Would Prism from bad PDs cause damage?

Discussion in 'Optometry Archives' started by Conor, Oct 24, 2009.

  1. Conor

    Conor Guest

    Hi all. I wore a pair of glasses for a long time, circa 8 years
    actually, with the PDs set wider than my eyes. I'm a -5.5 myope with
    some cylinder (-0.5 in left, -0.75 in right - I think it should be -1
    but whatever...). The PDs were probably about 63 and I'm 57.

    I know now, after some research, that a lot prism was being induced.
    How bad is this? Are my eye muscles damaged now? I have glasses now
    where (presumably) the PDs are correct and I get the opposite effect
    from the previous glasses - my eyes feel pulled together a bit and
    things are hard to focus on. Not always, but sometimes... If I turn my
    head slightly sideways it's better - I rarely sit in front of the TV
    or movie screen, mostly to one side now.

    I'm at the stage where I'll either fly to Wauwatosa, Wisconsin or get
    LASEK ! Seriously! Contact lenses are better for me but I can't wear
    them too long...

    Why 8 years with those bad glasses? Well, I did have trouble initially
    and they (Specsavers, Ireland) gave me new glasses with rounder lenses
    (PD still at 63) and that helped. They said "you'll have to get used
    to them". And I did I suppose. Then the industry went to tiny
    rectangular glasses that mash your face and l didn't get new ones
    after my usual 4 years. I did get optician check ups several times

    Only when I was at an optician in Canada for a checkup did the guy
    look at my glasses and say "whoa. The PDs are way off". First optician
    ever to check this. Great. I got new glasses when I came back and had
    to return to the dispenser to get the panto tilt done so I could read.
    I think I know more than they do now which is a poor reflection on the


    Conor, Oct 24, 2009
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  2. Conor

    Dr Judy Guest

    The induced prism is (pd error in cm) x power, so 0.6 x 5.5 or about
    3prism diopters Base In. Not a lot. Did you tend to see double with
    the old glasses?
    No permanent damage. For many people a little prism Base In makes
    reading more comfortable. Maybe the previous doc did it on purpose to
    create the Base In effect if you have a large exophoria at near.

    Dr Judy, Oct 24, 2009
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  3. Conor

    Conor Guest

    (late reply after weekend, sorry)
    No I didn't. My eyes could feel strained though and I blinked heavily
    a lot. When I was doing a lot of sports it was sometimes a relief to
    put in contact lenses, which are simple -5.25 non-torics. Can't get
    that wrong. But I don't like wearing contacts a lot because my eyes
    start burning after a while; so I don't really consider contacts as a
    solution. Which is why I've started throwing around the idea of Lasek.
    Bit extreme though! I'm allergic to pain!
    I'm certain it was by accident (well, incompetence really - the PDs
    were simply not supplied to the lab and they guessed) and it didn't
    make reading more comfortable. Plus I started to become very sensitive
    to minor alignment changes in my glasses fit. Still am with these
    glasses. I guess higher myopes are a bit sensitive to slight changes
    in cylinder and angle.

    Anyway, I was worried that a prism would be like wearing dental
    retainers - ie: over time my sight would be realigned. I guess that is
    not the case so thanks for the replies.

    Conor, Oct 27, 2009
  4. Conor

    Conor Guest

    ANSI Z80.1-2005 fabrication standards for horizontal prism imbalance  are ± .67^
    Well given that Specsavers here is akin to Lenscrafters over in the
    US, the quality of the labs tends to vary a bit. I'm positive that it
    was an error given that there was space on the original prescription
    form (which I still have) for prism and it was left blank. That's the
    form that went to the lab.

    I do know that they specifically measure PDs now and they didn't back
    in 1997 so I'm guessing they must have had trouble with unsatisfied

    I was just concerned that unwanted prism could cause me binocular
    fusion issues into the future, especially as I'm considering Lasek.
    I'm aware that people with incorrect glasses PDs who then get a new
    pair of glasses with correct PDs sometimes report dissatisfaction with
    the new pair! Indicating that they've become accustomed to a certain
    degree of induced prism.

    Thanks for the replies, Conor.
    Conor, Oct 30, 2009
  5. Conor

    Neil Brooks Guest

    From a fairly informed patient (not an eye doctor), I have to agree
    with all who said it's unlikely to cause you any harm ... whether or
    not it WAS intentional.

    My $0.02: if you were NOT diagnosed with an eye alignment issue as a
    young child, then you probably developed a fairly healthy and robust
    fusion system (in your brain). You may have ... even if you DID have
    an alignment issue, by the way.

    I've heard some AMAZING stories about how elastic these "fusion
    mechanisms" are ... such as ... a pro volleyball player who had a
    horrible car wreck, was "wall-eyed" as a result, and whose well-
    developed fusion mechanism "forced" his deviating eye to turn back to
    "straight ahead" in a matter of months.

    Whether or not you have THIS sort of plasticity ... I don't know ...
    but it doesn't sound like your binocular vision suffered THAT sort of
    insult, either.

    If you are genuinely concerned, though, you may want to locate a
    strabismus ophthalmologist (or an optometrist who has some specialty
    in binocular function disorders), and ask that they thoroughly check
    your binocular function.

    If they DID find something wrong, it would be verrry difficult to
    blame it on the specs.

    If they found NOTHING wrong, though, your mind might be put at ease.

    Best of luck...
    Neil Brooks, Oct 30, 2009
  6. Conor

    Conor Guest

    My $0.02: if you were NOT diagnosed with an eye alignment issue as a
    Um. Well, I did have a right-eye strabismus (inward squint), corrected
    surgically in 1978 when I was 6 years old or so (damn I'm old). Which
    is why I was thinking about it so much.
    Yup. Went and did that. They're pretty darn expensive aren't they!?
    230 euro later he said I was fine and my eyes were healthy. If you
    aren't seeing double you are good to go pretty much.

    I went for another (standard) prescription today from a place I hadn't
    gone to before. She said I was slightly esophoric but nothing she'd
    put prism in for. She also said that the fact that my OD and OS
    cylinder axes were back to front in my current glasses really isn't
    helping matters much (90 and 75 degrees so the effect isn't terrible).
    I was pretty disappointed at that but given the competence of the labs
    over here, not overly surprised. I guess the labs just don't give a

    It also seems common for the optician to ramp up cylinder without
    realising the patient is accomadating. One of my earlier prescriptions
    has -1.75 cylinder instead of -0.75. Those glasses got binned almost
    immediately. Idiots...
    Well... My mind is at ease in one way - my eyes are pretty much fine
    apart from minor muscular disparaties that most myopes have to one
    degree or another. Next time I get glasses I'm going to get them to
    dot the centres and recheck the prescrip. I'll bring a baseball bat
    for leverage. Getting LASEK makes me wonder. If the process is the
    same - take a standard glasses prescription - but then burned into
    your eyes, I can't imagine I have much confidence. Ooops, we got the
    prescription wrong (again), too bad, this time it's permanent, sorry.

    Cheerfully, Conor.
    Conor, Nov 5, 2009
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