Strabismus

Dr HAN WeiThe 1st Affiliated Hospital, Medical College,

Zhejiang University

Basic knowledge of ocular motility

Extraocular muscles

Not playing role in vision procedure directly, b

ut critically important for eyeball motility and b

inocular vision function.

Anatomy of extraocular muscles

Six extra-ocular muscles for the human eye. Namely: Medial rectus m. Lateral rectus m. Superior rectus m. Inferior rectus m. Superior oblique m. Inferior oblique m.

Insertion positions of four rectus m.

MR: Medial rectus m. LR: Lateral rectus m. SR: Superior rectus m. IR: Inferior rectus m.

Nerve innervation for extraocular m.

III cranial n.III cranial n. Medial rectus m. Superior rectus m. Inferior rectus m. Inferior oblique m.

IV (Trochlea) cranial n.IV (Trochlea) cranial n. Superior oblique m.

VI (Abduction) cranial n.VI (Abduction) cranial n. Lateral rectus m.

Basic motility function of the eye ball

Elevation and depression (A, B)Elevation and depression (A, B)

Adduction and abduction (C, D)Adduction and abduction (C, D)

Intorsion and extorsion (E, F) Intorsion and extorsion (E, F)

Motility functions of right eye’s extraocular muscle

Inferior oblique m. Extorsion Elevation Adduction

Superior rectus m. Elevation Intorsion Adduction

Inferior rectus m. Depression Adduction Extorsion

Superior oblique m. Intorsion Depression Abduction

Lateral rectus m. Abduction

Medial rectus m. Adduction

Terminology of extra-ocular muscle regarding their physiological functions

Antagonist m.:Antagonist m.: the muscle that counteracts the agonist (or the prime mover); lengthening when the agonist muscle contracts. e.g., medial rectus and lateral rectus m..

Yoke m. : Yoke m. : The contra-laterally paired extra-ocular muscles of two fellow eyes that

work synergistically to direct the gaze in a given direction. Example: in directing the gaze to the right, the right lateral rectus and

left medial rectus operate together as yoke muscles.

Synergist m.: Synergist m.: The muscles moving one single eye ball in the same direction as the

prime moving muscle. e.g., inferior oblique m. is the synergist of superior rectus m. when the

eye turns upward.

Nervous innervation laws

Sherrington law:

A muscle will relax when its antagonist muscle

(e.g., lateral and medial m.) is activated.

Hering law:

The yoke m. are innervated equally by nervous

system in eye movement.

Eye position for examination

Primary position:

With condition in which head being put vertically and

straightforward and two eyes looking straightforward.

Secondary position:

The two eyes being in adduction or abduction or elevation or

depression position.

Tertiary position:

Two eyes gazing in oblique directions (up or downward).

Left superior rectus m. Right inferior oblique m.Right superior rectus m.

Right medial rectus m.Left lateral rectus m.

Left inferior rectus m.Right inferior rectus m.

Right superior oblique m.

Right Superior rectus m.Left inferior oblique m.Left superior rectus m.

Left medial rectus m.Right lateral rectus m.

Right inferior rectus m.Left superior oblique m.Left inferior rectus m.

Right Superior rectus m.Left Superior rectus m.

Right Inferior rectus m.Left Inferior rectus m.

Definitions

Strabismus: A condition in which the eyes are not properly aligned with

each other, i.e., manifest deviation of the eyes exist.

Heterophoria: A condition in which the visual axes of two eyes fail to rem

ain parallel after elimination of visual fusional stimuli. e.g, covering one eyee.g, covering one eye

Classification Based on concomitancy

Concomitant: Angle of squint is the same in all directions of gaze.

Exotropia Esotropia

Inconcomitant: Angle differs in different directions of gaze.

