Strabismus

Omar Abughanimeh

Seminar content

• Introduction

• Definition

• Causes

• Classifications

• Consequences

• Approach to patient with strabismus

• Management

Introduction

• Eye movement controlled by:

1- extraocular muscles

•2-cranial nerves ( III, IV, VI)

3- higher cortical functions through the

gaze centers

Yoked movement vs. antagonistic

movement

• Suppose that you ask the patient to

look to the right side , which muscles

will work ????

Hering‟s law vs sherrington‟s law

Normal Vision Actions of EOMs

• Normal binocular single vision (BSV) involves the simultaneous use of both eyes with bifoveal fixation directed to the same target, so that each eye contributes to a common single perception of the object of regard.

• Stereopsis : the perception of depth produced by the reception in the brain of visual stimuli from both eyes in combination; binocular vision “3D”

• Projection is the subjective

interpretation of the position of an

object in space on the basis of

stimulated retinal elements.

• Corresponding „points‟ are areas on

each retina that share the same

subjective visual direction.

Advantages of Binocular Single Vision &

Stereopsis

1-Increased field of vision

2-Elimination of blind spot

3-Binocular acuity (see fine details &

color, better than with monocular acuity)

4-Depth perception (stereopsis)

Abnormal Binocular Single Vision

•If the visual axis of the 2 eyes are not aligned , Binuclear vision Is NOT possible . Results in :

•different places.2 ;An object is seen to be in Diplopia>>

•separate objects appear to be at the same 2 ; >>Visual confusionpoint.

-A non-alignment of the visual axis of the 2 eyes ( SQUINT) results in suppression of the image in the squint eye ,this means when vision is tested in the 2 eyes together no diplopea .

- If prolonged during period of visual development reduced visual acuity in the squint eye ( strabismic Amblyopia).

- Amblyopia will develop only if constant squint affects the same eye.

- children Alternating the squinting eye will NOT develop Amblyopia but do NOT develop Stereopsis either.

Definition

• Strabismus : is deviation of an eye’s visual axis from it’s normal position.

• Strabismus = squint = الَحَول

• Strabismus can be either:

– a lack of coordination between the extraocular muscles.

– a disorder of the brain in coordinating the eyes.

– or of one or more of the relevant muscles' power or direction of motion

•why squint is important

•● A squint may show that the acuity of the eye is impaired

•● A squint may itself cause amblyopia in a child

•● A squint may be a sign of a life threatening condition like retinoblastoma

CLASSIFICATION OF STRABISMUS

• 1.DIRECTION OF DEVIATION

- Hyper deviation - Hypo deviation - Divergent - Convergent

• 2. COMITANCY - concomitant / non-paralytic - incomitant / paralytic

• 3. CONSTANCY - constant - intermittent

Another classification

• Apparent squint or pseudostrabismus • Pseudoesotropia

• Pseudoexotropia

• Latent squint (heterophoria) is only present after binocular vision has been interrupted, typically by covering one eye

• Esophoria

• Exophoria

• Hyperphoria

• Hypophoria

• Cyclophoria (deviation In the ant.post axis)

• Manifest squint (heterotropia) is present while the patient views a target binocularly, with no occlusion of either eye. The patient is unable to align the gaze of each eye to achieve fusion

– Concomitant squint ( angle of deviation remains the same

whatever the eye movement) the deviating eye accompanies the leading eye in every direction of gaze .

• Esotropia

• Exotropia

• Hypertropia

• Hypotropia

– Incomitant squint:result from paralysis of one or more eye muscles ,which differs from the first type in that the angle of deviation it’s not constant in every direction of gaze

• Paralytic strabismus

• ** Concomitant usually occurs in children because it mainly congenital within the first few years of life , whereas Paralytic strabismus primarily affects adults because its usually acquired “post-traumatic.

Terminology !!

