Strabismus
_Strabismus is a misalignment of the eyes, such that the visual axes of each eye are not simultaneously directed at the object of regard.
_The misalignment may be present in aparticular direction of gaze or in all directions of gaze. STRATIGY OF MANAGEMENT OF
_Strabismus implies an impairment of binocular vision. The close interrelationship between sensory and motor system development means
that strabismus may arise from a disturbance of either sensory or motor development, particularly in the younger patient. STRABISMUS
Classification of strabismus 1-Establish the presence of squint
definition & classfication Broadly, strabismus can be classifiedas below: 2-Determine the type of squint
I. Apparent squint or pseudostrabismus. 3-Ruleout organic causes (secondary squint)
II. Latent squint (Heterophoria) 4-Treat amblyopia
III.Manifest squint (Heterotropia) 5-Correctsquint(if possible)
a.Concomitant squint
b.Incomitant squint.
🔶 1-PSEUDOSTRABISMUS
🔸
In pseudostrabismus (apparentsquint), the visual axes are infact parallel ,but the eyes seem to have asquint:
1.Pseudoesotropia or apparent convergent squint may be associated with a prominent epicanthal fold,(which covers the normally
🔸2.Pseudoexotropia or apparent divergent squint maybe associated with hypertelorism, acondition of wide separation of the two eyes.
visible nasal aspect of the globe and gives a false impression of esotropia).
🔶 2-HETEROPHORIA
Heterophoria also known as ‘latent strabismus’ ,is acondition in which the tendency of the eyes to deviate lis kept latent by fusion.
Therefore, when the influence of fusion is removed the visual axis of one eye deviates away.
🔸
Types of heterophoria
🔸 1.Esophoria. It is atendency to converge.
🔸 2.Exophoria. It is atendency to diverge.
🔸3.Hyperphoria. It is atendency to deviate upwards, while hypophoria is a tendency to deviate downwards.
4.Cyclophoria. It is atendency to rotate around the anteroposterior axis.
🔶 Etiology
A .Anatomical factors
Anatomical factors responsible for development of heterophoria include:
1.Orbital asymmetry.
2.Abnormal interpupillary distance(IPD). A wide IPD is associated with exophoria and small with esophoria.
3.Faulty insertion of extraocular muscle.
4.A mild degree of extraocular muscle weakness.
5.A nomalous central distribution of the tonic innervation of the two eyes.
6.Anatomical variation in the position of the macula in relation to the optical axis of the eye.
1-PSEUDOSTRABISMUS &
2-HETEROPHORIA 🔶 Examination of a case of heterophoria
🔸
It should include the following tests:
1.Testing for vision and refractive error.
It is most important ,because are fractive error may be responsible for the symptoms of the patient or for the deviation it self. Preferably,
🔸
refraction should be performed under full cycloplegia, especially in children.
2.Cover-uncover test.
It tells about the presence and type of heterophoria. To perform it, one eye is covered with an occluder and the other is made to fix an
object. In the presence of heterophoria, the eye under cover will deviate. After afew seconds the cover is quickly removed and the
movement of the eye (which was under cover) is observed. Direction of movement of the eye ball tells the type of heterophoria (e.g.,the
🔸3.Prismcover test.
eye will move outward in the presence of esophoria) and the speed of movement tells whether recovery is slow or rapid.
🔸
🔸4.Maddoxrod test.
5.Maddoxwing test.
🔷Treatment
🔹
It is indicated in decompensated heterophoria (i.e.,symptomaticcases).
🔹 a.Correction of refractive error when detected is most important.
b.Orthoptic treatment.
It is indicated in patients with heterophoria with out refractive error and in those where heterophoriaand/or symptoms are not corrected
by glasses. Aim of orthoptic treatment is to improve convergence insufficiency and the fusional reserve. Orthoptic exercises can be done
🔹
with synoptophore. Simple exercises to becarried out at home should also be taught to the patient.
c.Prescription of prismin glasses.
It may betried in selected cases of hyper phoria and introuble some cases of esophoria and exophoria.
Prism is prescribed with apex towards the direction of phoriato correct only half or at the most two-thirds of heterophoria.
🔶Manifest squint
🔸 1) CONCOMITANT STRABISMUS It is atype of manifest squint in which the amount of deviation in the squinting eye remains
constant (unaltered) in all the directions of gaze ;and there is no associated limitation of ocular movements .
