When to use different seg heights

[Himyope]

A great debate has begun in our office, so I'm taking an informal survey.

Everyone agrees that when fitting a PAL, you would always measure and specify different seg heights if there is a discrepancy in pupil height

HOWEVER........

When measuring and fitting a Flat Top bifocal, if there is a difference is pupil height, would you also specify different seg heights?

Yes? No? Under what circumstances, and what is your reasoning?

Thanks

[Homer]

For the exact same reasons you use monocular measurements on a PAL.

[chip anderson]

In a normal situation I would suspect the frame is not properly alighned.

On patients that have a true physical anomaly from genetic defect, trauma or surgery, and the orbit(s) are displaced then one should go by the existing pupillary hight. Yes this apples to Staight tops or progressives.

Chip

[paw]

If everyone in your office agrees that the PAL is measured as is, but there is a debate about the flat tops, then the debate must be centered around the unappealing cosmetic appearance of uneven flat tops.

[chip anderson]

Dear Paw:

You can do all the cosmetics you want with the frame. The lenses are vision correcting devises and should be done as best benefits the vision of the wearer with no other conciderations.

Chip

(Hope some other old guys will add an A-men {which translates: "Truth" incidentally}).

[docwatson]

Chip: What about the considerations of your customer? If he is concerned about the cosmetics of the lenses do you allow him to choose?

[chip anderson]

Doc and Paw:

I know I sound a little harsh and I try never to force anything on anyone. I will leave a bifocal off if the patient request me to (after telling them about the consequences and denial, etc.) But before I would compromise the Rx I would at least tell the patient: "You need this and why."

Ask yourself this: Would you want a physician to compromise an Rx for medicine because one option was prettier or tasted better?
If an Rx is truly an Rx it should be done in the most benficial manner for the patient. Not the most consmetic way or the most profitable way for the optical shop.

Maybe this is how they sell the "Purple pill."

Chip

[Jedi]

Chip: What about the considerations of your customer? If he is concerned about the cosmetics of the lenses do you allow him to choose?

If the patient is concerned about the cosmetic appeal of their glasses they shouldn't be in a FT to begin with. ;) Fit them in a PAL.( with anti glare and high index lenses, if necessary)

[Homer]

docwatson said:
Chip: What about the considerations of your customer? If he is concerned about the cosmetics of the lenses do you allow him to choose?

The person who has "a true physical anomaly" , as Chip mentioned, will have other issues much greater than a difference in segment hight placement. Probably not an issue of patient choice at all.

Just a one does not discuss the variance in optical system positioning of a PAL, it should not be an issue in a flat top.
By and large, there will not be much more than a 1 to 3 mm difference in the hight and will probably not even be noticed. If it should be noticed, the reasoning for the variance will be explained and also able to be demonstrated by frame manipulation (purposely mis-aligning the segments).

Having mis-aligned segments increases the band of unseable area that happens automaticly as the pupil passes from distance to near. I have had many lined-multifocal patients who complain if the line is off by less than 1 mm.

Truth is that you could more easily ignore a 1 to 2 mm variance in vertical optical system placement on a PAL than you could on a flattop.

[palfi]

- it assumes that the spex won't slip or twist.

Given that you should (1) only do things in your patients interest - then everyone will have a different answer depending on what is important. (2) Also only do what you need too and leave the rest alone.

Then, you should follow what the patient is already wearing. Also = some people who have one pupil higher will also have the ear on that side a little higher = so the glasses will naturally fall a little twisted and so correct for their vertical displacement.

Vertical displacement for varios is only done to keep the eyes within the transition channel when they are looking down to read. This does not apply to bifoc's - so you would not automatically place one segment higher. In anycase as someone said the patient is likely to howl if she/ he notices that one seg is abit higher anyway.

If the patient has a binocular problem with one eye being higher then this would normally be corrected with a prism. However - although one eye being higher is not unusual - have a binocular instability due to it is very rare and it seems uncommon to have a prism prescribed for it. I wonder if that is because it is so easy for the patient to adopt a compensating head tilt which they habitually use anyway. In anycase - the phoria induced by a facial assymetry is going to be incomitant - depending on whih way the patient is looking = so where are you going to put the prism?

So = people with a eye higher up tend to get away with it because they have a slight head tilt and their ears are uneven anyway.

I did a study on this once - ploughing through the books and found that there is little guidance to go on - but I will say that a mate of mine used to always do bifocal heights unevenly to counteract the pupil heights. Here, we never do it = I think he has had more complaints that we have =

It is an interesting thread and I take in everyone's reply - I suppose you just do your measurements and hope for the best.

If the frame is placed as close to the eye as poss and gien bags of pantoscopic tilt - wouldn't that alsohelp to minimise any difficulty without resorting to altering seg heights? = Palfi

[Texas Ranger]

There are those folks that do require monocular seg placements; we usually dis the fact that when they are made equally in the "frame. then when their eyes cross the seg line, it's like a double cross, and the image jump is compounded, and much more noticeable., so, if we make one higher, or lower , it will make their glasses more comfortable; now, it is quite important, that we have this conversation BEFORE dispensing them! they need to know this, when we're ordering the lenses; then they won't be surprised that they are different.

[aaron]

This is where the best judgement of a capable optician must be used. The segments really should be offset to give the patient the best possable vision.

This is rarely a cosmetic consideration because it will usually be only a couple of mm. Almost noone with notice that on there face. And of course if it is an extreme malformity than I am sure they have much greater cosmetic concerns.

I almost never will lower a seg by one mm for the sake of good old every day non-symetrical faces.

But I will use my best judgement based on what I see with the patient in front of me.

ad