Download Synergistic Divergence: A Distinct Ocular Motility Dysinnervation

Case Report
Synergistic Divergence: A Distinct Ocular Motility
Dysinnervation Pattern
Dr.Vishnu Suryaprakash, Dr.Shashikant Shetty, Aravind Eye Hospital
Case Report
A 6 year old female child came for review to our
hospital with complaints of squinting in the left
eye which was first noted by her parents when she
was 3 months of age. She was the 3rd child of a
non consanguineous marriage. Prenatal history
was uneventful except for pregnancy induced
hypertension. The baby was born after a full term
by a normal delivery. Birth weight was normal.
The baby had been immunized to date and
developmental milestones were attained normally.
On examination, she had a pronounced head
turn to the right. Squinting of the left eye was
noticed and it was about 30 degrees of exotropia
and 15 degrees of hypertropia. On cover test the
left eye did not take up central fixation. Visual
acuity measured by Snellens chart was 6/6 in the
right eye and 6/18 in the left eye. The child had
been advised patching in the right eye 5 years
back but had discontinued the practice for the
past 2 years. Extraocular movements in the left
eye were restricted in all directions of gaze, more
so in adduction.
Figure 1 shows pictures in all directions of gaze
shows a LE exotropia and hypertropia in primary
position. In attempted dextroversion the left eye
shows an exaggeration of the exotropia along with
Figure 1. Montage of extraocular movements
an upshoot of that eye thus giving the appearance
of both eyes diverging simultaneously.
Discussion
Synergistic divergence (SD) is a congenital ocular
motility pattern characterized by paradoxical
abduction during attempted horizontal gaze
to the contralateral side1. This rare condition
is generally unilateral and is always associated
with limited adduction of the affected eye. The
pathophysiology of anomalous abduction remains
unclear but has been variously attributed to
mechanical factors, anomalous innervation of the
ipsilateral medial and lateral recti muscles2, and
even anomalous cross innervation between the
two lateral recti3. SD is usually an isolated ocular
motility abnormality, but it has been described
several times in conjunction with ocular motility
phenotypes consistent with congenital fibrosis of
the extraocular muscles types 1 (CFEOM1) and
3 (CFEOM3).
Patients reported previously 1 had small
medial recti on the affected side, perhaps due
to maldevelopment of the medial rectus muscle.
However, hypoplasia of the affected medial rectus
alone would not explain abduction of the affected
eye on attempted contralateral gaze.
Figure 2 : Montage of brain imaging. Images
of patient 1. (A) Axial CT image of orbit showing
smaller medial rectus muscle on right. (✱) Right
optic nerve; arrows: medial recti. (B) Coronal
T2W MRI image of orbits again showing smaller
medial rectus muscle on right. Arrows: medial
recti. (C) Axial CISS MRI image showing normalappearing oculomotor nerves (arrows) bilaterally.
A likely scenario is that a developmental
anomaly in SD prevents the inferior branch of
Vol. XIII, No.4, October - December 2013
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Figure 2 : Montage of brain imaging.
the oculomotor nerve from correctly innervating
the medial rectus. The presence of synergistic
divergence of the affected globe suggests that
oculomotor fibers that should innervate the medial
rectus actually innervate the lateral rectus, causing
anomalous abduction on attempted contralateral
gaze. Medial rectus denervation would explain a
small medial rectus and absence of adduction on
the affected side, and electromyographic studies in
SD have documented reduced or absent firing in
the medial rectus compatible with denervation1.
Congenital cranial dysinnevation disorders,
under which synergistic divergence falls result from
the congenital absence or misdirection of specific
brain stem lower motor neurons, leading to the
loss of correct innervations of certain extraocular
and/or cranial muscles, often with subsequent
anomalous innervation (dysinnervation) by other
nerves.
SD has certain similarities to Duanes
retraction syndrome, the most common CCDD
ocular motility pattern. Both SD and DRS affect
predominantly horizontal ocular muscles, they
both occur unilaterally or bilaterally, and they
sometimes coexist. However, the SD clinical
phenotype differs from DRS in several ways.
It involves a different motility pattern from all
three DRS types; the muscle most involved is the
medial rectus rather than the lateral rectus; and
it does not include the DRS clinical hallmarks of
globe retraction and lid fissure narrowing. DRS
is more common in females for unclear reasons,
whereas SD is more common in males in currently
reported patients.
SD deserves recognition as a distinct ocular
motility pattern of CCDD, comparable to DRS
but much less common. It is possibly caused by
congenital denervation of the medial rectus with
dysinnervation of the ipsilateral rectus, resulting in
the characteristic anomalous abduction bilaterally
on attempted contralateral gaze.
References
1. Wilcox LM Jr, Gittinger JW Jr, Breinin GM. Congenital adduction palsy and synergistic divergence. Am J
Ophthalmol. 1981;91:1–7.
2. Znajda JP, Krill AE. Congenital medial rectus muscle palsy with simultaneous abduction of the two eyes.
Am J Ophthalmol. 1969; 68:1050 – 1052.
3. Freedman HL, Kushner BJ. Congenital ocular aberrant innervation: new concepts. J Pediatr Ophthalmol
Strabismus. 1997;34:10-16.