This document provides information about strabismus (squinting): - It affects 7.5 million people in the US and an estimated 130-260 million worldwide. Strabismus occurs when the eyes are not properly aligned on the point of focus. - The anatomy of the extraocular muscles that control eye movement is described, including the actions of the six muscles and their nerve supply. - Paralytic squints can be caused by neurogenic or myogenic factors. The document discusses third and fourth nerve palsies as examples. Treatment options for strabismus include optical devices, botulinum toxin injections, orthoptic exercises, and surgery.

1. STRABISMUS
Dr. Joe M Das
Senior Resident
Dept. of Neurosurgery

2. A squint is not a sign of luck, it may
indicate poor vision. Get it checked
immediately.
• Greek strabismos, from
strabizein "to squint,"
from strabos "squinting,
squint-eyed.“
• 7,500,000 people suffer
from strabismus in the
US
• A worldwide estimate
would be 130 to 260
million

3. • Binocular single vision (BSV) is one of the
hallmarks of the human race that has
bestowed on it the supremacy in the hierarchy
of the animal kingdom
• ~ 60% of the brain tissue and more than half
of the twelve cranial nerves subserve the eyes
• BSV is accomplished by a perfect sensorimotor
coordination of the two eyes both at rest and
during movement

4. ANATOMY

5. Anatomy
•
•
•
•
•
The two obliques are abductors
The two recti are adductors (RAD)
The two superiors are intorters (SIN)
The two inferiors are extorters
Each is supplied by 2 anterior ciliary arteries, except
lateral rectus which is supplied only by one.
• Recti muscles pull the eye in the direction of their
name in the abducted position
• Obliques push the eye in the direction opposite to their
name in the adducted position

9. • The eye movements when tested uniocularly –
Ductions (Adduction, abduction, elevation or
sursumduction, depression or deorsumduction,
intorsion or incycloduction, extorsion or
excycloduction)
• In paresis, normal ductions may be observed.
This is due to the extra innervation called in to
compensate for the paresis. In version, this is
picked up as the extra innervation goes to the
yoke muscle, which overacts

10. • The eye movements when tested binocularly –
Versions
– Same direction (Conjugate)
– Opposite directions (Disjugate) - vergence
• Dextroversion, levoversion, dextroelevation,
levoelevation, dextrodepression,
levodepression, sursumversion,
deorsumversion, dextrocycloversion,
levocycloversion

11. • Vergence – Convergence, divergence
– Positive vertical divergence – right up, left down
– Negative vertical divergence – Left up, right down
– Incyclovergence- both intort
– Excyclovergence – both extort

13. Fun fact
• People blink, on
average, once every 5-6
seconds.
• Women blink almost
twice as often as men.

14. Sherrington’s law of reciprocal
innervation
• EOM working in pairs – yoke, synergist,
agonist
• Opposing muscle – antagonist
• For any movement, the synergists receive
equal and simultaneous innervation. In
addition, the respective antagonists are
inhibited to facilitate a smooth and
unobstructed movement

15. • Each fovea has a primary visual direction (the
direction of its straight-ahead gaze)
• The two fovea share a common visual
direction
• Any object imaged on the visual direction of
either of the fovea would be superimposed
and seen in the common visual direction,
which is of neither eyes, but of an imaginary
cyclopean eye

17. • One fovea as well as other areas in the retina
have a corresponding point on the other retina
• Objects imaged on the corresponding areas are
seen binocularly single
• Imaginary plane on which corresponding points
are projected – horopter
• A little area on either sides of horopter, which
allows the sensory fusion, despite the disparity –
Panum’s area of fusion  Stereopsis

19. • Normally, the two visual axes meet at the point of
regard or the object of attention – orthophoria /
orthotropia
• If the two visual axes are not aligned to the point
of regard, one eye fixates, other eye does not 
Strabismus
• When this tendency is overcome by the fusional
vergence, the person does not manifest squint 
Latent squint (heterophoria)
• When the squint is present at times, and
controlled at other times – intermittent squint

20. Classification
• Concomitant (comitant) – when the deviations
are equal in all the different gazes
• Incomitant – When deviations are more in one
gaze than the other

21. Concomitant
• Horizontal strabismus: Exotropia (divergent)
and esotropia (convergent) /
Latent ones (heterophorias) – Esophoria,
exophoria
• Vertical tropias: Hypertropia and hypotropia –
described by the hypertropic eye
• Torsional – Incyclotropia / Excyclotropia

