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Paralytic strabismus, features and investigations of paretic strabismus
PARALYTIC AND PARETIC
FEATURES, IMPORTANCE OF
HERINGS LAW, INVESTIGATIONS
OF PARETC STRABISMUS
Presenter Pabita Dhungel
Institute of Medicine
1) BINOCULAR VISION & STRABISMUS –GK VON
2) CLINICAL MANGEMENT OF STRABISMUS-
ELEZABETH E.CALAROSSA &
MICHAEL W. ROUSE
3) AAO- SECTION: PEDIATRIC OPHTHALMOLOGY &
4) STRABISMUS SIMPLIFIED- PRADEEP SHARMA
5) PRACTICAL ORTHOPTICS IN THE TREATMENT OF
SQUINT- LYLE AND JACKSON’S
Introduction to extra ocular muscles
Few related terms
• Introduction to paralytic and paretic strabismus
Importance of Herings law
Investigations of paretic strabismus
There are 6 extraocular muscles – 4 rectus muscles, 2
5 muscles arise from the apex of the orbit, the inferior
oblique arises form the inferonasal angle of the orbit
The 4 recti muscles originate form the apex of the
orbit at the level of the Annulus of Zinn
The recti muscles are inserted in front of the ocular equator, the
obliques are inserted behind
Movements occur about 3 primary axes around the centre of
rotation – the vertical, horizontal and saggital axes
The action of a muscle depends on the angle of its plane and
the anterio-posterior axis of the eye.
It follows that the action of the muscle may vary according the
positions of the globe in the orbit.
Few related terms
Agonist= muscle producing a specific ocular
Antagonist= muscle having the opposed action
Synergist = muscle having the same actions
Ipsilateral = on the same side
Contralateral = on the opposite side
Contracture = increased resistance against passive
stretching of the muscle, loss of elasticity
Hering’s Law of Equal
An equal and simultaneous innervation flows from
the brain to a pair of muscles of both eyes (yoke
muscles) which contract simultaneously in different
Eg. Equal and simultaneous innervation flows to:
1.RLR and LMR muscles during dextroversion
2.Both MR during convergence
3.RSR and LIO muscles during dextroelevation
Sheringtons Law of Reciprocal
concerned with the co-ordination of muscle pairs of one eye.
ie the contraction of each ocular muscle is accompanied by a
simultaneous and proportional relaxation of its antagonist.
e.g. during dextroversion , an increased innervational flow to
the RLR and LMR is accompanied by decreased flow to the
RMR and LLR muscle
Sequelae of Ocular Muscle Palsy
Underaction of the primary affected muscle
Overaction of the contralateral synergist
Overaction of the ipsilateral (direct) antagonist
Underaction of the antagonist of the contralateral synergist
Overaction of the ipsilateral synergist??
Overaction of the contralateral
This overaction occurs when the affected eye is fixing as
a result of increased innervation being required to rotate
the affected muscle into its field of action.
Due to Herings Law an overstimulation of the
contralateral synergist follows
This is always the largest overaction in the sequelae.
Overaction of the ipsilateral
can lead to a permanent contracture of the muscle and a
loss of elasticity
If the patient fixes with the non-involved eye within a few
days a contracture will develop in the direct antagonist
because the normal contracture of the direct antagonist is
unopposed by the weak muscle.
Underaction of the antagonist of the
contralateral synergist (contalateral
with the involved eye fixing, the movement of the eye
into the field of action of the weak muscles antagonist
requires less innervation than normal due to the
Therefore less innervation is supplied to the contralateral
antagonist which under-acts
For example in paralysis of the
right superior rectus
underaction of right superior rectus
overaction of the left inferior oblique
overaction of the right inferior rectus
underaction of the left superior oblique
(overaction of the right inferior oblique)
Introduction to paralytic strabismus
Terms paretic and paralytic often are used
interchangeably in clinical ophthalmology
Paralytic strabismus is an incomitant strabismus due
to motor deficiency of one or a group of extra ocular
Incomplete paralysis is called paresis and complete
deficiency is called paralysis, while palsy is used for
both without specifying
DIPLOPIA-A)Uncrossed diplopia with an
esotropia. B)Crossed diplopia with an exotropia.