• Eso : inward

• Exo: outward

• Hyper: superiorly

• Hypo: inferiorly

-----------------------------

• Tropia : always deviated ( manifest squint)

• Phoria : sometimes deviated (latent squint)

Pseudostrabismus

• False appearance of crossed eyes

• Occurs in infants and toddlers whose facial

features are not fully developed

• With age, the nose bridge will narrow and the

epicanthal folds in the corner of the eyes will

go away. This will cause the eyes to appear

wider, and thus not have the appearance of

strabismus

Heterophoria

• It can be : • Esophoria

• Exophoria

• Hyperphoria

• Hypophoria

• Cyclophoria (deviation In the ant.post axis)

• Heterophoria is a latent tendency for misalignment of the two eyes that becomes a manifest only if binocular vision is interrupted such as by covering one eye.

• Heterophoria only occurs during dissociation of the left eye and right eye, when fusion of the eyes is absent. If you cover one eye (e.g. with your hand) you remove the sensory information about the eye's position in the orbit. Without this, there is no stimulus to binocular fusion, and the eye will move to a position of "rest".

Heterophoria

• A minor degree of heterophoria is normal for most individuals

• Both esophoria and exophoria can be classified by the distance at which the angle is greater: (respectively, convergence excess or weakness, divergence weakness or excess and mixed).

• Treatment – Orthoptic treatment is of most value in convergence

weakness exophoria

– Symptom relief may otherwise be obtained using temporary stick-on Fresnel prisms and may be subsequently incorporated into spectacles (maximum usually 10–12 , split between the two eyes)

– Surgery may occasionally be required for larger deviations

• So to differentiate by examination paralytic from non paralytic we measure the angle of deviation by prism

• The angle of deviation is measured with a cover test in combination with the use of prism lens of various refractive powers

• If the angle is the same in all directions then it is non paralytic

• If it is different then it is paralytic

• This angle is important for follow up and deciding upon surgery

CONCOMITANT(NON-

PARALYTIC)

• Movement of both eyes are full (there is no paresis) but only one eye is directed towards the fixated target.

• The angle of deviation is constant and unrelated to the direction of gaze

Concomitant strabismus almost exclusively in children.

In 60-70% of all cases manifests within the first two years of life

• Under age of 6, it is rarely caused by serious neurological disease. It’s usually primary in this age group.

• Strabismus arising later in life may have a specific and serious neurological basis.

- could be : monocular, alternating or intermittent.

The causes of concomitant are often unclear . But the following causes have been identified to date :

Genetic factors : 60% of children with strabismus have family history of increased incidence .

Uncorrected refractive errors : Children with hypertropia tend to have esotropia

,this is because accommodation always triggers a convergence impulse that can cause esotropia

Unilateral visual impairment : like corneal scarring , cataract , macular changes ,retinal disorder “retinoblastoma” etc..

Insufficient fusion :this occur in conjunction with anisometropia (unequal refractive power in the both eyes ) and aniseikonia (unequal retinal image size )

Other possible causes:

• perinatal lesion as preterm &asphyxia

syndromes “Noonan syndrome

Prader-Willi syndrome

• cerebral trauma and encephalitis

Pathophysiology: Deviation of the visual axis of the deviating eye causes objects to be projected to noncorresponding points on the retina. One would expect these patients suffer from constant double vision because the left and right eyes supply different information to the brain. A central inhibiting mechanism suppresses the visual stimuli from the deviating eye.

Instead of seeing two different images or double vision (diplopia), the brain suppresses the blurrier image. The inhibition process (suppression) can result in a permanent decrease in the vision in the blurry eye that can not be corrected with glasses, lenses, or lasik surgery. This will lead to Amblyopia

Esotropia

is one of the most commonly encountered forms of

strabismus .

Esotropia (convergent strabismus) occurs more frequently

than Exotropia (divergent strabismus) in Europ and north

america .

