How is Fitting Cross Placement Decided?

[PALwearer]

Is the placement of the fitting cross by PAL designers arbitrary in nature? If not, what considerations are used to decide where it goes? How is the performance of the PAL design affected by placement of the fitting cross? Can changing the location of the fitting cross for a given design make the wearer feel like they are wearing a compeltely different design?

[OPTIDONN]

Hmmm...smells like a consumer! :finger: Please refer to the posting guidelines.

[chip anderson]

In case you are not a consumer, fitting cross goes at optical center of patient's distance visual axis. Cross lines are places on cylinder axis(s) if cylinder present.

[PALwearer]

:angry:

[Fezz]

Ask your lab manager, they would know for sure!

[OPTIDONN]

Then you must be a vary new lab tech. What lab do you work at?

[HarryChiling]

PALwearer,

The designer decides where the fitting cross goes, the distance fitting cross is above the prism reference point at a spot where the designer feels the distnce viewing zone has an adequate amount of peripheral area. If you were to move the cross furthe rup the lens it may have an effect of making the viewing zone wider or narrower depending upon the design used on the lenses, if you were to move the cross lower in the lens you would make the distance portion narrower. Also the corridor would be effected by this change in fitting cross it would require the patient to move their eyes further down the lens if the cross was moved up or to move the eyes to a lesser degree if the cross were to be moved down the lens. It may also mess with the binocular field of view or the inset of the lens. The lesn is desinged with the cross in a specific area and if the cross is moved by the optician all the desing charcteristics get comprimised not just where the distance or the near power is.

[Barry Santini]

The fitting cross placement had alot to do with the default value used for pantoscopic tilt by the lens designer:

0 degress = 0mm above MRP
4 degress = 2mm above MRP
8 degrees = 4mm above MRP

It really falls apart with Zeiss's 6mm setting...12 degress of panto?

It's a theory, at least...

B

[hipoptical]

Can changing the location of the fitting cross for a given design make the wearer feel like they are wearing a compeltely different design?

Yup.
The good folks at Signet Armorlite can answer this question (if they were being honest). They're not the only ones, by-the-way. How many of you thought that the original Kodak was a good lens? (I heard a pin drop) That's what I thought. It was terrible. How about the Precise? Much better. The Concise? (crickets chirping) Well, the reason you didn't like it, is because it is just the old Kodak with the fitting cross moved down 2mm. Instead of fitting a bad lens, now you can fit a bad lens lower, in smaller frames. For proof, look at the actual progression of the Concise- it starts about 1-2mm ABOVE the fitting cross. Like I said, it's not just Armorlite that did it, they were just first to come to mind.
Anyone see the new Precise Short? I'm guessing it's actually a new lens, but I can't say for certain.

[OPTIDONN]

We have great success with Concise and Precise, not to mention the Navigator lenses. But I get what you mean.

[hipoptical]

Have you tried the Navigator Short? I had an office who had better success with that than the Concise. They would fit the Precise and the Nav Short and had 2 non-adapts in one year (one was an Exec-Tri wearer who insisted on trying a PAL, the other was a man who said he just wanted to go back to his old ST-28 to irritate his wife).

[OPTIDONN]

Yeah we like the Navigator Short. The patient that wanted to go back to FT's just to annoy his wife...thats funny!!:D

[Darryl Meister]

Post on 'Progressive Lens Drops' (http://www.optiboard.com/forums/showpost.php?p=172064&postcount=21)

[Robert Martellaro]

The good folks at Signet Armorlite can answer this question (if they were being honest). They're not the only ones, by-the-way. How many of you thought that the original Kodak was a good lens? (I heard a pin drop) That's what I thought. It was terrible. How about the Precise? Much better. The Concise? (crickets chirping) Well, the reason you didn't like it, is because it is just the old Kodak with the fitting cross moved down 2mm.If this is true, it would be dishonest and unethical, and would be the final nail in the coffin in my relationship with SA (backorders on the Concise Trivex and big problems with the Unique- more on this at a later time).

However, if the Concise was just a Kodak PAL with the fitting cross lowered, then the true BCs would be the same. I looked at SA's web sight to check the lens specs-

Concise Poly

http://www.signetarmorlite.com/lab/availability/p06.htm

Kodak Poly

http://www.signetarmorlite.com/lab/availability/disp05.htm

and the BCs do appear to be different, across the board, for all materials.

It seems unlikely, although not impossible, that they made all new molds without tweaking the lens design i.e., changed the corridor length, rate of change, etc., leading me to believe that the Concise is not a re-marked and re-labeled Kodak PAL.