Limitation of movement in the field of action of the
Difference in primary and secondary deviations
variable ocular deviation in different position
which is maximum in the field of action of the muscle
(eg. In a LLR palsy esotropia is maximal in the
abduction of LE)
ii)Limitation of movement
of the eye in the field of action of the EOM( in
LLR palsy the abduction of the LE is deficient or
iii) difference in primary and secondary deviation
deviation of the squinting eye with normal eye fixing
is called primary deviation
Deviation of the normal eye with the paretic eye
fixing is called secondary deviation
In paralytic strabismus secondary deviation is greater
than primary deviation
This is because the paretic eye requires more effort
to straighten (come to the primary position to take
up fixation) and this extra effort is passed on to the
contralateral synergist, which is normal, increasing
the ocular deviation
The reverse is true for spastic strabismus i.e primary
deviation is greater than the secondary deviation
differences Paralytic comitant
Age of onset Usually late Usually early childhood
Type of onset Sudden Gradual, sudden
Usually head injury , systemic
Rarely present. Even if
present no cause effect
May be present None
Comitance May develop in late stages Usually present (except
in extreme gazes)
Differences Paralytic Comitant
Diplopia Usually present Absent
Head posture Usually present Absent
Cyclotropia Usually present (except
with horizontal muscle
associated A.V. patterns
or oblique over-actions
Past pointing Present in recent cases absent
Stages of paralytic squint
Undergoes three stages
1. Paresis of the particular muscle
2. Overaction of the ipsilateral antagonist
3. Underaction of the antagonist of the
1. First stage
The maximal deviation is in the field of action of
the paretic muscle for e.g. In a case left LR palsy,
the deviation is maximum in levoversion
2. Second stage
As the overaction of the ipsilateral antagonist
occurs the deviation overacting, the duration
increases in the dextroversion
3. Third stage
The underaction of the contralateral synergist
occurs.this is known as inhibitional palsy
Importance of hering’s law
1. Secondary deviation( fixating with squinting eye)
is more than primary deviation in paralytic strabismus
This is based in hering’s law because when the patient
fixates with the squinting eye an excess innervation
is required to the paralysed muscle to fixate and the
concomitant excess supply to the yoke muscle from
the normal eye causes excess contraction leading to
more, the so-called secondary deviation
2. Inhibitional palsy
of the contralateral antagonist muscle developing in
patients with paralytic squint is based on Hering’s law
for e.g if a patient has RSO muscle paresis and fixates
with RE on object located on patient’s left, less
innervation of RIO is required to move the eye in this
gaze, because it doesn’t have to overcome the normal
antagonistic effect of RSO muscle
Third nerve palsy
The III nerve divides into two branches.
The superior branch supplies the LPS and SR
The inferior branch supplies the MR, IR and IO
A complete lesion of the III nerve involving both
branches will result in a deficit of elevation, adduction
and depression in abduction.
There will be an accompanying ptosis and pupil
Localisation of lesion
Nuclear III often produces bilateral defects of ocular
motility and lid function.
The levator palpebral superioris muscles share a
common central nucleus that produces
Clinical Orthoptics, Third Edition. Fiona J. Rowe.C
2012 John Wiley & Sons, Ltd. Published 2012 by Blackwell Publishing Ltd.
A nuclear lesion may also result in the following:
Unilateral III with bilateral ptosis
Unilateral III with contralateral superior rectus
Isolated extraocular muscle palsy of inferior rectus,
inferior oblique or medial
rectus muscles (Brown 1957)
Bilateral III with spared levator function
(Biousse & Newman 2000, Saeki et al. 2000).
Weber’s syndrome: III and contralateral hemiplegia
due to lesion of corticospinal tract
Benedikt’s syndrome: III and contralateral ataxia and
Claude’s syndrome: Lesion of the red nucleus and III
nucleus producing an
ipsilateral III nerve palsy and contralateral ataxia
(Broadley et al. 2001)
Third nerve palsy may be central, sparing the pupil or
peripheral with pupil involvement.
If the pupil is spared, the cause is most likely
When the pupil is involved, the cause is likely to be
aneurysm (Goldstein&Cogan 1960).
However, pupil sparing in children (unlike in
adults) may not be helpful in differentiating the causes
of the palsy and third nerve
It is necessary to lift the ptotic lid to evaluate visual
May be reduced due to mydriasis, particularly for near
An exo- and hypo-deviation is present
There will be limited elevation, depression and
adduction,which may be complete or partial
limitations, depending on the extent of paresis/palsy.
The examiner should always check for the presence of
IV nerve function by asking the patient to attempt to
look down and outwards and observe for the presence
of incyclotorsion during this movement.
In case of presence of ptosis the upper lid will have
to be raised by the examiner (or an assistant) in order
perform the ocular motility assessment.
It is important to check for unilateral versus bilateral
signs and extent of limitations (ductions) versus
The affected eye will show a markedly constricted
whereas the other eye demonstrates overaction of its
There will be constant diplopia unless complete
ptosis is present and blocks the vision of the affected
Hess chart of right 3rd
This will be absent if the medial rectus muscle is
This is usually absent unless the III nerve paresis is
mild and partial.
