Strabismus - Fundamentals of Clinical Ophthalmology.pdf

ADULT STRABISMUS
such as in older patients with microvascular
disease, particularly in the presence of diabetes
mellitus. Compressive lesions may be the cause
of a third nerve palsy with pupil sparing. In older
patients (60–70 years) who present with cranial
nerve palsies, consideration should also be given
to the diagnosis of temporal arteritis.
Fourth nerve palsy
The fourth nerve is the longest and most
commonly injured cranial nerve. Usually a V
pattern of movement due to associated
overaction of the inferior oblique muscles occurs.
Abnormal head posture with contralateral head
tilt, contralateral turn and chin depression is
often found. Congenital fourth cranial nerve
palsies not uncommonly become symptomatic in
adult life. This is due to the increasing muscle
imbalance exceeding reserves of fusion. Such
patients will have cyclofusional reserve exceeding
that anticipated in adult onset fourth nerve palsy.
This, together with old photographs showing an
abnormal head posture, is diagnostic. Trauma,
atherosclerotic microvascular disease and
diabetes are the common causes in adult
patients. Aetiology of fourth nerve palsies should
be considered at a number of different levels.
Sixth nerve palsy
A sixth nerve palsy may affect the nerve
anywhere from the pons to its innervation of the
lateral rectus. It is important to realise that sixth
nerve palsy may occur as a non-localising sign
of raised intracranial pressure. Microvascular
disease from diabetes and hypertension and
trauma are often causes in adults. In the
aetiology of sixth nerve palsies, it is important to
consider this at a number of levels, namely
nuclear (including a number of congenital
disorders), fascicular (infarction, demyelination
and tumour), subarachnoid (vascular, infective,
tumours), petrous temporal (infection, sinus
thrombosis and trauma), cavernous sinus
and superior orbital fissure (vascular causes
from internal carotid aneurysm, dissection,
Figure 5.2 A long-standing left sixth nerve palsy
associated with hypertension, development of cataract
and reduced vision from 6/12 to 6/60
pituitary fossa tumour, Tolosa–Hunt syndrome)
(Figure 5.2).
Other causes of adult strabismus
Convergence insufficiency
Diplopia at near due to convergence difficulty
may be seen in patients following head trauma,
Parkinson disease or Huntington disease.
Skew deviation
Differential diagnosis of inferior oblique
overaction is a skew deviation. Skew deviation is
a vertical deviation that cannot be isolated to a
single extraocular muscle. It is almost always
associated with other manifestations of the
posterior fossa disease.
Acute diplopia in adults
Vertical diplopia of sudden onset in the adult
includes the need to consider thyroid eye disease,
myasthenia gravis, third and fourth nerve palsy
and, rarely, myositis, on the background of microvascular
disease such as diabetes or hypertension.
In older patients, Steel-Richardson syndrome
and giant cell arteritis may also be an important
consideration.
53