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 vssherrington’s law
Normal Vision Actions of EOMs • Normal binocular single vision (BSV) involves the simultaneous use of both eyes with bifovealfixation 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 : • >>Diplopia ;An object is seen to be in 2 different places. • >>Visual confusion ; 2 separate objects appear to be at the same point. • 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 ( strabismicAmblyopia). • 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 = الحَوَل • Strabismus can be either: • a lack of coordination between the extraocularmuscles. • 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 • Incomitantsquint: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) • Heterophoriais 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) • Surgerymay 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.
Etiology • 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 withhypertropiatend to have esotropia ,this is because accommodation always triggers a convergenceimpulse 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-Willisyndrome • 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 • 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 .
Types of esotropia strabismus • 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 pattern deviation :refers to inward angle of deviation that increase in upgaze and decrease in downgaze • V pattern deviation : refers to inward angle of deviation that decreasein upgaze and increasein downgaze
Types of esotropia strabismus • Acquired strabismus : two forms • 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 • 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
Types of esotropia strabismus • 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
Types of esotropia strabismus • 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 • 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 .
Types of exotropia • 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
Types of exotropia • Secondary exotropia Occurs with reduced visual acuity in one eye resulting from disease or trauma . • 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. • In most cases there is not a complete loss of action of a muscle but a partial loss.
third nerve palsy • 1. ptosis • 2. dilated pupil • 3. limitation of eye movement
4th nerve palsy • the defect is maximal when the patient tries to look “ down when the left eye is adducted( becausethe contribution of the superior oblique muscle to downward gaze is greater in this position.) • Vertical diplopia, 2 visiual fields seperatedvertically.To compensate for this, patients learn to tilt the head forward (tuck the chin in) • Alfred Bielschowsky'shead tilt test is a test for palsy of the superior oblique muscle . • Torsionaldiplopia, Torsion is a normal response to tilting the head sideways. • torsionaldiplopia, in which two different visual 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.
6th nerve palsy • Theaffected individual will have an esotropia or “convergent squint” on distance fixation. Happens usually unilaterally • Horizontal Diplopia children with the condition will develop amlyiopia. • in the long term it can lead to a lack of appropriate development of the visual cortex giving rise to permanent visual loss • unilateral abducens nerve palsy is the most common of the isolated ocular motor nerve palsies
Consequences of strabismus • 1) Amblyopia • 2)decreased vision acuity • 3)Loss of stereopsis • 4)double vision