Lenscrafters and the base curve: What is the problem?

Discussion in 'Optometry Archives' started by midwest_46, Aug 25, 2007.

  1. midwest_46

    midwest_46 Guest

    I am a 33-year-old male.

    In 2004, I bought a pair of -5.25, -5.25 glasses at Lenscrafters.
    These glasses were meant to be used for driving and other "long
    distance" activities. These glasses have a base curve of 2.0 - 2.75
    (depending on who is measuring the base curve). The base curve was not
    specified in the prescription. Thus, Lenscrafters itself determined
    what the base curve would be. These glasses have been comfortable for

    Also, for years, I have been using -4.25, -4 glasses for "up close"
    activities, such as reading, computer use, etc. These glasses have a
    base curve in the 3.0 - 3.75 range (depending on who is measuring the
    base curve). These glasses are old, and I can't remember which store
    made them. I also don't know who determined what the base curve would
    be. However, these glasses are comfortable for me.

    In the early part of this year, I bought -5, -5 glasses from
    Lenscrafters. Lenscrafters determined that the appropriate base curve
    was in the 3.5 - 4.0 range. Well, these glasses gave me headaches, and
    my doctor said that this base curve was too high. So, I returned the
    glasses for a refund.


    In the last few weeks, I bought -4.25, -4.25 glasses from
    Lenscrafters. I asked that Lenscrafters make the glasses with a base
    curve of 3.5, which is the base-curve measurement that my doctor came
    up with for the -4.25, -4 glasses. The doctor said that, because these
    prescriptions were similar, they should have the same base curve. The
    Lenscrafters optician who took my order acted as if Lenscrafters would
    comply with my base-curve request.

    Well, the -4.25, -4.25 glasses gave me headaches. An optician at the
    Lenscrafters store where I bought the glasses (NOT the optician who
    took the order) told me that only a doctor can ask Lenscrafters for a
    certain base curve. So, when I specified a base curve with my order,
    Lenscrafters disregarded my specification and gave me a base curve
    that Lenscrafters thought was appropriate. This base curve was in the
    4.75 - 5.00 range. I believe this base curve also is too high.

    If -4.25, -4 glasses have a base curve of 3.5, then a slightly
    stronger pair of glasses should have a base curve that is 3.5 or
    slightly smaller. The base curve should not be a lot higher than 3.5.


    Lenscrafters opticians tell me that Lenscrafters uses computers to
    determine the appropriate base curve. Well, my question is as follows:
    Why has Lenscrafters given me two pairs of glasses with incorrect base
    curves? Lenscrafters got the base curve right with the -5.25 glasses.
    So, why is Lenscrafters all of a sudden getting the base curve wrong?
    midwest_46, Aug 25, 2007
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  2. what kind of lens? hi index? aspheric? same rx in different materials
    can have different curves.
    an optician is perfectly competent to order you lenses with the same
    base curve as your previous pair and does not need a doctor for this
    (especially given how the 2 rx's are nearly identical). doctors almost
    never specify a base curve or lens material for glasses on
    prescriptions- they leave it to the dispenser to decide.
    michael toulch, Aug 25, 2007
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  3. midwest_46

    Mark A Guest

    The base curves are specific to each manufacturer's lens design/material and
    are not transferable to other lenses or materials. So an OD would not
    specify that on an Rx unless they specify the exact lens it applies to (not
    likely unless they are dispensing the lens also).

    Although the base curves are supposed to be predetermined for a specific Rx
    (for that specific lens) based on the sphere and cylinder power, sometimes
    someone in the lab may use a different base curve if they don't have the
    correct one in stock. This is more likely to happen at an in-store lab like
    Lenscrafters because their lens stock is limited compared to a large lab
    which services many retail outlets (for chains or independent retailers who
    do not have in-store labs).

    In other cases, if you are "right on the border" between 2 different base
    curves they may choose to use a different base curve than the charts tell
    them to use because they think they know better (maybe in some cases they

    If you purchase glasses at Lenscrafters you are likely to be sold polycarb
    material. Polycarb has the worst optical properties (measured as abbe value)
    of any commonly dispensed lens material, although it has very good tensile
    strength and impact resistance. If you must have these features try Trivex
    lens material (available as Hoya Phoenix material, and also sold by Younger
    Optics). Otherwise, I would go with a 1.60 material for your lenses. If you
    think those are too thick, than 1.67 is OK, but with slightly less optical
    quality than the 1.60.
    Mark A, Aug 25, 2007
  4. midwest_46

    midwest_46 Guest

    The -4.25, -4.25 glasses that I bought recently are made from photo
    mid-index plastic. Therefore, the Lenscrafters store sent my order to
    an outside lab. I waited for my glasses for about 10 days.

    So, I'm guessing that this outside lab had all the base curves in

    The -5, -5 glasses that I bought earlier this year (and later
    returned) were also made from photo mid-index plastic. If I remember
    correctly, those were made by an outside lab as well.

    Also, the -5.25, -5.25 glasses that I bought in 2004 were made from
    photo mid-index plastic. I can't remember whether these glasses were
    made at an outside lab.

    As for the -4.25, -4 glasses, they are made from some kind of glass.
    midwest_46, Aug 25, 2007
  5. midwest_46

    midwest_46 Guest

    The -4.25, -4 glasses (old glasses) are made of some kind of glass.

