Bifocal Heights..or Lows

[Clive Noble]

I suppose I'm lucky that I've had experience as a Dispensing Optician in two countries, England and Israel.

My practice in London was in the West End but residential, and my present situation in Haifa is similar, and the type of patients are also similar.

It struck me, a few days ago, when a tourist from the UK came in for an SOS repair on his glass bifocals, how high the seg heights were, they were placed on the lower lid.

Now, I remember when I fitted bifos in the UK we nearly always put seg heights like this, maybe a little lower, and it was very acceptable by the patients.

When I first came here 20 yrs ago, I fitted the same way and had a lot of problems, until I realised that Pts here like them very low..and I mean VERY low.

I can't think what the reason can be for this regional variation... the only thing I can come up with is the weather? you see it's very hot here compared to Britain, and the young female generation walk around in this hot weather dressed as though they're ready for the beach.

Which right minded guy wants a 28mm line blurring his field of view from the neck down?

That's the men, the women... well, I can't work that one out.

Do you have any seg peculiarities in other parts of the world?

All best, Clive

[Darris Chambless]

Hello Clive,

Always a pleasure to talk with you. As far as peculiarities on segs the only thing I can think of is that some patients that we have started out with segs set low and won't wear them any other way. But what you are talking about seems to be country wide. Perhaps that was just the standard there and has become the norm for whatever reason.

The lady's always being dressed for the beach sounds pretty good. Hopefully that will remain the standard and or norm for many years to come ;-)

Darris C.

[David Wilson]

Hi Clive and Darris,
The preference downunder appears to be bottom lid margin, howver I have always subscribed to the view that this is OK for round segs (I'm showing my age here) but D segs need not be set quite so high. I normally suggest 2mm below lower lid margin.
Hopefully this will become less of an issue in the future as progressives continue to take more of the market. We will still be left with Clive's 'beach factor', though. Fortunatly progressives are no problem here, unless you are lying on your back on your beach towel (but I digress, it is winter down here and my thoughts are wandering).

Regards
David

[harry a saake]

Hello Clive, i suppose there is always be those area or regional differences as to what is worn how. Years ago when i was with B&L, they made unknown to most people here in the states a G-50 lens for the italian market, while we had G-15 and G-31

[Darryl Meister]

Hi Clive,

Have you considered the regional demographics in your new area? Perhaps the locals don't perform many near vision tasks... If few of them are literate, for instance, they may prefer to have the segments placed low and out of the way. Most US and UK authors do recommend placing the segment ledge at the lower lid (or limbus), or slightly below.

Also, exactly how many persons are we talking about? Is it a widespread issue? Or could it be that one or two local opticians have just been incorrectly placing bifocals on the locals over the years -- so that now many of them are accustomed to lower seg heights?

Physical characteristics also play a role. For instance, taller wearers will prefer lower seg heights since their gaze will generally be depressed more than that of shorter persons. Is the average spectacle wearer taller in your new country?

Best regards,
Darryl

[Fabian Corio]

Hello Clive,
Although I agree with Darryl Meister, I believe that you should also pay attention to your patient's noses.Wide noses tend to increase the vertex distance.If you notice that your patient's V.D is greater than usual, you should consider placing seg heights a bit lower for a better performance.Seg heights set at the lower lid usually work fine for vertex distances of about 12 mm., if you keep this reference for higher V.D's you would be "blurring your patient's field of view from the neck down", as you say.
Best regards,
Fabian.
Originally posted by Clive Noble:
I suppose I'm lucky that I've had experience as a Dispensing Optician in two countries, England and Israel.

My practice in London was in the West End but residential, and my present situation in Haifa is similar, and the type of patients are also similar.

It struck me, a few days ago, when a tourist from the UK came in for an SOS repair on his glass bifocals, how high the seg heights were, they were placed on the lower lid.

Now, I remember when I fitted bifos in the UK we nearly always put seg heights like this, maybe a little lower, and it was very acceptable by the patients.

When I first came here 20 yrs ago, I fitted the same way and had a lot of problems, until I realised that Pts here like them very low..and I mean VERY low.

I can't think what the reason can be for this regional variation... the only thing I can come up with is the weather? you see it's very hot here compared to Britain, and the young female generation walk around in this hot weather dressed as though they're ready for the beach.

Which right minded guy wants a 28mm line blurring his field of view from the neck down?

That's the men, the women... well, I can't work that one out.

Do you have any seg peculiarities in other parts of the world?

All best, Clive[/QUOTE]

[chip anderson]

Since lid ht's vary, lower limbus might be more reliable, however, look at what the patient had in old glasses and ask if he was happy. i.e. if it was low ask if you feel you have been having to hold reading material too low. If exceptionally high: "was it in your way." If he was happy don't rock the boat. If not move to or closer to the norm.

Chip

[Sara]

Well opticians may differ in setting seg.heights.My personal practise is first to check type of seg.of bifocal lenses customer wants.Round seg I fit 1mm above lower eyelid.Flat-tops seg at lower eyelid margin.E style 1-2mm below lower eyelid.
Also patient occupation,vocational requirement and his height should be taken into consideration when deciding his seg height.
Thanks,
Sara

[Homer]

Originally posted by Clive Noble:

Which right minded guy wants a 28mm line blurring his field of view from the neck down?

