SOVOTO, Strabismus, and Vertical Phoria/Tropia

If you’re not already signed up for Sovoto, what are you waiting for?  More importantly, if you’re signed up, be sure to visit the adult strabismic patients’ forum for some really good discussion by patients who are in a unique position to describe what they are feeling as they go through vision therapy.

There’s no business, like stra-bismus … at least when it comes to strabismus surgery.  Why?  Read Dr. Dominick Maino’s outstanding editorial in the current issue of Optometry and Vision Development, and you’ll learn more about the double standard in the field, pun intended.

Patients like those who have spearheaded the discussion forum on Sovoto are ones who have been reassured by their surgeons that “everything’s fine”, even when it isn’t.  That “there’s nothing left to be done” without ever giving the patient the option of vision therapy.  What a business.  Perhaps one day eye surgeons will discover the synergistic principles that orthophedic surgery and physical therapy employ in the patient’s best interests.

Susan and Anna raised the issue on Sovoto about vertical imbalances, and this is a hallmark residual issue after strabismus surgery. Susan noted this:

When looking at the Brock string and fusing the bead and seeing the strings crossing, am I “really” fusing if I see the strings both go into the bead but one is consistently just on top of the other? (I am seeing both strings throughout my visual field while doing this). My VT says it’s normal, but since I’m sensitive about my hyperphoria, I always thought that I should keep working until I get the two strings to enter the bead side by side and just sort of become one when they get to the bead.”  To which Anna replied:

I very much sympathize with the challenge that is the vertical trope/phoria. I’ll chime in quick with the suggestion that you get both your central gaze and side gazes checked before getting vertical prisms. I don’t know how often this happens, but the direction of my vertical deviation reverses between my central and side gazes from a left to a right hyper, which means that efforts to address the vertical with a prism did not work well because neutralizing one gaze exacerbated the deviation in the other. This proved to be a fast track to some unpleasant symptoms.  I’ve started doing some vertical training, so hopefully this will help. Good luck!

How great is that!  Sometimes we forget what a complicated pulley system the external eye muscles comprise, and that surgery remains as much an art as a science.  The surgeon is realigning the pulley system, but can’t always predict precisely how the brain will work in concert with the new pulley forces.  By the way, if you go to the website from which I pulled this image, and scroll down about half way, there’s a nice video showing you the pulley forces in normal operation.

Susan and Anna are both correct.  The brain’s tolerance for vertical offset of images before it interferes with fusion is much less than for horizontal offset.  Yet when vertical imbalance exist for long periods of time, we know that some patients can develop incredible vertical fusion ranges.  These are typically seen in large noncomitancies, where fusion can be maintained with an adaptive head or chin tilt or turn.

What’s really interesting is that the range of the normal extent of vertical fusion has never really been explored much.  It certainly pales in comparison with all the attention that has been paid to convergence, particularly of late.  Well it turns out that the two concepts are related, because the extent of vertical fusion that someone exhibits varies depending on the amount of convergence, according to research done by optometrists published in Investigative Ophthalmology and Vision Science.

This factors into the way we go about helping patients with uncompensated vertical phoria or tropia through vision therapy:

1) probe to see if compensating or yoked prism puts the patient in a better position to maximize fusion potential

2) probe to learn if the patient’s vertical posture varies with their angle of gaze (whether on versions laterally/vertically, or with the viewing angle in near vs. intermediate vs. far space) —- work on free space fusion (like eccentric circles and life savers), Brock String, pointer-in-straw, and space fixator in different angles of gaze.

3) probe the influence of visual-vestibular/cerebellar interaction.  This can be done with head tilts or turns.

4) once head,body and visual postures are best integrated for fusion, add loose prism jumps to expand vertical ranges.

These procedures are typically best done with red/green or red/blue stimuli as opposed to polaroids because the cancellation between R and L isn’t influenced by the angle of gaze or head/body movement.  But as you can see, there are lots of vertical variations on the theme.

– Leonard J. Press, O.D., FCOVD, FAAO

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