Special types: e.g., Duane syndrome Based on etiology

Functional Paralytic (secondary to traumatic or pathological lesions)

Based on constancy Constant

Single eye deviation Alternative deviation

Intermittent

Examination and diagnosis

Disease and familial historyDisease and familial history Onset ageOnset age Visual acuityVisual acuity RefractionRefraction Strabismus typeStrabismus type Compensative head positionCompensative head position Test for strabismus*Test for strabismus*

Epicanthal fold – should be ruled out in child patients

Simulated esotropiaSimulated esotropia

Cover test and uncover testCover test and uncover test Alternative cover testAlternative cover test

Unilateral gaze (A) or alternative gaze (B)

Strabismus test (1)

A

B

Strabismus test (2)

Corneal reflex testCorneal reflex test Simple, easy methodSimple, easy method Broadly applied in clinicBroadly applied in clinic

Strabismus test (2)

Other methodsOther methods Prism and cover tPrism and cover t

estest Perimeter arc testPerimeter arc test Maddox rod testMaddox rod test Synoptophore testSynoptophore test

Concomitant strabismus

Accommodative Complete accommodative Partially accommodative

Non-accommodative First deviation angle = Secondary deviation angle

First deviation angle: When the normal eye gazing target, the strabismus angle of the deviated eye.

Second deviation angle: When deviated eye gazing target, the strabismus angle of the normal eye.

Concomitant esotropia

Most commonly seen type, closely assMost commonly seen type, closely associated with accommodation function.ociated with accommodation function.

First angle = Second angleFirst angle = Second angle Usually no diplopiaUsually no diplopia Normal ocular motilityNormal ocular motility Intermittent in incipient stage and turIntermittent in incipient stage and tur

n to be constant gradually. n to be constant gradually.

Treatment Treatment

Spectacle correction for ametroSpectacle correction for ametropiapia

Treat amblyopiaTreat amblyopia Eye position trainingEye position training SurgerySurgery

An example of concomitant esotropia

After operation, the two eyes’ position is corrected to be normal. (Lower figure)

An example of partially accommodative concomitant esotropia

With spectacle, squint was partially corrected, but still existed. (lower figure)

Concomitant exotropia

Associated with:Associated with: Central nervous biocular balancing function, Central nervous biocular balancing function, Imbalance of accommodation and convergence,Imbalance of accommodation and convergence, AnisometropiaAnisometropia Visual impairment in one eyeVisual impairment in one eye

Intermittent early stage to constant stage. Intermittent early stage to constant stage. Treatment:Treatment:

Ametropia correctionAmetropia correction Prism spectaclePrism spectacle SurgerySurgery

An example of concomitant exotropia treated by surgery

Deviation was correctly after surgery. (Figure left)

An example of concomitant exotropia due to visual impairment in left eye

Nonconcomitant strabismus

Usually paralytic secondary to: Embryo development anomalies Trauma Inflammation Hypertension and hemorraghe & ischemia Tumor Metabolism disorder like diabetes, thyroidism, etc

Symptoms

Diplopia Diplopia Compensation head positionCompensation head position Deviation of affected eyeDeviation of affected eye First angle First angle ＜ ＜ second anglesecond angle Compromise of ocular motilityCompromise of ocular motility

Hess screen test

Shift of the square denotes the muscle Shift of the square denotes the muscle being paralytic.being paralytic.

Compensation head position in paralysis of the right eye’s lateral rectus muscle

An example of paralytic esotropia

Lateral rectus m. of right eye paralysis. Note the 1st angle (figure right) is less than second angle (figure left)

An example of paralytic vertical strabismus of right inferior rectus m.

Treatment Primary diseases treatmentPrimary diseases treatment Drug Drug

Vit B1, B12, ATPVit B1, B12, ATP SteroidSteroid AntibioticsAntibiotics Botulinum A injection to relief the muscle spasmBotulinum A injection to relief the muscle spasm PrismPrism

SurgerySurgery Usually 6 months after onset, with deviation being stable.Usually 6 months after onset, with deviation being stable.

Differentiation of paralytic and concomittent strabismus

Paralytic Concomittent

Onset SuddenlySuddenly GraduallyGradually

Eye motility Compromised in affected Compromised in affected m. movement directionm. movement direction

NormalNormal

Deviation angle 22ndnd angle > 1 angle > 1stst angle angle EqualEqual

Diplopia YesYes NoNo

Compensative head position

YesYes NoNo

Amblyopia

Definition of amblyopia: otherwise known as lazy ey

e, is a disorder of the visual system that is characterize

d by poor or indistinct vision in an eye that is otherwis

e physically normal.

It has been estimated to affect 1–5% of the population.

Etiology: The nerve pathway from one eye to the brain

does not develop during childhood or the abnormal ey

e sends a blurred image to the brain.

