New glasses causing trapezoidal distortions

[dadol...@gmail.com]

A bit of history:
Age 27
Been wearing glasses since middle school, nearsighted, getting
slightly moreso over time.
I wear only glasses. I think this new pair is my 6th.
This new pair is my 2nd polycarbonate on Silhouette rimless frames.

As I recently moved, this set of glasses was made by a new shop and
eye exam done by a new doctor.

I'm pretty sure this new set has some astigmatism (cylindrical)
correction that I think, based on what I've read in other threads here
and elsewhere, I may not need, or they corrected it poorly, or too
much.

The new glasses cause SEVERE trapezoidal distortion, like this: \ /
instead of | |
It's very distracting when using a computer (guess what I do for a
living) or watching TV, and disorienting when walking or driving.
My previous pair of glasses do not exhibit this AT ALL.

There is also bowing at the edges, such that it looks like ( on the
left of the lens and ) on the right of the lens instead of |
My previous pair had some distortion of this type, but I would say it
was less than half as much. There is also more color mis-alignment in
the new pair at the edges, though I understand that is just the nature
of polycarb. This effect doesn't bother me all that much.

I've only worn the new glasses for about a day. I think I would prefer
to get them redone with the same prescription, sans astigmatism
correction, as the older glasses only look ever-so-slightly-blurrier
at distance.

What do the experts here recommend? I don't have the exact
prescription specs for the new and old pair in front of me, but I will
get them from the doctor if you all think it would help.

Would a different shape lens help? The old pair is very oval shaped,
whereas the new pair is a bit more squarish on the top half. Would the
shape of the lens cause the trapezoidal distortion?

At this point the old glasses are significantly more comfortable to
see through, only downside is faraway objects are ever so slightly
harder to see clearly. I really only wanted new glasses to get a pair
that isn't scratched up, and the ability to have a "backup pair" that
works very well (my set of glasses three-ago is pretty hard to see
through, quite blurry).

I would love to try non-polycarb but the glasses shop said the rimless
Silhouette frames require polycarb as they have to drill into the lens
to mount them. Is this correct?

The glasses shop (same place the eye doc is located) told me after I
complained today that I should try the new ones for a week so see if
my eyes/brain adjust. Considering I want to be able to use my old
glasses as a backup, I hesitate to do this. I believe at this point I
would prefer to just get the new lenses remade in my old prescription,
or in the new but without the cylindrical/astigmatism correction (if
that is what causes the trapezoid thing), and I should be able to get
this done free under the glasses warranty.

Thanks much!
- David

[otis...@embarqmail.com]

Dear Friend,

You might have an adverse reaction to excessive astigmatism (Cyl).
"correction".

To find out, just ask them to convert to "spherical
equivalent" (consistent with passing the DMV Snellen), and see if that
works for you.

Also, you might wish to post your "new" prescription.

You OD will be pleased to acceed to your sincere request.

[Mark A]

<dadol...@gmail.com> wrote in message
news:378ea88a-6c19-436b...@w40g2000yqd.googlegroups.com...

It would help to post your Rx. There are other lens materials such as Trivex
(sold as Hoya Phoenix and other names by other lens manufacturers) that have
similar tensile strength as polycarb but much better optics. If you Rx is
mild this might be a good choice, especially if you could get it in a
spherical lens design (not aspherical). In addition to problems with
polycarb, aspherical lens designs can also cause the distortions you are
experiencing, but they are often used for higher Rx powers.

[dadol...@gmail.com]

Thanks everyone. I should be able to get my new in writing tomorrow
and the old one shortly thereafter.
I will make a note to ask about Trivex as a "drillable" alternative to
polycarbonate. If they don't carry it, do you have a recommendation
for a place that could make Trivex lenses for Silhouette frames? I'm
in the Twin Cities area, Minnesota...

One other thing I wasn't clear about above... I'm 99% sure my old
glasses have ZERO astigmatism correction.

[Mark A]

<dadol...@gmail.com> wrote in message
news:03e7b74f-3b97-44ef...@h11g2000yqb.googlegroups.com...

Hoya uses Trivex lens material (they call it Phoenix). If you have a mild Rx
(you did not post your Rx) the a spherical design like the Hoya HiLux lens
in Phoenix (Trivex) would be best. Any provider that can order from a Hoya
lab can get this lens.

Other lens manufacturers that have Trivex include Younger Optics Trilogy,
Augen Optics Centurion, Exceilte TVX, Shore Lens.

