Strabismus - Fundamentals of Clinical Ophthalmology.pdf

ADULT STRABISMUS
patient presenting with vertical diplopia. There
is a variable association between the time of onset
of the thyroid eye disease and the other clinical
manifestations, for example Graves disease.
In a third of cases, the disease may precede
thyrotoxicosis, a third may be concurrent with,
and a third may occur years after the disease is
quiescent. Patients may complain that the
normal eye with unrestricted movement may be
riding too high or tending to overshoot (Hering’s
Law). CT and MRI may reveal characteristic
thickening of the posterior half of the muscle
with normal sized muscle tendons. 8 Principles of
management include ensuring the patient is
euthyroid, to minimise surgical risks, and waiting
for the muscle balance to be stable for at least
6 months before operating. Prisms may help
to control the ocular deviation and reduce
compensatory head posture. Adjustable “hang
back” sutures are preferred when the condition is
stable (see Chapter 7). Caution in recession of
inferior rectus must be exercised.
Blowout fractures
Classically occurring as a result of blunt
injury, such as a fist, elbow or cricket ball,
blowout fractures usually involve the floor and/or
the medial wall of the orbit, and the fracture
may include trapping of the inferior rectus,
inferior oblique or their fasciae. Patients should
be observed for a few weeks to see if the
restrictive strabismus resolves as the oedema
subsides. Diagnosis is made clinically from
diplopia with anaesthesia over the infraorbital
nerve and enophthalmos. Entrapment of the
extraocular muscle can be verified with a positive
forced duction test and evidence of prolapsed
orbital contents into the maxillary sinus from CT
and MRI scans. In most patients, functional
recovery occurs without surgery. Indications for
surgery include persistent diplopia in the primary
position, diplopia in the reading position, and
enophthalmos. Surgical treatment involves
freeing of the muscle, followed by the insertion of
a silicone sheet to cover the fracture separating
the contents of the orbit from the adjacent sinus.
The decision to operate will often be determined
by the forced duction test. Blowout fracture may
be mimicked by haemorrhage into an inferior
rectus muscle and may resolve spontaneously.
Trochlear injury
Injury to the trochlea may mimic Brown
syndrome. In some cases the patient displays a
“band phenomenon”, where they may have a
band of normal binocular single vision that
includes the primary position. Above and below
this band of normal binocular vision they will
have diplopia. In such cases, they may be able to
drive and read in comfort. More extreme cases
may have little or no evidence of normal
binocular vision. In this instance, about a 50%
success rate can be achieved with surgery similar
to that entertained for Brown syndrome.
Surgical treatment of restrictive oblique function
in adults more often results in a symptomatic
unhappy patient than in childhood.
Restriction of extraocular muscles
following retinal detachment surgery
This may occur if the encircling band and the
sutures fixing it to the globe interfere with
extraocular muscle action; for example, the
superior oblique, which is not uncommonly
involved.
Muscular causes of adult strabismus
Myasthenia gravis
Myasthenia gravis is a not uncommon
autoimmune disorder characterised by destruction
of acetylcholine receptors on the neuromuscular
endplate of skeletal muscles. Myasthenia gravis
may also occur in patients with thyroid eye
disease and may occur at any age, including
infants, but most often in the third and fourth
decades. It should be considered in all patients
with thyroid eye disease who present with
diplopia, particularly if they are exotropic. The
condition may mimic any isolated ocular motor
palsy or internuclear ophthalmoplegia. The
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