1) Congenital or infantile :-

present at birth or after 6 months which characterized by:-

large alternating angle of deviation “ as in the next pic”

lack of binocular vision

primary oblique muscle dysfunction “hypertropia”

A or V pattern :-

a. A pattern deviation :refers to inward angle of deviation that

increase in upgaze and decrease in downgaze

b. V pattern deviation : refers to inward angle of deviation

that decrease in upgaze and increase in downgaze

2) Acquired strabismus : two forms

A. Strabismus begins at the age of incomplete sensory development i.e. between the ages of one to three years and usually the disorder manifests itself at the age of two and lead to sensory adaption syndrome in the form of unilateral strabismus .

• Amblyopia is usually already present , and correspondence is primarily anomalous

B. Strabismus manifests itself between the age of three and seven years . This form of late strabismus with normal sensory development is encountered far less frequently than other form

• As a binocular vision is already well developed cannot immediately suppress the visual of the deviating eye , as a result , they suffer from sudden double vision ,which they attempt to suppress by closing one eye

3) Microstrabismus

Is defined as unilateral esotropia with minimal cosmetic

effect,

i.e., an angle of deviation of 5 degrees or less .

As a result, is often diagnosed too late “ only at the age of

four to six “ by the time the resulting Amblyopia in the

deviating eye may be sever

Another sequel is retinal correspondence ,

However ! It can no longer be improved by treatment , for that

treatment is limited to occlusion therapy to correct amblyopia

4) Accommodative esotropia in accommodative esotropia the angle of deviation is larger

with close objects than with distant objects this is When the

accommodative convergence /accommodation ratio is abnormal , the

angle of deviation depending on whether the fixated object is far or near .

• This disorder is corrected with bifocal eyeglasses which in

this case we have a strong near-field correction

• A residual angle of deviation may remain despite the

eyeglass ,however the angle may also improve to the point

that the visual axes are parallel with good binocular vision.

Exotropia (divergent strabismus “outward” )

is less common than esotropia , as it is usually acquired ,

more often in adults .

exotropia less frequently leads to amblyopia because is often

alternating .

Occasionally what is known as “panorama vision” will occur

in which case the patent has an expanded binocular field

vision .

1) Intermittent exotropia

this is the most common form of divergent strabismus , in

this case an angle of deviation is present only when the

patient gazes into the distance , the patient has normal

binocular vision in near fixation .

• The intermittent exotropia only become manifest under certain

conditions such as fatigue

2) Secondary exotropia

Occurs with reduced visual acuity in one eye resulting from

disease or trauma .

3) Consecutive exotropia

Occur after esotropia surgery . Often the disorder is

overcorrected

=> RECALL <=

- Amblyopia will develop only if constant squint affects the same eye.

- Children Alternating the squinting eye will NOT develop Amblyopia but do NOT develop Stereopsis either.

Incomitant (paralytic)

• The degree of misalignment varies

with direction of the gaze.

• One or more of the extraocular muscles

or nerves may not be functioning

properly, or normal movement may be

restricted mechanically.

• This type of strabismus may indicate

either a nerve palsy or extraocular

muscle disease.

-Peripheral lesion of an extraocular muscle or its nerve supply results in impaired eye movements. The size of the squint is dependent on the direction of the gaze and thus, for nerve palsy, is greatest in the field of action in the affected muscle ( the direction in which the muscle normally take the globe ). Ends with diplopia

Paralytic squint

• Isolated nerve palsies • systemic disease ( DM, hypertension)

• Orbital disease (neoplasia)

• Trauma most common cause of palsy of 4th,6th

• Raised intracranial pressure may cause a 3rd or 6th nerve palsy

• Extraocular muscle disease • Dysthyroid eye disease (thyroid eye disease)

• Myasthenia gravis

• Ocular myositis

• Ocular myopathy

• Browns syndrome (malfunction of the superior oblique tendon).

•mostly in adults, acquired •present mainly with diplopia

•greatest deviation in field of action of the weakened muscle

•visual acuity is usually unaffected in either eye, unless CN II is involved

History and examination

The patient complain of diplopia, there may be head posture to compensate for the eye to move in particular direction.