Etiology
It is not clearly defined. The causative factors differ in individual cases. As we know, the binocular vision and coordination of ocular
movements are not present since birth but are acquired in the early child hood. The process starts by the age of 3-6 months and is
STRABISMUS completed up to 5-6years.
Therefore, any obstacle to the development ofc
these processes may result in concomitant squint.
These obstacles can be arranged in to three groups, namely: sensory, motor and central.
1.Sensory obstacles.
These are the factors which hinder the formation of aclear image in one eye. These include:
_Refractive errors,
Normal binocular vision _Prolonged use of incorrect spectacles,
Normal binocular single vision is the ability of the brain and visual cortex to fuse and integrate the image from each eye into a single _Anisometropia,
_Corneal opacities,
perception. It implies bifoveal fusion and a high degree of stereopsis. Normal binocular vision develop safter birth from early infancy and is
completed with fusion and stereopsis by the age of 8–10 years. Its maturation is associated with a maturation of visual functions in both
_Lenticular opacities, 1)CONVERGENT SQUINT
_Diseases of macula(e.g.,centralchorioretinitis), Concomitant convergent squint or esotropia denotes inward deviation of one eye. It can be unilateral (the same eye always deviates
sensory and motor system. _Opticatrophy. inwards and these condnormal eye takes fixation) or alternating (either of the eyes deviates inwards and the other eye takes upfixation,
Strabismus affects vision, since both eyes must aim at the same spot together to see properly. If some one’s eyes are lined up properly during _Obstruction in the pupillary area due to congenital ptosis. alternately).
childhood, vision should develop well. 2.Motor obstacles. Clinico-etiological types Depending upon the clinico-etiological features convergent concomitant squint can be further classified in to
But if the eyes are not aligned, a condition called amblyopia can develop. These factors hinder the maintenance of the two eyes in the correct positional relationship in primary gaze and/or during different ocular
🔹 🔶
following types:
Amblyopia is defined as the reduction of best- corrected visual acuity of one or both eyes that can not be attributed exclusively to a movements. 1.Accommodative esotropia.
A few such factors are: It occurs due to over action of convergence associated with accommodation reflex. It is of three types:
structural abnormality of the eye. Amblyopia develops during childhood and results in the interruption of normal cortical visual pathway
_Congenital abnormalities of the shape and size of the orbit.
development. It is clinically defined as a difference in best- corrected visual acuity of 2 or more lines of acuity between the eyes.
In amblyopia visual acuity and contrast sensitivity reduced. A number of ophthalmic conditions can cause amblyopia including; uncorrected
_Abnormalities of extraocular muscles such as faulty insertion, faulty innervation and mild paresis.
_Abnormalities of accommodation, convergence and AC/Aratio.
🔸
refractive, non-refractive and mixed.
i.Refractive accommodative esotropia: It usually develops at the age of 2to3 years and is associated with high hypermetropia.
refractive errors, strabismus, and central visual axis obstruction. 3.Central obstacles. 🔸
Mostly it is for near and distance (marginally more for near) and fully correctable by use of spectacles.
ii.Non-refractive accommodative esotropia: It is caused by abnormally AC/A (accommodative convergence/accommodation) ratio.
🔹Accommodation and convergence are inter-related and they develop together so that a single clear image is appreciated. The
These may be in the form of: This may occur even in patients with no refractive error. Esotropia is greater for near than that for distance (minimal or no deviation for
_Deficient development of fusion faculty, or
ratio accommodative-convergence(AC) over accommodation(A) indicates therelation¬ship between the amount of convergence produced _Abnormalities of cortical control of ocular movements as occurs in mental trauma and hyper excitability of the central nervous system
during teething
🔸iii.Mixed accommodative esotropia: It is caused by combination of hypermetropia and high AC/Aratio.
distance). It is fully corrected by adding +3DS for near vision.
by a stimulus to accommodate and the amount of accommodation which produces that convergence.
Abnormalities of the AC/A ratio are very important causes of strabismus.
Types of concomitant squint
🔶 2.Non-accommodative esotropias.
This group includes all those primary esodeviations in which amount of deviation is not affected by the state of accommodation. It
AhighAC/A ratio may cause excessive convergence& produce aconvergent squint during accommodation on a near object. AlowAC/A ratio Three common types of concomitant squint are:
may cause adivergent squint when the patient looks at a near object. 1.Convergentsquint(esotropia),
2.Divergentsquint(exotropia),and
🔸
includes:
i. Essential infantile esotropia. It usually presents at 1-2 months of age. However, it may be detected shortly after birth or any time
with in the first 6months of life. Previously, it was known as congenital esotropia. It is characterised by fairly large angle of squint (>30o) ,
3.Verticalsquint(hypertropia).
