motor adaptation in paretic and nonparetic strabismus

KO PI LA KAF LE B . OP TOM ET RY

TH I R D Y EAR

MOTOR ADAPTATION IN PARETIC AND NONPARETIC

STRABISMUS

Moderator : Mr. Gaurishankhar Shrestha

PRESENTATION LAYOUT

Introduction to strabismus and its types

Ways of motor adaptation

Reasons for motor adaptation

Motor adaptation in different conditions of

muscle palsy

Motor adaptation in restrictive disorders

STRABISMUS

Aka SQUINT is deviation of eye

Misalignment of the visual axes of the two eyes

TYPES OF STRABISMUS

Can be COMITANT or INCOMITANT

INCOMITANT COMITANT

Results when there is limitation of ocular movement

Result of abnormality in establishment of normal BSV

Can be paralytic or non paralytic

Always non paralytic

limitation of ocular movement normal extraocular motility

particular abnormal head posture develops ,I.E motor adatation occurs

no head posture ,instead sensory adaptation occurs

Muscle sequelae present in old cases

Absence of muscle sequelae

EXAMPLES

INCOMITANT STRABISMUS COMITANT STRABISMUS A . NEUROGENIC A . PRIMARY STRABISMUS due to palsy of third ,fourth and sixth cranial nerveB . MYOGENIC B . SECONDARY STRABISMUS due to problem affecting muscle itselfC . MECHANICAL C .CONSECUTIVE STRABISMUS due to interference with muscle contraction and relaxation

CONSEQUENCE OF STRABISMUS

WHAT TO DO NOW?

I THINK I NEED TO ADAPT

SENSORY ADAPTATION

MOTOR ADAPTATIO

N

Neither I want to see double

Nor I want to be confused

IN COMITANT STRABISMUS

Sensory adaptation occursAbnormal retinal correspondence

suppression

amblyopia

IN INCOMITANT STRABISMUS

Motor adaptation occurs

WAYS OF MOTOR ADAPTATION

Control of ocular deviation by an alteration of tone of extraocular muscles

Compensatory head posture

Blind spot syndrome

Blind spot mechanism

Control of ocular deviation by an alteration of tone of EOM

Can control only small degree of ocular deviation

active contraction or an active relaxation

compelling fusion reflexes

disappearance of squint(manifest deviation converted to latent one)

BLIND SPOT SYNDROME

In esotropia of 12 – 18 ˚ with good visual acuity in both eye

Normal retinal correspondence and normal fusional vergence present

Eye further moved to esotropic side projecting image seen by deviating eye onto blind spot

BLIND SPOT MECHANISM

Coincidental type of esotropia

Image of fixated object falls on the blind spot

BLIND SPOT SYNDROME BLIND SPOT MECHANISM

Good visual acuity in both eyes Amblyopia of the non dominant eye

Normal retinal correspondence Abnormal retinal correspondence

No suppression other than fovea of the deviated eye

ARC and suppression may coexist

Compensatory head posture

Used by visually mature patients(does not necessarily develops in every patients)

Occurs in paralytic strabismus and alphabet pattern strabismus

Has 3 components

HEAD TILT

FACE TURN

CHIN ELEVATION

OR DEPRESSIO

N

WHAT ACTUALLY IS PARALYSIS?

Malfunctioning or dysfunctioning of nerves

Paralysis = no movement is possible

Paretic = some movement is possible

Palsy = includes both paresis and paralysis (generally used )

CRANIAL NERVES SUPPLYING EOMs

Occulomotor (3rd cranial nerve) : supplies SR,IR,IO and MR

Trochlear nerve (4th cranial nerve) : supplies SO

Abducens nerve(6th cranial nerve) : supplies LR

TO KNOW THIS FIRST WE MUST KNOW ACTIONS OF EXTRAOCULAR MUSCLES

WHAT HAPPENS WHEN THESE NERVES GET PARALYSED?

