Progressive lens measurements

[Optician1960]

Question for the opticians who measure progressive lenses. Keep in mind that the question is about your "normal" fitting height and not the ones where you have made a change due to a consideration of a persons job, posture... If your answer is different based on the brand of lens you are dispensing, please comment.
Thanks, Optician 1960

[FVCCHRIS]

It would be curious to know if there are manufacturers out there that DO NOT advise fitting their Progs at pupil center.

[Johns]

I usually measure at least 2-3mm below the pupil, depending on the frame, whether they are a myope or a hyperope, and the add power.

[FVCCHRIS]

I usually measure at least 2-3mm below the pupil, depending on the frame, whether they are a myope or a hyperope, and the add power.

Chicken!:shiner:

[DragonLensmanWV]

We usually shoot for bottom of pupil, sometimes 1 mm lower.

[Barry Santini]

I usually measure at least 2-3mm below the pupil, depending on the frame, whether they are a myope or a hyperope, and the add power.

Ok, Johns. I'm officially calling you crazy...

(like me!)

Seriously, this technique may have been appropriate for Hard designs, but me thinks you are shortchanging the performance of today's lenses if you routinely fit this way.

Evidence of absence (aka "problems") is not absence of evidence!

Barry

[optical24/7]

No one answer for me. It depends on several factors; Lens design, frame fit (panto, vertex, wrap, ect), posture, stature, intended uses and previous complaints/likes of the patient.

[Aaron N]

Some lens designs in their media, might suggest a lower fitting. I have come across a couple that ask for the fitting height to be "lower" than normal. A computer aimed lens said it was a best practice to measure it higher.

I don't like this poll, as an optician there shouldn't be a normal or standard. There should only be what is best for the patient and situation.

[drk]

We just had a discussion on this...great timing.

I'm intrigued by Dragon's approach, and I think there is good rationale for it (although his may be "because that's the way I like it" :D).

Consider this: pupil size. We currently do not "individualize" the progressive for pupil size, and that may matter.

Consider that the worst visual condition we experience is driving at night. Normal pupils are about 4-6 mm in light, and about 1-2 mm larger when dark-adapted.

Won't we cause "sampling" of the top portion of the corridor, if we put the fitting cross pupil center? We're going to get minimum of 1 mm larger, and 2 is not uncommon.

(BTW, how far down does the corridor sit in most progressives, again? 2 mm below the fitting cross on most, right? 4 mm on some older Zeiss, right?)

So, Dragon's method may be prudent on most lenses...put the cross to the pupil edge in light conditions so you know it won't be too high in dark conditions.

[Johns]

Seriously, this technique may have been appropriate for Hard designs, but me thinks you are shortchanging the performance of today's lenses if you routinely fit this way.

That does explain a lot, as I guess most of the products we use are "yesterday's" lenses...:o (Picolo, Genisis, etc...)

[kcount]

Typically measure 1-2mm below pupil center.

Learned along time ago about the "Blue Line Meathod"
Measure the seg you want, drop 2MM, mark Demo with line at new height, ask patient to "Stand up, walk around, and tell me if the line is above, below, or through the center of your vision, when you look straight ahead."
Works every time, allows for head positioning and posture.
Great technique as an apprentice and still works great now.

[DC Optix]

I use a multiple posture technique. Measure pupil center, then have the patient rest against the seat back and note the dot location. Finally have them turn their head left or right and come back to focus at center. All the while checking the location of where the pupils match up with your dots. Generally this will showcase the pt's "comfortable resting head position" and allow for an accurate measurement. Have not had a height remake since I started doing this.

Except for sunglasses...usually drop sunglass seg measurements by 1-2 mm and tell the patient why and what it means for their vision.

[kcount]

Except for sunglasses...usually drop sunglass seg measurements by 1-2 mm and tell the patient why and what it means for their vision.

Ditto.

