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346 Theory and Practice of Squint and Orthoptics
Features due to aberrant
regeneration of third nerve
Aberrant regeneration can occur following
congenital or acquired third nerve palsy. It may
occur even without a preceding oculomotor
paralysis in patients with a slowly growing
intracavernous meningioma or with a carotid
aneurysm. Aberrant regeneration is thought to
result from a miswiring of axons from the
proximal portion of the nerve into the peripheral
segment of the nerve. The misdirection syndrome
(aberrant regeneration) follows more commonly
in a compressive injury of the oculomotor nerve,
e.g. those associated with birth trauma.
Features due to aberrant regeneration of third
nerve (all of which may not necessarily be
present in a given patient) are as follows:
1. Pseudo-Graefe's sign. It refers to elevation of the
upper lid on attempted downgaze. It perhaps
occurs due to miswiring of the nerve fibres
originally meant for inferior rectus with the nerve
fibres going into levator palpebrae superioris.
2. Widening of the palpebral fissure on adduction
and narrowing of the fissure on abduction.
3. Pseudo-Argyll Robertson pupil. It refers to a
dilated fixed pupil that does not react to direct
or consensual light stimulation but does react
slightly on convergence and also on adduction.
4. Retraction of the upperlid occasionally may be
accompanied by contraction of the pupil.
5. Eyeball may be retracted and adducted on
attempted upgaze.
Cyclic oculomotor paralysis
It is the rarest but an interesting form of third
nerve paralysis which is usually congenital in
origin. As the name implies, it is characterized
by an alternate paresis and spastic contraction
of the extraocular and intraocular muscles
supplied by the third cranial nerve. The spastic
phase is shorter than the paretic phase. The two
phases continue to alternate even in sleep but
disappear in deeper stages of anaesthesia.
1. Paretic phase is characterized by occurrence
of ptosis, dilatation of pupil, impairment of
accommodation, weakness of adduction,
weakness of vertical movements and an
outward turning of the globe.
2. Spastic phase is characterized by contraction
of the muscles—beginning with adduction and
elevation of the lid. It is followed by pupillary
constriction and improvement in accommodation. Ultimately, the eye may return to
primary position to be followed, shortly by the
paretic phase.
MANAGEMENT
Management of third cranial nerve palsy remains
the most difficult, incomplete and least satisfying.
In general, the management includes investigations, treatment of the cause, conservative
treatment and surgical treatment.
Investigations
Third nerve palsy of acute onset, especially if
non-pupil sparing, should be subjected to
through neuro-ophthalmic evaluation and be
investigated with prompt and appropriate
neurologic studies.
1. Magnetic resonance imaging (MRI) and
carotid angiography. Probably, it is best to
perform MRI in such cases and then proceed
further as below:
a. In children below 10 years of age regardless of
the state of pupil, if MRI is normal, carotid
angiography is not essential because of the
less likelihood of aneurysm.
b. In patients above 10 years of age with pupil
involvement, if MRI shows a mass compatible
with an aneurysm or even if MRI is normal,
perform carotid angiography to rule out
aneurysm.
c. In patients above 10 years of age with pupil
sparing, if MRI is normal, a thorough medical
evaluation should be conducted. In patients
of vasculopathy age group (>40 years),
hypertension and atherosclerosis should be
taken care of. Further, diabetic mononeuropathy should always be ruled out by glucose
tolerance test in patients with pupil sparing
third nerve palsy.
All such patients should be observed
frequently and if pupil is involved or signs and
symptoms of subarachnoid haemorrhage
develop immediately, angiography is required
to rule out aneurysm.
Incomitant Strabismus
347
2. Tensilon test. One should remember the
dictum that any unexplained cause of diplopia
or ptosis requires a Tensilon test to exclude
myasthenia gravis.
3. ESR. In patients of more than 55 years of age
with symptoms of polymyalgia rheumatica, ESR
estimation should be done. If ESR is found high,
then temporal artery biopsy should be performed to rule out temporal arteritis.
Treatment of the cause
If on investigation, a definite cause of third nerve
palsy such as intracranial aneurysm, diabetes,
myasthenia gravis, etc. is found, patient should
be referred to neurosurgeon or neurophysician
depending upon the indication. However, if no
surgical cause is found, patients should be
managed conservatively followed by extraocular muscle surgery, if required.
Conservative treatment
1. Observations and monitoring. Like any other
paralytic squint, wait and watch for the selfrecovery should be done at least for 6–8 months.
