Strabismus

Strabismus
Neuro-ophthalmology

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 subservethe 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 obliquesare abductors
•The two rectiare adductors (RAD)
•The two superiors are intorters(SIN)
•The two inferiors are extorters
•Each is supplied by 2 anterior ciliaryarteries, except
lateral rectus which is supplied only by one.
•Rectimuscles pull the eye in the direction of their
name in the abducted position
•Obliquespush 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,
intorsionor incycloduction, extorsionor
excycloduction)
•In paresis, normal ductionsmay be observed.
This is due to the extra innervationcalled in to
compensate for the paresis. In version, this is
picked up as the extra innervationgoes 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’sarea 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: Hypertropiaand hypotropia–
described by the hypertropiceye
•Torsional–Incyclotropia/ Excyclotropia

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

24. •Hering’slaw 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 (upto6-7 years of age)
–Suppression (if in peripheral retina)
–Anomalous retinal correspondence (Fovea with
extrafovealarea)

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
•Fusionalvergences

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 pseudostrabismuscan be due to
abnormality of adnexalstructures 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 Ξstrength 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
•Alternate cover test detects total deviation
•Uncover test detects heterophoria

45. Hirschberg’s test
•Corneal reflection
•In esodeviation, the corneal reflection falls
more temporally and vice versa
•1 mm shift Ξ5°deviation
•If reflex falls on nasal limbus, the exodeviation
is 30°

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

48. Diplopiatesting
•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. M e d i c a l T r e a t m e n t
•T r e a t m e n t o f A m b l y o p i a
–O c c l u s i o n t h e r a p y
•I n i t i a l s t a g e
•M a i n t e n a n c e s t a g e
–A t r o p i n e t h e r a p y
•O p t i c a l D e v i c e s
–S p e c t a c l e s
–P r i s m s
•B o t u l i n u m T o x i n
•O r t h o p t i c s

55. S u r g i c a l T r e a t m e n t
•S u r g i c a l p r o c e d u r e s
–R e s e c t i o n a n d r e c e s s i o n
–S h i f t i n g o f p o i n t o f m u s c l e a t t a c h m e n t
–F a d e n p r o c e d u r e
•C h o i c e o f m u s c l e s f o r s u r g e r y
•A d j u s t a b l e s u t u r e s

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 ductiontest
•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 limbusin 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 myositisof the medial rectus muscle must be
considered

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

62. •(A) Left ptosis, mydriasis,
exotropia, and right
hypertropiain 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. •Exotropia with hypotropia, ptosis and possible
dilation of pupil and accommodation palsy
Complete Third Nerve Palsy

65. •A characteristic feature is that the affected eye
is hypotropicin upgazebut hypertropicin
downgaze, because of the combined
weakness of the superior and inferior rectus
muscles.

66. 3
rd
N nuclear lesion
•Specifically, there is bilateral ptosis(because
the central caudal nucleus supplies both
levatorpalpebraemuscles) and
•A bilateral elevation deficit (because the
superior rectus subnucleussends fibers
through the contralateralthird nerve nucleus
to join the opposite nerve)

67. Unilateral nuclear 3
rd
N palsy
•Ipsilateralmydriasis
•Ipsilateralweakness of the medial rectus,
inferior rectus, and inferior oblique muscles
•Bilateral ptosisand
•Bilateral superior rectus weakness.

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

69. Microvascular3
rd
nerve palsy
•Risk factors including hypertension, diabetes,
hyperlipidemia, advanced age, and smoking
•This disorder results from impairment of
microcirculation leading to circumscribed,
ischemic demyelinationof axons at the core of
the nerve, typically in the cavernous sinus portion
where a watershed territory exists.
•Most of these patients exhibit pupillarysparing,
because the pupillaryfibers are located
peripherally, closest to the blood supply provided
by the surrounding vasanervorum.

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

71. Treatment
•The treatment of diplopiadue to acute third
nerve palsy may include monocular patch-ingor
prisms.
•Once ocular misalignment from third nerve palsy
has been stable for 6 to 12 months, surgical
correction can be considered.
•Supramaximallateral 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. 4
th
nerve palsy
•Fourth nerve palsy presents with vertical diplopiaand is
commonly accompanied by compensatory contralateral
head tilt.
•Parks-Bielschowskythree-step test
•First, hypertropiasuggests weakness of the ipsilateral
superior oblique, ipsilateralinferior rectus, contralateral
inferior oblique, or contralateralsuperior rectus muscle.
•Second, increased hypertropiain contralateralgaze narrows
the possibilities to the weakness of the ipsilateralsuperior
oblique or contralateralsuperior rectus muscles.
•Third, increased hypertropiaon ipsilateralhead tilt further
reduces the possibilities, ultimately identifying ipsilateral
superior oblique weakness.

77. Bilateral 4
th
nerve palsy
•Hyperdeviationalternates such that it is
contralateralto the direction of gaze and
ipsilateralto 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 torsionalmovement that indicates intact
superior oblique function is best appreciated
by observing a conjunctivalvessel

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

80. 6
th
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 ductionis easily observed.
•Nuclear sixth nerve palsy affects the ipsilateral
sixth nerve as well as the interneuronsdestined
for the contralateralmedial rectus subnucleus.
This lesion causes an abduction deficit of the
ipisilateraleye as well as an adduction deficit of
the contralateraleye; together, this is a conjugate
gaze palsy.

82. Duane syndrome
•3 varieties of Duane syndrome
•A paradoxicco-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-tiallyfull 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
esotropicon 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
hypoplasiaof 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. •Mobiussyndrome describes congenital facial
diplegiathat is frequently associated with
sixth nerve palsy

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

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 sarcoidosisand
idiopathic pachy-meningitis.
•Neoplasticprocesses include carcinomatousand
lymphomatousmeningitis.
•Peripheral demyelinatingdisorders including
Guillain-Barresyndrome, 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
‘V’ pattern esotropia
•Bilateral medial rectus recessions +
downward transposition
•Bilateral lateral rectus recessions
+ upward transpositions
‘V’ pattern exotropia
•Difference between up-and
downgaze is 15 or more
Signs Treatment

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