23. Incomitant
• Paralytic – Neurogenic (supranuclear, nuclear /
infranuclear) or myogenic
• Restrictive
• Spastic

24. • Hering’s law of motor correspondence:
– Whenever an ocular movement is performed,
simultaneous and equal amount of innervation
flows to the corresponding yoke muscles in the
direction of gaze
• Sherrington’s law of reciprocal innervation:
– Whenever an agonist receives an impulse to
contract, an equivalent inhibitory impulse travels
to the antagonist muscle, which actively relaxes
and lengthens

26. Consequences of strabismus
• Strabismus  Two fovea get two different images
 Rival cortical perception  Confusion 
Suppression of one image
• Tries to overcome by fusion (converting tropia
into phoria)
• Head posturing  other image falls on the
periphery of retina / blind spot
• Sensory adaptations (upto 6-7 years of age)
– Suppression (if in peripheral retina)
– Anomalous retinal correspondence (Fovea with
extrafoveal area)

28. AMBLYOPIA
• Condition with u/l or b/l ↓ of visual functions,
caused by form vision deprivation and / or
abnormal binocular interaction, that cannot
be explained by a disorder of ocular media or
visual pathways itself
• Caused by abnormal visual experience in early
childhood

30. What is Phrenology?
• Phrenology is the study of the morphology of the
skull,
• Developed by Franz Josef Gall (1758 – 1828).
• Gall felt there was a direct link between the
shape of the skull and human character and
intelligence.
• Gall was one of the first to consider the brain the
source of all mental activities.
• People with “high brows” were considered more
intelligent than those with “low brows.”

31. Examination of a case of squint
• Motor status
• Sensory status

32. Motor status
• Head posture
• Ocular deviation
• Limitations of movements or extent of
versions
• Fusional vergences

33. Head posture
• 3 components
– Chin elevation / depression
– Face turn to right / left
– Head tilt to right or left shoulder
• Ocular torticollis: Congenital SO palsy
• RSO palsy  Chin depression, face turn to left,
head tilt to left shoulder

34. Measurement of interpupillary
distance
• Ordinary millimeter scale
• Pulzone-Hardy rule
• Synoptophore

35. Pseudostrabismus
• A true squint is a misalignment of the two visual axes,
so that both do not meet at the point of regard
• An apparent squint is just an appearance of squint in
spite of the alignment of the two visual axes
• Apparent squint or pseudostrabismus can be due to
abnormality of adnexal structures or due to abnormal
relationship between the visual axis and optical axis of
the eyes
– Telecanthus (broad nasal bridge) / epicanthus 
Pseudoesotropia
– Lateral canthoplasty  Pseudoexotropia

36. Pseudo-deviations
Pseudo-esotropia
•
•
•
Epicanthic folds
Short interpupillary distance
Negative angle kappa
Pseudo-exotropia
•
•
Wide interpupillary distance
Positive angle kappa

37. Angle kappa

39. Fun facts
• Eyes can process 36,000 bits of information
every hour.
• Only 1/6th of the eyeball is exposed to the
outside world

40. Cover test
• Proper fixation target – figure / letter of size 6/9
of Snellen’s -- Distance – 33 cm (near) /
6 m (distant)
– Eyes appear to fixate (no apparent squint)
– One appears to fixate as other deviates (apparent
squint)
• Cover the fixating eye 
– If the other eye moves to take up fixation  Manifest
squint (heterotropia)
– Same eye deviates

41. • Uncover 
– Covering breaks the fusion and if there is any
heterophoria, the eye behind the cover deviates
– If it remains deviated  latent squint with poor
fusion
– Speed of recovery Ξ strength of fusion
– If uncovered eye reassumes fixation as the other
eye deviates  Dominant uncovered eye, visual
acuity unequal

42. Cover tests
• Cover test detects heterotropia
• Prism cover test measures total deviation
• Uncover test detects heterophoria
• Alternate cover test detects total deviation

45. Hirschberg’s test
• Corneal reflection
• In esodeviation, the corneal reflection falls
more temporally and vice versa
• 1 mm shift Ξ 5° deviation
• If reflex falls on nasal limbus, the exodeviation
is 30°

47. Hirschberg test
• Rough measure of deviation
• Note location of corneal light reflex
• 1 mm = 5
Reflex at border of pupil = 15
Reflex at limbus = 45

48. Diplopia testing
• Red and green glasses over the right and left
eyes respectively
• Esodeviations  Uncrossed diplopia
• Exodeviations  Crossed diplopia
• Esodeviation  Image falls on nasal retina 
projected on temporal field  uncrossed

49. Maddox rod test
• Multiple cylindrical high plus lenses stacked
on top of each other
• Light is seen as linear streak oriented 90° to
the cylindrical ribs

51. Worth-four dot test

53. • 4 dots  Normal binocular response or
anomalous retinal correspondence with
manifest squint
• 5 dots  Manifest deviation
– Eso (uncrossed) – red on right
– Exo (crossed) – red on left
• 3 dots  Suppression of right eye
• 2 dots  suppression of left eye