🔸
alternate fixation in primary gaze and crossed fixation in lateral gaze.
ii.Essential acquired or late onset esotropia. It is acommon variety of concomitant convergent squint. It typically occurs during first
🔶EVALUATION OF ACASE OF CONCOMITANT STRABISMUS: few years of life. It is of three types:
_Basic type. In it the deviation is usually equalat distance and near.
I.History: _Convergence excess type. In it the deviation is large for near and small or no deviation for distance.
🔶
A meticulous history is very important. It should include: age of onset, duration, mode of onset (sudden or gradual), any illness preceding _Divergence insufficiency type. It is characterized by agreater deviation for distance than near.
by fatema okoff
squint (fever, trauma, infections, etc.), intermittent or constant ,unilateral oral ternating, history of diplopia, family history of squint,
history of head tilt or turn and soon. 🔸 3.Secondary esotropia. It includes:
i.Sensory deprivation esotropia. It results from monocular lesions (in childhood) which either prevent the development of normal
🔸
II.Examination: binocular vision or interfere with its maintenance. Examples of such lesions are: cataract, severe congenital ptosis, aphakia, anisometropia,
🔸 1.Inspection. Large degree squint (convergent or divergent) is obvious on inspection.
2.Ocular movements. 🔸
opticatrophy, retinoblastoma, central chorioretinitis and soon.
ii.Consecutive esotropia. It results from surgical over correction of exotropia.
🔸
Both uniocular as well as binocular movements should be tested in all the cardinal positions of gaze.
3.Pupillary reactions.
🔸
These may be abnormal in patients with secondary deviations due to diseases of retina and optic nerve.
4.Media and fundus examination.
2)DIVERGENT SQUINT
Concomitant divergent squint (exotropia) is characterised by outward deviation of one eye while the other eye fixates Clinico-etiological
🔸
It may reveal associated disease of ocular media, retina or optic nerve.
5.Testing of vision and refractive error.
types It can be classified in to following
🔸
clinicoetiological types:
It is most important ,because are fractive error may be responsible for the symptoms of the patient or for the deviation itself. Preferably,
1.Congenital exotropia.
🔸
refraction should be performed under full cycloplegia,especially in children.
6.Covertests It is rare and almostal ways present at birth. It is characterised by a fairly large angle of squint, usually alternate with homonymous fixation
🔸
i.Direct cover test (Fig.13.16) . in lateral gaze, and no amblyopia.
It confirms the presence of manifest squint. To performit, the patient is asked to fixate on apoint light. Then, the normal looking eye is 2.Primary exotropia.
covered while observing the movement of the uncovered eye. In the presence of squint the uncovered eye will move in opposite direction It is acommon variety of exodeviation (unilateral oral ternating). It presents with variable features. It may be of:
to take fixation, while inapparent squint there will be no movement. This test should be performed for near texation(i.e.,at33cm) distance _Convergence insufficiency type (exotropia greater for near than distance),
fixation(i.e.,at6metres). _Divergence excess (exotropia greater for distance than near) or
ii.Alternate cover test. It reveals whether the squint is unilateral or alternate and also differentiates concomitant squint from paralytic _Basic non-specific type (exotropia equal for near and distance). It usually starts as intermittent exotropia at the age of 2years. It is
🔸
squint (where secondary deviation is greater than primary). associated with normal fusion and noamblyopia. Stereopsis is usually absent. Precipitating factors include bright light, fatigue, ill health
🔸
7. Estimation of angle of deviation and day-dreaming. If not treated in time it decompensates to become constant exotropia.
i.Hirschberg corneal reflex test. It is a rough but handy method to estimate the angle of manifest squint. In it the patient is asked to 3.Secondary(sensory deprivation)exotropia. It is a constant unilateral deviation which results from long standing monocular
fixate at point light held at a distance of 33cm and the deviation of the corneal light reflex from the centre of pupil is noted in the lesions(in adults), associated with low vision in the affected eye. Common causes include: traumatic cataract ,corneal opacity,
🔸
squinting eye. Roughly, the angle of squint is 15o and 45o when the corneal light reflex falls on the border of pupil and limbus, opticatrophy, anisometropic amblyopia, retinal detachment and organic macular lesions.
respectively. 4.Consecutive exotropia. It is aconstant unilateral exotropia which results either due to surgical over correc tion of esotropia, or
ii.The prism and cover test (prismbar cover test). Prisms of increasing strength with apex towards the deviation are placed in front of spontaneous conversion of small degree esotropia with amblyopia in to exotropia.
one eye and the patient is asked to fixate an object with the other. Thecover-
uncovertestisperformedtillthereisnorecoverymovementoftheeyeundercover.
