Corridor placement on major brand progressives...

[drk]

Help me out with this subject, please, by either briefly rehashing or leading me to the right thread, if you remember it!

Do we have a database of how high the major manufacturers' position the corridor in reference to the fitting cross?

I had the impression that, for example, the Zeiss Gradal had a 4 (?) mm drop from the fitting cross before the corridor began, and that is a little longer than normal...

Some of us fit progressives to the bottom of the pupil, for example, on some lenses to increase the distance between pupil center and the corridor...essentially modifying the progressive design (I have done this with essilor lenses, habitually).

What's going on with this?

[bigeyejim]

drk,

Try getting ahold of the OLA's Progressive Identifier, which you should be able to obtain from your wholesale lab. It has minimum fitting heights for all Progressives, as well as the drop from the center of the pupil. I find that it is a great tool to use, especially when someone comes in who is not our patient, we can find out what kind of lens they are using, and materials, etc. very easily just by looking at the etchings.

Hope this helps!

Jim Williams, ABOC, MBA

[Fezz]

DRK-

I believe the drop on the Gradal top to be 6mm. This is the most drop of any progressive, I believe. Most Varilux lenses are 4mm, Shamir Genesis is 4, etc. Sola lenses are mostly 2mm, Younger Image is 2mm. I am not sure how this affects patient success. I guess we also have to take into account corridor length. Bigeyejim was right on with the Progressive Lens Identifier, I would also suggest the Lens book/guide put out by the Frames catalog folks. It should be part of the subscription to the Frames book. The lens book goes into more detail on blank size, drop, material, etc. Hope this helps.


Fezz
:cheers:

[rinselberg]

Where to get the OLA Progressive Identifier 2006 edition:
http://www.ola-labs.org/i4a/pages/index.cfm?pageid=43


See why computing with those tedious, old-fashioned bits (binary digits) is becoming so 20th century ...
http://www.optiboard.com/forums/showthread.php?t=17515

[Robert Martellaro]

I believe that Drk is questioning where the corridor starts in reference to the fitting cross, not the distance from the fitting cross to the datum or 180 line.

If true, then the answer is who knows? Same for the corridor length, although I think it's safe to say that we have three primary lengths- long, medium, and short, and in most cases the shorter the corridor the closer the first measurable (.25DS?) power change occurs referenced to the fitting cross.

Dr Sheedy, in his 2004 PAL study said "All lenses had a distance zone level with the fitting cross, three lenses did not have a distance area 1 mm below the fitting cross, and 15 of the 28 lenses did not have a distance area 2 mm below the fitting cross. Only two lenses had a distance area 3 mm below the fitting cross, and none extended to 4 mm below the fitting cross."

Regards,

[drk]

Thank you to all posters!

Yes, Robert, that's what I'm getting at. It seems proprietary. I'd suppose that I could take a few of my own measurements and let you know!

[Fezz]

Should we assume that the manufacturers start measuring the corridor from the 180 / prism reference point? My understanding was that that point is the start of the corriodor, whether it was 6mm below the fitting cross, 4, or 2. Although, we could all argue that we pick up power at different points starting above or below this depending on power, brand of lens, etc. I would assume that the average lensometer is not sophisticated enough to give much of an accurate measurement. Honestly, I do not know how this info would affect our dispensing or measureing the lens. Good thread, thanks DRK. Your posts are always thought provoking.


Fezz
:cheers: