Barry, could I persuade you to elaborate?Quote:
Originally Posted by Barry Santini
Barry, could I persuade you to elaborate?Quote:
Originally Posted by Barry Santini
Almost all current PD or DCDs use objective cornea reflex measurements to obtain centration metrics. The assumptions used are now being reconsidered. Try using a subjective measurement, where the wearer performs the alignment. There are at least two devices in development that do this accurately and to an acceptable level of precision. It is the future, and will make all current methods appear for what they are - estimates.
Enlightening! If you have any links to research or lit, I'd love to peruse them! Thanks for your post!
+1
I just had a gentleman today saying he was promised a progressive that would have the intermediate and reading the whole way across the lens by another optician/optical shop. He could not tell me what progressive brand this was. I was stumped. He said he wants to be able to not have to move or turn his head EVER to see intermediate and up close. I told him all multifocal lenses require at least some head adjustment - you can't read a book held to the side of your face, and why would you? But he swore he was told that. And then he whipped out a grainy print out of PAL lens diagrams and showed me that he wanted one that frankly looked wider than a 35mm straight top, but being that it was a printout, there's no way to know if that was actual size and again it had no clues as to PAL brand/type. He wanted me to guarantee that whatever PAL I sold him would at least have that wide of a corridor, and although I have confidence in our Varilux lenses, I was not about to promise that any Varilux would have a 35mm wide or more corridor for intermediate and near work that he would never have to move his head with. Seems like you would end up straining your eyes more if you NEVER adjusted your head posture to read. Who is reading out of the side of their eye? He didn't look like a chameleon to me, either.
Tell him to purchase the lens from that other place if they will offer a money back guarantee if he’s not happy. And then tell him to return to you after he finds out that there is no PAL with near and intermediate all the way across the lens.
It’s impossible to make a progressive power ( or progressive prism for that matter) without having an umbilic corridor.
I politely directed him elsewhere, because I just know that's a refund waiting to happen.Quote:
Originally Posted by optical24/7
If he is going to be able to read clearly out of the edge of the lens, can we assume that God has also redesigned his eyes?
Averted this potential disaster a few years ago when a patient came in with Foster grant multifocal readers.
Available in sphere powers only and the near was virtually edge to edge as a magnification,
Post #5:
https://www.optiboard.com/forums/sho...+grant+readers
So, it's essentially an executive style lineless trifocal? I don't think I've seen anything like that before.Quote:
Originally Posted by Uncle Fester
https://www.fostergrant.com/reading-glasses/multi-focusQuote:
Originally Posted by Lelarep
Ahhh...........2014.........what a wonderful year!
Good thread topic!
I wonder if Nikon's Online Wide NEO, Home and Office NEO, or Relaxsee NEO would qualify for inclusion in the "all across the bottom" category?
Or even a Shamir Duo?Quote:
Originally Posted by uncut
How can they make the useful area across the entire width of the lens without a line?Quote:
Originally Posted by Uncle Fester
What I don't understand is why they bother to put any +SPH at the top in the "interactive" zone. Why not make it plano?
I do not know either but I do know if someone with these comes in to be very wary what you promise your lenses can do.Quote:
Originally Posted by Lelarep
I think they are really magnifiers and not refracting light.
They can't. But then these are not general purpose PALs- the distance has about +0.75 D of the add power, reducing by the same amount the degree of progressivity, reducing the unwanted astigmatism proportionately, reducing the blur boundaries, especially for the lower value adds, to the point where the perceived blur is better tolerated.Quote:
Originally Posted by Lelarep
Best regards,
Robert Martellaro
Ah, that would explain everything. They don't make the top portion plano to reduce the chance people will notice the oblique astigmatism, and the gradual nature of the + transition generally prevents people from noticing the oblique astigmatism during the transition as the lens adds more plus. That makes sense. I didn't think the lens had some kind of ultra secret sauce, because no matter how I tortured the associated equations, I couldn't make a progressive lens not produce oblique astigmatism.Quote:
Originally Posted by Robert Martellaro
Although OA is an aberration that causes blur towards the periphery of the lens, in this instance we are talking about 'unwanted surface astigmatism' that without exception, can be found around the umbilical line of all PALs, where the value is directly proportional to the add power.Quote:
Originally Posted by Lelarep
For example, a two diopter add will generate about two diopters of cylinder/astigmatism.
Robert