If the underlying cause of the lesion has resulted in
pupillary dilatation, then fibres to the ciliary body are
also likely to be involved so that accommodation will
change in the actions of muscles supplied by the third
nerve due to regrowth of damaged nerve fibres
following complete or severe third nerve palsy
(Shuttleworth et al. 1998).
It is liable to occur when either trauma or an
has caused the lesion (Cox et al. 1979, Rossillion et al. 2001).
May occur from weeks to months after the onset of
the III nerve paresis.
Combined horizontal and vertical deviations are
Abnormal movements often involve the eyelids and
There may be horizontal gaze and lid synkinesis
(Chua et al. 2000)
Limited elevation and depression with globe
retraction on attempted vertical movements or
ipsilateral adduction on attempted elevation or
The lid may rise on attempted depression, adduction
and occasionally abduction (pseudo-Graefe
This may constrict on attempted adduction, elevation
(pseudo-Argyll Robertson pupil).
This may occur on attempted elevation
Cyclic oculomotor palsy
This rare condition is usually congenital and
unilateral in origin
(Burian & Van Allen 1963).
It is often associated with a partial III nerve palsy with
some degree of ptosis.
Acquired cyclic ocular motor palsy may occur
following irradiation of the skull base and is similar to
(Miller & Lee 2004).
It may also be due to a compressive lesion
(Bateman & Saunders 1983).
The condition is described as having cyclical
fluctuation in two phases:
1. Paralytic phase: There is a partial III nerve palsy.
2. Miotic phase: There is convergence, lid retraction,
accommodation and pupil constriction.
Single muscle palsy
1. Medial rectus
This produces an exo-deviation, which is greater for
2. Inferior rectus:
This produces hyper- and exo-deviation
3. Superior rectus:
This is often bilateral and may present with a V exo
4. Inferior oblique:
This is a feature of an A eso pattern
Double elevator palsy
This often has a congenital origin and is presumed to
be caused by a supranuclear defect.
The superior rectus and inferior oblique muscles of
the same eye are affected
(Jampel & Fells 1968, Strachan & Innes 1987).
There is a hypo-deviation in the primary position that
may be manifest or latent.
There is limited elevation of one eye in both
adduction and abduction.
Ptosis and/or pseudoptosis may be present.
Bell’s phenomenon is usually present.
Abnormal head posture
The chin is elevated to compensate for the palsy
If there is only a small angle of deviation in the
primary position, this may be controlled with or
without an abnormal head posture, resulting in a
In these circumstances, binocular single vision is
Forced duction test
There may be full passive movement (negative result)
or it may be positive, depending on cause that is
important for surgical planning
Differential diagnosis double
The following conditions should be differentiated
from double elevator palsy as they will have a positive
forced duction test:
Thyroid eye disease
Congenital fibrosis of the inferior rectus muscle
General fibrosis syndrome
IV (fourth) cranial nerve
The IV cranial nerve supplies the superior oblique
Any lesion affecting the nerve may result in
difficulties of depression, incyclorotation and
abduction of the eye
Location of lesion
Fourth nerve palsy may be due to lesions in the
nucleus or fascicular lesions of the midbrain.
It can be difficult to differentially diagnose nuclear
and fascicular lesions as the IV nerves decussate
immediately after exiting the nuclei and exit the
dorsal midbrain after a very short intra-midbrain
The IV nerve is not only susceptible to damage as it
exits the midbrain but also is vulnerable in the
cavernous sinus and orbital apex.
congenital or acquired.
Acquired group may be caused by the following:
Particularly bilateral cases, as the IV cranial nerve is
the only nerve to arise from the dorsal surface of the
midbrain, and therefore follows a long, winding route
that renders it susceptible to injury.
Vascular, for example hypertension.
In congenital superior oblique palsy, the tendon is
usually lax and abnormally long
(Plager 1990, Plager 1992).
In congenital cases, the patients are often affected
They may present with any of the following:
1. Manifest strabismus without binocular function
2. Binocular function, but there may be an abnormal
head posture, depending on the extent of
There is often facial asymmetry in congenital superior
oblique palsy consisting of shallowing of the midfacial
region between the lateral canthus and the edge of the
mouth (Parks 1958).
This is found in three-fourth of patients with
congenital palsy (Wilson &Hoxie 1993, Paysee et al. 1995).
In acquired cases, the paresis may be unilateral or
Bilateral case is often associated with major closed
Symptoms of cyclovertical diplopia are experienced,
which worsen on downgaze.
The presence of an abnormal head posture tends to
indicate more long-standing deviations.
Abnormal head posture
In unilateral IV nerve paresis, the patient may present
with chin depression with face turn and head tilt
away from the affected side.
Bilateral cases demonstrate chin depression but there
may well be no face turn or head tilt unless one side is
affected more than the other.
