Lens thickness

Are there any tools online for giving a rough idea how thick glasses
lenses will be at their thickest point given the prescription, size of
lens and lens type? I've ordered some 1.67 thinnest lenses online and
these are much thicker a pair from an almost identical prescription with
normal 1.57 thickness I ordered from the same place a year ago (as they
were just meant to be temporary!). I do admit the lenses in my latest
pair are widerr, but at the point where the others would have stopped
(from the middle out) they are about the same.

I've always gone for high index and am used to what size they roughly
end out at, but to me these don't look right. This was as part of an
order of 2 pairs (along with a reading pair with a +1.00 Add) and they
are insisting the distance pair are correct from the one email they've
responded to. Now they seem to be refusing to answer my emails!

 

If you have a progressive lens, there are etchings on the lens that will
reveal (almost always) the lens model, material, and index of the lens.
Check it out and make sure you actually got a 1.67 lens. You will have to
have a progressive lens identifier guide (the actual index numbers are not
etched on the lens) to decipher it, or take it to a local optician and ask
them to check it.

 

You've pretty much answered your own question, in admitting the thick
lens is the wider one (as always), but for verification, click on:

http://www.opticampus.com/tools/thickness.php


w.stacy, o.d.

 

In message <eqifj.33362$>

Neat tool - thank you. For lens size, do you measure diagonally at the
longest point, or across at the longest point?

Actually when comparing these there is very little difference in size -
maybe a couple of mm. Because the top edge of the lens is wider than
the bottom edge in both pair, one pair looked bigger than the other when
I held one above the other

For some reason my last pair from them seem to be thinner than the tool
predicts and I didn't pay extra for thin lenses (I still have my email
to them to prove it)

 

There are things that can make one lens thinner than another even with the
same material. These include whether the lens is aspheric (as opposed to
spherical), and of course the frame size.

 

The term "high index" has no real meaning anymore since there are so many
different indexes available now. At one time the most common material was
1.50 index and 1.60 or polycarb (1.59) were considered high index, but now
1.67 is quite common (and sometime the only index available in certain
models), and there are even higher indexes available.

So unless you know exactly what index lens you had to begin with,
speculating about whether a different (unspecified) index lens will make it
any thinner is like a dog chasing its tail.

 

Are you saying the same prescription lenses can be different thicknesses
on the same index but made with different plastics? If I post pictures
would someone be happy to give an opinion

 

No, not even different plastics. The lenses can have a differenct thickness
even with the same plastic if one is aspheric design and the other is
spherical design. Also, the size of the frame makes a difference.

No, you need to go back to your optician and find out what lens
manufacturer, lens design, and lens material are. Looking at pictures will
not suffice.

 

You measure horizontally. If you fit a lens precicely into an rectangle
that is oriented so that the widest dimension (length) is on the
horizontal, the horizontal measured in mm is the "eye size". The
diagonal measurement you mention is useful to lens grinders, and often
the thickest part of the lens is found on this diagonal.