This will tell the amount of deviation in prism dioptres. Both heterophoria as well as heterotropia can be measured by this test.
iii.Krimsky corneal reflex test. In this test the patientis asked to fixate on apoint light and prisms of increasing power (with apex towards
the direction of manifest squint)are placed infront of the normal fixating eye till the corneal light reflex is centred in the squinting eye.
The power of prism required to centre the light reflex in the squinting eye equals the amount of squint in prism dioptres.
iv.Measurementofdeviationwithsynoptophore.(instrument)
3-Manifest squint 🔷 TREATMENT OF CONCOMITANT STRABISMUS:
Goals of treatment.These are to achieve good cosmetic correction,to improve visual acuity and to maintain binocular single vision.
However,many a time it is not possible to achieve all the goals in every case.
Treatment modalities.
🔹
These include the following:
1.Spectacles with full correction of refractive error should be prescribed in every case. It will improve the visual acuity and at
🔹
times may correct the squint partially or completely(as in accommodative squint).
2.Occlusion therapy: It is indicated in the presence of amblyopia. After correcting the refractive error,the normal eye is occluded and
the patient is advised to use the squinting eye. Regular follow-ups are done in squint clinic. Occlusion helps to improve the vision in
🔹
children below the age of 10 years.
🔹 3.Preoperative orthoptic exercises. These are given after the correction of amblyopiato overcome suppression.
4.Squint surgery. It is required in most of the cases to correct the deviation.However,it should always be in stituted after the
correction of refractive error, treatment of amblyopia and orthoptic exercises.
PARALYTIC STRABISMUS
It refers to ocular deviation resulting from complete or incomplete paralys is of one or more extraocular muscles.
Etiology
🔸
The lesions may be neurogenic, myogenic or at the level of neuromuscular junction.
I.Neurogenic lesions
1.Congenital. Hypoplasia or absence of nucleus is a known cause of third and sixth cranial nervepalsies. Birthinjuries may mimic congenital
lesions.
2.Inflammatory lesions. These may be in the form of encephalitis, meningitis, neurosyphilis or peripheralneuritis (commonlyviral). Nerve
trunks may also be involved in the infectious lesions of cavernous sinus and orbit.
3.Neoplastic lesions. These include brain tumours involving nuclei, nerve roots or intracranial part of the nerves; and intraorbital tumours
involving peripheral parts of the nerves.
4.Vascular lesions.
2)INCOMITANT SQUINT These are known in patients with hypertension, diabetes mellitus and atherosclerosis. These maybe in the form of haemorrhage, thrombosis,
It is a type of heterotropia (manifest squint) in which the amount of deviation varies in different directions of gaze. It includes following embolism, aneurysms or vascular occlusions.Cerebrovascular accidents are more common inelderly people.
conditions: 5.Traumatic lesions. These include head injury and director in direct trauma to the nerve trunks.
1.Paralytic squint, 6.Toxic lesions. These include carbonmonoxi depoisoning, effects of diphtheria toxins(rarely), alcoholic and lead neuropathy.
🔸
2.‘A’and‘V’pattern heterotropias, 7.Demyelinating lesions. Ocular palsy may occur in multiple sclerosis and diffuse sclerosis.
3.Restrictivesquint. II.Myogenic lesions
1.Congenital lesions.These include absence, hypoplasia, malinsertion, weakness and musculofacial anomalies.
2.Traumatic lesions. These may be in the form of laceration, disinsertion, haemorrhage in to the muscle substance or sheath and
incarceration of muscles in fractures of the orbital walls.
3.Inflammatory lesions. Myositisis usually viral in origin and may occur in influenza, measles and other viral fevers.
4.Myopathies. These include thyroid myopathy, carcinomatous myopathy and that associated with certain drugs. Progressive external
🔸
ophthalmoplegia is abilateral myopathy of extraocular muscles; which may be sporadic or inherited as an autosomal dominant disorder.
III.Neuromuscular junction lesion It includes my asthenia gravis.
The disease is characterised primarily by fatigue of muscle groups, usually starting with the small extraocular muscles, before involving
other large muscles.
Management
1.Treatment of the cause.An exhaustive investigative work-up should be done to find out the cause and, if possible, treat it.
