Strabismus - Fundamentals of Clinical Ophthalmology.pdf

THERAPY OF STRABISMUS
examination, underlying pathology may be
found. Congenital third nerve palsy may spare
the pupil; where there is pupil paralysis,
amblyopia is extremely difficult to avoid, even
with intense patching. Testing for a fourth
nerve palsy in the presence of a third is
important. Excyclotorsion may be suspected
with malalignment of the macula relative to the
optic disc. Observation of a conjunctival vessel
when the child looks down and in may reveal
residual torsional action of the superior oblique.
The depressor action of the oblique in the
presence of a third nerve palsy is frustrated by
the divergence.
The fourth nerve is the commonest of the
cranial nerves supplying extraocular muscles
to be affected and cause disturbance of motility.
It may be bilateral and asymmetrical in its
presentation. The bilaterality may not be realised
until correction of one side. By inducing a
vertical deviation, fourth nerve palsy may break
down normal binocular vision and if underlying
esophoria is present, it may be the underlying
cause of the presentation of a convergent squint.
In less severe cases, vertical deviations may be
compensated for by head posture. Children may
develop larger amplitudes of fusion. If there is
decompensation in adulthood not controlled by
prisms, surgery for weakening the inferior
oblique should aim at undercorrection because
the patient’s fusion capacity can deal with
undercorrection but not overcorrection.
Benign sixth nerve palsy of childhood usually
occurs in a healthy child following a mild
respiratory illness. Its occurrence in an otherwise
healthy child and its tendency to resolve justifies
the rationale for observation in distinguishing
these from brainstem tumours.
Bilateral sixth nerve palsies may represent a
false localising sign from causes such as
aqueduct stenosis or sagittal sinus thrombosis. It
is possible that some cases of congenital
esotropia represent transient bilateral sixth nerve
palsies although this is difficult to demonstrate
or identify as an aetiology.
In considering palsies of the ocular muscles, it
is important to remember the differential
diagnosis of the congenital absence of a muscle.
The recognition of this may occur first at surgery
and later be confirmed by MRI or CT
scanning. 10
Specific surgical techniques
The ocular posture of an eye represents a
balance of the tone of the extraocular muscles
acting upon the globe. The extraocular muscles
may be thought of as consisting of antagonistic
pairs, and strabismus can be considered to be
the result of an imbalance of the antagonistic
pairs when the eyes are aligned. From this, the
principle of the surgical approach is to restore
alignment by weakening one antagonist and/or
strengthening the other in its particular direction
of action, including changing the direction of
muscle action.
Weakening procedures
Recession + /− posterior fixation suture
(Faden procedure)
When performing rectus muscle recession
(particularly any significant recession) we prefer
the hangback suture technique (Figure 7.7). The
principle involves the assumption that the
muscle is suspended from the insertion together
with the assumption that the muscle will gain
attachment to the sclera through the insertion
without being directly sutured to it. The
procedure has the advantage of placing sutures
through the thickened insertion stump and the
ability to adjust the exact position of the muscle
by shortening or lengthening the two sutures
suspending each end of the muscle. The further
back the recession, the more dangerous the
procedure of posterior suture placement
especially in myopic eyes or those with thinned
sclera. Whilst recession of both medial rectus
muscles is often performed for esotropias, the
procedure may not only correct any horizontal
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