Justifying unequal fitting heights

[TheRobotious]

When measuring for PALs, does anyone 'split' the fitting heights or average the heights, rather than using measured unequal fitting heights? If so, can someone justify why they do this? Is there some risk involved with using unequal heights, assuming the frame is fully adjusted and sitting straight on the face? Admittedly I lack experience in this area, but I always take measurements 'by the book' whereas most all of my colleagues measure one eye only and use that measurement for both eyes.

No one at work has really justified using equal heights, so is there something I'm missing? The way I see it, using unequal heights would only solve more problems compared with using equal 'fabricated' heights when the pupil heights are in fact not level. Any thoughts to the contrary?

[mervinek]

I have used unequal heights on occasion, but it's rare. The most obvious time was with a patient who had cancer and had a huge (5mm+) asymmetry between the eyes. And I always measure both eyes.

[Boldt]

First how much of a split? .5mm-1mm go with the lower seg if you're not worried about it.
For my self though I do split at 1mm, I'vbe found that it helps with new p[progressive users, and those with a wonky or high RX. Think about it like this, you want to have the segs fit at the pupil for the best use on progressives. When fit to low people have to raise their head to use the reading part. Now think about having one spot on and one to low. How messed up would that make the person's vision? Generally 1mm is ok, but I'd rather them be better than ok my self.
I do the same with SV and have people loving it.
So I guess for me it's stepping up my own game and going that extra mile

[theyeshaveit]

You are doing it the right way. 90% of the population is asymmetrical so why would anyone assume the seg hts are the same? Laziness in my opinion. I always pre fit the frame and the measure seg hts on both eyes. It takes a couple minutes longer, but is worth it for the benefit of the wearer. Keep on doing it the right way. Your customers will appreciate it in the long run.

[edKENdance]

What do you do for clients who could be wearing uneven segs but have been wearing aligned segs for years?

[Boldt]

I explain to them what I'm doing, and that it may seem off at first. I tell them to give it two weeks of constant use and If they don't like it still I'll swap them back to what they had. It's generally a lab redo that is at no charge. So no worries for both of us.

[TheRobotious]

Thanks very much for the insight everyone. Patients who come in having happily worn poorly measured glasses is always a bit tricky, but I agree with Boldt in terms of explaining exactly what you'll be doing and what to expect.

[edKENdance]

Thanks very much for the insight everyone. Patients who come in having happily worn poorly measured glasses is always a bit tricky, but I agree with Boldt in terms of explaining exactly what you'll be doing and what to expect.

Just curious as to what you say when you're telling your client what to expect.

[TheRobotious]

To be honest I've only had to deal with this in terms of PDs being off, rather than seg height. Either way, I can't tell them exactly what to expect, instead I tell them they've gotten used to the 'wrong' measurements, and so they might feel as though the new glasses are a bit off. They might feel a little eye strain if it's a huge error, or a high power, but that it should become more comfortable reasonably quickly. Often though, the error isn't a huge problem, or they come in saying they're old glasses have never really felt right, so this makes it easy to explain why.

I suppose it's a similar conversation as if they're switching to an aspheric for the first time, and have gotten used to the distorted edge look in standard spherical lenses. It might seem somewhat 'off' at first, but once they're used to it, there's no problems.

[optilady1]

There are some people (not a lot) who for whatever reason do better when the segs are the same, no matter what. It may be psychosomatic, because they don't want to admit that they aren't perfect. One thing that I've learned over the years is, you cannot argue that you know better to the patient. If you explain the situation calmly and logically, 99% of patients will agree with you, but the 1% who don't, you going over it again and again will only give you a headache.

[TheRobotious]

One thing that I've learned over the years is, you cannot argue that you know better to the patient.

I've a barely been in the business for one year, and would agree this is absolutely paramount.

[EyeCare Rich]

I'm confussed here! Why tell the patient the measurements at all, YOU are the expert. Fit the glasses accordingly. The more time you spend telling them you did something different, the more problem you are going to encounter. Just adjust the frame, measure, record the information and order the glasses. If there is an issue as far as adaptation, deal with it at the dispense, but if they were previously fit equal, and you find an unequal measurement, and order accordingly, they should be more comfortable as the eyes will track through the progressive channel a little easier, assuming the PD is measured correctly as well.

I'm surprised WMMCDONALD hasn't jumped all over this thread, as this is what he is always ramped up on, and it is showing here.

Good luck TheRobotious, and welcome to Optiboard, read and learn as much as you can here, but also go and seek more knowledge from either coarsework/school/CE, and find a couple good optics books.

[TheRobotious]

Thanks EyeCare Rich, so far I've been doing just that!

[optilady1]

I'm confussed here! Why tell the patient the measurements at all, YOU are the expert. Fit the glasses accordingly. The more time you spend telling them you did something different, the more problem you are going to encounter. Just adjust the frame, measure, record the information and order the glasses. If there is an issue as far as adaptation, deal with it at the dispense, but if they were previously fit equal, and you find an unequal measurement, and order accordingly, they should be more comfortable as the eyes will track through the progressive channel a little easier, assuming the PD is measured correctly as well.

I'm surprised WMMCDONALD hasn't jumped all over this thread, as this is what he is always ramped up on, and it is showing here.

Good luck TheRobotious, and welcome to Optiboard, read and learn as much as you can here, but also go and seek more knowledge from either coarsework/school/CE, and find a couple good optics books.