Category of etiology

Strabismus Strabismus (Most common type, due to crossing eye)(Most common type, due to crossing eye)

Anisometropia Anisometropia (Imbalance of visual input)(Imbalance of visual input)

Ametropia Ametropia (Double eye onset)(Double eye onset)

Form deprivation Form deprivation (Refractive media opacity)(Refractive media opacity)

Others Others (Pathological lesions)(Pathological lesions)

Symptoms

Vision acuity lossVision acuity loss Mild:Mild: 0.6-0.80.6-0.8 Moderate:Moderate: 0.2-0.50.2-0.5 Severe: Severe: less than less than

0.10.1 Abnormal fixationAbnormal fixation Crowding phenomenonCrowding phenomenon

Treatment (1)Treatment (1)

Early treatment. Early treatment. As early as possible. Critically As early as possible. Critically

important!important! Treatment effect is poor after 9 years Treatment effect is poor after 9 years

old.old.

Ametropia correction: spectacle even LASIK, surgery fAmetropia correction: spectacle even LASIK, surgery for congenital cataract.or congenital cataract.

Occlusion therapyOcclusion therapy Occluding normal eye, allowing amblyopic eye tOccluding normal eye, allowing amblyopic eye t

o develop o develop Red light therapyRed light therapy

Stimulating the macular function developmentStimulating the macular function development After image therapyAfter image therapy Depression therapyDepression therapy

Using atropine or over- or under-correction lensUsing atropine or over- or under-correction lens Synoptophore therapySynoptophore therapy Drug (L-Dopa)Drug (L-Dopa)

Treatment (2)

Nystagmus

A condition of involuntary rhythmically oscillation of the globe. According to the rhythm, it is divided into two sorts:

jerky and pendular.

Physiological and pathological Category:

Perpetual Opticokinetic Labyrinthine Environmental

Binocular vision

Normal human’s vision is the matter of the co-Normal human’s vision is the matter of the co-ordination of the two eyes. ordination of the two eyes.

The eyes must be capable of aligning themselves in The eyes must be capable of aligning themselves in such a manner: the retinal images of a fixated target such a manner: the retinal images of a fixated target can easily be placed and maintained on the foveae of can easily be placed and maintained on the foveae of the two eyes. the two eyes.

Normal binocular vision is established in about 5-6 Normal binocular vision is established in about 5-6 years.years.

Binocular vision

Condition of the normal binocular Condition of the normal binocular vision : vision : (1) in good focus;(1) in good focus; (2) similar image size (within 5% (2) similar image size (within 5%

disparity); disparity); (3) similar image shape;(3) similar image shape; (4) normal eyes’ motility; (4) normal eyes’ motility; (5) fusion ability and area; (5) fusion ability and area; (6) normal neural pathways.(6) normal neural pathways.

Grade of binocular visionGrade of binocular vision Simultaneous perception

Ability to simultaneously percept the retinal image of the two eyes

Fusion Images formed on the retina o

f the two eyes are combined into a single percept.

Stereopsis Highest grade of binocular vis

ion. Perception of depth and distance.

Normal binocular vision Sensory aspectsSensory aspects

Corresponding retinal pointsCorresponding retinal points Panum fusional areasPanum fusional areas HoropterHoropter Physiological diplopiaPhysiological diplopia

Motor aspectsMotor aspects Conjugate movementConjugate movement

Saccadic movementSaccadic movement Following movementFollowing movement

Disconjugate movement Disconjugate movement ConvergenceConvergence DivergenceDivergence Motor fusionMotor fusion

Abnormal binocular vision

Diplopia Diplopia pathologicalpathological

ConfusionConfusion misalignment of the two eyes in paralytic strabismusmisalignment of the two eyes in paralytic strabismus

SuppressionSuppression amblyopiaamblyopia

Abnormal retinal correspondenceAbnormal retinal correspondence strabismusstrabismus

Eccentric fixationEccentric fixation amblyopiaamblyopia

Low vision Definition of low vision (WHO 1992)

Best corrected visual acuity <0.3, Semi-visual field narrower than 10 degree

Treatment Etiological diseases if viable

Visual aid instruments Telescope Magnifier Electronic apparatus like CCTV, computer display

Low vision aid products

QuestionsQuestions

State refractive components of the eye’s optical system.

The category of myopia and the clinical management?

The classification of the concomittent strabismus and the clinical management?