Is this what prism correction is for?

Discussion in 'Optometry Archives' started by Susanna, Aug 17, 2009.

  1. Susanna

    Susanna Guest

    If I stare with one eye at a time (the other covered) at an object in
    front of me (eg the front edge of the keyboard I am using now, or the
    horizontal top of a door frame - ie distance doesn't matter) the image
    from the left eye is higher than that from the right. Is this the
    sort of effect usually corrected by prism in glasses?

    I am 51 and have worn glasses for 40 yrs but never had a prism
    prescribed or discussed. The amount of vertical separation between
    the L and R images is a 2-3 cms at about 1 meter distance (best
    example is the top of the monitor, which is a flat screen LCD). The
    reason I am curious - for a couple of years I've been using my 'spare
    glasses'. The reason they were the spares was that the main pair were
    damaged and I never got round to getting new ones. My right eye is the
    dominant eye but my spare glasses were spare precisely because I
    always felt like something was 'off' in the right lens and never took
    them back to the optician to query it. (It's a long story with many
    transatlantic flights getting in the way of life). Anyway I got by
    with the spare glasses and finally went to get an eye test and new
    prescription (very similar to the old) and some new glasses.

    Now I can see better through the new right lens but UH! I have
    clashing images and my brain is struggling to reconcile them. Is it
    because the left eye has gotten used to taking over for the last year
    or two and now is not relishing giving up to the back-in-business
    right eye? Will this go away if I persevere? It's been a month and
    it isn't getting better. In addition to the vertical separation the
    in the left image horizontal lines slope down left to right by about 3
    degrees and in the right image slope down right to left about 1

    Like this but not nearly so sharply (thank heavens)
    L \
    R /

    At distance, believe it or not, this isn't a problem - my right eye
    appears to more or less take over. At reading distance, using reading
    glasses with a +1.75 ADD, this isn't a problem either. I seem to
    manage fine. But at screen distance (typically 30-36 inches) I have
    horrible sensations looking at a lot of horizontal information - text,
    spreadsheets, graphs. Since I need to do precisely this (stare at
    spreadsheets and graphs and all kinds of textual data tables) for 12
    hrs a day - this is a problem. Is this type of thing sorted out by a
    prism? The last OD was a stand-in after the OD at the nearest eye
    test place passed away, he seemed very much in a hurry, and although
    he tested both eyes separately he never put tested both together and
    in fact separately each eye could indeed read the charts fine. He
    never tested horizontal/vertical alignment between the eyes. I went
    back but he was not there and had taken his records with him and now
    they have someone else standing in so I made another appt but it isn't
    for a week so I'm trying to learn as much as possible before I have to
    go through it with someone new. But I have a pair of glasses from 15
    yrs ago and I can see fine in them (apart from a bit blurry) and the
    \/ effect & vertical separation is still there if I 'look' for it but
    somehow my brain gets over it in those glasses but not in the super
    sharp new glasses. I've worked with computers for 30 yrs and in over
    40 yrs of eye tests and various ODs/optometrists this has never come
    up before but it is a very real effect.

    Is prism the answer? Is the slope due to axis corrections being wrong
    or is that also prism?

    OD -1.5 -2.5 90 Add +1.75
    OS -3.5 -2.0 108 Add +1.75

    Re sph: Left eye has always been weaker, since the last prescription
    the right eye improved 0.25 but the left stayed the same. I think the
    3.5 could instead be 3.25 without ill effect going by the new glasses,
    there wasnt much difference when the OD was testing.

    Re axis: Previous glasses OD 92 and OS 102, not much of a change, it's
    always been measured somewhere around these values
    Susanna, Aug 17, 2009
  2. Susanna

    Jan Guest

    Susanna schreef:

    Susanna, what kind of glasses do you wear that causes the problem?

    Progressive ones or bifocals or just monofocal (one for reading the
    other for distance)

    Jan (normally Dutch spoken)
    Jan, Aug 18, 2009
  3. Susanna

    Susanna Guest

    Thank you for replying.

    Okay, it's becoming clearer now, conceptually if not yet visually.
    The vertical imbalance is there without glasses, always has been, so I
    guess it is adding prism that will help. Distance viewing is fine and
    so is reading with a +1.75, but being confronted with lines of text or
    horizontal lines at 30-36" is making my eyeballs want to explode and
    is so bad that I can't sometimes accurately locate the mouse pointer
    on the screen. That makes me go back to my older or oldest glasses
    because the blur or lack of focus is much easier to cope with than the
    swirling kaleidoscope effect with the new glasses. I hope the next
    OD is going to know or figure out some way to test for the effect of
    prism correction at this specific distance of 30-36".