_Strabismus is a misalignment of the eyes, such that the visual axes of each eye are not simultaneously directed at the object of regard.
_The misalignment may be present in aparticular direction of gaze or in all directions of gaze. STRATIGY OF MANAGEMENT OF
_Strabismus implies an impairment of binocular vision. The close interrelationship between sensory and motor system development means
that strabismus may arise from a disturbance of either sensory or motor development, particularly in the younger patient. STRABISMUS
Classification of strabismus 1-Establish the presence of squint
definition & classfication Broadly, strabismus can be classifiedas below: 2-Determine the type of squint
I. Apparent squint or pseudostrabismus. 3-Ruleout organic causes (secondary squint)
II. Latent squint (Heterophoria) 4-Treat amblyopia
III.Manifest squint (Heterotropia) 5-Correctsquint(if possible)
a.Concomitant squint
b.Incomitant squint.
🔶 1-PSEUDOSTRABISMUS
🔸
In pseudostrabismus (apparentsquint), the visual axes are infact parallel ,but the eyes seem to have asquint:
1.Pseudoesotropia or apparent convergent squint may be associated with a prominent epicanthal fold,(which covers the normally
🔸2.Pseudoexotropia or apparent divergent squint maybe associated with hypertelorism, acondition of wide separation of the two eyes.
visible nasal aspect of the globe and gives a false impression of esotropia).
🔶 2-HETEROPHORIA
Heterophoria also known as ‘latent strabismus’ ,is acondition in which the tendency of the eyes to deviate lis kept latent by fusion.
Therefore, when the influence of fusion is removed the visual axis of one eye deviates away.
🔸
Types of heterophoria
🔸 1.Esophoria. It is atendency to converge.
🔸 2.Exophoria. It is atendency to diverge.
🔸3.Hyperphoria. It is atendency to deviate upwards, while hypophoria is a tendency to deviate downwards.
4.Cyclophoria. It is atendency to rotate around the anteroposterior axis.
🔶 Etiology
A .Anatomical factors
Anatomical factors responsible for development of heterophoria include:
1.Orbital asymmetry.
2.Abnormal interpupillary distance(IPD). A wide IPD is associated with exophoria and small with esophoria.
3.Faulty insertion of extraocular muscle.
4.A mild degree of extraocular muscle weakness.
5.A nomalous central distribution of the tonic innervation of the two eyes.
6.Anatomical variation in the position of the macula in relation to the optical axis of the eye.
1-PSEUDOSTRABISMUS &
2-HETEROPHORIA 🔶 Examination of a case of heterophoria
🔸
It should include the following tests:
1.Testing for vision and refractive error.
It is most important ,because are fractive error may be responsible for the symptoms of the patient or for the deviation it self. Preferably,
🔸
refraction should be performed under full cycloplegia, especially in children.
2.Cover-uncover test.
It tells about the presence and type of heterophoria. To perform it, one eye is covered with an occluder and the other is made to fix an
object. In the presence of heterophoria, the eye under cover will deviate. After afew seconds the cover is quickly removed and the
movement of the eye (which was under cover) is observed. Direction of movement of the eye ball tells the type of heterophoria (e.g.,the
🔸3.Prismcover test.
eye will move outward in the presence of esophoria) and the speed of movement tells whether recovery is slow or rapid.
🔸
🔸4.Maddoxrod test.
5.Maddoxwing test.
🔷Treatment
🔹
It is indicated in decompensated heterophoria (i.e.,symptomaticcases).
🔹 a.Correction of refractive error when detected is most important.
b.Orthoptic treatment.
It is indicated in patients with heterophoria with out refractive error and in those where heterophoriaand/or symptoms are not corrected
by glasses. Aim of orthoptic treatment is to improve convergence insufficiency and the fusional reserve. Orthoptic exercises can be done
🔹
with synoptophore. Simple exercises to becarried out at home should also be taught to the patient.
c.Prescription of prismin glasses.
It may betried in selected cases of hyper phoria and introuble some cases of esophoria and exophoria.
Prism is prescribed with apex towards the direction of phoriato correct only half or at the most two-thirds of heterophoria.
🔶Manifest squint
🔸 1) CONCOMITANT STRABISMUS It is atype of manifest squint in which the amount of deviation in the squinting eye remains
constant (unaltered) in all the directions of gaze ;and there is no associated limitation of ocular movements .