54. Medical Treatment
• Treatment of Amblyopia
– Occlusion therapy
• Initial stage
• Maintenance stage
– Atropine therapy
• OpticalDevices
– Spectacles
– Prisms
• Botulinum Toxin
• Orthoptics

55. Surgical Treatment
• Surgical procedu res
– R e s e c t io n a n d r ec e s s io n
– S h iftin g o f p o in t o f m u sc l e att ac h m en t
– F ad e n p ro c ed u r e
• Choice of muscles for surgery
• Adjustable sutures

57. Fun facts
• Eyelashes have an average life span of 5
months.
• The eyeball of a human weighs approximately
28 grams.
• Your eye will focus on about 50 things per
second.

58. PARALYTIC SQUINT

59. Forced duction test
• Simple and most useful method for diagnosing the
presence of mechanical restriction of ocular motility.
• 4% lidocaine
• The eye is then moved with two-toothed forceps applied to
the conjunctiva near the limbus in the direction opposite
that in which mechanical restriction is suspected.
• To distinguish between lateral rectus paralysis and
mechanical restriction involving the medial aspect of the
globe, apply the forceps at the 6- and 12-o’clock positions
and move the eye passively into abduction.
– No resistance  paralysis of the lateral rectus muscle.
– Resistance +  mechanical restrictions do exist medially and
contracture of the medial rectus muscle, conjunctiva, or Tenon’s
capsule or myositis of the medial rectus muscle must be
considered

61. 3rd Nerve Palsy
• Complete, isolated third nerve palsy causes
ipsilateral weakness of elevation, depression,
and adduction of the globe, in combination
with ptosis and mydriasis.

62. • (A) Left ptosis, mydriasis,
exotropia, and right
hypertropia in primary
gaze.
• (B) Absent left elevation.
• (C) Reduced left
depression.
• (D) The left pupil shows
minimal consensual
response to light, with
greater anisocoria.

63. Aneurysm site to cause IIIrd CN palsy

64. Complete Third Nerve Palsy
• Exotropia with hypotropia, ptosis and possible
dilation of pupil and accommodation palsy

65. • A characteristic feature is that the affected eye
is hypotropic in upgaze but hypertropic in
downgaze, because of the combined
weakness of the superior and inferior rectus
muscles.

66. 3rd N nuclear lesion
• Specifically, there is bilateral ptosis (because
the central caudal nucleus supplies both
levator palpebrae muscles) and
• A bilateral elevation deficit (because the
superior rectus subnucleus sends fibers
through the contralateral third nerve nucleus
to join the opposite nerve)

67. Unilateral nuclear 3rd N palsy
• Ipsilateral mydriasis
• Ipsilateral weakness of the medial rectus,
inferior rectus, and inferior oblique muscles
• Bilateral ptosis and
• Bilateral superior rectus weakness.

68. • Disruption of the superior division causes
ptosis and impaired elevation
• Disruption of the inferior division causes
impaired depression, adduction, and mydriasis

69. Microvascular 3rd nerve palsy
• Risk factors including hypertension, diabetes,
hyperlipidemia, advanced age, and smoking
• This disorder results from impairment of
microcirculation leading to circumscribed,
ischemic demyelination of axons at the core of
the nerve, typically in the cavernous sinus portion
where a watershed territory exists.
• Most of these patients exhibit pupillary sparing,
because the pupillary fibers are located
peripherally, closest to the blood supply provided
by the surrounding vasa nervorum.

70. AN ISOLATED DILATED PUPIL IS NEVER A
MANIFESTATION OF THIRD NERVE
DYSFUNCTION IN AN AWAKE AND ALERT
PATIENT.

71. Treatment
• The treatment of diplopia due to acute third
nerve palsy may include monocular patch-ing or
prisms.
• Once ocular misalignment from third nerve palsy
has been stable for 6 to 12 months, surgical
correction can be considered.
• Supramaximal lateral rectus recession (a
weakening procedure that completely abolishes
abduction), potentially in combination with a
medial rectus resection (a tightening procedure
to augment the muscle’s action).

73. • Under the right conditions, the human eye can
see the light of a candle at a distance of 14
miles.
• The external muscles that move the eyes are
the strongest muscles in the human body for
the job that they have to do. They are 100
times more powerful than they need to be.

