Squint By

Ahmad Mostafa

Professor of Ophthalmology

Applied Anatomy

Vertical recti Vertical recti (superior & (superior & inferior) inferior) are best tested in are best tested in abductionabduction

& & ObliquesObliques (superior & inferior) (superior & inferior) are best tested in are best tested in adductionadduction..

Superior rectus Superior rectus is the is the onlyonly elevator of the eye in elevator of the eye in abductionabduction

while the while the inferior oblique inferior oblique is is the the only only elevator in elevator in adduction.adduction.

Inferior rectus Inferior rectus is the is the onlyonly depressordepressor of the eye in of the eye in abductionabduction

while the while the superior oblique superior oblique is is the the only depressor only depressor of the eye of the eye in in adductionadduction..

Subsidiary Actions

• Superior muscles (SR & SO) Intortion• Inferior muscles (IR & IO) Extortion• Recti Adduction• Obliques Abduction

Eye Movements

► There are 3 types of eye movements:

1. Ductions

2. Versions

3. Vergences

1. Ductions

● Ductions are monocular eye movements including abduction, adduction, elevation, depression, intorsion, and extorsion.

● ● AgonistAgonist is the primary muscle moving the eye in any given direction.

● SynergistSynergist is a muscle acting in conjunction

with the agonist to produce a given movement.

● AntagonistAntagonist acts in the opposite direction to

the agonist.

• Sherrington's law

• States that a contraction of a muscle is automatically associated with a simultaneous decrease in innervation and relaxation, of its antagonist.

22 . .VersionsVersions

● ● Versions are Versions are binocularbinocular movements movements in which the 2 eyes move in which the 2 eyes move synchronously and symmetrically in synchronously and symmetrically in the the same direction same direction (conjugate eye (conjugate eye movement ) as follows:movement ) as follows:

• Dextroversion (right gaze), levoversion (left gaze), sursumversion (elevation), dorsumversion (depression), dextroelevation (gaze up & R.), dextrodepression (gaze down & R.), levoelevation (gaze up & L.), levodepression (gaze down & L.). Dextrocycloversion is rotation of the superior limbus of both eyes to the right and levocycloversion is rotation of the superior limbus of both eyes to the left.

33 . .VergencesVergences

● Vergences are binocularbinocular movements in which the 2 eyes move synchronously and symmetrically in oppositeopposite directions.

Convergence is the ability of the 2 eyes to

turn inwards, and divergence is their ability to turn outwards from a convergent position.

Ocular Motility Examination

• The positions of gaze are referred to as follows:

• Primary position (straight ahead).• Secondary positions (straight up, straight

down, right gaze, and left gaze).• Tertiary positions (the four oblique positions

of gaze = up and right, up and left, down and right, down and left).

► The six cardinal positions of gaze include

• Dextroversion (right gaze), • Levoversion (left gaze), • Dextroelevation (gaze up & R.), • Dextrodepression (gaze down & R.), • Levoelevation (gaze up & L.), and • Levodepression (gaze down & L.).

Yoke Muscles:Yoke Muscles: When the eyes are moving into each of When the eyes are moving into each of

the six cardinal positions of gaze, a muscle the six cardinal positions of gaze, a muscle of one eye is paired with a yoke muscle of of one eye is paired with a yoke muscle of the opposite eye e.g. on abduction of the the opposite eye e.g. on abduction of the right eye, the right-LR is paired with the right eye, the right-LR is paired with the left MRleft MR

Hering's Law:Hering's Law: States that during any conjugate States that during any conjugate

eye movement, equal and eye movement, equal and simultaneous innervation flows to simultaneous innervation flows to the yoke muscles.the yoke muscles.

• Accommodation/convergence:• For each dioptre of accommodation there

is 4-5 (prism diopter) of accommodative convergence.

• A high AC/A ratio: • may cause excessive convergence and

produce a convergent squint (esotropia), during accommodation on a near object.

Binocular Single Vision• BSV is achieved when both eyes are used

together

• Importance:(1) Stereopsis (depth perception).(2) Binocular visual field is larger than the

uniocular field alone.(3) Field defects in one field are masked by the

other overlapping field.