    The -4.25, -4.25 glasses (new glasses) are made from photo mid-index

    As for the optician's competence, the optician stated (rather rudely,
    I might add) that the optician will not honor any requests that *I*
    make. He will follow doctor's orders. If there are no doctor's orders,
    then he will have the lab computer determine the base curve.
    midwest_46, Aug 25, 2007
  6. midwest_46

    Mark A Guest

    They went to a Lenscrafters lab. If that particular lens in not widely in
    demand (which we can assume if the in-store lab did not have it) then there
    is a chance that the lab did not have the correct base curve in stock

    However, the more likely explanation is one of these:

    1. Your Rx is right on the border of two base curves, which means that
    neither one of them will be optimal, or

    2. Your problem has nothing to do with bases curves.
    Mark A, Aug 26, 2007
  7. just curious, why photochromic for computer glasses?
    is the frame more wrap-around? sometimes a higher base is used to
    accommodate more curved frame.
    michael toulch, Aug 26, 2007
  8. midwest_46

    midwest_46 Guest

    I believe that the out-of-store lab takes the photo mid-index plastic
    in the lab's possession and *gives* the plastic a certain base curve.
    The plastic with the appropriate base curve is then sent to the store,
    and the store technicians give the plastic the prescription written by
    the doctor (-4.25, -4.25, in my case). Is that correct?

    The base curve is not something that is in stock. The plastic is in
    stock, and the outside-of-store lab *gives* the plastic a certain base
    This is the procedure that was described to me by a Lenscrafters

    Besides, the optician (at the Lenscrafters where I bought the new
    glasses) did say that, if my doctor had specified a base curve, that
    base-curve specification would have been honored.

    Well, my doctor measured the base curve of my old glasses (-4.25, -4)
    at 3.5, and Lenscrafters gave my new glasses (-4.25, -4.25) a base
    curve of 4.75 - 5.00. Those two base curves (3.5 and 5.00) are far
    apart, are they not?

    I should point out that the optician (at the Lenscrafters where I
    bought the new glasses) did adjust my new glasses in one way: He
    altered the angle of the lenses with respect to the temples. He made
    the angle of my new glasses match the angle of my old glasses.

    That seems to have alleviated some of the discomfort produced by the
    new glasses. However, when I use the new glasses to read printed words
    in newspapers, magazines, etc., I have trouble focusing on the words.
    After reading for a few minutes, I have to look away from the words.
    Reading with these glasses is difficult.

    This problem with focusing may be a base-curve problem.


    Also, for my old glasses, the optical centers are about 4 - 5 mm below
    the centers of my eyes. For my new glasses, the optical centers are at
    the centers of my eyes.

    In a different thread in this newsgroup, an optician named Robert
    Martellaro comments that the optical centers in my new glasses should
    also be 4 - 5 mm below the centers of my eyes.

    You can see this thread here:

    midwest_46, Aug 27, 2007
  9. midwest_46

    midwest_46 Guest

    Prior to 1997, I used the -4.25, -4 glasses for "long distance"
    activities like driving AND for "up close" activities like reading,
    using the computer, etc. That is, I used these glasses for everything.

    These glasses are photochromic.


    Since 1997, I've been using them for "up close" activities only.


    "Up close" activities include talking to people face-to-face.
    I have been in situations where I have been face-to-face with people
    in the outdoors, in the sun. It is in these situations that
    photochromic glasses in the -4.25 range are useful.
    midwest_46, Aug 27, 2007
  10. midwest_46

    Mark A Guest

    The lens manufacturer gives the labs the base curve stock lenses. Please see
    page 2 of this document which shows the base curves for Sola One Lens in
    various materials. This is a progressive lens, but the same concept applies
    to SV except there is no add power in a SV lens.
    I am not sure we are talking about the same thing (base curve). What I am
    talking about is the base curve of the blank stock before it is custom
    ground to your Rx. A particular lens usually has about 5-7 different fixed
    bases curves to choose from that they use as a starting point, and then
    custom grind it in a lab to your exact Rx. See the document I referenced
    above for more info. Base curves are not transferable from one lens to
    another as you can see from the document. There are some high-tech lenses
    that are custom ground from scratch (without a base curve) but so far as I
    know these are only available in certain very expensive progressive lenses.

    You can also get a completely finished lens from the manufacturer for
    certain model lenses. These lenses are also made from base curves but the
    manufacturer stocks every combination of finished lens (since lenses powers
    are prescribed to the nearest .25 diopter). I don't know if this is
    available for photochromatic materials.
    Robert is probably the most competent optician in the USA, so I would listen
    to what he says.
    Mark A, Aug 27, 2007
  11. midwest_46

    midwest_46 Guest

    Well, I went to see the optician who works in my eye doctor's office.

    First of all, this optician expressed surprise that Lenscrafters will
    not honor my base-curve request without a doctor's note.

    Furthermore, this optician believes that the base curve in the new
    glasses is too high, and I received a written order from the doctor's
    office that asks that the base curve from my old glasses be put into
    my new glasses.

    As for the optical centers, the optician stated that, because my old
    glasses have very big lenses, it is a good thing that the optical
    centers of these glasses are 4 - 5 mm below the centers of my eyes.
    However, because my new lenses are small, the optician recommends that
    the new glasses' optical centers align directly with my eyes. If that
    does not work, then we can always move the optical centers down 4 - 5

    Also, Robert Martellaro said that I should use the distance PD, not
    the near PD, for my "up close" or "reading" glasses. However, the eye
    doctor's optician said that distance PD should be used for "long
    distance" glasses and that near PD should be used for "reading"

    As for my new glasses, I know that the optician at Lenscrafters
    measured my distance PD with the PD device, but I don't know whether
    my near PD was determined.
    midwest_46, Aug 29, 2007
  12. midwest_46

    Mark A Guest

    The is a big difference between 5mm and 0mm below center, especially if you
    have an aspheric lens that is more sensitive to placement than a spherical

    Maybe try a compromise of 2-3mm ?
    Mark A, Aug 29, 2007
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