Choosing new Anti-r. coating and "poly carb." vs "high-index"

Dear folks:

I am a layman who is getting a new prescription filled soon. I am
seeing an eye specialist next week for an eye exam. I am posting this
bc I am trying to determine whether the advice I got from an optician
recently seems valid or not. Any light you might be able to shed on
this would be highly appreciated!!

The optician looked at my current glasses to ascertain the current
prescription. I don't know what this reflects, but he said it the
power was a "-6". I have progressive lenses with a Zeiss
anti-reflective coating. After a short time wearing these glasses,
they developed small scratches and a round smear mark on my left lens
which he said resulted from a poor chemical bonding process in the
anti-reflective coating procedure. I've had the glasses for about 5
years and have noticed a drop off in my vision, so I am going for a
eye- exam in a few days to get a new prescription.

His advice which I would like your imput if possible was this: He
suggested I go with "Crizal" anti-reflective coating for a superior
chemical bonding process and less chances of more scratches and
defects. He also suggested I get a "high-index" 167 Verilux
progressive lens. He said that with my current prescription ("-6) he
didn't recommend "poly-carbonate" lens (he didn't recommend this lens
for lens over "450"). Does this seem like sound advice? If my
prescription changes (ie., is no longer "-6") when I go for my
upcoming eye exam, could this alter this advice-- in other words,
might "poly-carbonate" lens actually be better for me than the "high
index 167" depending on how strong the prescription is?

I don't really understand most of the sophisticated terminology in
this field, or what the numbers I shared with you really represent,
so if you could explain things in as simple terms as possible, this
would really help!!! I really appreciate any help you can give or any
places you can recommend I check out on the Web for more info...

Thanks!
Craig Smith

 

You have received some good advice.

Crizal is one of the most durable AR coatings on the market, but no AR will
likely last 5 years unless you are exceptionally careful. There is a new
version called Crizal Alize, which is supposedly easier to clean than
regular Crizal, but I don't have any first hand knowledge of that. There has
been a definite improvement in the durability of AR coatings available from
some labs, although there are plenty of inferior coatings still around.

Polycarbonate is very impact resistant and has a high tensile strength. It
is relatively thin and light (1.59 index). Optically, polycarbonate is crap
compared to almost all other lens materials, which is more noticeable in the
higher diopter corrections like yours. The only reason to get polycarbonate
is if you need safety glasses, although there are some advantages of using
it for rimless frames which need to be drilled. Trivex (Hoya Phoenix, etc)
is also a safety lens (with a 1.53 index), but has much better optics than
polycarbonate.

1.67 is thinner and lighter than polycarb and usually has better optics
(even though the optical quality usually goes down when the index goes up).

There are many high quality progressives on the market. Varilux makes two
models, the Comfort and the Varilux (the premium model). Other premium
progressive lenses are available from Rodenstock, Zeiss, Hoya, Seiko, and
others.

 

Correction:

Varilux makes two models, the Comfort and the Panamic (the premium model).

 

Dear Mark:

Thanks very much for your detailed and useful reply! Based on what you
and the optician I saw have said, I'm now strongly leaning towards
the Crizal Alize A-R coating with the hi-index Verilux comfort
progressive lens.

Could I ask a follow-up question? Should I also get the same hi-index
1.67 Verilux comfort progressive lens (withouth the A-R coating) with
my new *polarized sunglasses*? Or does hi-index not apply to
sunglasses?

Thanks again!
Craig

 

The index applies to any prescription lens material. Generally the higher
the index, the thinner the lens (less material is needed to bend the light
waves) and therefore the lighter the lens (for a given frame/lens size). As
Robert M suggested, sometimes the difference in thickness and weight is not
all that noticeable, but it depends somewhat on your frames and Rx (high
power minus lenses can be thick at the edges).

In addition to the Varilux Comfort, I would get a price on the Varilux
Panamic, which is their premium lens and is better for some people. You
might also want to get a price on the 1.60 index material, that has better
optics than polycarb and 1.67, but less expensive than 1.67 (1.60 is usually
about the same price as polycarb).

The Varilux Comfort polarized grey lenses (Panamic is available in grey or
brown polarized) probably only comes in one lens material, and according to
the availability chart I looked at, it is only available in 1.50 index
standard plastic (also known as CR-39). This is material will be thicker at
the edges than the other materials mentioned because of its lower index, and
hence it will be heavier because of the additional thickness. However, 1.50
plastic has excellent optical qualities compared to the higher index
materials. If thickness and weight are important, and the polarized lenses
are only available in 1.50 plastic, you might want to consider just getting
regular Rx lenses tinted with at least 1.59 index to make a pair of
sunglasses (albeit without polarization).

 

Dear Mark:

Thanks once more. It never dawned on me that the sunglasses wouldn't
have the same range of high-index that reg. glasses do. I hope to have
my new prescription early next week. May I reply again at that time
when I know more exactly what the prescription will be?

thanks again!
Craig

 

Dear Robert:

Thanks much for your post! I appreciate the feedback....
Craig

 

Prescription sunglasses are just normal lenses that are soaked in a dye to
the desired amount of tint. You can get any of your existing glasses tinted
at most chain optical stores (unless they are made of glass). Most in-store
labs also have automated "dipping" machines that can cause the lenses to be
tinted more at the top than the bottom (if you like that feature).

Polarized lenses are a special case. These are made by bonding a polarizing
film in-between two pieces of plastic to make the lens blank, and then the
lens is ground to your Rx. In the case of Varilux, they only has polarized
lenses available in regular 1.50 plastic (according to their availability
chart I saw on their website). I believe that the Varilux polarized lenses
are pre-tinted also.

Varilux uses Nupolar by Younger Optics polarized lens material in 1.50
plastic for their polarized lenses, but I know that Nupolar is also
available in polycarb from Younger optics, so maybe the Varilux availability
chart I looked at was incorrect. In any case, you could get Younger Image
progressives in polycarb polarized lenses if Varilux does not have them (but
the Image progressive lens design may not be quite as good as Varilux).

If you don't absolutely need polarized lenses, just get regular progressives
lenses of your choice tinted to your specifications.

 

Your welcome. Informed optical consumers are a good thing. Keep the
questions coming.

Unless thickness is a priority I would not use 1.67 in the sunglasses.
Instead, use a less expensive material and take the money saved and
put it into a coated lens. A back surface AR coating will eliminate
surface reflections reducing interference resulting in increased
visual comfort. Both surfaces can be coated for improved cosmetics.

Robert