see at 40 cm, then there is less power required for a 60 cm working dist. If f = 60 cm, then D = 100/60, or +1.62 D
(round either way, close enough).


In a short corridor, there is much less space, so the design has to get to the bottom at a faster rate. Short corridor PALs are useful for lots of life tasks, except computer use, or cubicle environment.

When I refer to the 4 to 5mm vertical area, I am not referring to an intermediate area, but at the bottom, for nearview...not at a computer screen.


And, besides all of that, I would not suggest ANY PAL, short or conventional, for computer use...

I would suggest a conventional or short corridor for other times in the day/evening, and a variable occupational lens for computer use...(but that's another thread). : )

With all of the talk of short corridors, there have been misconceptions, like "bumping the add", etc. All of these make-shift strategies hurt the optics, giving short corridor PALs a bad name.

Opticians/Dispensers need a scientific method to compare/contrast lens designs for different uses. We need consistent parameters to compare, like the 34mm distance between laser markings/180 line. These are measurable parameters that we can use to neutralize a lens and judge its quality. Dr. Sheedy is the first I know of to use what standards are out there, and to bring attention to areas that need standards, like the relationship between corridor length and recommended fitting heights.

It would be nice if we could establish the same kind of norms (like contour plots with diopter charts) to corridor length and amount of add power. You know, try to keep it simple, so that we can all speak a language of apples and apples.


Too much rambling? sorry...a topic that is near and dear to me.



: )



Laurie

[QDO1]

Opticians/Dispensers need a scientific method to compare/contrast lens designs for different uses. We need consistent parameters to compare, like the 34mm distance between laser markings/180 line. These are measurable parameters that we can use to neutralize a lens and judge its quality. Dr. Sheedy is the first I know of to use what standards are out there, and to bring attention to areas that need standards, like the relationship between corridor length and recommended fitting heights.

It would be nice if we could establish the same kind of norms (like contour plots with diopter charts) to corridor length and amount of add power. You know, try to keep it simple, so that we can all speak a language of apples and apples.


Too much rambling? sorry...a topic that is near and dear to me.



: )



LaurieFunny - i said a virtually similar thing in a thread a couple of months ago

[Laurie]

you must have been copying me.

: )

Let me dig out some notes to post here on heights.

Laurie

[Jerry Thornhill]

I agree with Laurie in that there should be a standardized method of measuring corridor length. I like to see for myself what it really is and have the measurements in cold hard undisputable facts measured by all companies one way and not slanted for their product.

I also want at the fitting height the full add not 85% or less of it. I want it least a full 5mm of reading depth. I read a lot and I am not satisfied with less.

I think that the Sheedy report should be read by all with an open mind as it is an eye opener for people who are so biased in their opinions of lenses and manufacturers.

Bobie, how do you get English on the website you posted?
Are you employed by one of the companies, or is your club sponsered by or accept donations from lens manufacturers? It sounds like you are a manufacturers rep.

Jerry

[Snitgirl]

Hey folks, to help you out prior to getting the information that you are needing, get out your layout guide for these progressives and visual see what works. I never go by what the manuf or rep says is the minimum height because there are so many different frames designs it will vary. I place it on the guide and make sure there is plenty of room for both the distance and the near..

anyhow, just my 2 cents. really gets me when people only go by numbers.

[Jerry Thornhill]

Snitgirl,
Excellent post, as a lab manager most of the non-adapts that I saw were because of the frame design, combined with the PD and height causing large areas of either the near area or distance area being cut off. On a few frames both were missing.

Jerry