Grades of Binocular Vision

1- First grade: Simultaneous perception.• This consists of the power to see two dissimilar images (objects)

simultaneously e.g. a bird and a cage.

2- Second Grade: Fusion.• This entails the power to super impose two incomplete but similar

pictures to form one complete picture, e.g. a rabbit with a tail and no ears and the other rabbit with two ears and no tail , to form one rabbit with a tail and two ears (the tail and ears are called controls).

3- Third grade: Stereopsis• Is the ability to see three-dimensional vision or stereopsis or

depth perception.

Tests of binocular vision

• Worth four dot test• Maddox rod test for distance.• Maddox wing test for near.• Synoptophore.

SQUINT (STRABISMUS)

Definition• Abnormal deviation of the visual Abnormal deviation of the visual

axesaxes• N.B. N.B. Normally the 2 visual axes are Normally the 2 visual axes are

parallel except in convergence where parallel except in convergence where they meet at the object of regardthey meet at the object of regard

Classification of SquintClassification of Squint

ApparenApparentt

TrueTrue

ManifesManifestt

LatentLatent(Heterotropia) (Heterophori

a)

PseudostrabismPseudostrabismusus

ConcomitanConcomitantt

incomitantincomitant

ParalyticParalyticRestrictiveRestrictive

I. APPARENT I. APPARENT SQUINTSQUINT

PseudostrabismusPseudostrabismus

APPARENT SQUINT(Pseudostrabismus)

Definition: There is an appearance of squint but it is not a true squint because the 2 visual axes are normally directed

Types & CausesTypes & Causes Apparent convergent squint- - Epicanthus Epicanthus- - High myopia (-ve angle alpha)High myopia (-ve angle alpha)- Narrow interpupillary distance- Narrow interpupillary distance

Apparent divergent squint- - High hypermetropia (large +ve angle alpha)High hypermetropia (large +ve angle alpha)- Wide interpupillary distance- Wide interpupillary distance

DefinitionsDefinitions• Visual AxisVisual Axis: A line passing from the

object of fixation, nodal point, and fovea.

• Optic AxisOptic Axis: A line passing through centre of cornea, centre of lens, nodal point to cut the retina at the posterior pole (which normally lies between the optic disc and fovea)

• Angle AlphaAngle Alpha:: it is the angle it is the angle between the optic axis and visual axis between the optic axis and visual axis at the nodal pointat the nodal point

NormallyNormally: it is + 2 – 5 : it is + 2 – 5 ○○

.. It is considered +ve when the visual It is considered +ve when the visual axis cuts the cornea on nasal side of axis cuts the cornea on nasal side of the optic axis.the optic axis.

a.a.It is +ve in It is +ve in emmetropeemmetrope

b. It is large +ve in b. It is large +ve in hypermetropehypermetrope

c. It is -ve in c. It is -ve in high myopia high myopia due to change due to change in the posterior segment of the eye, in the posterior segment of the eye, therefore, the posterior pole becomes therefore, the posterior pole becomes on the temporal side of the fovea and on the temporal side of the fovea and the visual axis cuts the cornea on the the visual axis cuts the cornea on the temporal side of the optic axis. temporal side of the optic axis.

Fovea

Optic AxisVisual axis

NN

Posterior Pole

Fovea

Optic Axis Visual axis

NN

Posterior Pole

DIAGNOSISDIAGNOSIS

(1) Of the cause

(2) Corneal reflex: Normal (central)

(3) Cover test: Negative

TreatmentTreatment

• Treatment of the cause

II. TRUE II. TRUE SQUINTSQUINT

(1) LATENT SQUINT(1) LATENT SQUINTHeterophoriaHeterophoria

• Definition:Ocular deviation with abnormal direction of the visual axes of both eyes when the binocular vision is dissociated.

Classification (Clinical Types)Classification (Clinical Types)– Esophoria: Tendency of the eye to deviate in.– Exophoria: Tendency of the eye to deviate out.– Hyperphoria: Tendency of the eye to deviate up.– Hypophoria: Tendency of the eye to deviate

down.– Cyclophoria: Tendency of the eye to rotate:

• Inwards: In-cyclophoria.• Outwards: Ex-cyclophoria.

Aetiology(1) Uncorrected errors of refraction: Due to dissociation

between accommodation and convergenceHypermetropia: Leads to esophoria.Myopia: Leads to exophoria.

