Executive Bifocal Revisited

[CME4SPECS]

What is the concern of image "jump"? I've been fitting PALS for nearly 30 years, 20 some years ago we started prism thinning. The thinning produces about 1 1/2 bd prism in the distance of those lenses, which causes image "jump" in the distance of those lenses. I have fitted thousands of PALS and have had 1 engineer complain of the image "jump" in his lenses. If you don't think there is "jump" in the distance of those lenses, take a look at an object in the distance withou glasses on, then put on a pair of PALS and watch what happens!

[William Stacy O.D.]

[Technically, you're seeing the prismatic effects of the distance and reading (not segment) optical centers at whatever point on the lens you've positioned in front of the focimeter. The actual location of the reading optical center can vary greatly depending on the lens power, cylinder axis, segment inset, and so on. In some cases, it can even exist above the distance optical center.
[/QUOTE]

Right, and I'm not overly concerned about the optical centers at this point, only the vertical prismatic difference between the distance and the near optical centers at thinnest point of the seg ledge. Should be zero. Nowadays is often not zero. And this difference should not depend on the powers of either upper or lower, or on any prescribed prism, except obviously for slab off.

Prescribing execs today seems a bit like a crap shoot to me, but thanks for all the info.

[William Stacy O.D.]

What is the concern of image "jump"? I've been fitting PALS for nearly 30 years, 20 some years ago we started prism thinning. The thinning produces about 1 1/2 bd prism in the distance of those lenses, which causes image "jump" in the distance of those lenses. I have fitted thousands of PALS and have had 1 engineer complain of the image "jump" in his lenses. If you don't think there is "jump" in the distance of those lenses, take a look at an object in the distance withou glasses on, then put on a pair of PALS and watch what happens!

The common use of the term jump refers to prismatic displacement of the image as one crosses a multifocal segment line. By definition it does not exist in PALs, since there is no seg line. Yes, there is prismatic displacement when removing/putting on any prismatic correction, but this is normal, well understood, and certainly the main reason I try to avoid prism thinning.

[Chris Ryser]

What's a "frame wholesaler"?

It's a distributor of whole frames..................fully assembled.........:D :D :D

[Darryl Meister]

I started this thread in search for why "modern" execs are showing up with jump in them (still far less than the flat tops), when they used to have zero, but still very annoying at least to me)

AO's implementation of the Executive bifocal placed the optical center of the segment directly on the ledge, but keep in mind this doesn't necessarily mean that every implementation of an Executive "style" bifocal must be made the same way. Of course, it very well could be poor control over the segment optical center location. However, if you're using decentered plastic Executive-style bifocals (quite popular for cut-out purposes), which may have the ledge below the geometric center of the blank and the optical center of the segment is inset slightly, this may just be how they're made. You could still make these with the segment center at the ledge, but it might take extra manufacturing steps. I 'd have to double-check our E-line bifocal specs to see how SOLA made our plastic Executive-style bifocals in the past. I should add that I would normally expect to see base up prism in this case, so I may be way off base with this speculation.

[Darryl Meister]

If you don't think there is "jump" in the distance of those lenses, take a look at an object in the distance withou glasses on, then put on a pair of PALS and watch what happens!

Of course, if they have any prescription in their lenses, they're constantly looking through prismatic displacement anyway. ;)

Yes, there is prismatic displacement when removing/putting on any prismatic correction, but this is normal, well understood, and certainly the main reason I try to avoid prism thinning.

James Sheedy actually did an experiment sometime ago on the effects of vertical yoked prism (e.g., prism-thinning), and found that all of the subjects tolerated 2.0 prism diopters, while most had problems or significant postural adjustments with 4.0 prism diopters. Consequently, as long as the prism-thinning isn't over 2.0 or 3.0 prism diopters, you shouldn't have any problems.

[Andrew Weiss]

It is nice to have a thread that does not turn into a urinating contest - my lens is better than your lens. And it’s great when we can “remember when” with fellow laborers in the optical vineyard. Lets see if we can come up with another historical pearl to pass around.

How about:

The introduction of the Tillyer Masterpiece and the big issues it brought about, + vs. – cylinder lenses.
The eventual demise of the + cylinder lens.
Our local AO and B&L labs.
Frame wholesalers

I worked one summer in the B&L lab in Hartford, CT, summer 1964. My father was friends with Johnny Lowe, the B&L sales manager for the region, and he got me the job. It was the first, and last, time I spent time in a surfacing lab, and worked on the old spherical and cyl generators. We had a large wooden pigeonhole cabinet on the walls where the laps were stored. The guy who ran the generators -- I've forgotten his name -- was fast, precise, and a good teacher.

Frame wholesalers: I worked for a month or two for Eddie Winston in his New England Optical wholesale warehouse. Remember, the frames came in two packages, one for the front and one for the temple, and we actually mixed and matched depending on what the Dr needed for the patient? If you needed a 44 eye with a 6 inch skull temple, no problem :) (and remember, the temples were all measured in inches, not mm).

The same year my father opened his office in New Britain, CT (1933), Louis Budd opened Budd Optical in Boston. Budd was a long-time frame and lens wholesale house. The last of the family in the business, Bert Budd, now works and a salesman for Alray, one of the last wholesale frame houses.

Rabbis: Charlie Bronczek, the manager of EB Meyrowitz on 5th Avenue at 44th in New York: a master dispenser, who taught me how to custom-make shields for patients with dry-eye out of thin sheets of plastic, meticulously glued and trimmed so the contour of the shield fit the eye socket precisely. I made the last of those back in the early 1990's. Punctal plugs have made them a dinosaur.

[William Stacy O.D.]

I 'd have to double-check our E-line bifocal specs to see how SOLA made our plastic Executive-style bifocals in the past. I should add that I would normally expect to see base up prism in this case, so I may be way off base with this speculation.[/QUOTE]

That's what I would expect, but in this case didn't get. I'll double check it on Tues (unless they've been dispensed already). Thanks for the help. Oh, and Re prism thinning, I probably get it a lot more than I know about because labs these days seem to do it automatically. Probably a good thing if it's under 2^, well, I'd prefer under 1^ due to color dispersion.