If I have a new patient purchasing progressives, I dot the old ones up so I can see what they've been wearing. If it looks relatively normal, I do the new pair my way with no discussion. If things are really weird, like a seg that starts at their eyelids for a progressives, I'm gonna ask why. I don't care what the rules say, some patients want what they want, and if they are happy with what they have and they can articulate to me why they've worn their glasses like this happily, I'm not arrogant enough to tell them how they need to wear something. This happens like twice a year. Everything I do is to prevent someone coming back with issues.

[TheRobotious]

I think both points are valid, depending on the circumstances. If a previous patient is returning and gets an updated Rx, and I can see from the file that the previous optician was too lazy to measure near PDs for a reading pair (and just went with distance PDs), I will rectify this for the new pair without consulting the patient, and have never had any issues with this kind of thing. I think this is what EyeCare Rich is getting at.

If however, a patient comes in, and has a pair of glasses that deviate from the 'norm' considerably (as in Optilady's example), then I think it is both fair and safe to bring it up with the patient. It's likely been made up differently for a specific reason, and changing this with no discussion is asking for a remake.

[EyeCare Rich]

That makes absolute sense optilady1. Good points made in your post. I don't disagree with asking why something is odd and addressing it accordingly. That is what I am talking about when I say be the professional. I just don't think there needs to be a discussion for a slight uneven measurement. Just adjust fit and dispense.

Just my 2 pennies.

[MakeOptics]

For progressives and SV (hi RX) unequal fittings heights are preferred, but for lined multifocals experience has show me that the segments should be placed symmetrical in the frame otherwise the client assumes short work. In lined multifocals however I will specify the DRP so the compromise is kept in the segment only and if the difference is too great then I use a larger set like a 35mm to avoid reducing the visual field. Of course I'm talking about horizontal placement in this scenario. Vertically the same holds true but I use the higher of the two measure in a bifocal and the lower in trifgocals. The reason for not splitting lined is the average person can handle up to a difference of 3 prism diopters so I rely on their eyes to work a little harder which they are more than likely used to if they have been in eyewear in the past.

[rbaker]

Hopefully everyone responding to this query has worn either a FT or a PAL lens.

[DanLiv]

One thing to consider if segs are significantly different (2+mm) and fitting variable corridor freeform lenses, you will produce different corridor lengths between the lenses, which doesn't sound good to me. 1mm may not make much difference (although the fitting heights might be right on the cusp of where the software differentiates, and for some designs with only a few different corridor length this could end up with a 2mm corridor difference), but at 2+mm you are certainly going to alter the design and each eye will reach full add with a different downward gaze angle. For theses few patient's that I have had to do 2+mm dissimilar segs I either swapped into a fixed corridor design, or since I edge just ordered them from the lab at equal segs (to force the software to calculate equal corridors) and then edged dissimilar myself.

[Robert Martellaro]

One thing to consider if segs are significantly different (2+mm) and fitting variable corridor freeform lenses, you will produce different corridor lengths between the lenses, which doesn't sound good to me. 1mm may not make much difference (although the fitting heights might be right on the cusp of where the software differentiates, and for some designs with only a few different corridor length this could end up with a 2mm corridor difference), but at 2+mm you are certainly going to alter the design and each eye will reach full add with a different downward gaze angle. For theses few patient's that I have had to do 2+mm dissimilar segs I either swapped into a fixed corridor design, or since I edge just ordered them from the lab at equal segs (to force the software to calculate equal corridors) and then edged dissimilar myself.

More Optiboard gold! Another reason to avoid variable corridor length designs altogether.

[DanLiv]

Another reason to avoid variable corridor length designs altogether.

Do you consider them problematic in general Robert? I have had a few failures with deep 25mm+ seg heights where the near vision angle was too low, solved by just swapping in a fixed corridor.

[Paul Smith LDO]

Not to play the role of the Devil's Advocate here but, would not the refracting Dr pick up on any vertical image discrepancies and notate said correction for any unwanted vertical imbalance in the written Rx. I can think of few reasons for denoting separate/split seg heights for PAL wearers.

[Robert Martellaro]

Do you consider them problematic in general Robert? I have had a few failures with deep 25mm+ seg heights where the near vision angle was too low, solved by just swapping in a fixed corridor.

You've cited two really good examples of when the variable fails to provide proper function.

Not to play the role of the Devil's Advocate here but, would not the refracting Dr pick up on any vertical image discrepancies and notate said correction for any unwanted vertical imbalance in the written Rx.

I've never seen it. You give the docs and techs too much credit. I filled a -19 D Rx yesterday from an OD without a vertex distance noted. That will be my first call this morning.

[Paul Smith LDO]

Robert, you mean to say that you have never seen an Rx with a correction for vertical image imbalance. That is exactly what I am referring to. If a patient is displaying noticeable orbital asymmetry would we not expect vertical visual displacement and a prismatic correction for said vertical displacement. I am speaking in general, as there are always exceptions.

[ak47]

One thing to consider if segs are significantly different (2+mm) and fitting variable corridor freeform lenses, you will produce different corridor lengths between the lenses, which doesn't sound good to me. 1mm may not make much difference (although the fitting heights might be right on the cusp of where the software differentiates, and for some designs with only a few different corridor length this could end up with a 2mm corridor difference), but at 2+mm you are certainly going to alter the design and each eye will reach full add with a different downward gaze angle. For theses few patient's that I have had to do 2+mm dissimilar segs I either swapped into a fixed corridor design, or since I edge just ordered them from the lab at equal segs (to force the software to calculate equal corridors) and then edged dissimilar myself.

You will be asking for trouble if you put someone like this in a variable corridor lens.