•In third nerve palsy: failure of adduction, elevation and deprssion of

the eye. Ptosis in some cases, a dilated pupil due to involvement of autonomic fibres.

•A fourth nerve palsy result in defective

depression of eye when attempted in adduction.

•A sixth nerve palsy results in failure of abduction of the eye.

Cranial nerve palsy:

•Each nerve may be affected at any

point along its course from

brainstem nucleus to orbit.

•not a In most cases there is of a muscle complete loss of action

but a partial loss.

third nerve palsy

•1. ptosis

•2. dilated pupil

•3. limitation of eye

movement

nerve palsy th4

•the defect is maximal when the patient tries to

look “ down when the left eye is adducted(

because the contribution of the superior oblique

muscle to downward gaze is greater in this

position.)

•Vertical diplopia, 2 visiual fields seperated

for this, patients learn compensate Tovertically.

tilt the head forward (tuck the chin in)to

•is a test for head tilt test 'sBielschowskyAlfred

palsy of the superior oblique muscle .

•a normal response Torsion is , diplopia Torsional

.to tilting the head sideways

-two different visual in which ,diplopia torsional

fields, tilted with respect to each other, are seen

.at the same time

•a When the patient tilts her head to the left (toward the

normal side),the right eye does not deviate upward

•when the normal left eye fixates.

•b When the patient tilts her head to the right (toward the side

of the paralyzed muscle), the right eye deviates upward when

the normal left eye fixates.

The most common cause of acute fourth nerve palsy is head trauma

nerve palsy th6

•or esotropiaaffected individual will have an The“convergent squint” on distance fixation. Happens usually unilaterally

• DiplopiaHorizontal .amlyiopiawith the condition will develop children

- in the long term it can lead to a lack of appropriate development of the visual cortex giving rise to permanent visual loss

-the most is nerve palsy abducensunilateral common of the isolated ocular motor nerve palsies

6th nerve palsy

Consequences of strabismus

• 1) Amblyopia

• 2)decreased vision acuity

• 3)Loss of stereopsis

• 4)double vision

• Amblyopia is the medical term used

when the vision in one of the eyes is

reduced because the eye and the

brain are not working together.

•developmental Amblyopia is a

in the brain, not an problem

organic problem in the eye.

The part of the brain

corresponding to the visual

system from the affected eye is

stimulated properly, and not

normally. abdevelops

Amblyopia

Amblyopia presentation :

• Most cases are asymptomatic, which make it often

goes undetected. In severe cases: poor depth

perception may be found. poor spatial acuity , low

sensitivity to contrast, reduced sensitivity to motion

Causes of amlyiopia

•1- congenital cataract.

•2- refractive error.

• 3- squint(strabismus)

•. opacity in one eye-4

.congenital retinal detachment -5

•Reversible before 7-8 years

Amblyopia secondary to suppression

•. Constant suppression in strabismus can lead to severe amblyopia, especially in children below the age of six. The prospects for successful treatment decrease with age, and amblyopia becomes irreversible beyond the age of six to eight. Amblyopia only occurs in unilateral strabismus. In alternating strabismus, fixation or deviation alternates between both eyes so that both eyes learn to see.

Amblyopia

• Treatment:

– Correcting the optical deficit (wearing the

necessary spectacle prescription)

– Forcing use of the amblyopic eye, either

by patching the good eye, or by instilling

topical atropine in the eye with better

vision

P/E and Tests

• Observe features that simulate SQUINT :

- Epicanthus ( crescentric fold of skin on the

side of the nose , incompletely covers the

inner canthus).

- Facial Asymmetry.

• Assess Visual Acuity

• Do corneal inspection

• HIRSCHBURG TEST”

• Perform Cover/Uncover Test to

detect tropia.

