I have been talking to a few labs about this job and was currious what the brains of optiboard had to say.
Patient comes in with an Rx that reads:
OD +0.25 -1.50 105 2BI
OS Plano 2BI
Add +2.50 4.5BI ou.
Typically this would be made in a lined prism seg. but this person wants a PAL.
So, in this digital world how would you do this?
- Optician
- Frame Maker/Designer
- Teacher of the art of crafting handmade eyewear.
A Franklin PAL! :bbg:
Axe de patient: You wanna see or you wanna look pretty?
Chip
sell them two pairs, one distance and one near, and tell them that one is their 'distance progressive' and the other is their 'near progressive'.
It ain't gonna happen. The best you can do is a Franklin or prism seg. Freeform won't even do it.
Ain't it strange that for really difficult things, all our modern high tech stuff won't cut it and plain old ancient mechanics will?
In my mind you would want to create a lens with 2BI throughout the entire lens. Then after polishing flip the lens over and make a separate cut for the additional 2BI below the prism ref. point. The first cut would have to leave the necessary thickness to make this happen, as we are now needing the effectively 'add' material to the face. Your going to have to remove material to reveal the new front with the 2BI prism. It woould probably be best if the 2 degrees maxed out at the reading point giving a gradual build. Thus we are in effect creating a variable prism front from Plano to 2BI at the reading seg.
Given we have these amazing freeborn generators and such, I would think this had already been thought out. Albeit this is a very odd Rx and one you don't see very often.
KC
Sent from iPhone.
Last edited by kcount; 07-08-2011 at 08:52 AM.
Kevin, I explored this a few years back when searching for a subject for my Master's Paper. ( A variable prism that would progessively get stronger. )Originally Posted by kcount
A "progressive prism" would be ideal for replacing bicentric grinding. Even a FT wearer would benefit from one. ( in a perfect world you could correct imbalance throughout the segmented area.)
The chief problem is that you would be inducing cylinder (horizontally on a vertical variable). The closest you could come to making one would be to create a corridor where you could counter the induced cyl. (similar to a PAL corridor). Then, where do you tapper off on your "corridor" without creating new, unwanted astigmatism? (just like a PAL.)
There is a big can of problems to be worked through before you will see something like this available.
You and I are thinking along the same lines. The problem is that software developers are money driven, if they can't see enough sales they don't write the program.
blended bifocal is the best compromise.
You know, Three Rivers Optical might be able to make you a backside blended seg you could decenter more for your near prism.
DragonlensmanWV N.A.O.L.
"There is nothing patriotic about hating your government or pretending you can hate your government but love your country."
A compromise sounds like we are in optical politics. We are here to make people see!
I see a lot of these- make sure they want 8.5Δ BI total at near and not 4.5. In almost all cases I supply Trivex or CR39 SV readers for near, and the PALs for general purpose use.
Science is a way of trying not to fool yourself. - Richard P. Feynman
Experience is the hardest teacher. She gives the test before the lesson.
Guess Monovision is not in your vocabulary?
The options are:
Franklin = no intermediate, "bad cosmetics"
SVN = no distance, no intermediate
PAL = no fusion at near
Blended = no intermediate
My "compromise" has been used by billions of people around the world, it's called a bifocal.
....Invented by a Federalist.
It is possible to make a Franklin Trifocal. While I do believe in giving the patient the best vision possible, I don't actually think any thing we do is going to make one under 30 again.
Chip
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