(2) Relative weakness of one or more of the extraocular muscles.

(3) Over-straining of the eyes: Close-work may lead to

esophoria.

Clinical Picture (a) Symptoms

1) Compensated heterophoria: No symptoms.2) Decompensated heterophoria:

Symptoms occur after fatigue: 1- Muscular asthenopia (eye strain). 2- Blurring and running of letters. 3- Intermittent diplopia.

((bb ) )SignsSigns

1) No ocular deviation: If binocular vision is maintained.

2) Ocular deviation: If binocular vision is not maintained (latent strabismus becomes manifest strabismus).

DIAGNOSIS OF HETFRDPHORIA

Stressed on 3 diagnostic methods 3 diagnostic methods → based on dissociation of binocular vision to abolish fusion:

1. Cover test2. Maddox rod3. Maddox wing

(1 )Cover Test

• Aim: Dissociation of binocular vision by covering one eye to observe the movement of the covered eye only, on removing the cover.

• Method

1) The patient is asked to fix an object (as the examiner's finger).

2) One eye is covered by a card and observed under the cover.

3) If heterophoria is present behind the cover will move and on removing the cover it will return to its original position.

(2 )Maddox Rod Test

• Aim: Dissociation of binocular vision by changing the appearance of the retinal image in one eye.

Method• Maddox rod: Consists of 4 or 5 cylinders (rods) of

red glass side by side in a supporting disc.• The patient sits at a distance of 6 metres from a

white spot of light in a dark room and then the Maddox rod test is done

(3 )Maddox Wing Test

• Aim: Used to detect heterophoria for near (33 cm).

TREATMENT OF HETFRDPHORIA

(1) Compensated heterophoria: No treatment.

(2) Decompensated heterophoria:

(1) Correction of the refractive error: If present.

(2) Orthoptic treatmentAim: To strengthen the weak muscles:

1-Pencil-nose exercise.2-Exercising prisms (base of prism is in direction of

latent deviation).3-Synoptophore.

(3) Relieving prisms in spectacles:• To neutralize the deviation (in hyperphoria

only) if the orthoptic exercises fail (base of the prism is against the direction of the latent deviation).

(4) Rarely, Surgical: • If above measures fail (strengthening weak

muscles or weakening overacting muscles

(2) MANIFEST SQUINT(2) MANIFEST SQUINTHeterotropiaHeterotropia

(A) Concomitant Squint

(B) Incomitant (nonconcomitant) squint

A. CONCOMITANT STRABISMUSA. CONCOMITANT STRABISMUS

• DEFINITION: • Ocular deviation with abnormal direction of the

visual axes of both eyes relative to each other in which the angle of deviation is constant in different direction of gaze.

TYPES OF CONCOMITANT STRABISMUSTYPES OF CONCOMITANT STRABISMUS

(1) According to the direction of deviation:

• Esotropia (convergent): Deviated inwards.• Exotropia (divergent): Deviated outwards.• Hypertropia: Deviated upwards.• Hyportropia: Deviated downwards.

(2) According to the laterality of deviation:

• Unilateral (uniocular): If the deviation is always by the squinting eye.

• Alternating: If the deviation is by either eye at different times.

• Bilateral : the 2 eyes are squinting

Alternating exotropia

Clinical Picture

1. Symptoms:

1) Ocular deviation: With bad cosmetic appearance.2) Defective vision: In unilateral squint (poor vision

in squinting eye).

2. Signs1) Decreased visual acuity in unilateral squint (strabismic amblyopia) 2) Ocular deviation: With a constant angle of squint (either convergent or divergent)

Childhood Esotroipas

I. Accommodative I. Accommodative EsotropiaEsotropia

II. Non-AccommodativeII. Non-Accommodative EsotropiaEsotropia

= Infantile Esotropia= Infantile Esotropia

The angle of deviation is The angle of deviation is corrected corrected by wearing by wearing hypermetropic glasseshypermetropic glasses

The angle of deviation is The angle of deviation is not not affected affected by wearing by wearing hypermetropic glasseshypermetropic glasses

I. Accommodative EsotropiaI. Accommodative Esotropia

FullyFully AccommAccomm

Partially Partially AccommAccomm

Accomm Accomm Eso Eso

with with convergencconvergenc

e excesse excess

Clinical Features

• Presentation of this common condition is typically at 2.5 years (range between 6 months – 7 years).

