This 7-year-old boy presents with the clinical picture shown :  "A" pattern exotropia with "overaction" of the superior obliques.  Visual acuity is 20/20 in each eye, he is able to fuse the Worth four lights in the primary position but does no better on stereo testing.  The exodeviation is 6 prism diopters intermittent in the primary position, the boy is ortho in up gaze and has 45 prism diopters XT in down gaze.  There is 4+ overaction of the right superior oblique and 3+ overaction of the left superior oblique.  No dissociated vertical deviation or latent nystagmus is present.  The boy has very slight chin depression.  Refractive error is OD and OS +0.5 D.  This boy is having a very difficult time in school with reading, arithmetic, and concentrating in general.   How would you manage this case? To see views enlarged, click on the individual pictures...

Expert Commentary

Comments of Derek T. Sprunger, M.D.

This case of "A" pattern exotropia with excess depression in adduction (overaction of the superior oblique) bilaterally is not uncommon.  When surgically addressing these patients several factors must be considered:   1)  The primary position deviation.  If less than 20 prism diopters of exotropia are present, the superior oblique muscles should generally not be operated upon.  There is a significant chance of developing an esotropia in primary position in this situation.  Bilateral downshift of the lateral rectus muscles (with or without recession, depending upon the primary position deviation) should be considered.  If less than 20 prism diopters of exotropia were present in downgaze, a half tendon width shift would be recommended.  If more than 20 prism diopters of exotropia are present, a full tendon width downshift should be considered.   2)  Binocularity.  If stereopsis is present, the superior obliques should not be operated upon.  The possibility of losing binocular vision is significant.  If there is no stereopsis, there is 20 or more diopters of exotropia in primary, and 40 or more diopters of exotropia in downgaze, bilateral superior oblique weakening would be indicated.   Based upon the above, my choice would be to simply downshift both lateral rectus muscles one tendon width (10mm).

Comments of Richard A. Saunders, M.D.

This is a relatively straightforward case of A-pattern exotropia associated with primary superior oblique (SO) muscle overaction.  I will assume the apparent ptosis in primary gaze is an artifact.  The only effective treatment for large A-patterns in this context is bilateral superior oblique weakening, which would be my procedure of choice.  Interestingly, there appears to be only minimal inferior oblique muscle underaction, which is a bit unusual and may predispose to surgical overcorrection.  Since bilateral superior oblique weakening can induce a small eso shift, I would not consider horizontal muscle surgery for the small exodeviation in primary gaze.   There are three surgical procedures which should be considered for weakening the superior obliques.  The simplest and most predictable is posterior tenectomy (not to be confused with complete tenectomy which has a high overcorrection rate).  Posterior tenectomy, leaving the anterior 1-2 mm of tendon fibers at the scleral insertion, will take about one point off the superior oblique overaction (SOOA), close about 20 prism diopters of A pattern, and has essentially no risk of overcorrection.  Posterior tenectomy would be my choice were this boy a bifixator which does not appear to be the case (no stereo acuity).   A more powerful procedure to be considered is superior oblique tendon tenotomy.  I prefer (as a primary procedure) temporal fornix conjunctival incision (as described by Parks) with careful superior oblique tenotomy nasal to the superior rectus muscle.  This can usually be done atraumatically and produces excellent results in the majority of patients.  Superior oblique tenotomy would be my choice for this patient.   Gaining recent popularity in lieu of free tenotomy has been the superior oblique tendon spacer ("expander") which has been described by Wright.  This operation utilizes a section of #40 or #240 silicone retinal band which is sewn between the cut ends of the tendon after tenotomy.  In this case a 6 or 7 mm section would be indicated.  However, the procedure is time consuming and technically demanding, requires fine nonabsorbable suture and needles, and has yielded no better results in my hands than conventional superior oblique tenotomy.  While there may be fewer cases of postoperative superior oblique muscle palsy, other complications such as down gaze limitation due to adherence of the silicone implant to the sclera have been reported.

Comments of Daniel Thuente, M.D. (fellow of Edward G. Buckley, M.D.)

My first question regarding this patient is:  What was the response on his stereo acuity test?  I suspect that while he fuses the Worth four dot in primary position, he still does not have full stereopsis.  Next, with such a small horizontal deviation in the primary position, you cannot operate on the horizontal muscles to control his exodeviation that is worse in down gaze.  The gross overaction of both superior obliques points toward those muscles as the main surgical options.  The fact that the overaction is almost symmetrical allows for the potential for a good result.  Weakening of the superior oblique is the most likely procedure, with the caveat of knowing "beware of superior oblique procedures in the fusing patient".  I suspect this patient has limited fusional abilities.    The ideal procedure would only weaken the superior oblique in its field of action and have minimal effect in the primary position.  1) A superior oblique tendon spacer could be used in each eye, knowing that you would create a Brown syndrome.  2) If no torsion was present on downgaze, a partial superior oblique tenotomy of the posterior fibers could be done on each eye.  3) A recession of both superior obliques could be considered.  4) If the patient had no fusional abilities, then bilateral superior oblique complete tenotomies could be considered knowing that you may have to operate on overacting inferior obliques in the future.    In my opinion, a recession of both superior obliques is the best course of action.  It affects the main function of the muscle, has the least amount of effect in the primary gaze position, and is the most easily correctable if this does not control the problem.