• ALTERNATING COVER/ UNCOVER

TEST FOR HETEROPHORIA

Corneal inspection

Have the patient look at the six cardinal

positions of gaze to differentiate

between concomitant and non-

concamitant

HIRSCHBURG TEST

• In newborn and often in young children

• Normally the light is reflected on each cornea symmetrically and in the same position relative to the pupil and visual axis on each side

• In deviating eye the light reflection will be not centrally positioned and in direction opposite to that of the deviation

• Example…pupil margin 15’,limbus 45’,iris 30 !!!!

Hirschberg’s method

Cover/Uncover Test

• Easy, requires no special equipment and detect almost every case of tropia

• patients >6yrs

• patient look at the fixation point

• Note which eye seems to be fixating

• Cover it and observe the other

• If it moves to pick up the fixation=>this eye was not directed toward the object of regard originally

• Used to detect tropias

• No shift on cover testing means there is no tropia

Alternate test

• In the alternate cover

test, the occluder is

moved to and front

between the eyes. If

the eye that has been

uncovered moves,

then there is a latent

squint

• Used for detection of

phroias

• So can you differentiate between

heterophoria and heterotropia ?

-meaning?

- Test ?

Treatment

• Early detection is the most important prognostic sign as it helps to prevent permanent visual deficits

• Most children eventually recover from amblyopia by around age 10, if they have had the benefit of patches and corrective glasses

• The primary therapeutic goal for those with strabismus is comfortable, single, clear, normal binocular vision at all distances and directions of gaze

Treatment is generally for children long-term . The duration may extend from the first months of life to the age of twelve . And the healing process depending also on the child personality and parent’s cooperate , and it’s treatable until 6 year , may be until 9 years but not more

And we may divided the course of treatment into 3 phases

a) Eyeglasses such in hyperopia

Eyeglasses + Occlusion therapy to minimize amblyopia (better seeing eye is patched to try and stimulate the amblyopic eye thereby increasing its visual acuity)

c. Surgery: Different muscles in the eye will be made stronger or weaker.

• If the strabismus is not treated, the eye that the brain ignores will never see well. This loss of vision is called amblyopia. Another name for amblyopia is "lazy eye." Sometimes amblyopia is present first, and it causes strabismus

For adult , surgery and it’s for cosmetic improvement.

• Glasses can treat some or all of the

esotropia

In farsighted and may decrease deviation

in near sided with myopia

Treatment

• Advanced strabismus is usually treated with a combination of eyeglasses or prisms, vision therapy, and surgery, depending on the underlying reason for the misalignment. – Glasses affect the position by changing the

person's reaction to focusing.

– Prisms change the way light, and therefore images, strike the eye, simulating a change in the eye position.

– Surgery does not change the vision; it attempts to align the eyes by shortening, lengthening, or changing the position of one or more of the extraocular eye muscles and is frequently the only way to achieve cosmetic improvement.

Strabismus surgery

• The principle of surgery is to realign the eyes by

adjusting the position of the muscles on the globe or

by shortening the muscle.

• Access to the muscles is gained by making a small

incision in the conjunctiva.

• Moving the muscle insertion backwards on the globe

(recession)

• Weakens the muscle.

• Removing a segment of the muscle (resection)

strengthens the action

• It must be stressed that surgery is not

an alternative to glasses and patching

when amblyopia

• In paralytic strabimus treatment is

directed to underlying pathology

• Diplopia can be helped by fitting prisms

to the patients glasses

Prognosis

• With early diagnosis and treatment, the problem can usually be corrected. 90% will have good vision & maintained if treated < 4 years old

• Delayed treatment may lead to permanent vision loss in one eye. About one-third of children with strabismus will develop amblyopia.

• After surgery, the eyes may look straight but vision problems can remain.

• The child may still have reading problems in school, and for adults driving may be more difficult. Vision may affect the ability to play sports.

• Because many children will get strabismus or amblyopia again, they need to be monitored closely