It seems to me Clive, that it's a matter of distance. In Britan I would understand your comment but some cultures have smaller personal spaces and so the "DD" - i mean D 28 might be very much useful if set in the position you mentioned. ;)

[Maria]

Are you implying that British women aren't much to look at from the neck down? :)

Maria

PS You may not use the 'Mrs Thatcher, Queen Mother, Germaine Greer' argument in this matter.

[Homer]

Maria, my comment was about distance. "Brits" have the reputation of being a little standoffish which does not facilitate a clear picture through the highly set bifocals, other cultures naturally stand a little closer and this can enhance the view. So, come a little close and we'll take a good look. :) ;)

[Maria]

Just as long as you're not critisicing the Great British Pervert. Our perverts are the finest in the world. :)

Maria 'I don't wear patent shoes' K

[Homer]

You may have a point there! Course I'm not judge of such things. Do most of them wear sunglasses and shoes or just shoes?

Homer "I never got close enough to ge a good look" H.

[Maria]

If you are a girl growing up in a Catholic household, you are always warned by elderly relatives never to wear patent leather shoes. Because they are reflective, boys will be able to see up your dress.

[Homer]

Now us hayseed boys who were barefoot on the farm probably never would have thought of that. Guess that comes with social sophistication - something our ancestors forgot to pack onto the boat. Guess they were fleeing the Victorian era?

Nonetheless, this does bring up an interesting optical problem. Since patent leather shoes, while being highly refelctive, are generally a highly convex & cylinderical surface giving the same effect as a high minus lens with lots of cylinder, rendering the object quite small to say the least, just how many centemeters would the young boy have to hold his head from the shoe's surface to actually be able to see the big "E"?

[Corey Nicholls]

Does this mean I should flatten the toes of my shoes? I knew I was doing something wrong!

How I generally measure a flat top bifocal is-
* Mark a line on the frame insert at lower lid margin.
* Put a "Post it note" on the line to occlude the lower potion of the lens and trim the excess.
* Ask the patient if they feel they have enough room above the line.
* If they are not happy where the top of the "Post It" is you can move it up or down to where they are happy.
* When the Px is happy, I get them to sit down with some reading material in their hands (I usually pick out a kids book as they are usually full of big pictures).
* I then turn the "Post Its" around to occlude the distance, and ask if the have enough room under the line.
* When they agree I put the line there.

Doing this method I have found that I have not had one remake on a bifocal. I have found though that there is a lot of variance between patients as to where they feel comfortable with the positioning of the bifocal.

Hope this helps,

Corey.

[Joann Raytar]

Corey:

I like that technique. I have used Scotch Tape in the past but I like the idea of being able to flip the Post-It around to check the height.

[Corey Nicholls]

Jo,

The other good point to this technique is that it works well for both hyperopes and myopes. The patient also feels as though they have the line where they want it, not where I want it.

Corey.:D

[John R]

Just goes to show that you dont need to spend a lot of money just to get everything right. Simply is best sometimes.

Btw as to the "perverts" a caberdeen mac is a prerequsete for them with a pack of flash tied round their waist underneth with the string just loose enough to let it dangle down a few inches press studs instead of buttons help too for the quicker opening :hammer:

[harry a saake]

:hammer: Another idea to keep in mind is what kind of bifocal are you using in accordance to the prescription. I have always thought one of the worse things you can do is recommend a d-28 or 35 to a high plus patient. Knowing that the lens naturally magnifies everything, one has to think it also magnifies the very top of the bifocal, which in a flattop is the thickest part. If i remember right somewhere around the late 60,s i think it was Univis came up with this brilliant idea that they would have these little serrated marks on the top of the bifocal so you would know it was one of there lenses. As i recall that did not last long.

[Lyrix76]

Since lid ht's vary, lower limbus might be more reliable, however, look at what the patient had in old glasses and ask if he was happy. i.e. if it was low ask if you feel you have been having to hold reading material too low. If exceptionally high: "was it in your way." If he was happy don't rock the boat. If not move to or closer to the norm.

Chip

I agree w/Chip, if you've checked the original pair of bifocals that the patient has previously worn, then you've got a pretty good idea of where they're used to wearing it. I find asking alot of questions about their seg. height comfort zone is also helpful, making sure to avoid remakes whenever possible.

[Clive Noble]

I see this 6 year old thread has resurfaced.... well, 6 years later I've come to terms with the old saying, 'If you can't beat 'em. join 'em'

We have drastically reduced the quantity of Bifos these days, but when I take b/f heights I usually drop my (proper) findings by a couple of millimeters.

Never any problems any more............ funny ole world ehh?

[Chris Ryser]

Alway's fit as high as possible, depending on person of course. Needs some explaining and understanding by patiens that they will much more confortable by not having to raise the head when reading or working. However it will need a little more good will to adapt.

[William Stacy O.D.]

Which right minded guy wants a 28mm line blurring his field of view from the neck down?

Being a staunch defender of the venerable 28, I'd point out that the LINE does not blur the field from the neck down. It only gives a small horizontal sliver of blur. The seg itself blurs no more than the equivalent PAL if that was your point. The area of poor optics on a 28 is tiny compared to the areas of poor optics on any PAL.

w.stacy, o.d.