Etiology
It is not clearly defined. The causative factors differ in individual cases. As we know, the binocular vision and coordination of ocular
movements are not present since birth but are acquired in the early child hood. The process starts by the age of 3-6 months and is
STRABISMUS completed up to 5-6years.
Therefore, any obstacle to the development ofc
these processes may result in concomitant squint.
These obstacles can be arranged in to three groups, namely: sensory, motor and central.
1.Sensory obstacles.
These are the factors which hinder the formation of aclear image in one eye. These include:
_Refractive errors,
Normal binocular vision _Prolonged use of incorrect spectacles,
Normal binocular single vision is the ability of the brain and visual cortex to fuse and integrate the image from each eye into a single _Anisometropia,
_Corneal opacities,
perception. It implies bifoveal fusion and a high degree of stereopsis. Normal binocular vision develop safter birth from early infancy and is
completed with fusion and stereopsis by the age of 8–10 years. Its maturation is associated with a maturation of visual functions in both
_Lenticular opacities, 1)CONVERGENT SQUINT
_Diseases of macula(e.g.,centralchorioretinitis), Concomitant convergent squint or esotropia denotes inward deviation of one eye. It can be unilateral (the same eye always deviates
sensory and motor system. _Opticatrophy. inwards and these condnormal eye takes fixation) or alternating (either of the eyes deviates inwards and the other eye takes upfixation,
Strabismus affects vision, since both eyes must aim at the same spot together to see properly. If some one’s eyes are lined up properly during _Obstruction in the pupillary area due to congenital ptosis. alternately).
childhood, vision should develop well. 2.Motor obstacles. Clinico-etiological types Depending upon the clinico-etiological features convergent concomitant squint can be further classified in to
But if the eyes are not aligned, a condition called amblyopia can develop. These factors hinder the maintenance of the two eyes in the correct positional relationship in primary gaze and/or during different ocular
🔹 🔶
following types:
Amblyopia is defined as the reduction of best- corrected visual acuity of one or both eyes that can not be attributed exclusively to a movements. 1.Accommodative esotropia.
A few such factors are: It occurs due to over action of convergence associated with accommodation reflex. It is of three types:
structural abnormality of the eye. Amblyopia develops during childhood and results in the interruption of normal cortical visual pathway
_Congenital abnormalities of the shape and size of the orbit.
development. It is clinically defined as a difference in best- corrected visual acuity of 2 or more lines of acuity between the eyes.
In amblyopia visual acuity and contrast sensitivity reduced. A number of ophthalmic conditions can cause amblyopia including; uncorrected
_Abnormalities of extraocular muscles such as faulty insertion, faulty innervation and mild paresis.
_Abnormalities of accommodation, convergence and AC/Aratio.
🔸
refractive, non-refractive and mixed.
i.Refractive accommodative esotropia: It usually develops at the age of 2to3 years and is associated with high hypermetropia.
refractive errors, strabismus, and central visual axis obstruction. 3.Central obstacles. 🔸
Mostly it is for near and distance (marginally more for near) and fully correctable by use of spectacles.
ii.Non-refractive accommodative esotropia: It is caused by abnormally AC/A (accommodative convergence/accommodation) ratio.
🔹Accommodation and convergence are inter-related and they develop together so that a single clear image is appreciated. The
These may be in the form of: This may occur even in patients with no refractive error. Esotropia is greater for near than that for distance (minimal or no deviation for
_Deficient development of fusion faculty, or
ratio accommodative-convergence(AC) over accommodation(A) indicates therelation¬ship between the amount of convergence produced _Abnormalities of cortical control of ocular movements as occurs in mental trauma and hyper excitability of the central nervous system
during teething
🔸iii.Mixed accommodative esotropia: It is caused by combination of hypermetropia and high AC/Aratio.
distance). It is fully corrected by adding +3DS for near vision.
by a stimulus to accommodate and the amount of accommodation which produces that convergence.
Abnormalities of the AC/A ratio are very important causes of strabismus.
Types of concomitant squint
🔶 2.Non-accommodative esotropias.
This group includes all those primary esodeviations in which amount of deviation is not affected by the state of accommodation. It
AhighAC/A ratio may cause excessive convergence& produce aconvergent squint during accommodation on a near object. AlowAC/A ratio Three common types of concomitant squint are:
may cause adivergent squint when the patient looks at a near object. 1.Convergentsquint(esotropia),
2.Divergentsquint(exotropia),and
🔸
includes:
i. Essential infantile esotropia. It usually presents at 1-2 months of age. However, it may be detected shortly after birth or any time
with in the first 6months of life. Previously, it was known as congenital esotropia. It is characterised by fairly large angle of squint (>30o) ,
3.Verticalsquint(hypertropia).
