focal plane problem

Discussion in 'Optometry Archives' started by DIAMOND Mark R., Nov 2, 2004.

  1. I hope that someone on this newsgroup might be able to suggest how to go
    about solving a problem I have, that I am sure others must have as well.

    My latest prescription gives me excellent vision in each eye separately, but
    such horrible vision with both eyes open that I have abandoned my new
    spectacles in favour of a pair from two prescriptions ago!

    The problem is that the image in each of the two eyes is (it appears to me),
    of different magnification, and in a different focal plane. I would much
    prefer to have *less than perfect vision* in each eye, and trade off a
    decrease in the focus and individual image quality against a *reasonable*
    quality image that preserves stereopsis. I have heard several people of my
    age complain of a similar problem, and several times the person has said
    that their optometrist has acknowledged that there is likely to be an
    "initial" problem, but apparently without proferring any solution other than
    to "get used to the new prescription."

    So what can/should one do? Is there any simple way of calculating a "good"
    (not perfect) same-focal-plane prescription from my existing prescription?
    At the very least (though not having an optometry background), I would have
    thought that even a prescription based on the very old pair of spectacle I
    now use, but with the astigmatic rotation updated, would be better than
    either the old pair, or the new prescription.

    If you have any suggestions, about (1) reading about the subject; (2) how to
    approach the topic with an optometrist; or (3) how to do the calculations
    .... I would be very grateful.
    DIAMOND Mark R., Nov 2, 2004
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  2. DIAMOND Mark R.

    Dom Guest

    Yes if there is a big difference between the right and left lens power
    that is causing you problems (known as anisometropia), it should be
    possible to reduce the difference and improve the "balance" between your
    eyes, probably at the expense of individual sharpness. However, this
    would normally only be done once you have given the current arrangement
    a fair go, say a few weeks of wear. What was your optometrist's advice?

    Also you should have the optical centres of your lenses checked, just in
    case they aren't aligned closely enough with your pupils (in the
    horizontal and the vertical).

    I should stress that you should take this advice with a grain of salt,
    as I am only guessing at the problem based on your description.

    Dom, Nov 2, 2004
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  3. DIAMOND Mark R.

    Otis Brown Guest

    Dear Mark,

    The normal process of prescribing a lens is to ask you
    " it better, is this better", and work to
    clear each eye to pass the 20/20 line.

    In general, the vision with the two eyes together is
    generally better than each eye separately.

    It is considered that this operation of the phoropter,
    and "correct" lens places the focal plane of the
    eye (and lens) on the surface of the retina -- for
    each eye.

    I do not know what the problem is, but by classical
    definition, the focal plane of your eyes are
    correctly "set" by that external lens.

    Since you see well with the older pair of glasses,
    I would go bact the OD and discuss the specific
    issue you described to us. He will be responsive
    and will perhaps use a different prescription

    Please let us know what he says.


    (I am not an OD)

    Otis Brown, Nov 2, 2004
  4. DIAMOND Mark R.

    Dan Abel Guest

    Perhaps you could post your prescription, that would help us. I was
    diagnosed with cataract some years back. We discussed what strength of
    lens I wanted implanted. The doctor warned that I would probably not be
    able to wear glasses after the first surgery, since the prescription in
    the eyes would be so different that the brain wouldn't be able to merge
    the two images, due to the difference in magnification. He suggested
    switching to contacts, which I did, at age 45. After the first surgery, I
    got some glasses, mostly to see what happened. I sat in front of the
    house, after taking out my contacts and putting on my new glasses. I
    watched the cars go by. They were in pairs, one on the ground and the
    other about ten feet in the air!

    I would give your new glasses a couple of weeks, to see if your brain
    could merge the two images. If not, take them back and explain that they
    just don't work. The OD can verify if they were made correctly, and then
    advise you what to do to get glasses that work for you. He can adjust the
    prescription so they more closely match. Of course, if your problem is a
    difference in prescription between the two eyes, contacts will solve the
    problem. This is what I did for the five years between my two cataract
    surgeries. Now that I've had both done, I can go back to wearing glasses.
    Dan Abel, Nov 2, 2004
  5. Thanks to all three who replied.In reponse to the various questions that
    were raised, I wore the new prescription spectacles for a couple of months
    before reverting to the very much older pair, and in that time I never
    seemed to get either good stereopsis or a general sense of good vision,
    notwithstanding that the vision in each eye individually was very good.

    The prescription, given that you asked, is

    Right Sphere = +0.50 , Cyl = -1.50 axis = 18.0
    Left Sphere = +1.25 , Cyl = -1.50 axis = 175

    I shall go back and talk to the optometrist as you suggested, but if, given
    the extra information, you have anything to add, I would be glad to hear.

    DIAMOND Mark R., Nov 4, 2004
  6. DIAMOND Mark R.

    Dan Abel Guest

    Yes, the .75 difference in your sphere would not cause the problems I was
    referring to in another post. I believe that I was told that a difference
    of 2 or greater was needed to prevent the brain from merging the images.
    I had a difference of 10! Hopefully the OD can fix you up.
    Dan Abel, Nov 4, 2004
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