STRABISMUS

Dr. Joe M DasSenior Resident

Dept. of Neurosurgery

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

• 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

ANATOMY

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

• 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

• The eye movements when tested binocularly – Versions– Same direction (Conjugate)– Opposite directions (Disjugate) - vergence

• Dextroversion, levoversion, dextroelevation, levoelevation, dextrodepression, levodepression, sursumversion, deorsumversion, dextrocycloversion, levocycloversion

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

Fun fact

• People blink, on average, once every 5-6 seconds.

• Women blink almost twice as often as men.

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

• 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

• 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

• 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

Classification

• Concomitant (comitant) – when the deviations are equal in all the different gazes

• Incomitant – When deviations are more in one gaze than the other

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

Incomitant

• Paralytic – Neurogenic (supranuclear, nuclear / infranuclear) or myogenic

• Restrictive• Spastic

• 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

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)

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

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.”

Examination of a case of squint

• Motor status• Sensory status

Motor status

• Head posture• Ocular deviation• Limitations of movements or extent of

versions• Fusional vergences

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

Measurement of interpupillary distance

• Ordinary millimeter scale• Pulzone-Hardy rule• Synoptophore

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

Pseudo-deviations

Pseudo-esotropia

• Epicanthic folds• Short interpupillary distance• Negative angle kappa

Pseudo-exotropia

• Wide interpupillary distance• Positive angle kappa

Angle kappa

Fun facts

• Eyes can process 36,000 bits of information every hour.

• Only 1/6th of the eyeball is exposed to the outside world

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

• 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

Cover tests

• Cover test detects heterotropia • Prism cover test measures total deviation

• Alternate cover test detects total deviation

• Uncover test detects heterophoria

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°

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

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

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

Worth-four dot test

• 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

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

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

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.

PARALYTIC SQUINT

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

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.

• (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.

Aneurysm site to cause IIIrd CN palsy

• Exotropia with hypotropia, ptosis and possible dilation of pupil and accommodation palsy

Complete Third Nerve Palsy

• 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.

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)

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.

• Disruption of the superior division causes ptosis and impaired elevation

• Disruption of the inferior division causes impaired depression, adduction, and mydriasis

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.

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

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).

• 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.

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.

Bilateral 4th nerve palsy• Hyperdeviation alternates such that it is

contralateral to the direction of gaze and ipsilateral to the side of head tilt.

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

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

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.

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)

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

• 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

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.

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

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.

‘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

‘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

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