[ronnie daniels]

i learned to spot the pupil center and start the ruler at that (our rulers have 2 mm before the numbers start) If someone does alot of up close work ill raise it a mm or someone that doesnt ill lower 1. Has worked for me for the most part.

[Robert Martellaro]

Center pupil, with very few exceptions.

Consider this: pupil size. We currently do not "individualize" the progressive for pupil size, and that may matter.

There are many different PAL designs to choose from though.

Won't we cause "sampling" of the top portion of the corridor, if we put the fitting cross pupil center? We're going to get minimum of 1 mm larger, and 2 is not uncommon.

Depends on the design, i.e. corridor length, rate of change at the corridor high point, softness, and Add power.

So, Dragon's method may be prudent on most lenses...put the cross to the pupil edge in light conditions so you know it won't be too high in dark conditions.

Or we could choose a design that has a generous distance zone.

[finefocus]

kcount and dc have it right, always paint a line where you've measured to ensure that "table posture" and actual posture are the same. That still leaves the question of where you want the MRP. Mid-pupil is good most of the time, but you won't know, and neither will the patient until it's worn. However, if it's off, it will be off by a mm or two. If you can't refit the frame to accomodate that small difference, you're in the wrong business.

[drk]

Robert, I value your opinion, but tell me, doesn't "generous distance zone" reflect area? It's a "width thing" and not a "height thing", right?

You indeed do have to know the progressives you fit (which would be damned nice if a lens company would have the kindness to describe their lenses in detail).:angry:

[Robert Martellaro]

Robert, I value your opinion, but tell me, doesn't "generous distance zone" reflect area? It's a "width thing" and not a "height thing", right?

Both meridians. Most modern, medium to long corridor PALs start the power change (which ramps up quite slowly at first) far enough below the FC that even the most sensitive, large pupilled eyes won't experience starbursting/flare during scopotic conditions, with most folks finding that they can lift there chin slightly and still achieve acceptable distance acuity with the FC center pupil. Try that with a VIP or Super No-line!

Since there is no advantage in lowering the FC from the lens designers recommended position, I don't. There are disadvantages to mis-positioning it though, including, but not limited to: a depressed near zone resulting in decreased near utility, reduced near zone width, and a non-aligned corridor.

You indeed do have to know the progressives you fit (which would be damned nice if a lens company would have the kindness to describe their lenses in detail).:angry:

They can't talk about any weaknesses in their designs, only the strengths. IMO, if you want an unconditional evaluation, you must wear the len designs in front of your own eyes, or a test subject's eyes.

[drk]

I know you're not omnicient, but you do have a nose for news.

Given an average, modern, general-purpose, traditionally surfaced/molded progressive, how far down does the corridor begin?

1mm?
2mm?
3mm?

[kcount]

The Typical lens will have a 4MM drop.
Meaning that the progressive starts 4mm from the fitting cross.

[kaypaula]

I usually measure -1mm center of pupil, for myopes, espeically high myopes I go lower, hyperopes the opposite. This comes just from experience with my pt's tolerances. Of course there are always exceptions to the rule, but this usually works well.
PJ

[Happylady]

I use a penlight to mark the corneal reflex with a dot. I then draw a line right under it. I usually fit the progressive there but I adjust it a little depending on posture, use, and what progressive I am using.

I also like to look at patient's previous progressives and where they are wearing them.

[DC Optix]

[QUOTE=Happylady;332007]I use a penlight to mark the corneal reflex with a dot. I then draw a line right under it. I usually fit the progressive there but I adjust it a little depending on posture, use, and what progressive I am using.

I also like to look at patient's previous progressives and where they are wearing them.[/QUOTE]


Always a good thing to do! :cheers:

[350gt]

I generally measure center of pupil and go one mm below what my measurement is

[ilanh]

About 80% of the redos that I have to deal with are the result of the progressive's corridor swimming into the distance vision of the patient. This would have been avoided by using pupil center -1mm or -2mm.