Anisometropia PALs?

[HarryChiling]

I believe that in the case of Aniso, the freeform designs would allow for definate improvements over traditional progressives. The free form lens can have the inset compensated based on the specific scenario, where the traditional lens will have the inset set in the lens and is in some cases compensated based on base curve (prescription range that will fit into that base) and/or add power (the amount of additional inset needed due to the add powers prismatic effect). The problem with aniso (higher power anyway) is that generally when picking a base I will match both R and L lenses, however since the Rx is so different the Rx may call for different bases and if the bases are the same one of the eyes is going to recieve additional error. That's my take on thigns what do you guys/gals think?

[OPTIDONN]

Sure I know that the potential is there but can or will the manufacturers of free form lenses generate them to certain specifications. Of course by using different placement of the addition etc. it will have an over all effect on design and blending and will lack symetry between the right and left lens. It could neutralize some of the prismatic effect but would these over all changes effect the performance?

[HarryChiling]

I don't know if they will or won't, but the potential is there. The bases could be different between both eyes reduceing the difference in magnification without having to worry about the corridor being offset too much or too little for the patients Rx. It's not even difficult when you break it down into what needs to be done. I could almost definately say yes it is being done right now. I would only really trust a freeform progressive that was solely on the back of the lens, this way the compensations don't have to account for any errors in the inset on the front part of the design plus the reduction in the keyhole effect is greatest in the back side desgins which would further help in this case.

[OPTIDONN]

Key hole effect is greatest in free form. Like looking through a key hole the closer it is to your eye the larger the field of view. I wouldn't be surprised if soon free form lenses get so advanced in their design incorporates correction for anisometropia. Doubt if any free form lenses available today would do much better than a traditional PAL for anisometropic patients. But the technology is there, designers just need to find away to incorporate this into existing designs. But with the reading addition higher, a consideration to neutralize some of the verical imbalance, than the other this could create a lens that may have "harder" design charachteristics than the other. I wonder if this unequal amount of surface astigmatism could cause a whole other set of problems. I'm sure that with extereme amounts, over 3.00 to 4.00 diopters, this lack of symetry could be pretty significant. Shouldn't be too far into the future that lens designers can significantly reduce this problem without the use of slab off.

[Andrew Weiss]

I'd love Darryl to get into this discussion. My sense is that Zeiss already is doing much of this in their Individual lens; it'd be great to find out specifically how they handle Rxs such as the one I posted earlier in this thread.

[drk]

I think you're on to something, Harry, Andrew, and Donn.

Now, we have to be specific: which clinical problem are we talking about?
a.) prismatic imbalance induced by anisometropic Rxs or
b.) anisekonia with isekonic lens design

With prismatic imbalance, there is no new territory to cover, here, I don't believe.

With isekonic lens design, then we get into a whole lotta fun.

As you know exhaustively, spectacle magnification is a combination of two phenomena: "power" magnification and "shape" magnification.

Of course the simplest and therefore most common option is to manipulater power magnification and deal with the resultant blur.

The more difficult task is to manipulate the variables in shape magnification: CT and BC.

-Manipulating CT only leads to physical/cosmetic drawbacks.

-Manipulating BC leads to optical drawbacks in SV and segmented MF by going off "corrected curve"

-Manipulating BC in a progressive (as noted) leads to further optical/design drawbacks:
a.) Inset is varied based on base curve chosen. If one is prescribing a steeper base (which is usually the case), then the patient is getting less inset than necessary.

b.) Very probably, there is a reduction in width of distance, intermediate, and near zone in the lens that has been fabricated with the "incorrectly steep" base curve. I'm assuming that a modern design will vary according to base curve (I'll call that the Percepta Principle).



So, how can individualized progressives help?
1.) I think by having overall wider near zones (if add has back surface component) and more precise design by prescription (atoricity on cylinder lenses).

2.) By being able to customize features, someday/now:
a.) Corridor length can be ordered "short"
b.) By applying the correct inset to match the near pd, modified by the appropriate prismatic power of the overall lens
c.) Probably by being able to match subtle design intricacies (Percepta Principle) to achieve the best match for the best binocular vision.



