The Vestibular System and EOMs – Part 4


As noted in Part 3, Janice’s eye turn and double vision deteriorated to the point where she had no choice but to undergo eye muscle surgery on January 15, 2014.  Prior to the surgery, even when wearing her high power prisms, Janice was aware of more difficulty maintaining single vision when looking to the right.  Now, post- surgically, she was aware of more difficulty maintaining single vision when looking to the left.  Consistent with this, her compensatory head turn when I examined her was to the left.  But this wasn’t just an inconvenience.

Recall that Janice was in the habit of having to do vestibular/ocular exercises for many years, which she continued to do at home.

Gaze

The figure above is an example of gaze stabilization head rotations from an excellent overview of vestibular rehabilitation.  Janice noted that she experienced new bouts of dizziness after the strabismus surgery.  This was not surprising, given her history.  If you glance back at Parts 1 and 2 you’ll note how intimately the VOR (vestibulo-ocular reflex) involves calibration of the extra ocular muscles and the semicircular canals.  After the surgery Janice’s calibration of the VOR that she had worked hard to maintain was now in need of significant re-calibration since her head posture had to change, literally overnight, to maintain single vision by turning opposite to the direction in which she had adapted.

The eye muscle surgeon was pleased with the outcome of the surgery, and when Janice mentioned her increased dizziness he suggested that she change her spectacle lenses to remove the prism on one side.  After all, her trifocal lenses with prism were costly.  This left her with a 6^ lens in front of the right eye, but she soon discovered that felt better without the glasses on.  Janice was very specific when she called my office.  She told my intake staff that at no point was it suggested to her that she consider vision therapy.  But once she did her own research and asked the surgeon his opinion, he said: “Sure.  I suppose you can give it a try.”

MaddoxAs Janice sat in my examination room chair, her distance phoria neutralized at between 9 and 13 prism diopters base out.  Janice knew that prior to the surgery the ocular motility expert had always prescribed prism significantly less than what she measured with prism neutralization on the cover test.  Though Janice’s eyes looked cosmetically aligned, she exhibited somewhat more eso on gaze left than on gaze right.  In experimenting with different prism combinations, we obtained best comfort and stability using 2 prism diopters in front of the left eye and 1 prism diopter in front of the right eye.  I wrote her a single vision Rx with that prism in plano lenses.  There was no need to compromise her visual field with a trifocal when her primary dys-abilities were walking and driving.  I will consult with her ENT and we’ll set out on a course of vision therapy.  Janice had only one remaining question for me: “Why hadn’t vision therapy been suggested to her before?”

2 thoughts on “The Vestibular System and EOMs – Part 4

  1. Unless I missed something in the previous episodes, was it ever determined what functional/developmental problem was responsible for the eso? Was there a history (available?) of her ocular status prior to the first onset of diplopia and eso-posture? As her eso deviation reportedly increased over time didn’t anyone question the possible etiology?

    • Good to see you’re still checking in, Chuck! She’s had all the cadillac neuro workups including MRI and EEG, and no “apparent” cause – as indicated in Part 3. Since she’s a long-standing emmetrope, no shock she didn’t have a comprehensive eye exam until she hit presbyopia. There is no history available of ocular status prior to first onset of diplopia and eso posture 6 yrs ago. So the point of all this is that sometimes we need to look for etiologies that aren’t conventionally considered “disease” processes, but they really are. How many times do we toss divergence insufficiency into the category of decompensation of unknown etiology? But consider this: give the intimate link between semicircular canals and EOMs, and Janice’s long-standing history of BPPV onset 20 yrs ago with numerous rounds of VRT, is it not possible that her primary vestibular instabilities/adaptations translated into secondary adaptive EOM compensations? To map out why DE we’d have to be able to image the canals and EOMs in a way that isn’t clinically available. My intent here is to open a portal of thinking I haven’t seen discussed before. Proof of the pudding will be if VT stabilizes both EOM system and vestibular system for her.

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