[Neil Brooks]

Just so you know....

Nobody's ever gained anything by paying attention to Otis.

Quite a few have been harmed, though.

[dadol...@gmail.com]

This statement has zero credibility because it doesn't say "why" Otis'
advice is wrong.

My "new" prescription is:
OD: Sphere = -2.50, Cylinder = -0.50, Axis = 115
OD: Sphere = -2.50, Cylinder = -0.50, Axis = 047

My "old" prescription is in the mail on its way to me, should have it
tomorrow or Tuesday.

So I assume if I ask them to redo the lenses as "spherical" they would
just ignore the Cylinder component in the Rx?

[Mark A]

> My "new" prescription is:
> OD: Sphere = -2.50, Cylinder = -0.50, Axis = 115
> OD: Sphere = -2.50, Cylinder = -0.50, Axis = 047
>
>
> My "old" prescription is in the mail on its way to me, should have it
> tomorrow or Tuesday.
>
> So I assume if I ask them to redo the lenses as "spherical" they would
> just ignore the Cylinder component in the Rx?

No, a spherical lens design can have cylinder correction for astigmatism.
Not sure where you got that idea (but I have Otis blocked since he is a
quack).

With that Rx (or close to it) you would do quite well with a Trivex lens
material (would not be too thick).

[dadol...@gmail.com]

On May 23, 1:28 am, "Mark A" <some...@someone.com> wrote:
> > My "new" prescription is:
> > OD: Sphere = -2.50, Cylinder = -0.50, Axis = 115
> > OD: Sphere = -2.50, Cylinder = -0.50, Axis = 047
>
> > My "old" prescription is in the mail on its way to me, should have it
> > tomorrow or Tuesday.
>
> > So I assume if I ask them to redo the lenses as "spherical" they would
> > just ignore the Cylinder component in the Rx?
>
> No, a spherical lens design can have cylinder correction for astigmatism.
> Not sure where you got that idea

I just got it from looking up definitions of "spherical" and
"aspherical" and "cylinrical" lenses and corrections. I guess I got it
wrong.

Could you explain the difference between a "spherical" lens design and
an "aspherical" lens design and how they are both apparently able to
correct for Sphere and Cylinder in a prescription?

Thanks much!

[dadol...@gmail.com]

Also, if "spherical" and "aspherical" can both correct for Sphere and
Cylinder, how do you know that my new glasses are aspherical? How
would I be able to determine it myself?

Sorry for so many questions, just trying to arm myself with info for
when I go back to the doc. :)

[otis...@embarqmail.com]

Dear David,

Subject: Cyl -- is it necessary?

I am an engineer -- interested in science and prevention of a negative
STATE for the eye. I have no interest in "medicine", and prefer
neutral words to discuss the natural eye's proven behavior. (Just to
be clear on that point.)

You "astigmatism" is very mild at 1/2 diopter. There are ODs who
would not even bother with it, and would provide a "spherical" with no
cyl.

But here is how you "convert".

My "new" prescription is:
OD: Sphere = -2.50, Cylinder = -0.50, Axis = 115
OD: Sphere = -2.50, Cylinder = -0.50, Axis = 047

The exam typically will use a "sperical" lens FIRST, to get you to
20/20. This is probably the case with you. THEN, some cyl will be
added to see if your Snellen can be subjectively made sharper with
that cyl lens -- added to the first measurement.

Here is how you do the conversion. Just take 1/2 the "Cyl" value and
add it to the stated Sphere value, i.e., the "new" prescription would
be:

OD: Sphere EQUIVALENT -2.75
OS: Shpere EQUIVALENT -2.75

Also, OD is right eye, OS is left eye.

I personally use my own trial lens kit, and check for 20/20 using a
spherical lens.

Give the low value of "cyl", the choice would be yours.

Also, you are going to get a lot of "negative people" posting on a
pubic site, so you will have to "factor out", there poor judgments.

> when I go back to the doc. :)- Hide quoted text -
>
> - Show quoted text -

[Mark A]

<dadol...@gmail.com> wrote in message
news:75b61cbd-844e-4e52...@q16g2000yqg.googlegroups.com...