And, some day...gradient slab prism??????

Is this summary complete?

[eyepod]

The sources I have used are:

1.) College lecture notes, not in print
2.) In John Amos' Diagnosis and Management in Vision Care, Jimmy Bartlett's chapter "Anisometropia and Anisekonia" defines two levels of ansiometropia:
"...(1) low, in which the anisometropia does not exceed 2.00 D, and (2) high, in which the anisometropia exceeds 2.00D."

So, in reality, I think I owe eyepod an apology! :shiner: In fact, the 2D level is more of a clinical rule-of-thumb than a true defining criterion.

Interesting note: only about 3-4% of people have an anisometropia at the 1.5-2D or more level.


Borish's Clinical Refraction would be considered the "bible" on any refracting subject. I don't own a copy! It would be interesting what it says.

AWWWWWW, thanks, DRK!!

[HarryChiling]

Drk, sounds good. That is my greatest concern is the coridor placement when going off of manufacturers suggested base curves you run the risk of problems due to inset. I don't worry about the prism because like you've mentioned that area has been tread before and a slab can deal with any issues related to prism. The Zeiss Individual has variable inset and I believe others do as well, I know AWTECH with his Seiko Backside progressives can make the design just about anything you want so the Seiko lenses are also a great option. Just about any lens that's design is based upon the actual prescripiton (freeform) should do better than the traditional mono, multi or design by prescription series progressives. I say just about any (freeform), because I do see draw backs in using a design where the front surface has a progressive surface too it, because this surface is going to again have a set inset which will not be adequate, althogh they would still work better than the traditional lens due to low amounts of add powers on the front leading to wider widths throughout the lens, giving a little more leeway when it comes to corridor placement.

[Metronome]

Delete this post.

[Optowoman]

Don't know if this helps. My husband is over the two diopter mark in difference and ALL he can wear is the GP Wide. Could not adapt to Maui Jim (Image) Even after changing B.C. I can wear just about anything but he is the complete opposite. His dist. is plus and as long as he fit high and in his beloved GP he is happy. Can't abide short corriders at all. A bit disappointing as he is always my guinea pig for new lenses.

[bhess25]

ok lab person at work here back up....when we surface any progressive lens we dont use a prism ring to move the OC for any compensation, this usualy results in (in some cases) extreme prism in the lens..ive seen a -4.00 @ as much as 4dbu..same with a +3.00 seen them with as much as 4.00dbd..its much easier to compensate any prism with a FT or RT than with a progressive..typicaly even if you try to use the prism ring while surfacing a progressive the end result is the same...if a person has a problem with anisomatropia and is experiencing "double vision" through the reading..really the only way to fix this is by fitting a FT and using slab off prism...ok its safe to return to the area now!

P.S. the "double vision" in the reading is usualy experienced when the difference in RX is at or above 3.0 diopters...this is when a reverse slab on the more minus comes into play.

[tmorse]

... the "double vision" in the reading is usualy experienced when the difference in RX is at or above 3.0 diopters...this is when a reverse slab on the more minus comes into play.

Regular slab-off provides ^BU at the reading level, and if OD & OS are both minus, you slab the higher (or more) minus.

Reverse slab-off provides a ^BD, and is done to the lower minus. ;)

[bhess25]

Regular slab-off provides ^BU at the reading level, and if OD & OS are both minus, you slab the higher (or more) minus.

Reverse slab-off provides a ^BD, and is done to the lower minus. ;)

right..i thought i was detailed enough...thanks for catching that.:cheers:

[Win C]

Hi everyone, I have a patient who has difficulty adapting to her new Rx.

R pl /-1.50 x120 VA 6/9+
L +3.50 /-1.25 x5 VA 6/6

Add for both eyes is +2.50

Fitted her with XL transitions, previoulsly she was wearing Hoya GP.

The power difference for her previous RX was about 1.5D, but now it has increased to 3.5D. When she put on her new Rx , she felt uncomfortable and "giddy".

Prismatic difference measured thru the focimeter at the fitting height is about 1D BD. I put up a 1 prism BD in front of her right eye over her new progressve lens and she felt more comfortable for the distance. There is no noticeble difference for near.

