[snip]

Not sure.

But t is important for the person doing the opticianry work to make
sure the distance optical centers (aka "vertical PDs") are properly
positioned.

There are "charts" that state that for this size, power, etc. to use
these "base curves".

This is an oversimplification, but will give you an idea of how base
curves work:

A -5.00D lens can be made with a front curve of -1.00D and a back
curve of -4.00D, *or* it can be made with a front curve of -3.00D and
a back curve of -2.00D.  The distortions and vision from off-axis
viewing is different with both of those -5.00D lenses.  Some people
are sensitive to these changes, although for most people the base
curve change needs to be drastic for there to be complaints.  And even
if there are complaints, many times these go away as the brain adapt
to the new vision.

[snip]

Thank you, Mark, for this information..and Ann for your input re. the
polished edges. When I ordered the glasses, the salesperson held some
kind of machine up to my eyes and asked me to focus on a central point
in it.  He took some readings from this, but there was no fitting done
with regards to the actual frame and definitely no marks made on the
frame's sample lenses.  Does the machine's measurements provide the
equivalent of this? It would seem to me that it could not...

This afternoon, I took my glasses to the optician from whom I'd
purchased my previous pair (the Hoya 1.6's) to get his opinion.  He
said that the power of the new lenses is correct but the one thing that
struck him was the difference in curve between the old and new lenses.
He suggested that if I ask them to redo the new lenses, fitting them to
the curve of the old ones, he thinks I should see better.  I do not
quite understand what he meant... how do opticians determine which
curve of lens to use?

He also said, Ann, as was true in your experience, that they would have
to remake the lenses in order to resolve the polished edge issue...

Thanks again, so much for helping me sort this thing out.  You guys are
amazingly generous with your time and expertise!

Before your lenses are made, the optician must first "fit" the frame on your
face in a position that is relatively close to your eyes so that you can
achieve the best vision when the lens is mounted. Then they must mark the
fitting height (just below the horizontal center line of your pupils) and
the pupil distance (pd) which is the width of your pupils. The optician then
makes marks on the sample lens that comes with the frame where these two
points cross on each eye, which is where the optical center point of the
lens must be mounted in your frame.

The lens (which is usually about 75mm round) is then cut to fit the outline
of your frame so the optical center point of the lens is in the correct
position on the frame (as previously determined). I have left out a few
details, but hopefully you get the idea of what a proper fitting entails. In
order for you to have optimal, the fitting must be done properly, and done
accurately. It is not unusual for the fitting to be quite far off, and a
remake is sometimes required.

If you cannot find out from your optician what lens and AR your received, I
would take them to another optician and ask if they know.

Polished edges on a minus power lens can cause internal reflections and be
bothersome, depending on edge thickness and the type of frame.

Thanks, Mark, for your help.  I now have several questions to ask the
optician.  They actually didn't fit the glasses at all...he just handed
them to me and asked if I could read a paper he was holding and then
some signs across the street...

Would there be any way of identifying, independently, which
manufacturer's AR coat is on the lenses?  They are distinctly blue..

Also, would having the polish along the bottom edges of the lenses
removed reduce the awful glare (when the sun hits them)?  Is this
possible to do?

Thank you again, so much..

-- Elizabeth

It is possible you are seeing a difference in abbe value between the Essilor
1.67 and the Hoya 1.6, especially since the Hoya 1.60 has an especially high
abbe value compared to other 1.6 index lenses (and obviously higher than any
1.67 lens). But it is doubtful that this could be your only problem.

It is also possible that you have a fitting problem, either of the frame on
your face, or the lens in the frame. This is especially important for
aspheric lenses like the ones you likely have, which must be placed for good
vision. One way to determine if this is a problem is to try to move the
frame around and see if it improves your vision (but this is not foolproof).

I would also have your lens powers measured to make sure they were made
correctly.

One thing that puzzles me is that you say you have Varilux SV lenses.
Varilux is a brand of progressive (no line bifocals) which is owned by
Essilor and not SV lenses. So I am really wondering exactly what lenses you
have. Also, Essilor makes their own AR coating called Crizal, which is
highly regarded, and it is a bit puzzling why you would get Essilor (or
Varilux) lenses with Zeiss AR coating. There is something a bit fishy here.

I recently purchased a new pair of frames and lenses.  The frames are
my first pair of rimless.  The lenses are high-index.  I really like
the way the glasses look...but not so much how I see through them.  I
seem to be having two problems.  The first is that my vision does not
seem as clear and bright and natural to me as it does through my old
lenses.  My eyes seem to have to work harder to see well, if this makes
any sense, and my field of vision seems less flat.  Since the
opthamologist told me that my prescription had changed only slightly, I
am wondering if this could be a lens issue.

My previous lenses, according to my receipt, were Hoya 1.6 with an AR
coating.  The current lenses, my new optician tells me, are Varilux
single-vision 1.67 with a Zeiss AR coat.  Several years ago, I remember
trying a high-index lens and finding my peripheral vision quickly
degraded off-center, so I was switched into...I think, at the time,
spectralite?

I have been reading online that the lower ABBE value of high-index
lenses can cause blurring, but can it also cause the kind of dullness,
etc. that I am experiencing?  Is the difference in ABBE values between
these two lenses such that I would even notice it?

My other concern is that, when I am outside, the sunlight seems to be
reflected off the inner polished edge of the lenses right into my eyes.
It is painful and when I go back inside, I see dark artefacts from it
for a while.  Is there anything I can request be done to correct this
issue?  Sigh...these lenses were just so seductive in their sample
frames...like shiny little gems, I really had not anticipated any of
this, lol. :)

My prescription, if it matters, is:

-4.75, +1.00, 095
-5.75, 1.75, 080

Thanks so much for your time!

-- Elizabeth