> Also, if "spherical" and "aspherical" can both correct for Sphere and
> Cylinder, how do you know that my new glasses are aspherical? How
> would I be able to determine it myself?
>
> Sorry for so many questions, just trying to arm myself with info for
> when I go back to the doc. :)

An aspherical lens design refers to curvature on the front of the lens,
which is not constant across the entire surface with aspherical (note that I
said "constant" because all eyewear lenses have a curvature). Spherical lens
designs are appropriate for low power Rx's where the benefits of an
aspherical design are not needed (such as making the edges of the lens
thinner). Don't worry about the definitions. The bottom line is that a
spherical lens design will produce less noticeable distortion of the type
you mentioned, and would be appropriate if that is very important to you
and/or you are not able/willing to adapt to a aspherical design.

I am not sure where you are getting your lenses from (the OD office or at an
optical shop), but any of them should know the difference between a
spherical lens design and an aspherical lens design. If they don't know,
then go some where else immediately (your OD is required by law to give you
the Rx to take with you upon request at no extra charge) or ask to speak to
the chief optician in the store. Many opticians will sell an aspherical
polycarb design because they can charge more for it, and because it is sort
of a one-model-fits-all solution that is pushed by companies that hire
idiots to select your lens. Many aspheric designs also use high index lens
materials (which also makes the lens thinner). Both the polycarb (1.59
index) and aspherical design are somewhat overkill for your Rx and will
produce much more distortion than a spherical lens in Trivex or regular
plastic (CR-39) material.

In the Hoya SV line, the HiLux is spherical, and the Nulux and Nulux EP are
aspherical. You can find this information on the website of any lens
manufacturer.

[Neil Brooks]

On May 22, 11:16 pm, dadolph...@gmail.com wrote:
> On May 22, 11:07 am, Neil Brooks <neil0...@yahoo.com> wrote:
>
> > Just so you know....
>
> > Nobody's ever gained anything by paying attention to Otis.
>
> > Quite a few have been harmed, though.
>
> This statement has zero credibility because it doesn't say "why" Otis'
> advice is wrong.

Heads up was given. Do with it what you will....

Spend five minutes looking around this NG, and ye shall see (pun
intended).

[Mike Tyner]

<otis...@embarqmail.com> wrote

> Also, you are going to get a lot of "negative people" posting on a
> pubic site, so you will have to "factor out", there poor judgments.

Start by eliminating the ones who can't spell or punctuate.

-MT

[dadol...@gmail.com]

On May 23, 9:56 am, "Mark A" <some...@someone.com> wrote:

> An aspherical lens design refers to curvature on the front of the lens,
> which is not constant across the entire surface with aspherical (note that I
> said "constant" because all eyewear lenses have a curvature). Spherical lens
> designs are appropriate for low power Rx's where the benefits of an
> aspherical design are not needed (such as making the edges of the lens
> thinner). Don't worry about the definitions. The bottom line is that a
> spherical lens design will produce less noticeable distortion of the type
> you mentioned, and would be appropriate if that is very important to you
> and/or you are not able/willing to adapt to a aspherical design.
>
> I am not sure where you are getting your lenses from (the OD office or at an
> optical shop), but any of them should know the difference between a
> spherical lens design and an aspherical lens design. If they don't know,
> then go some where else immediately (your OD is required by law to give you
> the Rx to take with you upon request at no extra charge) or ask to speak to
> the chief optician in the store. Many opticians will sell an aspherical
> polycarb design because they can charge more for it, and because it is sort
> of a one-model-fits-all solution that is pushed by companies that hire
> idiots to select your lens. Many aspheric designs also use high index lens
> materials (which also makes the lens thinner). Both the polycarb (1.59
> index) and aspherical design are somewhat overkill for your Rx and will
> produce much more distortion than a spherical lens in Trivex or regular
> plastic (CR-39) material.

The place I'm going is "Yankee Eye Clinic" in Eagan, MN. They have a
staff of docs as well as an in-house lab. Hopefully they'd be willing
to outsource a Trivex lens if they wont do it in their own shop.
http://www.yankeeeyeclinic.com/

>
> In the Hoya SV line, the HiLux is spherical, and the Nulux and Nulux EP are
> aspherical. You can find this information on the website of any lens
> manufacturer.

I will definitely ask about getting a spherical lens made, hopefully
they will do Trivex instead of polycarb for a reasonable price.
I have VSP coverage which I have been told will cover a replacement
lens to fix a bad prescription, though I'm not sure that would also
cover a change in lens material. I'm guessing probably not. However if
Trivex is reasonable I think it will be worth the cost to upgrade, as
I tend to wear the same pair of glasses a long pair of time because my
eyes don't change much....