ACTIONS OF EOM

LATERAL RECTUS AND

MEDIAL RECTUS HAVE ONLY

PRIMARY ACTIONS

MEDIAL RECTUS adducts the eye

LATERAL RECTUS abducts the eye

NOTES

Vertical rectus i.e superior and inferior rectus have their primary function as elevator and depressor while secondary action as intorsion and extorsion

For oblique muscle opposite is true

SIN : all superiors are intorters

RAD : all vertical rectus are adducters

LET’S TRY THEN….

SUPERIOR RECTUSA. ELEVATORB. INTORTERC. ADDUCTOR

INFERIOR RECTUSD. DEPRESSORE. EXTORTERF. ADDUCTOR

SUPERIOR OBLIQUE

A. INTORSIONB. DEPRESSORC. ABDUCTION

INFERIOR OBLIQUE

D. EXTORSIONE. ELEVATOR

F. ABDUCTION

IN CASE OF PALSY,

Actions of muscles interrupted

SO, eye takes its position opposite to its action

For example,in LR palsy,eye is in adducted position

in MR palsy,eye is in abducted position

QUESTIONS

WHAT IS EYE POSITION IN

SUPERIOR RECTUS PALSY?

DEPRESSED

EXTORTED

ABDUCTED

WHAT IS EYE POSITION IN INFERIOR OBLIQUE

PALSY?

INTORTED

DEPRESSED

ADDUCTED

Less to be worried about…

In case of palsy, there is usually some direction of binocular gaze in which the visual axes are approximately parallel in which BSV can be obtained

COMPENSATORY HEAD POSTURE

Normal effect of tilting the head

LE is extorted ,so tilting to the right overcomes this disability,visual axes of both eye parallel

In primary position without head posture,LE hypotropic

In dextroversion ,parallelism of visual axes

Updrift of right eye in laevoversion

Congenital paresis of left superior rectus, motor adapted condition

REASONS FOR AHP

TO ACHIEVE BSV :

Head turned into the field of action of paralysed muscle

Eyes directed by DOLL’S HEAD PHENOMENON

Patient’s limited field of single vision coincides with his

egocentric position

Occurs when patient fixates with normal eye

TO ACHIEVE WIDE SEPARATION OF DIPLOPIC

IMAGES

In patients with no useful field of vision

Turn the head opposite to the field of paretic muscle

Deviation of the eye maximum

Occurs when patient fixates with affected eye

DOLL’S HEAD PHENOMENON

Aka tonic movements

Influenced by labyrinthine reflex from otoliths

When head is rotated to the right,the eye will rotate to the left and vice-versa

If the head is tipped backward, the eyes will rotate downward and vice-versa

ALSO KEEP IN MINDWhen head is tilted to the

right shoulder, right eye

intorts while left eye

extorts…..and vice - versa

LET’S TALK ABOUT

ISOLATED MUSCLEPALSY

IN HORIZONTAL RECTUS PALSY

Only one component of abnormal head posture i.e face/head turn

Face turn towards the action of paretic muscle

Head turn to right : - to maintain an ocular posture of laevoversion -compensate for defective abduction of RE or defective adduction of LE

To conclude,

Esotropic eye is made more esotropic

Exotropic eye is made more exotropic, BUT, BE CAREFUL It’s not true in case of cyclovertical

muscle

Head turn in case of cyclovertical muscle

Head is turned such that eyes are brought away from field in which muscle has its greatest vertical effect.

