Strabismus - Fundamentals of Clinical Ophthalmology.pdf

CHILDHOOD ONSET OF STRABISMUS
Figure 4.15 Moebius syndrome. The ocular features
include cranial sixth and seventh nerve palsies.
However, gaze palsies are equally common and may
be combined with these palsies. Bimedial rectus
recession will produce good ocular alignment but
often at the expense of convergence
chance that amblyopia will develop. Duane
syndrome is occasionally bilateral, although it
has a predilection for the left eye. For further
management of Duane syndrome see Chapter 7.
Moebius syndrome
Moebius syndrome consists of congenital
disturbance of eye movements and facial
diplegia (Figure 4.15). Accompanying features
include deformities of the head and face, atrophy
of the tongue, endocrine abnormalities and
malformations of the chest, including defects of
the pectoralis muscles, malformations of the
lower limbs and extremities. Ocular features of
Moebius syndrome include sixth and seventh
cranial nerve palsies with bilateral abduction
deficits, accompanied by bilateral facial nerve
weakness.
Many display a horizontal gaze palsy with
convergence substitution movements rather than
a sixth nerve palsy. Moebius syndrome is most
likely due to congenital compromise of the
abducens nerve, facial nerve and pontine
parareticular formation (PPRF). Neurovascular
insult and the possibility of teratogens have been
implicated, due to their effect on the developing
vasculature of the brain. 16 In some cases, a
pendular nystagmus is present. Patients with a
congenital absence of horizontal conjugate eye
movements may adapt strategies to compensate
for this. They substitute head saccades for eye
saccades and if the head is immobilised they may
use an intact vergence system to move the eyes
into abduction and then cross-fixate. In Moebius
syndrome it is important to differentiate this from
cases where there are sixth and seventh nerve
palsies. It is possible that this mechanism is more
common in Moebius syndrome than previously
supposed and that it may be confused for the more
commonly diagnosed combined nerve palsies.
Congenital myotonic dystrophy, congenital
horizontal gaze palsy and Duane syndrome can
all be confused with this syndrome. Moebius
syndrome may be accompanied by a variety of
systemic findings as well.
There is an unanswered question as to why
aberrant innervation seen in Duane syndrome is
so rarely seen as part of Moebius syndrome.
What is of interest is how frequently bilateral
medial recession corrects the deviation, suggesting
that there is residual tone in the lateral rectus,
although patients may still be left with defective
convergence.
At surgery, children with Moebius syndrome
may have extremely tight medial rectus muscles.
This may be caused by the fact that they are
unopposed by defective lateral rectus muscles
and therefore develop constriction and tightness.
Large medial rectus recessions are indicated and
will usually serve the purpose of straightening
the eyes in primary gaze. This contrasts with the
unrewarding results of medial rectus recession
for complete sixth nerve palsy.
Sixth nerve palsy
Acquired sixth nerve palsies in childhood
may be secondary to neurological disease,
hydrocephalus, transverse sinus thrombosis,
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