Here is my "old" prescription, it is almost 5 years old:
OD = Sphere -2.25
OS = Sphere -2.25
Cylinder is blank.

The sphere is remarkably close to the new prescription (-2.50).
Should I just ask them to make me lenses with no Cylinder as such:
OD = Sphere -2.50
OS = Sphere -2.50

Or is Otis correct in how he calculates the "spherical
equivalent" ("Just take 1/2 the "Cyl" value and add it to the stated
Sphere value") which would instead result in:
OD = Sphere -2.75
OS = Sphere -2.75

Again, many thanks for all the input. I'm glad I can be armed with all
this info when I head back to Yankee Eye Clinic next week!

Cheers,
David

[Mark A]

<dadol...@gmail.com> wrote in message
news:0b72346b-11b9-46ab...@j32g2000yqh.googlegroups.com...

> The sphere is remarkably close to the new prescription (-2.50).
> Should I just ask them to make me lenses with no Cylinder as such:
> OD = Sphere -2.50
> OS = Sphere -2.50
>
> Or is Otis correct in how he calculates the "spherical
> equivalent" ("Just take 1/2 the "Cyl" value and add it to the stated
> Sphere value") which would instead result in:
> OD = Sphere -2.75
> OS = Sphere -2.75

I don't understand why you want to avoid a cylinder correction for
astigmatism. If it is done correctly, it should not cause any distortion.
You need to focus on the lens design and the lens material and have the lens
made to your original Rx unless the OD thinks it needs to be revised.

Most OD offices and optical shops send out the Rx to a separate lab to make
the lens to your Rx. Some of them will cut the lens to fit the frame when it
comes back from the lab (all lenses are round until the are cut to fit the
frame), and others will have the lab do the whole thing (they send the frame
to the lab). Some stores deal with multiple labs to get various products,
but many like to stick with certain brands (and the associated labs) even
though they could deal with multiple labs if they wanted to. Some labs deal
with multiple lens manufacturers, and some are owned by lens manufacturer
and only make their own brands (I believe Hoya is like this).

The exception to that are the large chains which advertise 1 hour glasses
and have an in store lab. I would avoid them like the plague since the
quality of the lens designs are very mediocre and the choices are limited to
their house brands (unless they send it out to a lab).

Even Walmart sends out their lenses to a lab (although it is a lab owned by
Walmart).

[Dan Abel]

In article
<be7e1936-4045-4c07...@w40g2000yqd.googlegroups.com>,
dadol...@gmail.com wrote:

> On May 23, 1:28�am, "Mark A" <some...@someone.com> wrote:
> > > My "new" prescription is:
> > > OD: Sphere = -2.50, Cylinder = -0.50, Axis = 115
> > > OD: Sphere = -2.50, Cylinder = -0.50, Axis = 047

> > No, a spherical lens design can have cylinder correction for astigmatism.

> > Not sure where you got that idea
>
> I just got it from looking up definitions of "spherical" and
> "aspherical" and "cylinrical" lenses and corrections. I guess I got it
> wrong.
>
> Could you explain the difference between a "spherical" lens design and
> an "aspherical" lens design and how they are both apparently able to
> correct for Sphere and Cylinder in a prescription?

I certainly don't understand it very well, but my best explanation is
that the "sphere" and "cylinder" in your prescription refer to the
optical characteristics of your eye, and the "spherical" and
"aspherical" that I think are being discussed here refer only to part of
the eyeglasses that might be used for correction. It's unfortunate, but
vision professionals, as well as all other doctors, use a kind of
"shorthand". The same basic words are used, but they have a completely
different meaning depending what they refer to.

--
Dan Abel
Petaluma, California USA
da...@sonic.net

[Dan Abel]

In article
<355e035c-dcbd-4092...@k19g2000prh.googlegroups.com>,
Neil Brooks <neil...@yahoo.com> wrote:

Just to add my two cents, Otis is crazy. He is a very kind man and
means well. He has a long history on this group.

I haven't read his response (most here have him killfiled), but the
little part I saw seemed reasonable. If you go to your doctor and
cannot tolerate astigmatism correction, the doctor will decide what to
do.

If you decide to "tweak" your prescription, by law in the US, the
optician will refuse. Whether you want to follow Otis's advice, or just
dump the cylinder, the optician is not allowed to give you a different
prescription.

[dadol...@gmail.com]

Thanks again for all the helpful responses. I will let you know how it
turns out later this week.