During this period, patient should be followed
every 6 weeks, and at each follow-up visit,
following examinations should be done.
• Measurement of exotropia and hypotropia
with prism for cover test.
• Diplopia charting.
• Hess charting.
2. Amblyopia is frequently associated with third
nerve paresis in paediatric patients and must
be sought and treated aggressively. Therefore,
surgical treatment to raise the ptotic lid is
needed urgently in children. Alternate patching
should be done to prevent occurrence of
amblyopias.
3. Diplopia is difficult to treat with prisms,
because of its variable nature.
• Complete ptosis is useful in preventing diplopia
in visually mature patient. Therefore, ptosis
surgery should be deferred until after the eye
has been straightened.
• Alternate patching is required to prevent
diplopia in visually mature patients with
incomplete ptosis. Opaque contact lens or
blurred spectacles can be used as alternative
to patching.
4. Botulinum toxin. Use of botulinum toxin is
another nonsurgical option in the acute phase
of partial third nerve paresis. This is, especially
useful in cases of isolated involvement of MR
muscle. It paralyses the antagonist LR
temporarily and thus neutralizes horizontal
deviation in the primary position. It also
prevents contracture of LR muscle. After
recovery of the injected muscle, the remaining
vertical deviation may need to be corrected by
prisms or surgical therapy. Some patients may
not need surgery later on. Use of botulinum
toxin for vertical muscle imbalance is rarely
indicated, as SR should not be injected as ptosis
can occur if toxin is placed into the levator—SR
complex.
5. Vitamin B-complex may be used as neurotonic.
6. Systemic steroids may hasten the recovery in
patients with non-specific inflammation.
Further, in patients with temporal arteritis or
rheumatological disorder, high doses of steroids
are recommended.
Surgical treatment
General principles
1. Observation and monitor approach. Like any
other paralytic squint at least 6–8 months should
elapse before performing any surgical treatment
to straighten the eye.
2. Surgery should be undertaken continuously in
patients with complete palsy and good
binocular visual function, since elevation of the
lid and incomplete realignment without useful
single binocular fields may produce incapacitating diplopia.
3. Surgery for third nerve paralysis is challenging
and the outcome must be discussed with the patient.
Associated factors such as the presence of ptosis,
pupillary involvement, amblyopia, aberrant
regeneration, poor Bell’s phenomenon, superior
oblique (SO) overaction, and lateral rectus (LR)
contracture may further complicate the matter.
Further, it should be explained to the patient or
parents that several operations will most likely
be necessary to straighten the eyes and both
patience and understanding are important
throughout the course of treatment. It should
also be emphasized to the patient that inspite of
multiple operations, one can achieve functional
348 Theory and Practice of Squint and Orthoptics
and cosmetic correction only in primary position
and not in different gazes.
Goals of surgery
• To improve alignment in primary gaze.
• To produce or enlarge some degree of
binocular single vision.
• Relief of diplopia in primary position
• Correction of head posture, if present
• Cosmetic improvement
Surgical procedures
Surgery should be contemplated, only if the
strabismus measurement and diplopia remain
stable for 3 months (i.e. partial recovery has
stabilized). It usually occurs after 6–8 months
of paralysis.
Aim of surgery is to give alignment in the two
important positions, i.e. primary and downgaze.
Planning for the appropriate surgical procedure
must be dictated by the severity of the weakness
of the muscles as follows:
1. Surgery for exotropia (lateral rectus recession
and medial rectus resection)
• In an incomplete palsy, recess-resect procedure
should be planned as done for comitant
exotropia.
• In complete paralysis, Helveston and many
others have advised supramaximal recession
of lateral rectus (14–16 mm) and resection of
medial rectus (8–14 mm), to align the eye in
primary position. But this has limited success
as overtime chronic contracture of LR and
elongation of resected muscle, causes
exotropic drift again.
Myectomy of LR muscle to accomplish a supermaximal weakening effect of abduction in
patients with complete third nerve palsy has
also been recommended. However, this often
results in recurrence of exotropia.
• Adjustable sutures during recess-resect
procedure are quite useful in co-operative
patients.
2. Surgery for hypotropia include:
• Supraplacement of horizontal recti during recess-
resect procedure is preferred by some surgeons.
• Superior oblique tenotomy is preferred by some
surgeons over the supraplacement of
horizontal recti.