    I've never tried progressives and in fact this pair of reading glasses
    with +1.75 is the first pair of reading glasses I've ever had. I've
    read of the viewing area 'problems' with progressives and am not too
    keen to try them. I often have to look from one to another large
    screen quickly and to-and-from screen to paperwork or books/journals
    with small text so I'm often visually scanning a wide area and don't
    like the thought of moving my head so much as I've read occurs with
    progressives. Maybe I'm just lazy but until I can get the 30-36"
    range sorted out and get back to work I'm not inclined to do further
    experimenting with progressives ;)

    The sloping lines are also present without glasses, I should have
    mentioned it. I thought that's what astigmatism could produce and it
    has never bothered me until this recent problem with the latest
    prescription and reading the screen. My brain seems to figure out
    that (e.g.) the sea doesn't lean over and so I don't just don't 'see'
    the slope unless I separate out each eye's image by covering the
    other. I'm wondering if fixing the vertical imbalance with some
    degree of prism is going to relieve my brain from dealing with that
    and it can get back to making the slopes to 'go away'.

    I do think I'm better equipped to know how to talk to the next OD now,
    so thank you again.
    Susanna, Aug 18, 2009
  4. Susanna

    Susanna Guest

    Monofocal. I have 2 new pairs. One for distance (prescription per
    first msg in thread), one for reading (with ADD +1.75 - they are a bit
    difficult to use for screen work but for a few minutes at at time I
    can do it by moving closer - so I do it sometimes depending on what
    I'm trying to work on).

    (As a sidenote I'm wondering if I could read fine with a +1.50 and see
    the screen better but I haven't tried it)

    I've never had bifocals or progressives.

    Thanks for replying.
    Susanna, Aug 18, 2009
  5. Susanna

    Jan Guest

    Susanna schreef:

    You can try the following, move the frame or your head a little up and
    down when viewing to an object.
    Maybe there is a position were you have no jumb in the image your
    looking at, can you try that and respond?

    Jan (normally Dutch spoken)
    Jan, Aug 19, 2009
  6. Susanna

    Jan Guest

    Susanna schreef:

    You can try the following, move the frame or your head a little up and
    down when viewing to an object.
    Maybe there is a position were you have no jumb in the image your
    looking at, can you try that and respond?

    Jan (normally Dutch spoken)
    Jan, Aug 19, 2009
  7. Susanna

    Susanna Guest

    Yes I understand that's likely now. I did find an old pair (about 20
    yrs old) that I described in my reply to Jan. They're almost right
    for screen work (apart from still have clashing images but much less)
    so I'll take them to the appt (don't have the prescription for them)
    and see what the OD makes of them vs the latest prescription. I think
    they may be working better than the newest ones (given and taking into
    account for the fact that the newest are not ideal for this distance)
    because the left eye is blurrier and might be allowing the right to
    get more of it's own way (dominance) - I definitely think my brain
    wants the right eye to dominate (does this makes sense? It's how it

    I dont think so. I think it's just happened that my brain has
    learned to adapt and let the right eye dominate unless there's reason
    not to (as was the case with the pair before the newest glasses where
    the right eye was the blurrier). I don't know if that's how the image
    processing is supposed to work, I'm just trying to describe what
    appears to be happening. (I should state the last I studied optics
    was for telescopes but telescopes in those days didn't have dominant
    eyes and brains complicating the mix, I kind of hope they still don't,
    for a timeframe this was the 70s when CCD cameras were first being put
    into use in astronomy but I've forgotten it all now. I digress)
    Well I did do some quick reading around and found "minor defects may
    not become evident until adult life, when compensatory mechanisms
    begin to fail" at

    So I suppose the upside of getting older is that some of my old
    glasses might be useful again but the downside is that my eyeballs
    might fall over. Hummmm, not sure what to think about that.

    I don't have other symptoms - no head tilt, no head injuries and no
    known medical issues. I suppose it's possible though until it's

    Yes, seems so.

    I'll consider it then. I'll ask at the next appt and see what
    happens. But is 18" a bit far for reading things on the desk - maybe
    not as I tend to put things a little to the side. I'll give it some
    real thought.

    Thank you.
    Susanna, Aug 20, 2009
  8. Susanna

    Susanna Guest

    It took me some time to experiment. (it seems there is some sort of
    hysteresis effect in the brain - each time I switch glasses the brain
    remembers it's previous processing for a while so it gets confusing
    unless the eyes are given time to adjust. Also I wanted to check for
    any rotational effects vs holding the glasses in front of the eyes). I
    tried several different pairs, but there's no position where the jump
    goes away. I think I;m doing it right (as you asked). They are not
    very tall lenses (typically oval-ish or rounded rectangular) so there
    isn't much edge thickness or room for inducing prism. Unfortunately I
    don't have the written prescriptions for all the glasses.

    In all this experimenting I found an old pair of glasses from about 20
    yrs ago (no corresponding written prescription) and they are almost
    right for screen work. I can't read in them but they're not too-ooo
    bad (maybe even a +0.5 add would make them good enough for reading),
    and they're blurry for distance from about 6' out (also the cyl/axis
    may need adjusting). So maybe, maybe, I should take these to the next
    appt, show the OD and say 'I think I need something close to these for
    office work, please please take a look at them' and let her figure out
    the vertical thing.

    Thanks again for replying.
    Susanna, Aug 20, 2009
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