High Index Glass vs. Hi Index Plastic

Discussion in 'Optometry Archives' started by holytruthbc, Jan 19, 2008.

  1. holytruthbc

    holytruthbc Guest

    Hello,
    I am new to glasses and need some help. I have Keratoconus. I
    tried contact lenses and just couldn't handle them. They did provide
    excellent vision.
    Recently went to an optometrist and got a prescription for glasses.
    After the exam his assistant tried to fit me with a frame but it
    wasn't comfortable, so I said that I would need to see some other
    frames in another shop. I was very nice to them. But she go upset and
    showed her attitude.
    Just before she started showing me the frames the doctor told me that
    I would need to get a Crizal Alize with Clear Guard lens with a 1.6
    index.
    Now after I told her that I would have to see some more frames before
    I make my choice she went to the doctor's office and got a
    prescription from him. This is what the prescription says:
    Spherical I Cylindrical I Axis
    IO.D.I -1.00 -3.00 30
    D.V.
    I O.S I -.50 -1.5 180 (with a zero inside
    the 0)

    Why doesn't the prescription say Index 1.6 as the doctor specifically
    said before she tried to fit me with a frame?
    Also, it says nothing about Crizal Alize with Clear Guard.

    As I was leaving with my wife the assistant said that If get this
    prescription filled at another place it will probably not be done
    right since even if they say they use Crizal it will probably be done
    at a different lab and I would then end up coming to them and having
    it done right. She then said there is a difference between a Mercedes
    and a Volkswagen. I tried to take it in stride but didn't really like
    these kind of selling tactics. After all I came to see the doctor and
    I did. I never came there to buy something.

    I called Davis Vision (my vision plan) and was told that they do
    indeed use Crizal Alize with clear Guard. I then asked about the 1.6
    index and she said that they use 1.67 What is the difference? and if
    any is it better for me to get the 1.67 vs. 1.6 that the doctor
    specifically said.

    Also are these lenses going to be done at a Crizal Lab or is Davis
    going to get their lenses from another manufacturer and then send them
    to Crizal to apply the coating?

    How do I know which manufacturer Davis will use to get the lenses?
    They are not sure themselves.
    Which manufacturers and brands are better or even best?
    Also is it better to get the lenses in glass or plastic or
    polycarbonate?

    I will greatly appreciate any light anyone can shed on this..
     
    holytruthbc, Jan 19, 2008
    #1
    1. Advertisements

  2. holytruthbc

    Mark A Guest

    OD's don't make any money on exams theses days, and if you leave the office
    without buying your lenses there, then it is normal for them to be upset
    (and to tell you the world will come to end if you elsewhere for your
    lenses). They are required to let you leave with the Rx in hand because of
    the FTC (Federal Trade Commission), not by their own choice.

    It is not normal for a an OD to specify a lens material on the Rx. They may
    have a strong recommendation (just like an optician in an optical store
    might have strong opinions), but it simply is not normal practice to specify
    an exact lens index on an Rx.

    Lenses are made in various materials and may have coatings on them. I am not
    sure why your subject says "High Index Glass" because it is very unusual for
    people to use glass lenses these days because of extra weight that they
    have, and because of safety reasons in some cases. Therefore let's discuss
    plastic lens materials that might be appropriate for you.

    Plastic lenses come in various indexes, which sometimes have significantly
    different properties. For example:

    1.50 index (known as Regular Plastic or CR-39)
    1.53 Trivex (sold as Hoya Phoenix and other brands) - about as strong as
    polycarb but better optics
    1.59 Polycarbonate - These are sold as safety lenses but have poor optical
    qualities (chromatic aberration)
    1.60 plastic
    1.67 plastic
    and some others.

    Not all 1.67 lens materials are identical because they are made by different
    manufacturers (same with other indexes). The higher the index, the thinner
    the lens (and therefore lighter the lens) and the worst the optical quality
    (higher the chromatic aberration). One exception is polycarb, which has the
    worst optical qualities of any commonly dispensed lens even though it is not
    the highest index or the thinnest.

    So, if your Rx is moderate, you may not need a higher index (1.67) lens to
    keep the lens thin, because of your moderate lens power. 1.67 is fine, but
    not quite as good optically as 1.60 (but not everyone can tell the
    difference). 1.60 material is a good choice for your lens power that
    balances weight and optical quality.

    Crizal Alize is a lens coating that is AR (anti-reflective) to reduce glare
    and reflections. It is one of the better AR coats on the market and is
    fairly durable. The cheap AR coatings will scratch very easily and/or be
    difficult to clean. Crizal Alize is Crizal Alize no matter where you get it.
    But Cirzal is different than Crizal Alize, the later being easier to clean.

    If your optician cannot supply 1.60 with Crizal Alize (or other high quality
    coating such as Zeiss Carat Advantage) then call around elsewhere. But 1.67
    will not necessarily be a bad choice, and you may not notice the slightly
    reduced optical quality, and your glasses will be thinner and lighter.

    Avoid polycarb like the plague. If you need safety glasses, get Trivex.
     
    Mark A, Jan 19, 2008
    #2
    1. Advertisements

  3. holytruthbc

    holytruthbc Guest

    Spoke To Davis Vision again. They do offer Crizal Alize for a fee of
    $48.00 and high index of 1.67 for an additional $55.00. The optician
    was going to charge me $275.00 for the lenses plus at least that much
    more for the frames.
    The person I spoke to at Davis said that my doctor meant 1.67 when he
    said 1.6 Could this be true?
    Also, which manufacturers of lenses are best? Which ones would suit me
    best? My right eye is pretty bad and has some scarring (advanced
    keratoconus) The doctor was able to find a pretty good fit for me
    during the exam for my left eye, But not for my right eye primarily
    due to the scarring.
    Also, his assistant tried to fit my eye for the new IZON high
    definition lens but couldn't do it due to from what I understand high
    abberrations in the eye. She couldn't get the red dot to the center.

    Thank you
     
    holytruthbc, Jan 20, 2008
    #3
  4. holytruthbc

    Mark A Guest

    No, that is not true. 1.60 and 1.67 are both commonly dispensed lens
    indexes, and I am sure your doctor knows the difference. Typically, higher
    index lens materials are used with a stronger power lens to make it thinner
    (and therefore lighter). The higher the index, the more chromatic
    aberration, although not every one would notice it. For your moderate lens
    power, a 1.67 index lens is not necessary to get a reasonably thin lens and
    it makes perfect sense that your doctor would recommend a 1.60 index lens
    material for your Rx.
    For single vision lenses of moderate power (like yours), a spherical lens is
    probably what will be dispensed. There is not much of a difference between
    one lens manufacturer and another assuming the same material (index) is
    used. The choice of AR is more important, primarily because a cheap AR
    coating is easily damaged (ruining the lens) and harder to clean than a high
    quality coating like Crizal Alize (and some others).

    Lens designs, and hence the lens manufacturer, becomes more of an issue when
    you get into aspherical or atoric single vision lenses, or with progressive
    lenses.
     
    Mark A, Jan 20, 2008
    #4
  5. holytruthbc

    Alan Guest

    Hi All,

    Pls do remember that the thinner the plastic lenses the more likelyhood they
    become warpage especially fit on full rim frames, and crazing on the lens
    surfaces often in less than a year.
     
    Alan, Jan 22, 2008
    #5
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.