🔸
alternate fixation in primary gaze and crossed fixation in lateral gaze.
ii.Essential acquired or late onset esotropia. It is acommon variety of concomitant convergent squint. It typically occurs during first
🔶EVALUATION OF ACASE OF CONCOMITANT STRABISMUS: few years of life. It is of three types:
_Basic type. In it the deviation is usually equalat distance and near.
I.History: _Convergence excess type. In it the deviation is large for near and small or no deviation for distance.
🔶
A meticulous history is very important. It should include: age of onset, duration, mode of onset (sudden or gradual), any illness preceding _Divergence insufficiency type. It is characterized by agreater deviation for distance than near.
by fatema okoff
squint (fever, trauma, infections, etc.), intermittent or constant ,unilateral oral ternating, history of diplopia, family history of squint,
history of head tilt or turn and soon. 🔸 3.Secondary esotropia. It includes:
i.Sensory deprivation esotropia. It results from monocular lesions (in childhood) which either prevent the development of normal
🔸
II.Examination: binocular vision or interfere with its maintenance. Examples of such lesions are: cataract, severe congenital ptosis, aphakia, anisometropia,
🔸 1.Inspection. Large degree squint (convergent or divergent) is obvious on inspection.
2.Ocular movements. 🔸
opticatrophy, retinoblastoma, central chorioretinitis and soon.
ii.Consecutive esotropia. It results from surgical over correction of exotropia.
🔸
Both uniocular as well as binocular movements should be tested in all the cardinal positions of gaze.
3.Pupillary reactions.
🔸
These may be abnormal in patients with secondary deviations due to diseases of retina and optic nerve.
4.Media and fundus examination.
2)DIVERGENT SQUINT
Concomitant divergent squint (exotropia) is characterised by outward deviation of one eye while the other eye fixates Clinico-etiological
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It may reveal associated disease of ocular media, retina or optic nerve.
5.Testing of vision and refractive error.
types It can be classified in to following
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clinicoetiological types:
It is most important ,because are fractive error may be responsible for the symptoms of the patient or for the deviation itself. Preferably,
1.Congenital exotropia.
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refraction should be performed under full cycloplegia,especially in children.
6.Covertests It is rare and almostal ways present at birth. It is characterised by a fairly large angle of squint, usually alternate with homonymous fixation
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i.Direct cover test (Fig.13.16) . in lateral gaze, and no amblyopia.
It confirms the presence of manifest squint. To performit, the patient is asked to fixate on apoint light. Then, the normal looking eye is 2.Primary exotropia.
covered while observing the movement of the uncovered eye. In the presence of squint the uncovered eye will move in opposite direction It is acommon variety of exodeviation (unilateral oral ternating). It presents with variable features. It may be of:
to take fixation, while inapparent squint there will be no movement. This test should be performed for near texation(i.e.,at33cm) distance _Convergence insufficiency type (exotropia greater for near than distance),
fixation(i.e.,at6metres). _Divergence excess (exotropia greater for distance than near) or
ii.Alternate cover test. It reveals whether the squint is unilateral or alternate and also differentiates concomitant squint from paralytic _Basic non-specific type (exotropia equal for near and distance). It usually starts as intermittent exotropia at the age of 2years. It is
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squint (where secondary deviation is greater than primary). associated with normal fusion and noamblyopia. Stereopsis is usually absent. Precipitating factors include bright light, fatigue, ill health
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7. Estimation of angle of deviation and day-dreaming. If not treated in time it decompensates to become constant exotropia.
i.Hirschberg corneal reflex test. It is a rough but handy method to estimate the angle of manifest squint. In it the patient is asked to 3.Secondary(sensory deprivation)exotropia. It is a constant unilateral deviation which results from long standing monocular
fixate at point light held at a distance of 33cm and the deviation of the corneal light reflex from the centre of pupil is noted in the lesions(in adults), associated with low vision in the affected eye. Common causes include: traumatic cataract ,corneal opacity,
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squinting eye. Roughly, the angle of squint is 15o and 45o when the corneal light reflex falls on the border of pupil and limbus, opticatrophy, anisometropic amblyopia, retinal detachment and organic macular lesions.
respectively. 4.Consecutive exotropia. It is aconstant unilateral exotropia which results either due to surgical over correc tion of esotropia, or
ii.The prism and cover test (prismbar cover test). Prisms of increasing strength with apex towards the deviation are placed in front of spontaneous conversion of small degree esotropia with amblyopia in to exotropia.
one eye and the patient is asked to fixate an object with the other. Thecover-
uncovertestisperformedtillthereisnorecoverymovementoftheeyeundercover.