Right superior rectus palsy

e.g. for vertical rectus , having maximum effect on abduction,face is turned so that involved eye is adducted

i.e face is turned towards the affected eye

WHILE , for oblique muscles, having

maximum effect on adduction , face is turned such that the involved eye is abducted

i.e face is turned away from affected eye

IN PALSY OF CYCLOVERTICAL MUSCLE

Has all 3 components of abnormal head posture i.e chin elevation or depression , face turn and head tilt

CHIN ELEVATION

As chin is elevated , eye moves down

Occurs to maintain eye posture of depression to compensate for defective elevation of eye(s)

To conclude , hypotropic eye is eye is made more hypotropic

CHIN DEPRESSION

In chin depression , eye moves up

Adopted to maintain ocular posture of elevation to compensate for defective depression of eye(s)

To conclude hypertropic eye is made more hypertropic

HEAD TILT

In paresis of oblique muscle, head tilt occurs to compensate the torsion

caused by the direct antagonist of paralysed muscle

E.g.in RSO palsy,head tilt occurs to the left to compensate for the extorsion caused by RIO muscle

To conclude, extorted eye is made more extorted and intorted eye made more intorted BUT,its not true for vertical rectus muscle

In paresis of vertical rectus muscle , head tilt occurs to compensate the

torsion caused by contralateral anatagonist of the paralysed muscle

E.g in paresis of RSR, head tilt occurs to right to compensate for the extorsion of the left eye caused by overacting LIO muscle

To conclude,head is tilted to the side of hypotropic

eye

Muscle paralysed

Chin Face turn Head tilt

RSR elevation right right

RIR depression right left

RSO depression left left

RIO elevation left right

RLR _ right _

RMR _ left _

Muscle paralysed

chin Face turn Head tilt

LSR elevation left right

LIR depression left right

LSO depression right right

LIO elevation right right

LLR _ left _

LMR _ right _

EASY STEPS

1. Know the action of the muscle

2. Know the position of the eye

3. Know what should the head and chin do to keep the eye in that position or to make the eye more tropic(or other reasons discussed earlier)

EXAMPLES.. LEFT

LATERAL RECTUS PALSY

ACTION

OF LR

EYE POSITION

TO MAKE MORE ESOTROPIC

HEAD TURN TO

THE LEFT

LEFT MR

PALSYACTION

OF MR

EYE POSITION

TO MAKE MORE EXOTROPIC

HEAD TURN TO

THE RIGHT

Face turn to right to compensate palsy of left medial rectus

IN LSO PALSY ACTION OF

LSO

EYE POSITION

EXTORTED

ELEVATED

ADDUCTED

HEAD TILT TO

THE RIGHT

CHIN DOWN

FACE TURN

TO RIGHT

Left SO palsy,head turn with tilt in right side

Upshoot of LE due to contracture of LIO

Parallelism of visual axes in laevo-version

LIR PALSY ACTION OF IR

MUSCLE

EYE POSITION

ELEVATED

INTORTED

ABDUCTED

CHIN DOWN

HEAD TILT TO RIGHT

FACE TURN

TO LEFT

Compensatory head posture in RIR ,face turn to right,head tilt to left and chin depressed

Dextroversion showing depression of left eye

Dextrodepression,defective movement of RE with overaction of LSO

RSR PALSYACTION OF SR

MUSCLE

EYE POSITION

DEPRESSED

ABDUCTED

EXTORTED

FACE TURN

TO RIGHT

CHIN UP

HEAD TILT TO RIGHT

FIXING WITH NORMAL EYE FIXING WITH

PARETIC EYE

RSR palsy, chin elevation, head tilt to right with face turn to right(common occurrence)

RSR palsy, head tilt and face turn to the left (less common occurrence)

In primary position without head posture,LE hypotropic

In dextroversion ,parallelism of visual axes

Updrift of right eye in laevoversion

Congenital paresis of left superior rectus, motor adapted condition

LIO PALSYACTION OF IO

MUSCLE

EYE POSITION

INTORTED

ADDUCTED

DEPRESSED

FACE TURN

TO RIGHT

HEAD TILT TO LEFT

CHIN UP

LEFT INFERIOR OBLIQUE PALSY

-HEAD TILT TO LEFT-FACE TURN TO RIGHT-CHIN ELEVATED

Mnemonics for head turn and tilt in superior rectus and superior oblique palsy

SO U RS

SUPERIOR OBLIQUE

SAME SIDE

UNAFFECTED SIDE

sUPERIOR RECTUSTHIS HEAD POSTURE IS ADAPTED TO MAINTAIN BSV

LEFT SO PALSY

LEFT SR PALSY

ISOLATED VARIETIES OF OCULAR PALSY

Most common muscles to be paralysed singly : superior oblique and lateral rectusWHY ?

