Nystagmus and Prisms

Discussion in 'Optometry Archives' started by Dave, Sep 18, 2003.

  1. Dave

    Dave Guest

    I have congenital nystagmus and have heard that wearing base out prisms
    can help reduce nystagmus. This forces convergence and nystagmus is reduced.
    Has anybody heard of this? My eye doctor was not aware of this.

    Mike
     
    Dave, Sep 18, 2003
    #1
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  2. (TomKopan) wrote in
    Not so odd. Many nystagmus patients will have a convergence null, or
    some other eye position that works for them. If you observe the patient,
    you'll often know what the null is before you even measure for it. Many
    patients will try to get up close, and many will exhibit a head-turn.
    They do this because they see better this way, although they may not
    realize that's because the nystagmus calms down.

    Remember that if you use base-outs, you might consider adding a -1 to the
    correction to counteract the added accomodation. Patients also prefer to
    have the base-outs edge treated somehow to keep light from sneaking in.

    The contact lenses presumably work because they slightly increase
    afferent feedback, but this is still a matter of some conjecture.

    One other thing. There are two kinds of congenital nystagmus patients
    (at least you can think of them this way). There are those who don't see
    well because of the nystagmus who have otherwise healthy visual systems,
    and there are those who have really bad visual systems (chicken and egg
    problem-- do these guys have nystagmus because they can't see well, or
    did the nystagmus in such patients prevent proper visual development?--
    hard to tell) who wouldn't see well even if you stopped the nystagmus
    cold. The latter group will not likely be helped by base-outs, contact
    lenses, or surgery.

    Scott
     
    Scott Seidman, Sep 18, 2003
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  3. Sometimes it works dramatically.

    Scott
     
    Scott Seidman, Sep 18, 2003
    #3
  4. Dave

    Dave Guest


    How much diopter would need to be added to the base-out prism to know
    if the prisms have any effect on the nystagmus?
     
    Dave, Sep 18, 2003
    #4
  5. Dave

    nipidoc Guest

    Generally, it's not BASE OUT prism that's used. It's yoked prisms
    that are designed to shift the image towards the null point of the
    nystagmus. You need to find an eye doctor who has experience in
    evaluating and prescribing for these types of problems. Generally
    people who specialize in low vision have a particular skill for this
    type of problem.

    One poster mentioned RGP lenses. I have had only one patient out of
    about 10 where that worked, but it worked tremendously. If you have
    any sort of significant prescription, that might be a good place to
    start.

    nipidoc
     
    nipidoc, Sep 19, 2003
    #5
  6. (nipidoc) wrote in
    Depends on where the null point is, and how good they are. A colleague of
    mine tests about 20 or 30 CN patients a year, he's been doing this for
    maybe 20 years or longer, and I assisted him for about 5 of those years.
    He measures the nulls with precise eye movement recordings. Often, when
    there's a null at some eccentric position, there's also a null in
    convergence, and the latter often quiets the nystagmus waveform down more
    than the former.

    I think any bias you see toward yoked prisms might be because a head turn
    is a really visible clue that there is an eccentric null, and the
    convergence null might be missed. Granted, yoked prisms might be a little
    easier to get used to than base outs (especially if you forget to cut extra
    minus into the base outs for accomodation), but most of his patients
    haven't had trouble with them.

    RGPs can work quite well, just as you describe. Many patients who they
    work for also have convergence, or some other null, that works better, but
    some prefer to avoid the prisms if the contacts work, especially if frames
    interfere with sporting activities.

    Scott
     
    Scott Seidman, Sep 19, 2003
    #6
  7. My recollection is that biofeedback for this purpose has never really taken
    off. It works, but if the patients becomes excited, the techniques just go
    out the window.

    Scott
     
    Scott Seidman, Sep 19, 2003
    #7
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