This will tell the amount of deviation in prism dioptres. Both heterophoria as well as heterotropia can be measured by this test.
iii.Krimsky corneal reflex test. In this test the patientis asked to fixate on apoint light and prisms of increasing power (with apex towards
the direction of manifest squint)are placed infront of the normal fixating eye till the corneal light reflex is centred in the squinting eye.
The power of prism required to centre the light reflex in the squinting eye equals the amount of squint in prism dioptres.
iv.Measurementofdeviationwithsynoptophore.(instrument)
3-Manifest squint 🔷 TREATMENT OF CONCOMITANT STRABISMUS:
Goals of treatment.These are to achieve good cosmetic correction,to improve visual acuity and to maintain binocular single vision.
However,many a time it is not possible to achieve all the goals in every case.
Treatment modalities.
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These include the following:
1.Spectacles with full correction of refractive error should be prescribed in every case. It will improve the visual acuity and at
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times may correct the squint partially or completely(as in accommodative squint).
2.Occlusion therapy: It is indicated in the presence of amblyopia. After correcting the refractive error,the normal eye is occluded and
the patient is advised to use the squinting eye. Regular follow-ups are done in squint clinic. Occlusion helps to improve the vision in
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children below the age of 10 years.
🔹 3.Preoperative orthoptic exercises. These are given after the correction of amblyopiato overcome suppression.
4.Squint surgery. It is required in most of the cases to correct the deviation.However,it should always be in stituted after the
correction of refractive error, treatment of amblyopia and orthoptic exercises.
PARALYTIC STRABISMUS
It refers to ocular deviation resulting from complete or incomplete paralys is of one or more extraocular muscles.
Etiology
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The lesions may be neurogenic, myogenic or at the level of neuromuscular junction.
I.Neurogenic lesions
1.Congenital. Hypoplasia or absence of nucleus is a known cause of third and sixth cranial nervepalsies. Birthinjuries may mimic congenital
lesions.
2.Inflammatory lesions. These may be in the form of encephalitis, meningitis, neurosyphilis or peripheralneuritis (commonlyviral). Nerve
trunks may also be involved in the infectious lesions of cavernous sinus and orbit.
3.Neoplastic lesions. These include brain tumours involving nuclei, nerve roots or intracranial part of the nerves; and intraorbital tumours
involving peripheral parts of the nerves.
4.Vascular lesions.
2)INCOMITANT SQUINT These are known in patients with hypertension, diabetes mellitus and atherosclerosis. These maybe in the form of haemorrhage, thrombosis,
It is a type of heterotropia (manifest squint) in which the amount of deviation varies in different directions of gaze. It includes following embolism, aneurysms or vascular occlusions.Cerebrovascular accidents are more common inelderly people.
conditions: 5.Traumatic lesions. These include head injury and director in direct trauma to the nerve trunks.
1.Paralytic squint, 6.Toxic lesions. These include carbonmonoxi depoisoning, effects of diphtheria toxins(rarely), alcoholic and lead neuropathy.
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2.‘A’and‘V’pattern heterotropias, 7.Demyelinating lesions. Ocular palsy may occur in multiple sclerosis and diffuse sclerosis.
3.Restrictivesquint. II.Myogenic lesions
1.Congenital lesions.These include absence, hypoplasia, malinsertion, weakness and musculofacial anomalies.
2.Traumatic lesions. These may be in the form of laceration, disinsertion, haemorrhage in to the muscle substance or sheath and
incarceration of muscles in fractures of the orbital walls.
3.Inflammatory lesions. Myositisis usually viral in origin and may occur in influenza, measles and other viral fevers.
4.Myopathies. These include thyroid myopathy, carcinomatous myopathy and that associated with certain drugs. Progressive external
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ophthalmoplegia is abilateral myopathy of extraocular muscles; which may be sporadic or inherited as an autosomal dominant disorder.
III.Neuromuscular junction lesion It includes my asthenia gravis.
The disease is characterised primarily by fatigue of muscle groups, usually starting with the small extraocular muscles, before involving
other large muscles.
Management
1.Treatment of the cause.An exhaustive investigative work-up should be done to find out the cause and, if possible, treat it.