• Inferior rectus recession with resection of superior
rectus is preferred by some surgeons to correct
hypotropia is ease with preserved partial
function of vertical recti. But a caution is
required about the possibility of anterior
segment ischaemia.
• Faden recession of contralateral vertical recti is also
helpful in correcting the vertical misalignment
in primary position or downgaze.
3. Transposition of superior oblique tendon. If
eye remains still exotropic after 3 months of
above procedures, in this situation, a further
adduction effect can be obtained by transposition
of the insertion of the superior oblique tendon to
a point between MR and SR muscles about 2 to
3 mm anterior to the medial side of superior
rectus insertion. Transposition procedure is
meant to create a tonic adducting force to the
globe to keep it in primary position rather than
produce any true adductive force during
horizontal gaze. This is a difficult procedure.
Thus, transposition of superior oblique
tendon may be considered in a patient with
acquired third nerve palsy, only if the following
conditions are met:
• Palsy is complete
• Involved eye is fixing eye.
• Maximum recess-resect surgeries on the
horizontal recti have failed to restore the globe
to primary position.
4. In case of palsy of inferior division of 3rd
nerve. Transposition of lateral rectus muscle to the
site of insertion of inferior rectus muscle and
transposition of superior rectus muscle to medial
rectus area, combined with tenotomy of superior
oblique to align the eye in primary position
should be carried out. This also helps to correct
intorsion and provides a vector force in the
direction of palsied muscle.
5. In case of palsy of superior division. Hypotropia
is corrected as a first stage. Knapp's procedure
should be carried out (see page 460). Ptosis
surgery if indicated should be taken over in the
second stage.
6. Anchoring of the lateral rectus to periosteum
of lateral orbital wall by non-absorbable. 5-0
mersilene suture along with 8-0 mm of medial
rectus resection has also been recommended for
alignment of globe in the primary position.
Incomitant Strabismus
349
7. Surgery for ptosis. Once the paralytic strabismus is treated maximally, the paralytic ptosis is
treated with frontalis sling, taking care that the
globe is not overly jeopardized because of
impaired or absent Bell's phenomenon. Ptosis
should be corrected only to cover half of the
cornea with relaxed brow. Protective measures
to avoid exposure keratopathy must be taken.
Congenital third nerve palsies: Summary of
surgical treatment
• Treat exotropia followed by hypotropia
followed by ptosis correction
• Maximal recession of LR and resection of MR
with upward transposition of muscle tendon
for hypotropia, or
• Modified Nishidha's technique, or
• SR resection with IR recession
• Correction of ptosis with sling surgery should
be done 3–6 months after the squint surgery.
Summary of treatment of third nerve palsy is
depicted below in a Flowchart 12.1.
INTERNUCLEAR OPHTHALMOPLEGIA
Internuclear ophthalmoplegia results from a
lesion of the medial longitudinal fasciculus
(MLF) and that is why, is also known as MLF
syndrome. It is a supranuclear disorder
described on page 389.
EXTERNAL OPHTHALMOPLEGIA
External ophthalmoplegia refers to paralysis of
all extraocular muscles sparing the intraocular
muscles.
TOTAL OPHTHALMOPLEGIA
Total or complete ophthalmoplegia refers to
paralysis of all extraocular muscles including
LPS and intraocular muscles, viz., sphincter
pupillae and ciliary muscle. It results from
combined paralysis of third, fourth and sixth
cranial nerves. It is a common feature of orbital
apex syndrome and cavernous sinus syndrome.
RESTRICTIVE OCULAR MOTILITY DEFECTS
Restrictive strabismus is a type of incomitant
squint characterized by limitation of movements
due to causes other than paralytic. In such cases
limitation of ocular movements is out of
proportion to the amount of deviation in the
primary position.
Causes of restrictive strabismus can be arranged
in two groups:
A. Restrictive strabismus due to misdirected
muscles forces.
B. Restrictive strabismus due to mechanical
restriction.
A. RESTRICTIVE STRABISMUS DUE TO
MISDIRECTED MUSCLE FORCES
Misdirected muscle forces that work against the
normal agonist muscle function as seen in
following conditions:
1. Congenital cranial dysinnervation disorders
(CCDDs), e.g. Duane’s retraction syndrome.
2. Congenital ectopic extraocular muscle insertion
and/or pulley location.
3. Displaced extraocular muscle, e.g.
• Superior displacement of medial rectus as
seen in craniosynostosis.