I am thinking for grinding 1D BD for her right lens. Is this the correct approach? Any advice?

[bhess25]

Hi everyone, I have a patient who has difficulty adapting to her new Rx.

R pl /-1.50 x120 VA 6/9+
L +3.50 /-1.25 x5 VA 6/6

Add for both eyes is +2.50

Fitted her with XL transitions, previoulsly she was wearing Hoya GP.

The power difference for her previous RX was about 1.5D, but now it has increased to 3.5D. When she put on her new Rx , she felt uncomfortable and "giddy".

Prismatic difference measured thru the focimeter at the fitting height is about 1D BD. I put up a 1 prism BD in front of her right eye over her new progressve lens and she felt more comfortable for the distance. There is no noticeble difference for near.

I am thinking for grinding 1D BD for her right lens. Is this the correct approach? Any advice?

just taking a crack at this one (you might get a better response from one of the smarter people like harry, andrew or donn (not being a smart a**..i mean it)..being that the O.D. is a minus this would inherently have BU prism..and the O.S. being a plus would inherintly have BD prism...it might be easier to move the OC in the O.D. by grinding the prism there being that its the weaker Rx..to achieve the same effect in the O.S. being a +3.50 may lead to some thickness issues....my thoughts...1BD is a great idea in the O.D...what do the brains think?

[Win C]

just taking a crack at this one (you might get a better response from one of the smarter people like harry, andrew or donn (not being a smart a**..i mean it)..being that the O.D. is a minus this would inherently have BU prism..and the O.S. being a plus would inherintly have BD prism...it might be easier to move the OC in the O.D. by grinding the prism there being that its the weaker Rx..to achieve the same effect in the O.S. being a +3.50 may lead to some thickness issues....my thoughts...1BD is a great idea in the O.D...what do the brains think?

By grinding 1 BD in the distance solves the distance problem. What about the reading? :o

In the past I did not even do any prism compensation for anisometropia as much as 4D and did not have any problem.

[Win C]

I just dispensed a pair of Zeiss Individuals to a patient with the following Rx:

R: -1.25 -3.75 x 092, 1.0 prism down
L: -6.75 -2.00 X 090, 1.0 prism up
Add 2.50

She had been wearing progressives before with some difficulty. She put on the new ones and loved them immediately.

For years I relied on Rodenstock's Multigressiv II as my "go-to" lens for anesometropic patients who insisted on having progressives. Since it was discontinued, I've been using the Zeiss Individual and Individual Short with similar success.

those prism are usually ground in the distance part of the prescription?

at the prism reference point, there is no prismatic difference. when the prism is ground in , will there be a prismatic difference in the prism ref point?

[Just Optician]

Hi Eyepod,
R -1.50
L-0.75
Add+1.50
Patient used to have Vx.Physio, feel uncomfortable at intermediate?

By the way,could you guys tell me more about anisometropia patient which PALs more suitable for those patient with huge different power,One eye myopic, one hyperopic and with a lot of astigmatism

i mean which PALs suitable in which cases

I don't know what their previous rx was but in this prescription if the patient removed their glasses at the computer it would act as a monovision where the right eye would do the reading and the left eye would see the computer screen. If you compare the width the patient is seeing with the naked eye to any progressive I would complain too about the intermediate. Anisometropia is not the issue nor is it the type of progressive, (nor would a change in prism thining) ,it is a factor of the patient's present rx. I would explain that their glasses offer good stereo vision where both eyes see at all distances but the intermediate zone will never be as wide as the naked eye. When they reach a stronger add next time their prescription changes they'll probably work better.

Just an opinion

[bhess25]

By grinding 1 BD in the distance solves the distance problem. What about the reading? :o

In the past I did not even do any prism compensation for anisometropia as much as 4D and did not have any problem.

grinding the prism in would only comp. distance, with no effect on reading...the patients reading wouldnt change at all.
besides the patient isnt having any problems with the reading, with or without prism!

also some people can absorb prismatic differences in anisometropia better than others.I recently had to do a slab off for a patient that only had 1.00^ difference in Rx between eyes.

the Rx read like this

O.D. -1.50 -.50 X 180
O.S. +.50 _.50 X 13
Add +2.25

she experienced the usual diplopia with the reading card there were 2 #1's, one high one low.