?

BECAUSE THEY HAVE SEPARATE

NERVE SUPPLY

In case of MR, IO, SR and IR

Supplied by 3rd cranial nerve, less likely to occur isolated muscle palsy…

total 3rd nerve palsy3rd nerve palsy partial 3rd nerve palsy

Note: in both cases pupil may or may not be spared in total palsy : both division involved in partial : only one division involved in isolated muscle palsy : only one muscle

involved

TOTAL 3RD NERVE PALSY

Extraocular (IR, MR, IO and SR) , LPS muscle as well as intraocular muscle (sphincter pupillae and ciliary muscle) affected

Dilated pupil Complete

loss of accomodati

on

ptosis

MOTOR ADAPTATION IN TOTAL 3RD NERVE PALSY

Occcurs only if pupil is spared so that the patient experience diplopia requires adaptation

Eye is turned down ,out and slightly intorted

SLIGHTLY CHIN UP FACE TURN

TOWARDS OPPOSITE

SIDE

HEAD TILT TO SAME

SIDE

PARTIAL 3RD NERVE PALSY

SUPERIOR DIVISION PALSY :

-SR and LPS muscle involved

-ptosis with hypotropic eye

- Chin elevated , face turn and head tilt to affected side

INFERIOR DIVISION PALSY :

-IR, IO and MR in addition to sphincter pupillae and ciliary muscle involved

-exotropic,intorted and hypertropic eye with pupil dilatation

-unlikely to be any field of binocular vision

-So , no need for AHP

Restriction of movement of LE in all gazes except in abduction

LEFT THIRD NERVE PALSY

Head tilt and face turn to right with chin up to avioid diplopia

DOUBLE ELEVATOR PALSY

Aka monocular elevation deficiency paralysis of both elevators of same eye i.e superior rectus and inferior oblique

elevation deficiency in entire upgaze i.e both upward adduction and abduction

Head posture

Eyes made more hypotropic by doll’s head phenomenon i.e chin is elevated

DOUBLE DEPRESSOR PALSY

Aka monocular depression deficiency

both depressors of same eye i.e inferior rectus and

superior oblique are paralysed

depression deficiency in entire downgaze both in

adduction and abduction

Head posture

Eyes made more hypertropic by doll’s head phenomenon i.e chin is depressed

SPECIAL RESTRICTIVE DISORDERS

Disorders that are non –paralytic but restricts the ocular movement

Caused by elements within orbit that either interfere with muscle contraction or relaxation or otherwise prevent free movement of globe

Examples ..

Duane’s retraction syndrome

Brown’s syndrome

Grave’s ophthalmopathy

Fibrosis of EOM

DUANE’S RETRACTION SYNDROME

 there is fibrosis or inelasticity of the lateral rectus muscles and that the medial rectus muscle inserts abnormally far posteriorly myogenic cause

absent abducens nerve with anomalous innervations of the lateral rectus muscle by a branch of the oculomotor nerve,

Simultaneous activation of the medial and lateral rectus muscles the cause of globe

(neurogenic ) retraction

 there is fibrosis or inelasticity of the lateral rectus muscles and that the medial rectus muscle inserts abnormally far posteriorly myogenic cause

absent abducens nerve with anomalous innervations of the lateral rectus muscle by a branch of the oculomotor nerve,

Simultaneous activation of the medial and lateral rectus muscles the cause of globe

