A question for the guys: PALs and PDs

[Joann Raytar]

OK, here goes ... We fit PAL's using a patients far PD. Now, folks with wider PDs tend to have a greater difference between far and near PD. The question is how much grace room are you given in respect to a narrow Near PD and the edge of the channel when fitting using the Far PD?

I remember someone on this forum posting that fitting is more critical than PAL brand. I am just trying to develop a strong argument to back up this statement. Obviously certain brands are more suited to certain patients and certain Rx frame combinations but fitting is critical to a low non-adapt percent. Any thoughts anyone?

[don A]

In general I usually try and determine how much a pt. uses his or her near vs. distance vision. From there I can determine which PD to use to edge my PAL with. Of course there is more leeway with distance PD than with near PD. If however the pt. has a fairly wide difference between near & distance then w/out a doubt the intermediate may have to be compromised. In other words, communicating with your patient is the best defense. If they know what to expect then you will have better results. As for brand names I usually go with the brand that I have experience with, but as a rule I generally fit previous wearers with their same brand unless their unhappy with it.

don A.

[Jeff Trail]

Jo,

Fitting is about 99% of making it work :)
I tell this to my accounts and usually they say it's more "brand" thats the problem...well as a service I visit my accounts atleast once a month and give seminars etc. etc. and once every couple of months I have a "party" here at the lab and it has become a regular thing and alot of the OD's as well as the techs and opticians come now (makes it very nice) and to PROVE that point I let them pick anyone they wanted out of the people there that wore a PAL,( it was an OD btw) took the existing frame and we went through the lab and cut a Natural, Adaptar, SNL, Elegance, VIP, XL, Image.... and I fit them all to the same frame and took the PD and we changed them one after the other...they could USE every one of them they noticed the difference in design (soft to hard) but could have functioned in every SINGLE pair ..
I still say that if FIT correctly you can dispense every brand out their and the MAJORITY of the patients would be able to wear them..if they are a first time PAL wearer.. switching brands work but usually it's a far better rate of adaption if you go up in design quality and not down (hard design),it makes the transition of distant to near more natural and less abrasive if you increase the amount of steps the eye wades through when converging but making it less (hard design) usually it is more noticable in image jumps as you wade through the steps of power.
Remembering thats what that buzz word means (soft design & hard design)
I didn't mind eating those lens because in the long run it improved everyones confidence in their ability to fit and dispense PAL's..means more premium work for me :) When you actually look at the problems in PAL's its usually a material problem, like swapping an index or material, or backside reflections etc.etc...I know after those little talks the OD's like it because the amount of PAL's the sold increased and the non adapts have decreased by a great deal...
Here are the basic things I tell the techs..make sure you take the proper mono PD... adjust the FRAME before you take any fitting measurments...keep layout charts handy to check the cutout to make sure the design will WORK in the frame with the correct PD's and fitting hght.'s (I have supplied all these to my accounts) and they are avaiable from just about every one of the lens companies if you ask for one.. Most of them now keep them right on the fitting tables and then "dot" the demo's and then you just line up the dot to the fitting cross on the chart and you'll know exactly where the reading area will land on the frame.
I still think alot of the problem is either in the fitting or in the frame selection..it's easy to show someone exactly what the problem is when you can show them with that chart. :)
I know that their is always going to be a certian % of people who just not can adapt to a PAL but that should be a very LOW number (from my experience around 2%)
I don't consider my fitting any better then any one elses but by taking your time doing it correctly and understanding "how" it works will make fitting people alot easier.
As for having those "odd ball" cases where the decentration of distant to near being wider then 1.5 to 2mm (mono) you can cut the lens slightly off axis and "tilt" the lens a degree or two to move the near.. this works but you have to remember to fit the cross about 1 mm lower then usual, and when you tilt the "180" when edging it will raise that cross right back up when it's inserted...I've done this a number of times but never did it where it moved it more then a mm or so.. any more and the periphrel distortion would be to noticable to the patient....

Jeff" just my .02 worth" T.

[Raanan Bavli]

Great post Jeff. I have two related questions. 1) Wouldn't you consider rotating more then 1 or 2 degrees (if needed) in cases of low cylinder or none? 2) How do you deal with shorter vertical distances between far and near centers?

------------------

[Jeff Trail]

[QUOTE]Originally posted by Raanan Bavli:
[I] 1) Wouldn't you consider rotating more then 1 or 2 degrees (if needed) in cases of low cylinder or none?
--------------------------------------------

Actually no..unless you had a lens like a Hoya Wide or one like it, the reason being the disortion, the majority are designed with the consideration that you WON'T be tinkering with the 0-180 line... if you seen a chart of distortion on a PAL it is shaped like an hour glass )( .. so if you rotate it far you will have peripheral problems even in a sphere..next time you have a "sphere" power take a look through the lensomter out in the periphrel area and you'll see induced astgmatism and distortion..so you still have to be careful about using my little trick.. you can push it but just not to far :)


-----------------------------------------
2) How do you deal with shorter vertical distances between far and near centers?
-----------------------------------------

technically it's not "shorter" or "longer" you are not actually moving the reference points "closer or "further" from each other you are just rotating that same amount of distance :) Also if you ever run across someone that has a wider PD (Dis. to N.)you'll notice the they converge at a different angle naturally, the majority of times I have done this it involved someone that had a muscle problem in one eye so say I had a mono PD of 31/29.5 OD and 31/28.5 or 28 in the OD (just an example).. then you could do this trick.. a good tip is try to use one of the designs where the intermediate is shorter (AO Compact etc. etc.) so they don't notice the shifting of the coridoor as much..or in some cases I have mixed brands that had different coridoor lengthes putting the longer in the "rotated side" the major problem people are the ones that are a really true presbyop that actually need that intermediate then it's more tricky :)
Not saying this little trick works everytime but I have had pretty good results, the hard part is getting to know the exact limitations you can push with a design and not distort the optics to gain in convergence ..

Jeff "always willing to experiment if it helps out" T.

[Raanan Bavli]

Jeff,
After reading your answer to my first question, I'm not sure I correctly understood the tilting issue in your first post here. Were you talking about rotating around the eye-object axis? If not, what do you think of such rotation as a means of placing the near vision area closer to the patient's nasal?
Raanan.