Strabismus - Fundamentals of Clinical Ophthalmology.pdf

THERAPY OF STRABISMUS
Weakening of the superior oblique
Many cases of A pattern with superior oblique
overaction will be improved by a tenotomy of
the posterior fibres of the superior oblique. This
has the advantage of preserving the anterior
torsional fibres of the superior oblique.
Bilateral weakening of superior oblique will
cause an esotropic shift of 30–40 D in downgaze
for an A pattern, but little horizontal shift in the
primary position. If a horizontal deviation is
present, it should be addressed in its own right.
Weakening of the inferior oblique
Complete tenotomy may be carried out as
part of treatment of a Brown syndrome case.
The closer to the trochlea the tendon is severed,
the more marked is the response. The procedure
may be followed by marked inferior oblique
overaction. In cases of overaction of the inferior
oblique, we prefer inferior oblique recession as it
allows a graded operation. 12 Good results have
been reported from lengthening the superior
oblique tendon using a silicon “spacer” sutured to
the cut ends of the tendon within the sheath.
Secondary overaction of the inferior oblique
muscle occurs in patients with superior oblique
muscle paresis. The amount of vertical
correction is roughly proportional to the degree
of preoperative overaction. Weakening of each
oblique has little effect on horizontal alignment
in the primary position of gaze. 13
Transposition procedures
Hypotropia A vertical deviation may be
treated by a recession–resection procedure of the
appropriate vertical rectus muscles.
Double elevator palsy Vertical transposition
of both lateral and medial rectus muscles is a useful
manoeuvre.
Treatment of superior oblique underaction
Superior oblique underaction is associated
with a V pattern of movement. It is important to
recognise that in so-called superior oblique
palsy, the commonest cause is probably
developmental anomalies of the superior oblique
and its tendon, and that in paediatric practice
the strabismus surgeon will encounter this fairly
frequently. Facial asymmetry and photos from
childhood will help to identify this group where
superior oblique tendon laxity is common.
Fourth nerve palsy has been stated to be the
commonest isolated nerve palsy faced by the
ophthalmologist. In childhood, it must be
distinguished from developmental anomaly of
the superior oblique. In the neurogenic form,
laxity of the tendon is not a feature and there will
usually be an event or injury to explain this
group. The importance of distinguishing the two
groups lies in the different options that the
features of these two groups provide for surgical
management.
The clinician should consider the torsional
and vertical components of superior oblique
muscle action. Cases of pure excyclotorsion
without hypertropia are best treated with the
Harada–Ito procedure. This involves the splitting
and anterior transposition of the lateral half of
the superior oblique tendon. 14 Acquired large
hypertropia may be treated with ipsilateral
superior rectus weakening, matching the defect
with contralateral inferior rectus weakening. It
needs to be appreciated that hypertropias may be
treated with inferior oblique recession alone. 15
Surgical options Underaction of the
superior oblique is frequently caused by a
maldevelopment of the superior oblique tendon
and in some cases absence of the tendon,
particularly in those associated with craniofacial
dysostoses (Figure 7.11). In this group, undue
laxity of the oblique tendon is common and can be
demonstrated by exploring the tendon and
performing a traction test. It is this group where a
tendon tuck is useful and unlikely to induce
iatrogenic Brown’s syndrome. In superior oblique
palsy, weakening of the inferior oblique muscle is
the commonest first procedure, being performed
in over 90% of cases. 16 For weakening of the
contralateral yoke muscle, the inferior rectus is
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