• Slippage of lateral rectus muscle as seen
in some patients of high myopia with large
posterior staphyloma.
• Iatrogenic displacement of muscle as
reported after inferior oblique anteriorization.
CONGENITAL CRANIAL
DYSINNERVATION DISORDERS
Congenital cranial dysinnervation disorders
(CCDDs) encompass a group of disorders that
result from developmental errors in innervation
of the ocular and facial muscles and not from
primary dysfunction of the muscles themselves.
The CCDDs can be classified as below:
I. CCDDs primarily affecting horizontal ocular
motility
• Duane’s retraction syndrome (DRS)
• Horizontal gaze palsy with progressive
scoliosis (HGPPS)
II. CCDDs primarily affecting vertical ocular
motility
• Congenital fibrosis of extraocular muscles
(CFEOMs) type 1, 2 and 3
• Congenital ptosis
350 Theory and Practice of Squint and Orthoptics
Flowchart 12.1: Treatment of third nerve palsy
III. CCDDs primarily affecting facial muscles with
associated ocular motility defects
• Congenital facial weakness (CFP)
• Moebius syndrome
I. CCDDs PRIMARILY AFFECTING
HORIZONTAL OCULAR MOTILITY
These disorders result from developmental
anomalies of sixth cranial nerve and/or its
nucleus, and include:
• Duane’s retraction syndrome (DRS), and
• Horizontal gaze palsy with progressive
scoliosis (HGPPS).
DUANE'S RETRACTION SYNDROME
Duane's retraction syndrome is a common
entity. Stilling (1887) was probably the first
person to describe this condition followed by
Turk (1890). In 1905, Alexander Duane defined
the retraction syndrome to consist of six
characteristic features and since then his name
has been attached with this syndrome.
However, European literature prefers to refer
to it as 'Stilling-Turk-Duane' retraction syndrome.
The syndrome in its classic form is characterized
by the following features:
• Limitation of abduction and/or adduction
• Retraction of globe on adduction
• Narrowing of palpebral fissure on adduction
and widening on abduction.
• Frequently, upshoot or downshoot of eye on
attempted adduction.
Etiology
Currently, it is believed that Duane's syndrome
is a congenital cranial dysinnervation disorder
(CCDD) of brainstem origin rather than
occurring due to structural anomalies of the
muscles as thought earlier.
Paradoxical innervation of the horizontal rectus
muscles is the main etiological factor.
Electromyographic (EMG) studies have shown
that most cases of DRS have paradoxical
innervation of the horizontal rectus muscles as
shown in Fig. 12.43 and explained under the
pathogenesis of ocular features individually
(see pages 351–353).
Paradoxical innervation is there for both LR and MR
rectus muscles, so both co-contract during
abduction and adduction resulting in:
• Abduction—limitation
• Adduction—limitation
• Palpebral aperture—narrowing in primary
position as well as in adduction and abduction.
• Globe retraction.
Probable cause of dysinnervation is:
• Embryopathy, i.e. developmental disturbance
is responsible for dysinnervation. This fact is
Incomitant Strabismus
Fig. 12.43 Right eye illustration of potential innervation
patterns in different types of Duane syndrome. VI indicates
fibres of the sixth cranial nerve. III indicates fibres of the
third cranial nerve. Dashed lines indicate hypoplastic or
absent nerve fibres. Thin lines indicate relative decreased
innervation.
351
corroborated by the type of associated systemic
anomalies as well as the frequent association of
Duane’s syndrome in well documented cases of
thalidomide embryopathy.
• Hereditary basis for the anomaly has also been
suggested on the basis of familial occurrence
with dominant inheritance pattern of the
syndrome.
Classification of Duane's syndrome
Duane's retraction syndrome (DRS) has been
classified by various workers (Brown 1950, 1958;
Lyle and Bridgeman 1959, Huber, 1974).
However, to avoid confusion only the most
commonly accepted Huber's classification is
given here.
Huber's classification is not only most useful
one clinically, but is well supported by
electromyographic documentation. Huber
classified Duane's syndrome into three types
I, II, III and recently type IV has also been
added all associated with paradoxical
innervation.