(1) FullyFully Accommodative Esotropia Accommodative Esotropia

• The angle of deviation is fully corrected with the appropriate hypermetropic correction

It is chracterized by:

1. Angle is virtually the same for near and distance

2. Refraction shows high hypermetropia (+4 to +7 D)

3. Accommodative-convergence to accommodation ratio (AC/A) is normal.

(2) Partially (2) Partially Accommodative EsotropiaAccommodative Esotropia

• The angle of deviation is partially corrected with the appropriate hypermetropic correction

(3) Accommodative Esotropia with convergence excessconvergence excess

• Is characterized by: 1. Angle is marked for near, and nil or small for

distance (at 6 meters)2. Refraction usually shows emmetropia or small

degree hypermetropia3. AC/A ratio is high.

II. Non-Accommodative EsotropiaII. Non-Accommodative Esotropia (Infantile Esotropia)

• Clinical features• Presentation of this common condition is

within the first 6 months of life • Signs 1.Angle is large with crossed fixation on side

gaze 2. Nyslagmus is frequent 3. Retraction is normal for the patient's age (ex.

+1.5 D) (Physiological hypermetropia)

Management

• Initial1.Refraction and fundus examination.2. treatment of amblyopia if present.

• SubsequentSurgery between the age of 12 and 18 months (bilateral medial rectus recession).

Investigation of A Case of Investigation of A Case of Concomitant squintConcomitant squint

• Measure the VA without & with glasses• Cycloplegic refraction• Test for ocular motility to R/O paralytic squint• Cover tests• Measure angle of squint• Examine for binocular vision• Fundus Examination

Paralytic Paralytic SquintSquint

Paralytic Squint• DEFINITION:

Ocular deviation with abnormal direction of the visual axes of both eyes due to paralysis of one or more of the extraocular muscles in which the angle of deviation(of strabismus) is variable in different directions of gaze.

•

AETIOLOGY

(1) Nuclear lesions: • 1) Congenital: Aplasia.• 2) Inflammatory: Encephalitis. • 3)vascular: Haemorrhage.• 4) Neoplastic: Brainstem tumours.

(2) Nerve lesions

• 1)Congenital: Rare.• 2) Traumatic: Fracture skull base.• 3) Inflammatory: Diabetes, herpes zoster or

meningitis.• 4)Vascular: Subarachnoid haemorrhage.• 5) Neoplastic: Orbital tumours.

(3) Muscle iesions:

• 1) Congenital: Hypoplasia.• 2) Traumatic: Haemorrhage in the muscle

sheath.• 3) Myopathic : • 1. Myasthenia gravis.• 2. Thyrotroptic or thyrotoxic exophthalmos.

CLINICAL PICTURE(1) Symptoms:

1. Ocular deviation2. Diplopia : In all or certain directions of gaze.3. A compensatory head posture (to avoid

diplopia and to maintain binocular single vision).

4. dizziness, uncertain gait , nausea and vomiting: (Are due to diplopia or false projection of objects).

(2) Signs: All signs and symptoms of paralytic

strabismus occur in the direction of action of paralysed muscle.

1. Ocular deviation with limitation of the movements of the affected eye

2. Binocular Diplopia3. False projection4. Compensatory head posture

1 .Squint & Limitation of Ocular Motility

1. Primary ocular deviation : • Occurs in a direction opposite to that of action

of the paralysed muscle (as inwards in right L R paralysis).

2. Secondary ocular deviation: • Is deviation of normal eye when it is covered

by a screen to force the patient to fix with paralysed eye.

• 3. The angle of secondary deviation: • is much larger than the angle of primary

deviation: Due to overaction of the contralateral synergist of the paralysed muscle

(a) Normally: Brain sends nerve impulses to the eyes for fixation in any direction which are equally distributed between both eyes.

• (b) When the paralysed eye is fixing:• a) The brain sends more nerve impulses to the

paralysed muscle to force it to contract.• b) At the same time equal amount of these nerve

impulses are sent to the synergistic muscle of the other normal eye and so produce overaction of that muscle.