(neurogenic ) retraction

AHP in DRS

Adopted to centralize BSV

Determined by deviation in primary posistion

ESOTROPIC : face turn to affected side EXOTROPIC : face turn to unaffected side

TYPE I DRS

Marked limitation of abduction

Normal or slightly defective adduction

Narrowing of PFH on adduction

Widening of PFH on abduction

TYPE II DRS

Marked limitation of adduction

Normal or slightly defective abduction

Narrowing of PFH on adduction

DUANE’S RETRACTION SYNDROME,TYPE II

Head posture to compensate for left medial rectus paresis

Dextroversion , defective adduction of LE and narrowing of PFH of LE

Laevo version, parallelism of visual axis, slight widening of left PFH

TYPE III DRS

Marked limitation of adduction and

abduction

Narrowing of PFH on adduction and

abduction

BROWN’S SYNDROME

Aka superior oblique tendon sheath syndrome

Apparent/pseudo paralysis of inferior oblique muscle, limitation of elevation in adduction

Due to restriction of IO action by an overly taut superior oblique tendon of the same eye

Widening of PFH on adductionFew may have in primary

position responsible for head

posture

hypotropia

AHP in BROWN’S SYNDROME

Head tilt to affected side

Face turn to contralateral side

Chin elevation head posture confined to chin elevation

if syndrome is bilateral

GRAVE’S OPHTHALMOPATHY

May be associated with hyper, hypo or euthyroidism

Circulating thyroglobulins, and anti thyroglobulin immune complex bind to EOM ophthalmopathy

in sequence of I’M SLOWInferior rectusMedial rectus Superior

rectusLateral rectus

Oblique muscles

Common ocular mobility defect is U/L elevator deficiency followed by defective abduction

eye is hypotropic and esotropic

Chin elevation

with or without

Face turn to same

side

FIBROSIS OF EOMs

Group of congenital anomalies with restrictions of EOMs

Due to replacement of muscle fibres by the fibrous tissue

Ranges from isolated fibrosis to B/L involvement of all EOMs

GENERALIZED FIBROSIS SYNDROME

Fibrosis of all EOMs no elevation or depression little or no horizontal movementBilateral ptosisAHP : backward head tilt with chin elevated

STRABISMUS FIXUS

Rare disorder , commonly with marked esotropia associated with extreme tightness of MR muscle

Most patient adopt chin elevation

VERTICALLY INCOMITANTHORIZONTAL HETEROTROPIA

Aka alphabet patterns tropiasHorizontal deviation that change in

magnitude with upgaze and downgaze

A-PATTERN HETEROTROPIA

Increasing convergence in upgaze and increasing divergence in downgaze

For A-pattern esotropes,to make eyes relatively convergent in downgaze,the chin is elevated

For A-pattern exotropes,to make eyes relatively divergent in upgaze,the chin is depressed

V-PATTERN HETEROTROPIA

Increasing convergence in downgaze and increasing divergence in upgaze

For V-pattern exotropes,to make eyes relatively convergent in upgaze,the chin is elevated

For V-pattern esotropes,to make eyes relatively divergent in downgaze,the chin is depressed

INFANTILE ESOTROPIA

Manifest eso deviation with an onset between birth and 6 months of age

Etiology unknown

Head & face tilt towards the shoulder of the fixating eye

In some cases AHP associated with ML nystagmus Pt turn head towards the side of the fixing eyewhich

gets optimal visual acuity in the position of adduction

Congenital esotropia with manifest nystagmus,

left eye fixing in adduction, head turned towards left, the direction of the left fixing eye ; pre op

Post-op picture after bi-lateral medial rectus recession

no head turn

REFERENCES

Practical orthoptics in the treatment of squint ; T.KEITH LYLE

and KENNETH C.WYBAR

Squint by LYLE ;eighth edition

Orthoptics and squint;A.K KHURANA

Binocular vision and ocular motility by Von norden

Diagnosis and Management of Ocular Motility Disorders by

Alec M. Ansons and Helen Davis

INTERNET

SPECIAL THANKS TO :

Sanjeev Bhattarai sir

THANKYOU ….