Like Magnets That Attract And Repel


I was evaluating a very bright high school student the other day who has been having significant difficulty with standardized tests.  She has never had test accommodations in school, but at this point her parents realized that her visual problems are interfering with the sustained demands of the ACT.

“A” (we’ll use only her first initial to preserve confidentiality) exhibited 25^ intermittent alternating esotropia at distance and near, with a preference for left eye fixation.  She had a bifocal Rx since early childhood, and her only prior therapy was home-alone HTS.  “A” felt like she made gains that quickly dissipated after she stopped therapy.

Worth 4 Dot

On the Worth 4 Dot target she reported uncrossed (eso) diplopia on the two circles at the bottom, and as I tried to neutralize her subjective angle with progressively higher amounts of base out prism she made a clever observation:

“You know, every time you move that bar the two circles come closer to each other, and for a moment the one on the right side moved to the left.  But then they drift back a little toward the starting position.  It makes my eyes feel like two magnets that start to attract each other, but then repel.”  Wow!  I told her that I was so impressed with her analogy that I was going to quote her.  So think about that for a moment.

bar_magnet_fields_500_clr_7433

I’ve never quite thought about efforts at binocular vision in the way that “A” described it, and it’s quite elegant.  For those of us with normal binocular vision, the impulse to fuse is so strong that when we’re dissociated briefly our fusion reflex acts like two magnets that re-couple as soon as the images are brought back within Panum’s Fusional Area.  But for someone who is struggling to maintain fusion, there are competing forces between coupling and de-coupling the eyes.  The prism bar is manipulating the two images like an electro-optical magnet, setting up conditions that either attract or repel fusion.

Prism Bar

 

 

 

One thought on “Like Magnets That Attract And Repel

  1. From Dr. Arnie Sherman:

    HI Len,
    Love reading all your posts.
    I have seen at least a dozen patients like this. I consider them Horror Fusionis and most often present ONLY on subjective angle testing. They can fuse on large targets especially stereo in space (QUOITS) walking around a room at looping objects, door knob, Marsden Ball, and their favorite target, MY NECK. On other procedures, they “suppress” since the esotropic angle is between 25-35 prism diopters where one image is on the optic nerve (a built in Suppression area). I think it is called Swann’s Syndrome or Blind Spot Syndrome.
    These patients are very, very difficult to train for full functional binocular vision, but the cosmetic appearance does iprove and we often with up with ARC and NRC depending on the task. \
    I would love to hear from others as to their experience.

    Best Regards,
    Arnie

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