Cheers,
Dave

[dadol...@gmail.com]

OK, went back to the eye clinic today. Had great discussion with the
doc as well as folks in the lab. Results:
New lenses being made with the following changes:
- Cylinder dropped from the prescription
- Base curve adjusted to match old glasses
- Trivex instead of Polycarb

Apparently my old glasses have an unusually low base curve, it looks
pretty much flat to the naked eye. The new glasses were made with a
much bigger base curve because apparently that is "normal".

I'm pretty confident I will be much happier with the remake. Best of
all, cost to me is ZERO, even with the material change.

[Mark A]

<dadol...@gmail.com> wrote in message
news:a761113d-a1c2-4a45...@k38g2000yqh.googlegroups.com...

The part about the base curve is BS. They probably just switched to a
spherical lens design or had the wrong base curve. You do no need a big base
curve with your mild Rx.

Most lens manufacturer's and labs will do a remake for free. This is built
into the cost of the product and the actual material cost to the
manufacturer is usually negligible.

I would be interested in knowing exactly what brand of Trivex lens you got,
and exactly what model lens it is. There are only a limited number of lens
manufacturers who offer Trivex, unlike polycarb which is offered by everyone
since its patent has expired.

[Dan Abel]

In article
<a761113d-a1c2-4a45...@k38g2000yqh.googlegroups.com>,
dadol...@gmail.com wrote:

Great! Please let us know how it comes out.

[Mike Tyner]

<dadol...@gmail.com> wrote

> I'm pretty confident I will be much happier with the remake. Best of
> all, cost to me is ZERO, even with the material change.

Well, also the night-driving acuity you lost from that half-diopter of cyl.

I wonder why flat base curves aren't used very often.

Young people can get used to most anything.

-MT

[dadol...@gmail.com]

On May 27, 5:51 pm, "Mark A" <some...@someone.com> wrote:
>
> The part about the base curve is BS. They probably just switched to a
> spherical lens design or had the wrong base curve. You do no need a big base
> curve with your mild Rx.

Are you saying the "BS" is that a flat base curve is unusual? Or that
remaking with a flat base curve (like my old glasses have) will help
is BS?

> Most lens manufacturer's and labs will do a remake for free. This is built
> into the cost of the product and the actual material cost to the
> manufacturer is usually negligible.

The remake is free because it's covered by VSP warranty.

> I would be interested in knowing exactly what brand of Trivex lens you got,
> and exactly what model lens it is.  There are only a limited number of lens
> manufacturers who offer Trivex, unlike polycarb which is offered by everyone
> since its patent has expired.

I will make sure to ask when they arrive.

Mike, I can still see 20/20 with my "old" glasses, never had any
trouble seeing or driving at night, and I do plenty of it...

[Mark A]

<dadol...@gmail.com> wrote in message
news:d86d93d5-c86a-4c17...@y17g2000yqn.googlegroups.com...

> Are you saying the "BS" is that a flat base curve is unusual? Or that
> remaking with a flat base curve (like my old glasses have) will help
> is BS?

I am saying that if your new glasses had big base curve for a mild Rx that
was probably a mistake by the person who made the lens, or it was actually
an aspheric lens and not a base curve issue. I agree that having a flatter
base curve will probably help with your Rx.

> The remake is free because it's covered by VSP warranty.

Hmmm. I think someone without that plan could have gotten a free remake if
there was a problem with the lens. For progressive lenses, one free remake
is virtually standard industry practice regardless of form of payment. Many
optical shops have a money back guarantee for all lenses, which is the same
as a free remake.

You would surprised how little the frames and lenses actually cost to make
on a per unit basis. Part of the price you pay is for remakes when there is
a problem.

[Mike Tyner]

<dadol...@gmail.com> wrote

> Mike, I can still see 20/20 with my "old" glasses, never had any
> trouble seeing or driving at night, and I do plenty of it...

I don't doubt you.

-MT

[bluegrass native, UK alum '76]

Lets be clear on a couple of points. The functionality and behavior
of the human eye is all about science and medicine. Otis (the
"wacko") Brown likes to draw false distinctions about science versus
medicine. Medicine is the application of science to the function and
health of the human eye. Otis just doesn't get it. He likes to make
up his own language and definitions.

The "proven" behaviors of the eye that Otis likes to talk about were
in animals-- not humans. In some older studies, chicken, shrew and
monkey eyes have been manipulated surgically and shown to behave in
ways that the scientific literature has shown DO NOT APPLY to the
human eye. So Otis' "proven" remarks may be proven for four-legged
experimental animals but not for humans. Vision scientists have
clearly shown that the human eye behaves differently in significant
ways compared to animal eyes but Otis ignors this fact.

