On Wed, 15 Nov 2006 20:58:09 -0800, Anon E. Muss <anonymous[at]example.org> wrote:

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You could clock the lens to see if the BC is flatter but you can't easily
determine asphericity. If it really was aspheric trivex then I can't explain the
child's reaction except for the change in ocular curve. Don't you just love
surprises?

Robert Martellaro
~~~~~~~~~~~~~~~~~~
Optician/Owner
Roberts Optical
Wauwatosa Wi.
~~~~~~~~~~~~~~~~~~
"An expert is a person who has made all the mistakes that can be made in a very narrow field."
- Niels Bohr

On Tue, 14 Nov 2006 10:33:59 -0600, Robert Martellaro
<robopt[at]nospam.com> wrote:

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That's what was ordered.

On 14 Nov 2006 13:57:36 -0800, "dill" <dlanthomas[at]yahoo.com> wrote:

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They need to find a better lab.

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Yup. Furthermore, the problems I see are after a year or so of wear, when they
have been exposed to a chemical environment- hairspray, fingernail polish
remover, maybe perspiration and body oils.


- quote -

~~~~~~~~~~~~~~~~~~
Optician/Owner
Roberts Optical
Wauwatosa Wi.
~~~~~~~~~~~~~~~~~~
"An expert is a person who has made all the mistakes that can be made in a very narrow field."
- Niels Bohr

On Wed, 15 Nov 2006 03:15:59 GMT, "William Stacy, O.D." <wstacy[at]obase.netwrote:

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+3.00D poly 44 eye +5.50 BC .4p hyperboloid aspheric with 1mm ET gives a CT of
2.2mm and a lens height of 3.3mm.

+3.00D trivex 44 eye +7.50BC spherical with 1mm ET gives a CT of 2.4mm and a
lens height of 4.5mm. A very sensitive client might notice the difference in
lens height and the resultant magnification.

The same trivex lens using a .8p hyperboloid aspherical surface gives a CT of
2.3mm and a height of 3.5mm, almost identical to poly aspheric. To be sure, the
ocular curve will be slightly flatter with the higher index poly, the difference
is less than 11% and "should" be imperceptible from the clients perspective.



- quote -

Robert Martellaro
~~~~~~~~~~~~~~~~~~
Optician/Owner
Roberts Optical
Wauwatosa Wi.
~~~~~~~~~~~~~~~~~~
"An expert is a person who has made all the mistakes that can be made in a very narrow field."
- Niels Bohr

I don't think a +3 poly would magnify significantly less than a +3
trivex. If I'm wrong, tell me how. and they shouldn't be noticeably
thicker unless the frame has bigger lenses or the lab screwed up and
didn't grind to a thin edge. The differences in thickness AND mag should
be negligible.

w.stacy, o.d.

Anon E. Muss wrote:

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Hmm, the OD said the high index have greater tendancy to stress
fracture, so he ordered the polycarb. The first set had crack at the
top, the second set were broken at the lab, the third set were
scratched at the bottom of both lenses. Maybe he had it backwards in
his own mind?

Robert Martellaro wrote:
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Many thanks to everyone for your feedback. It seems there were several
issues that worked together to create the discomfort, including change
of lens material (the old ones were high index by unknown manufacturer,
the news ones were polycarb by Varilux), different base curves (1.0 to
1.0/2.0), different pupil distances (58 to 57), and new distance rx
(down .5 diopter) to get used to.

For the record, the old rx:
-8.25, -1.00 x 006
-8.00, -1.00 x 175
base curve 1.0, high index lens, PD 31/27 (I measure 55.5 but see
better at 58)

I do not know whether either the new or old lenses were aspheric, but
they didn't look alike at all - the new glasses that gave me trouble
were much more curved on both surfaces while the old lenses were
flatter on both surfaces, even though they have a stronger
prescription. So, to me, they looked like entirely different types of
lenses, although the OD insisted the new ones were right for me. And,
yes, there was a strange color tinge to things.

The one thing the OD did pay attention to was my occupation as a
writer, and he recommended I return to an older rx in the -7 range
versus the -8 range I've been wearing. (Which, for the record, when
they were made, I complained the -8 was too strong for me and made
things tiny up close, but the optician from the large chain that I will
never use again said that I just needed bifocals, which isn't the case.
At any rate, I adapted to my eagle eyes.)

I've learned a lot from this group by reading through the archives. I
think there are different schools of thought about the thicker
polycarbonate lens material. For me, the flatter high index lenses work
best, and now I'll better know what to request.

Thanks again for taking the time to weigh in.
dill

dill wrote:
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On Mon, 13 Nov 2006 22:03:23 -0800, Anon E. Muss <anonymous[at]example.org> wrote:

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Did you use aspheric Trivex?
Robert Martellaro
~~~~~~~~~~~~~~~~~~
Optician/Owner
Roberts Optical
Wauwatosa Wi.
~~~~~~~~~~~~~~~~~~
"An expert is a person who has made all the mistakes that can be made in a very narrow field."
- Niels Bohr

On or about 13 Nov 2006 08:31:04 -0800 did "dill"
<dlanthomas[at]yahoo.com> dribble thusly:

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Well, it looks like you're saying your old glasses were overcorrected,
to compensate for your astigmatism, while your current pair uses
(presumably) the correct power, but with direct astigmatism
correction.

That alone could produce a magnification effect, compared with your
original glasses.

The actual case is that your lenses are making the world look smaller
than it really is. At that strength, things will look about 15%
smaller to you than they would to someone without glasses (or to you
with contact lenses).

The drop in strength will produce a drop in image scale reduction,
which you'll interpret as a magnification.

Assuming the prescription is correct, it's something you just get used
to.
--
- Mike

Ignore the Python in me to send e-mail.

On Mon, 13 Nov 2006 21:04:52 GMT, William Stacy <wstacy[at]obase.netwrote:

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I had one patient, TODAY in fact, that I switched back from TRIVEX to
aspheric polycarbonate.

A 9 year old girl -- about +3.00DS -- she wore aspheric poly for the
previous 2 or 3 prescriptions until the last exam, when I switched her
to TRIVEX for the usual reason (better optics). She came in today and
her mom said she never liked the TRIVEX lenses because her daughter
felt they magnified her eyes worse than the aspheric poly, and they
were noticably thicker (n=~1.53 vs n=~1.586).