Duane's type I is the most common (78%)
followed by type III (15%) and type II is the least
common variety. A manifest ocular deviation
352 Theory and Practice of Squint and Orthoptics
Table 12.10 Khurana's modification over Huber's classification of Duane's retraction syndrome
Type Subtype Eye in primary position Other features
Ia Esotropic Marked limitation of abduction
Almost normal adduction
I Ib Exotropic Narrowing of palpebral fissure on adduction
Ic Orthotropic Retraction of globe on adduction
II IIa Esotropic Marked limitation of adduction,
almost normal abduction
IIb Exotropic Narrowing of palpebral fissure on
attempted adduction
IIc Orthotropic Retraction of globe on attempted
adduction
III IIIa Esotropic Marked limitation of abduction
IIIb Exotropic Marked limitation of adduction
Narrowing of palpebral fissure on
attempted adduction and abduction
IIIc Orthotropic Retraction of globe on attempted
adduction and abduction
in primary position may or may not be present
in Duane's retraction syndrome. Huber's
classification though most useful clinically, does
not tell about the associated type of deviation.
Khurana (1988) has modified Huber's
classification by dividing each type into three
subtypes depending on the deviation in primary
position, viz. a, b and c for esotropia, exotropia
and orthotropia, respectively (Table 12.10). This
minor modification has made the Huber's
classification complete and more specific.
Clinical features
Clinical features of Duane's syndrome can be
discussed as: (I) General features, (II) Features
related to ocular motility defect, (III) Associated
ocular abnormalities, and (IV) Associated
systemic abnormalities.
I. General features
1. Females are more frequently involved than
males.
2. Left eye is more commonly affected (75%)
than the right.
3. Bilateral involvement is less frequent (20%)
than unilateral occurrence.
4. Sporadic cases are most common, but familial
occurrence with dominant inheritance
pattern has also been reported.
II. Characteristic features of different types of
Duane's syndrome
Characteristic ocular features of DRS types I, II,
III have been described along with the
pathogenesis (see pages 351–353)
Duane's retraction syndrome type I
Pathogenesis. Electromyographic studies have
revealed that on attempted abduction, there is
lack of innervation to the LR causing marked
limitation of abduction and on attempted
adduction, along with MR, the LR also gets
innervation (paradoxical).
Characteristic features of type I DRS (Fig. 12.44),
thus, are:
In primary position eye may be orthophoric,
esotropic (more common) or exotropic.
On attempted abduction since LR muscle does
not receive innervation, so:
• Abduction is limited markedly,
• Palpebral fissure is normal or slightly widened,
and
• Globe is slightly protused. This happens as a
result of relaxation of both LR and MR muscles
during abduction.
On attempted adduction, since along with MR,
LR also gets anomalous innervation, so due to
contraction of MR and LR:
Incomitant Strabismus
Fig. 12.44 Type I Duane's retraction syndrome left eye with mechanical upshoot.
353
• Adduction is present but limited, due to co-
contraction of MR and LR
• Palpebral fissure becomes narrow, and
• Globe is retracted,
• Upshoot or downshoot of the globe may occur
due to slippage caused by co-contraction of
MR and LR
Duane's retraction syndrome type II
Pathogenesis. Electromyographic studies have
demonstrated that:
• On abduction, the LR receives normal or
subnormal innervation.
• On adduction, LR also gets innervation
(paradoxical) along with MR. Adduction and
other features similar.
Characteristic features of type II DRS (Fig. 12.45)
are:
In primary position, eyeball may be orthophoric,
esotropic or exotropic (more common).
On attempted abduction
• Abduction is normal or there may be slight
limitation due to subnormal innervation and/
or associated MR contracture.
• Palpebral aperture remains normal or slightly
widens.
Fig. 12.45 Type II Duane's retraction syndrome left eye (Courtesy: Dr Kanwar Mohan).
354 Theory and Practice of Squint and Orthoptics
On attempted adduction due to co-contraction
of MR and LR:
• Adduction is limited
• Palpebral aperture becomes narrow, and
• Globe is retracted.
Duane's retraction syndrome type III
Pathogenesis. Paradoxical innervation is present
for both LR and MR muscles.
Characteristic features. There occurs co-
contraction of LR and MR both during attempted
adduction and abduction resulting in:
• Marked limitation of adduction as well as
abduction along with associated
• Narrowing of palpebral aperture, and
• Marked retraction of the globe
• Upshoots and downshoots are frequently
present (Fig. 12.46).