74. 4th nerve palsy
• Fourth nerve palsy presents with vertical diplopia and is
commonly accompanied by compensatory contralateral
head tilt.
• Parks-Bielschowsky three-step test
• First, hypertropia suggests weakness of the ipsilateral
superior oblique, ipsilateral inferior rectus, contralateral
inferior oblique, or contralateral superior rectus muscle.
• Second, increased hypertropia in contralateral gaze narrows
the possibilities to the weakness of the ipsilateral superior
oblique or contralateral superior rectus muscles.
• Third, increased hypertropia on ipsilateral head tilt further
reduces the possibilities, ultimately identifying ipsilateral
superior oblique weakness.

77. Bilateral 4th nerve palsy
• Hyperdeviation alternates such that it is
contralateral to the direction of gaze and
ipsilateral to the side of head tilt.

78. Fourth nerve palsy in the setting of
concomitant third nerve palsy
• The failure of adduction prevents complete
testing of superior oblique function. In this
setting, the superior oblique can be evaluated
by assessing its secondary function: intorsion
of the abducted eye on attempted downgaze.
The torsional movement that indicates intact
superior oblique function is best appreciated
by observing a conjunctival vessel

79. Treatment
• Occlusion of the affected eye (or, if diplopia
occurs only in down-and-contralateral gaze,
occlusion of the lower half of the lens over the
affected eye) can serve as a temporary
measure
• IO / SR recession

80. 6th nerve palsy
• Weakness of the lateral rectus due to sixth nerve
palsy leads to horizontal diplopia, worse to the
affected side and at distance. Often, the
abnormal duction is easily observed.
• Nuclear sixth nerve palsy affects the ipsilateral
sixth nerve as well as the interneurons destined
for the contralateral medial rectus subnucleus.
This lesion causes an abduction deficit of the
ipisilateral eye as well as an adduction deficit of
the contralateral eye; together, this is a conjugate
gaze palsy.

82. Duane syndrome
• 3 varieties of Duane syndrome
• A paradoxic co-contraction of the lateral and medial rectus muscles
• A visible retraction of the globe and narrowing of the palpebral
fissure on attempted adduction
– Type 1, abduction is impaired with essen-tially full adduction;
– type 2, adduction is impaired with normal abduction
– Type 3, adduction and abduction are reduced.
• The abduction deficit in types 1 and 3 cause the patient to be
esotropic on lateral gaze to the affected side, but these patients can
be distinguished from those with acquired abduction deficits
because they have normal alignment (rather than esotropia) in
primary gaze.
• Pathologic studies of patients with Duane syndrome show
hypoplasia of the sixth nerve nucleus and abnormalities of the
fascicle, with branches of the third nerve supplying the lateral
rectus muscle.
• Sporadic / familial (CHN1 gene on chromosome 2)

84. • Mobius syndrome describes congenital facial
diplegia that is frequently associated with
sixth nerve palsy

85. ..
Mobius syndrome
Signs
•
Bilateral sixth nerve palsies - • Primary position - 50%
patient looking left
straight, 50% esotropic
• Horizontal gaze palsy in
50%
•
•
Bilateral, usually
asymmetrical facial
palsies sparing lower face
Paresis of 9th and 12th
cranial nerves

86. Treatment
• Occlusion / prism
• Treatment of partial sixth nerve palsy may include
a combined medial rectus recession and lateral
rectus resection on the affected side.
• In cases of complete sixth nerve palsy, the
affected lateral rectus is typically left intact to
preserve anterior segment circulation.
Restoration of abduction on the affected side
may be attempted by transposition procedures
that aim to move the vertically acting rectus
muscles into the horizontal plane.

88. COMBINED THIRD, FOURTH, AND
SIXTH NERVE PALSY
• fungal, or bacterial infection (including
tuberculosis, syphilis, and Lyme disease).
• Inflammatory diseases include sarcoidosis and
idiopathic pachy-meningitis.
• Neoplastic processes include carcinomatous and
lymphomatous meningitis.
• Peripheral demyelinating disorders including
Guillain-Barre syndrome, the Miller Fisher
variant, chronic inflammatory demyelinating
polyneuropathy, and idiopathic cranial
neuropathies

90. Fun facts
• It's impossible to sneeze with your eyes open.
• The eye of a human can distinguish 500
shades of the gray.
• People generally read 25% slower from a
computer screen compared to paper.

91. ‘V’ pattern deviation
Signs
Treatment
‘V’ pattern esotropia
•
•
Difference between up- and
downgaze is 15 or more
Bilateral medial rectus recessions +
downward transposition
‘V’ pattern exotropia
•
Bilateral lateral rectus recessions
+ upward transpositions

92. ‘A’ pattern deviation
Signs
•
Treatment
Difference between up- and ‘A’ pattern esotropia
• Bilateral medial rectus recessions
downgaze 10 or more
+ upward transposition
‘A’ pattern exotropia
•
Bilateral lateral rectus recessions
+ downward transposition