[bhess25]

those prism are usually ground in the distance part of the prescription?

at the prism reference point, there is no prismatic difference. when the prism is ground in , will there be a prismatic difference in the prism ref point?

yes

and

yes

[rdcoach5]

I just dispensed a pair of Zeiss Individuals to a patient with the following Rx:

R: -1.25 -3.75 x 092, 1.0 prism down
L: -6.75 -2.00 X 090, 1.0 prism up
Add 2.50

She had been wearing progressives before with some difficulty. She put on the new ones and loved them immediately.

For years I relied on Rodenstock's Multigressiv II as my "go-to" lens for anesometropic patients who insisted on having progressives. Since it was discontinued, I've been using the Zeiss Individual and Individual Short with similar success.

You didn't mention if you used high index, but I think that's the only way the Individual is made.The higher the index the better . The Individual probably has the least peripheral distortion which undoubtedly helps. I would think that the Definity would also be a good choice.

[Robert Martellaro]

Hi everyone, I have a patient who has difficulty adapting to her new Rx.

R pl /-1.50 x120 VA 6/9+
L +3.50 /-1.25 x5 VA 6/6

Add for both eyes is +2.50

Fitted her with XL transitions, previoulsly she was wearing Hoya GP.

The power difference for her previous RX was about 1.5D, but now it has increased to 3.5D. When she put on her new Rx , she felt uncomfortable and "giddy".

Prismatic difference measured thru the focimeter at the fitting height is about 1D BD. I put up a 1 prism BD in front of her right eye over her new progressve lens and she felt more comfortable for the distance. There is no noticeble difference for near.

I am thinking for grinding 1D BD for her right lens. Is this the correct approach?

Maybe. This will eliminate VI on the distance gaze, but will increase the VI on the near gaze. Doing this without a slab might cause more harm than good. However, if you slab the lens, you'll need to compensate for the 1^ BD in right eye by increasing slab-off an extra 1^BU (assuming a custom slab on the right eye). If there is vertical prescribed prism, then add this to the prism that was used to eliminate the distance VI. The (adjusted) slab prism remains the same. (Note- the prescribed prism might not measure correctly at the PRP, but will read correctly at the FC and near vision point).

http://www.zeiss.de/4125680f0053a38d...256cfd002b9e3d

Another approach is to use a short corridor PAL that has a 2mm distance from the FC to the PRP. This minimizes VI on the distance, and also for the near VI by reducing the reading depth. Or, use a standard PAL for general purpose use, and readers for extended close tasks (I've found this to be best solution for most of my clients). If there is reduced VA due to pathology, I'd strongly consider segmented multifocals, especially if the add is above +2.75.

[HarryChiling]

I just recently had a patient with a Rx of:

-1.75 -0.50 x 175
+1.75 -0.50 x 180
Add +2.00

DPD = 29.5/30
NPD = 27.5/26

Interestingly enough the lenses were made using a progressive that had a 2.5mm inset now looking at the powers she would have less issues with ocular rotation in the right eye and more in the left eye if we factor the power and the prism into it. This became evident when I took the NPD and DPD's seperately. Her eyes roated 2mm in OD and 4mm in OS when viewing up close. At first I ordered this job complete since she wanted AR, the lens came back with a flatter base no doubt optimizd for the right eye. She is having a hard time seeing out of the left though and is really having a problem with it. I looked through my lens book and the ovation I believe has a 3.3mm inset, this makes it easier for the left eye and makes it so the right eye needs to work to get into the sweet spot. I also chose to split the bases to optimize for each lens seperately. I'll post when she picks them up and let you all know what went down.

[TradeoffH8er]

This became evident when I took the NPD and DPD's seperately. Her eyes roated 2mm in OD and 4mm in OS when viewing up close.

Harry, what was the reading distance (lens to reading target) you used? Also did you make sure that the reading distance was identical for both eyes?