Duane retraction syndrome type IV
Type IV Duane syndrome has also been called
as simultaneous abduction, synergistic
divergence, the “splits”, and perversion of the
extraocular muscles by various workers from
time to time. (Wilcox et al, 1981 and Wagner et
al 1987). Schliesser et al (2016) have recommended
that synergistic divergence (Fig. 12.47), a rare
entity with features similar to those of Duane
syndrome, should be classified as Type IV
Duane syndrome as it has unique findings and
an innervation pattern different from the other
three types.
Pathogenesis. In the case of simultaneous
abduction, the oculomotor nerve sends nerve
fibres to the lateral rectus and the signal causes
the eye to abduct and co-contract when it should
simply adduct.
Characteristic features of Type IV Duane
syndrome include (Fig. 12.47):
• Exotropia in primary gaze,
• Face turn opposite the involved eye,
• Essentially full abduction of the involved eye,
Fig. 12.46 Type III Duane's retraction syndrome left eye with innervational upshoot.
Fig. 12.47 Photograph of patient with type IV Duane syndrome.
Incomitant Strabismus
355
• Absent adduction of involved eye with
simultaneous abduction in gaze opposite the
involved eye, and
• Narrowing of the palpebral fissure.
Associations of type IV Duane reported include:
• Abnormal MRI—midbrain finding,
• Goldenhar syndrome,
• Cerebral palsy,
• Nystagmus, and
• Anisometropia
Treatment Weakening by recession of the tight
lateral rectus is the key treatment in these patients.
Inverse Duane’s syndrome
Inverse Duane’s syndrome has the following
features:
On abduction, there occurs
• Abduction limitation either due to co-contraction
of MR along with LR muscle (congenital
inverse Duane’s syndrome) or due to some
fibrosis or entrapment of MR along the medial
orbital wall following trauma (acquired
inverse Duane’s syndrome).
• Palpebral aperture narrowing, and
• Globe retraction.
On adduction, the LR relaxes normally so
following features are noted:
• Adduction may be normal or slightly limited
especially in acquired cases due to fibrotic bands.
• Palpebral aperture usually remains normal, and
Globe also remains within normal position.
III. Other ocular features
1. Horizontal deviation. The eyeball in primary
position may be esotropic, orthotropic or
exotropic.
• One series has reported orthotropia in 31%
cases, esotropia in 53% cases and exotropia
in 16% cases.
• Esotropia has been reported to occur most
frequently with type I, followed by type III
and type II.
• Exotropia is associated more commonly with
type II than types I and III.
• Orthotropia is more frequent with type III
than types I and II.
Deviation should be measured in both habitual
head position and forced straight head primary
position both for distance and near and also in
up, down and lateral gazes. The poor abducting
saccade in affected eye undercover makes the test
less accurate, so the prisms should be placed in
front of the affected eye and fellow eye should
be observed under partial cover. The deviation
in esotropic patients is usually less than 30 PD in
unilateral cases with the non- affected eye fixing.
However, in bilateral non-fusing Duane’s or
unilateral Duane’s fixing with the affected eye
there may be large degree of esodeviation.
Patterns: A large incidence of increased
anomalous innervation of LR in elevation or
depression explains the frequent observation of
V, A or X pattern in these patients.
Y or lambda patterns are seen in patients with
anomalous LR recruitment only in upgaze or
downgaze, respectively. Bilateral Duane's with
fusion often displays A-pattern. In DRS, the
patterns are not due to oblique dysfunction but
by co-contraction of lateral and vertical muscles.
2. Vertical deviations are often present with
characteristic upshoot or downshoot, when the
affected eye is adducted. These occur more
frequently in severe anomalous lateral rectus
recruitment. Two types of upshoots and
downshoots have been described;
a.Mechanical upshoots and downshoots are
reported to result from a tight lateral rectus
muscle (leash effect). In this condition, the
affected eye begins to adduct normally and
then suddenly upshoots or downshoots.
b.Innervational upshoots and downshoots are
reported to result from misinnervation of the
vertical recti muscles. In this condition, there
occurs a progressively increasing vertical
deviation of the affected eye as it starts
adducting.
Electromyographic studies have also demonstrated an abnormal synergistic innervation
between the medial rectus and the superior and
inferior oblique muscles in some cases; and this
may also explain the upshoot or downshoot in
adduction, i.e. frequently seen in this syndrome.
Gradual upshoots may be due to superior rectus
contracture or inferior oblique overaction
(IOOA).
3. Abnormal head posture. Unilateral cases are
frequently accompanied by a head turn for