TO ALL READERS: BEWARE-- there are wacko posters in this forum like
Otis Brown and Zetsu who continually post misinformation. Otis Brown
is an old retired zealot who wears thick nearsighted glasses yet he
tries to tell people how to avoid nearsightedness!! Why should anyone
listen to him-- it obviously didn't work for him. And Zetsu is a kid
who is a social cast-off who sits in front of his computer all day and
night trying to stir-up trouble. Get a life Zetsu-- meet some kids
your own age and develop some healthy social interests.

[dadol...@gmail.com]

Last post here for now - new glasses arrived and they are great. No
noticeable distortion when compared to my old glasses, just crisper
vision!

Thanks everyone!

[David Combs]

In article <MOydnSFDL5wLUIDX...@giganews.com>,

Mike Tyner <mty...@mindspring.com> wrote:
>
><dadol...@gmail.com> wrote
>
>> I'm pretty confident I will be much happier with the remake. Best of
>> all, cost to me is ZERO, even with the material change.
>
>Well, also the night-driving acuity you lost from that half-diopter of cyl.

For us non-optics people, could you explain that -- seems to me
that if "they" put in half-diopter of cyl, it was for a reason,
to make the vision better. IF that is or could-be the case,
then why the difference at night?

>
>I wonder why flat base curves aren't used very often.

What does that mean? That one side of the lens (ie towards or
away from the eye) is flat?

>
>Young people can get used to most anything.

Indeed.

Good thing, too, with the coming global warming, high water,
soylent green, etc!

(We not-so-young, of course, will be long dead.)

David

[David Combs]

In article <X_oRl.532$Xl4...@bignews5.bellsouth.net>,

Mark A <som...@someone.com> wrote:
><dadol...@gmail.com> wrote in message

>news:378ea88a-6c19-436b...@w40g2000yqd.googlegroups.com...
>
>It would help to post your Rx. There are other lens materials such as Trivex
>(sold as Hoya Phoenix and other names by other lens manufacturers) that have
>similar tensile strength as polycarb but much better optics. If you Rx is
^^^^^^^^^^^^^^^^^^^^^^

Could you please give some kind of an explanation or short-tutorial
on that?

Assuming that both materials are equally clear (pass same amount of light).
Of course the index-of-refractions will be different.

But other that that, how does one get better vision with one than
the other, assuming that they've each been ground properly?

THANKS!

David C.

>mild this might be a good choice, especially if you could get it in a
>spherical lens design (not aspherical). In addition to problems with
>polycarb, aspherical lens designs can also cause the distortions you are
>experiencing, but they are often used for higher Rx powers.
>
>

[Mark A]

"David Combs" <dkc...@panix.com> wrote in message
news:h11hs7$rit$2...@reader1.panix.com...

> Could you please give some kind of an explanation or short-tutorial
> on that?
>
> Assuming that both materials are equally clear (pass same amount of
> light).
> Of course the index-of-refractions will be different.
>
> But other that that, how does one get better vision with one than
> the other, assuming that they've each been ground properly?
>
> THANKS!
>
> David C.

Lens materials differ in the amount of chromatic aberration, which is
measured as "abbe value." Chromatic aberration is a type of lens distortion
that is present in all lenses to some degree (even camera lenses) and is
more noticeable in some Rx's than others (and more noticeable by some people
more than others).

Generally speaking, the higher the index of refraction, the lower the abbe
value (the more chromatic aberration distortion). The exception is
polycarbonate lens material which has the lowest abbe value of any commonly
dispensed lens material. Here are some examples of lens indexes and abbe
values (actual abbe values may vary depending on the lens manufacturer):

1.50 Regular Plastic (CR-39), abbe value 58
1.53 Trivex, abbe value 43
1.54 Sola Spectralite, abbe value 47
1.59 Polycarbonate, abbe value 30
1.60 Plastic, abbe value 42
1.67 Plastic, abbe value 36

Note that both Trivex and Polycarb (the two lenses that are considered
"safety" lenses because of their excellent tensile strength and impact
resistance) sort of violate the direct relationship between index and abbe
value in the above data, but the polycarb is so low (compared to the Trivex)
that it is often unacceptable to many people, especially those with
moderately high to high Rx lens powers. It is particularly bad for those
with a plus lens (farsighted).