Strabismus - Fundamentals of Clinical Ophthalmology.pdf

STRABISMUS
drawn underneath the lateral rectus (see
Figure 7.8). Once joined the tone in the muscles
is balanced and the suture inserted. It is
important not to allow the muscles to slip
behind the equator of the globe and occasionally
a suture is used to prevent this.
In incomplete sixth nerve palsy, for example
residua of raised intracranial pressure from a
sagittal sinus thrombosis, if the child is left with
a concomitant esotropia, it can be treated with
bilateral medial rectus recession.
Case example A 20-year-old student was
involved in a motor vehicle accident with fracture
of the base of the skull involving petrous temporal
bone, producing a complete sixth nerve palsy. A
large medial rectus recession 10 mm with
transposition and balance of tone in the lateral half
of superior and inferior rectus muscles sutured
beneath the lateral rectus restored binocular vision
in the primary position. Nine months later the
ocular posture was still maintained. The patient
was enjoying good binocular vision in the primary
position for both near and distance without the
need for prism correction, only experiencing
diplopia beyond 5° from primary position in the
field of the paralysed muscle action.
Third nerve palsy
If a complete third nerve palsy including pupil
occurs as a congenital lesion in a child, it is
extremely difficult to manage the amblyopia and
this may be followed by aberrant regeneration.
The divergent eye can be straightened in a
child if the superior oblique with innervation
from the trochlear nerve is intact; opposing tone
may be created by dislocation of the superior
oblique tendon from the trochlea using curved
mosquito forceps. The tendon of the superior
oblique is then aligned along the upper border of
medial rectus, creating a balancing tone to the
previously unopposed action of the lateral
rectus. This is easier to do in children; in adults,
the trochlea may become ossified, so that freeing
the tendon is not possible.
Treatment of the ptosis using a silicone sling
may be considered. However, exposure keratitis
is a real risk because of the absence of a Bell’s
phenomenon.
If aberrant regeneration is marked, cosmetic
improvement is almost impossible.
Fourth nerve palsy
Although superior oblique palsy is common it
is important that it be distinguished from skew
deviation (frequently associated with other
brainstem signs), Brown syndrome, mechanical
restriction (blowout fracture or thyroid eye
disease) and double elevator palsy (associated
pseudoptosis).
Superior oblique muscle paresis is not
infrequently bilateral and asymmetrical,
particularly after head trauma. This should be
suspected if torsion on looking down is more
than 10 dioptres. It is important to remember
there are two actions to the superior oblique
muscle: anterior fibres have a torsional effect and
the posterior fibres act as depressors.
Abnormal head posture is usually a
manifestation of the torsion, and the Harada-Ito
procedure is helpful in treating the excyclotorsion
unless complete palsy is present. In marked
bilateral superior oblique palsy a bilateral tuck of
both superior oblique tendons taking up to 6–8
mm of slack may be performed, recognising the
risk of creating a pseudo-Brown syndrome.
In a long-standing fourth nerve palsy there
may be contraction in the superior rectus. If on
examination there is concomitance, recession of
the superior rectus may relieve symptoms.
Recognition of torsion can be measured using the
double Maddox rod test or the synoptophore.
Treatment of paretic strabismus
in children
The third, fourth, and sixth nerve palsies
may be encountered in children; they have
been reported as congenital lesions. They may
be progressive in children and on careful
80