Prism glasses for exotropia?

Discussion in 'Glasses' started by Nicole, Mar 13, 2005.

  1. Nicole

    Nicole Guest

    My left eye has been exotropic, since my teens. It was never corrected
    fully. I am also quite shortsighted with astigmatism. With my full
    prescription, my eye normally focuses fine, but still wanders off when
    tired. I'd like to know if wearing prism glasses would help the weak
    eye to focus. If there is someone or something in my side vision, I
    find my eye veers off, without my turning my head, in their direction
    instead of looking straight ahead. This is so frustrating. Has anyone
    else had the same problem as me?

    My optometrist never prescribed these glasses in the past, but then
    again my last optometrist said I didn't even have a lazy eye so...

    Any advice is welcomed.
     
    Nicole, Mar 13, 2005
    #1
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  2. Nicole

    drfrank21 Guest

    Prism in spectacle lenses are not to help in "focusing" but rather to
    keep the
    eyes in proper alignment. In your case, it really depends upon the
    amount
    of fusion (ie. binocularity- how the two eyes are working together) if
    prism
    can be of help. Seeing someone familar in treating strabismus for an
    opinion
    would be your best bet.

    If the "wandering eye" is 20/20 corrected, it would not be considered
    amblyopic (ie "lazy").

    frank
     
    drfrank21, Mar 14, 2005
    #2
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  3. Nicole

    Neil Brooks Guest

    Dr. Frank,

    If--as in my case, you have a pretty darned inadequate or
    dysfunctional accommodative system--wouldn't it be true that *wearing
    the appropriate prism* to correct an exotropia *could* reduce load on
    the accommodative mechanism, actually *facilitating* focusing,
    especially at near?

    I'm thinking of the near vision triad: accommodation > convergence >
    pupillary miosis. Without the prism, an excess of accommodation would
    be needed to overcome the exo- even before focusing.

    Correct?

    Neil
     
    Neil Brooks, Mar 14, 2005
    #3
  4. Nicole

    Dr Judy Guest

    Don't confuse focus (clear vision, achieved at near by accommodation) with
    fusion (single vision, achieved at near by convergence). Prism helps with
    fusion but does nothing for focus.
    When the eye accommodates to clear an object at near it also converges; if
    the convergence is not exact and single vision is not achieved, then
    convergence changes (independant of accommodation) to achieve single vision.
    Convergenance can be changed without changing accommodation but a change in
    accommodation always causes a change in convergence.

    Accommodation in excess of that needed for the viewing distance would cause
    blur. It is true that sometimes a person with a large exophoria may over
    accommodate thus achieving single, blurred vision and this may be a cause of
    pseudomyopia, however, this is rare and more likely seen with exophoria, not
    exotropia. Exotropes are likely to accommodate correctly and suppress the
    second image, thus achieving single, clear vision.

    A person with poor accommodation may have a large exophoria at near due to
    the lack of accommodative convergence. In that case, prism will solve the
    exophoria but will not help the poor accommodation and only single, blurred
    vision is achieved.

    If your personal problem is accommodative dysfunction without a large
    exophoria or exotropia then prism will make no difference at all, you will
    converge less with prism but accommodation is still dysfunctional. You have
    single, blurred vison without prism and single, blurred vision with prism.

    Dr Judy
     
    Dr Judy, Mar 15, 2005
    #4

  5. No. Accommodation does not happen "without focusing". Accommodation IS
    focusing. So, if an excess of accommodation is required, yet get too much
    focusing, that is, one should focus inappropriately closer than needed.
     
    David Robins, MD, Mar 15, 2005
    #5
  6. Nicole

    Nicole Guest

    Thank your for your responses, but if possible I would like to hear
    the experiences from people who suffer from the same problem ...

    Does anyone have a picture of what prism glasses look like. I may need
    them and want to know what they look like. I am shortsighted, have
    astigmatism and my left eye is exotropic. I can't remember whether it
    is a base-in or base-out prism I need.

    If anyone out there has a similiar prescription and is also exotropic,
    could you please send me a private mail telling me about your
    experiences:



    Thank you!
     
    Nicole, Mar 17, 2005
    #6
  7. Nicole

    Neil Brooks Guest

    Nicole,

    You need base-in prism.

    Do you have the actual prescription? I can tell you that I'm very
    farsighted, have a moderate amount of astigmatism, and am exotropic,
    more so at near than at distance.

    A *few* diopters of prism don't detract much from eyeglasses. If
    you're up in the double digits (10d or more), it can get a bit ugly.

    *If* you have a fairly strong prescription for your myopia and/or
    astigmatism, you may be able to wear contact lenses to correct the
    underlying refractive error, then wear prism-only glasses over the
    contacts. The doctor can likely divide the base-in prism equally
    between your two eyes, further reducing the cosmetic effect of the
    lens. For example: if you need 8d of base-in, the doc will usually
    prescribe 4d worn in each eye.

    The new high-index lenses are pretty incredible. They get a lot of
    power out of pretty thin pieces of plastic. The glasses made for me
    are pretty darned nice looking. Sending a pic without understanding
    how your Rx compares to mine won't tell you much. Suffice to say,
    they just look like eyeglasses :)
     
    Neil Brooks, Mar 17, 2005
    #7
  8. Nicole

    Dr Judy Guest

    Your first step is to ask your eye doctor if prism will do anything for you.
    If you are suppressing or amblyopic, prism will not stop the wandering. If
    prism will help, then you may also need to have vision training to learn to
    control the wandering eye. You also need to know how much prism is
    required, as the appearance of the glasses will depend upon the amount of
    prism. Two to four prism diopters will not be noticable, but larger amounts
    will be and very large amounts may require a Fresnel lens which degrades
    optical quality. Base in prism, the kind you need, results in the lens
    edge being thicker towards the nose.

    The amount of prism required totally depends upon your individual situation
    and comparison to other people with different amounts will not yield useful
    information.

    Dr Judy
     
    Dr Judy, Mar 17, 2005
    #8
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