Which progressive design for high fit heights?

[drk]

Question to 'Board:

If the fitting height is NOT the modern 18mm norm, but 22 or more, what designs make more sense?

Do we use the recent, GT2/Physio/etc. designs? Are they not optimized for "today's frames", though, giving up corridor length and compromising distance zones?

Or, do we use the earlier Comfort, Genesis, Gradal Top designs?

Thoughts?


(I think Definity may be a good answer, here.)

[chip anderson]

Mostly fitting heights are for minimum fitting height if you have more than this, so much the better. I wouldn't use a "shortie (14mm or less) although it might work fine. The idea behind minimum fitting height is to make sure enough plus available for the patient to see at 14 to 18 inches, it doesn't continue to get stronger (or weaker) than marked power from being too high. Patient probably can't hold material in close enough to his chest to see much below 25mm (if that) anyway.
Probably different rules apply if the patient is the size of Shakel O'Neal though.

Chip

No need to use high octane if the compression ratio is less than 6 to 1.

If I have offended any ladies with this post I am deeply appologetic. If I have offended any women, who cares.

[Fezz]

I don't really change my lens of choice for high fits. Obviously we wouldn't use a Hoya Summit CD or Varilux Ellipse. I would suggest just use your judgement like you do in any other situation. What are the patients needs? How are they using the lens. You know..

You are on the right track with the earlier lenses. Heck..most of them came out with 22 or 24 mm minimum seg heights when they where first introduced. Just be careful with cut out. It pays to always double check with your cut out charts to be sure the lens and frame combo will work. I am seeing more and more folks using there older frames for back-ups and sunglasses, and have seen more than a few aviators that I had to play around with various lens designs to get them to work.

[bren_03825]

I don't really change my lens of choice for high fits. Obviously we wouldn't use a Hoya Summit CD or Varilux Ellipse. I would suggest just use your judgement like you do in any other situation. What are the patients needs? How are they using the lens. You know..


Dead Bang On, Fezz
:bbg:

[Scott R]

Pleanty of patients want large avaitor SGs. Hoya, Zeiss, Essilor, Shamir and other manufactures top shelf progressives give pts the performance they are looking for at 25+ heights as long as the blank cuts out. Just watch out for too great of a wrap.

[Andrew Weiss]

I notice alot more peripheral astigmatism in short-corridor lenses. If I remember correctly, when Rodenstock came out with the XS they suggested that it not be fit if the height exceeded 20 mm, and I tend to follow that as a general rule.

While I generally go with lenses with fitting heights of 20 or more if the frame allows that, I may use a shorter-corridor lens like the GT2 or the Rodenstock Life2 if the patient wants the reading area higher up.

Of course, in frames that large the Definity has that "ground view advantage" going on when fit at heights greater than 24 (it does limit the size of the reading area, though).

drk, you're an experienced and skilled dispenser as well as OD -- I know everything will work just fine if you use your best judgment. :bbg:

[tntborden]

If I'm really not sure I look here.

http://www.optometry.osu.edu/research/coor/4059.cfm

[drk]

Yeah, but isn't it true that if a lens is designed with an "x mm" corridor, that using it in a frame that would allow "x+4 mm" corridor will have some drawback?

Can't we generally say that the shorter corridor designs (all other variables held constant) will have either a harder periphery below the 180 or a softer distance portion?

If so, then why not use a design that manages all that junk over a larger area?

[Robert Martellaro]

Question to 'Board:

If the fitting height is NOT the modern 18mm norm, but 22 or more, what designs make more sense?In general, I choose a corridor length that provides the best vision and comfort i.e., Adds over +1.75 with frequent close tasks get the shorter corridors, low frequency close tasks get the longer corridors. In other words, I establish the visual needs first, and then select a frame that will accommodate the lens design. I don't believe we'll see any notable problems fitting short designs at 22mm, as long as they need that type of lens, and the vertex distance is kept as short as possible.

[drk]

Good way to think about it. Thanks, all.

[dweinstein]

In my experience, the customers that come in looking for that old school double bar large frame look are already wearing either Zeiss Gradal Top or Varilux Comfort with no problems. Those are my go-to lenses for seg heights 25+. For the longest time I remember both of those lenses having minimum fitting heights of 22, and I don't believe the designs actually changed when the recommended heights were brought down to 18.

[chansc]

the best solution for this situation, if the patient's willing to pay more, impression free sign is the best, because the reading portion and distance portion can be adjusted according the fitting that you need, there's no specified fitting on free sign.basically you just like the designer of the lens. you may consider about it

[Freedom]

For standdard PALs ... may be 14 mm. corridor

22 mm. is optimum fitting high.
20 mm. is recommend fitting high.
18 mm. is minimum fitting high.

IF have more than 22 mm. THAT say. .... Big frame
Big frame will have more distortion in peripheral field

But suitable frame for PALs that have B high about 32-34 mm. is best
Distotion in peripheral field will not stay on the frame.

[rdcoach5]

In general, I choose a corridor length that provides the best vision and comfort i.e., Adds over +1.75 with frequent close tasks get the shorter corridors, low frequency close tasks get the longer corridors. In other words, I establish the visual needs first, and then select a frame that will accommodate the lens design. I don't believe we'll see any notable problems fitting short designs at 22mm, as long as they need that type of lens, and the vertex distance is kept as short as possible.

I agree. I replaced a pt's Comfort with the GT2, thinking I had upgraded him.He did get a wider near zone and less peripheral distortion, but didn't like the fact that it was a short corridor. He's tall and found he was tilting down a lot on downgaze, compared to the long corridor. He's also retired and doesn't do that much computer. I re-adjusted them a lot lower and made him happy. But, a long corridor free-form would give him less peripheral distortion and also lengthen the corridor to adjust for the higher fit. I woild think that the Definity woild work, also, as it is a more gradual change in add power.

[AdmiralKnight]

Your safest bet would be to go with lenses with higher minimum heights. You have to be carefull with some of the newer short lenses, because not only do they have minimum recomended heights, but some have recommended MAX heights as well (The Ellipse for example with an 18mm "max").

[Barry Santini]

I think that since Varilux Comfort was originally recommended for 22mm high, but Essilor found out that people had acceptable "utility" at 18mm high, that this is the primary reason for Comfort's continued acceptance: It's design has the forgiveness of a longer-corridor (with respect to peripheral aberrations) with the utility of an 18mm Fitting height progressive.

For whatever reasons, engineered or otherwise....

I'd select Comfort (or Sola Percepta, if still around)

FWIW

Barry

[bhess25]

ummm AO pro anyone?...24mm fitting height!!

[chip anderson]

Any of them except the "Shorties" and the computer designs.