Persistent abnormal head posture following surgery
for IV nerve palsy should be investigated to exclude
tightness that may have developed in congenital cases
(Lau et al.2009).
The test is performed with and without the abnormal
head posture for comparison.
A latent deviation exists if a compensatory abnormal
head posture is adopted.
When the test is repeated with the head straight, the
deviation will increase and may become manifest
The affected eye shows a hyper-deviation and an
(However, an exo-deviation may be seen if this was
present before the onset of the palsy.)
It is useful to note that the vertical deviation is
commonly greater on near testing than for distance.
In bilateral cases, the main deviation usually tends to
be a small-angle horizontal deviation.
The primary underaction of the affected superior
oblique muscle results in a number of sequelae.
There is overaction of the contralateral inferior rectus
and of the ipsilateral inferior oblique muscles.
The contralateral superior rectus shows secondary
The combination of these muscle effects is variable
and often depends on whether or not the deviation is
In bilateral cases, a V pattern is often present.
In the presence of this, one should always suspect a
bilateral case, especially where there is an
excyclotorsion of greater than 7 and a tendency◦
towards reversal of any hyper-deviation or diplopic
images on lateral gaze
This may be reduced, either due to convergence
insufficiency or the vertical deviation.
Differentiation is achieved by correcting the
deviation and seeing if convergence improves
Field of binocular single vision
The area in which binocular single vision is retained is
displaced upwards to the affected side
The patient experiences a greater degree of diplopia
on near testing when looking down.
The diplopia is vertical and usually uncrossed.
However, if an exo-deviation is present, the
horizontal element of diplopia will be crossed
Assessment of binocular function is carried out with
and without the abnormal head posture, if one is
Binocular single vision cannot be maintained if there
is a significant degree of torsion and therefore is often
not present in acquired bilateral palsies.
Patients who maintain binocularity tend to have a
small angle of deviation associated with a congenital
Some patients with long-standing acquired palsies
can maintain binocularity if there is a good fusional
control with an extended vertical fusion range
Torsion Diagnostic prisms
Excyclotorsion is frequently present in acquired
Fresnel prisms may be used temporarily to correct the
angle of deviation.
If the prism alleviates the need for an abnormal head
posture, then the indication is that the IV nerve was
responsible for the abnormal head posture rather
than a non-ocular cause
thyroid eye disease, ocular surgery, orbital
fracture, neurosurgery, childhood strabismus,
skew deviation, third nerve palsy, myasthenia
gravis and decompensated hyperphoria (Tamhankar
et al. 2011).
Typically, excyclotorsion is seen in IV nerve palsy
and incyclotorsion is seen in skew deviation.
Furthermore, the deviation in IV nerve palsy
remains when the patient is lying down whereas
skew deviation resolves on lying down (Wong 2010).
Investigations unilateral bilateral
Cover test Hyper-deviation in primary
position reflects extent of
Often only slight hyper-
deviation in primary
Ocular motility No reversal of hypertropia or
and diplopia on lateral
Slight V pattern may be noted
Reversal of hyper-
diplopia on lateral
Large V pattern
Chin depression, head tilt and
Torsion Slightly extorsion Extorsion >10◦
VI (sixth) cranial nerve
The VI cranial nerve supplies the lateral rectus muscle
A lesion affecting the nerve will result in defective
abduction of the eye.
The commonly recognised causes of sixth nerve palsy
include space-occupying lesions, trauma, vascular
insults and inflammation.
Sixth nerve palsy secondary to raised intracranial
pressure is also commonly regarded as a typical false
Other causes have included pseudotumor cerebri
(idiopathic intracranial hypertension), post-operative
complications, viral infection, multiple sclerosis and
Following birth trauma
Failure of lateral rectus development
This differs according to age:
Children (Afifi et al. 1992):
– Space-occupying lesions
– Infections, bacterial or viral
Birth history may be significant.
The patient may complain of horizontal diplopia,
which is worse in the distance and/or on lateral
gaze and relatives or friends may notice the presence of
squint (esodeviation) or an abnormal head posture
This may be reduced if the affected eye fails to fixate
properly due to the presence of a marked deviation.
Amblyopia will develop in children with unilateral
Abnormal head posture
The face is turned towards the affected side.
An eso-deviation is present that is often greater on
The test should be carried out with and without an
abnormal head posture, if one is present.
The deviation increases without the head posture but
does not necessarily become manifest
The primary underaction of the affected lateral rectus
results in limited abduction and is followed by a
number of sequelae.
There is overaction of both the contralateral and
ipsilateral medial recti.
There is also secondary underaction of the
contralateral lateral rectus
This is often retained in the presence of an abnormal
As the angle of deviation is often smaller for near
fixation, binocular function is usually present on near
In cases of head trauma, fusion may have been lost.