• c) This leads to increased movement of the normal eye under the cover with increased angle of secondary deviation.

2. Binocular Diplopia

• Double vision by the use of both eyes because two retinal images fall on non-corresponding points of retina:

1- It disappears when one eye is covered: • Unlike uniocular diplopia.2- Two different images are seen:• (a) True image (clear → by the fovea of the normal

eye).• (b) A false image (blurred → by a point outside

the fovea of the paralysed eye).

Clinical Types

(a) Uncrossed (homonymous) diplopia:• False image falls on the nasal side the fovea.• So will be projected on the temporal side of the paralysed eye

(e.g. LR paralysis).

(b) Crossed (heteronymous) diplopia:• False image falls on the temporal side of the fovea.• So will be projected on the nasal side of the paralysed eye (e.g.

MR paralysis).

Uncrossed Uncrossed DiplopiaDiplopia

Crossed Diplopia

3 .False Projection(Past Pointing)

• The affected eye does not see objects in their exact location (in the direction of action of the paralyzed muscle).

• Cause:Cause: is due to increased innervation to the paralysed muscle by the brain in an effort to force it to act

4 .Compensatory Head Posture

• Aim: To avoid diplopia

• Direction: movement of the head is always in the direction of action of the paralysed muscle i.e. in which the diplopia is greater

Compensatory Head Postures

• 1. Face turn (to R. or L.) in Horizontal muscle palsy.

• 2. Head tilt (torticollis) towards the shoulder of the side of the higher image i.e. that of the hypotropic eye in Vertical muscle palsyValue: to neutralize the vertical & torsional displacement, so that the 2 images are brought to the same level

• 3. Chin elevation or depression: in an elevator or depressor palsy respectively

                   

 

                   

 

                   

 

                   

 

Secondary Changes in the EOMs following Paralytic Squint

• 1) Overaction (contracture) of the ipsilateral antagonist.

• 2) Compensatory overaction of the contralateral synergist (excessive impulses) .

• 3) Secondary inhibitional underaction of the contralateral antagonist (inhibitory impulses),

Diagnosis of Paralytic squint

• (1) Signs and symptoms: Diplopia , limitation of movements, ... etc.

• (2) Examination of ocular motility• (3) Diplopia chart• (4) Hess screen

Diplopia chart• 1) A red glass in front of the right eye and a green

glass in front of the left eye of the patient (to differentiate between the 2 images) in a dark room.

• 2) A torch with a stenopaeic slit is used to project a linear light.

• 3) The patient is asked about data to investigate diplopia: – 1- Areas and type (uncrossed or crossed) of diplopia.– 2- Relative position of the 2 images.– 3- Distance between the 2 images.

Hess Screen• Aim: • l)To determine the degree of the paralysed

muscle.• 2) To determine the secondary changes

affecting the other muscles. • Principle: Special screen records the degree of

false projection in different directions of gaze by dissociating the images of the 2 eyes with coloured goggles (red and green glasses).

DD between Conc. & paraltic squint.Character:Character:Concomitant strabismusParalytic squint

(1) Diplopia:(1) Diplopia:Absent.Absent.Present.Present.

(2) Limitation of (2) Limitation of movementsmovements

Absent.Absent.Present.Present.

(3) Ocular torticollis:(3) Ocular torticollis:Absent.Absent.Present.Present.

(4) Vertigo, nausea,... (4) Vertigo, nausea,... etc:etc:

Absent.Absent.Present.Present.

(5) False projection:(5) False projection:Absent.Absent.Present.Present.

(6) Angle of deviation:(6) Angle of deviation:Constant.Constant.Variable.Variable.

(7) 1ry and 2ry (7) 1ry and 2ry deviation:deviation:

Equal.Equal.2ry deviation is larger2ry deviation is larger

Types Of Ophthalmoplegia

• 1. Total ophthalmoplegia: = palsy of EOMs + intrinsic (internal) Ms (sph. P, dilator p, ciliary ms)

• 2. External ophthalmoplegia = palsy of EOMs• 3. Internal ophthalmoplegia = palsy of internal

ms

Treatment of SquintTreatment of SquintA)A) Treatment of Concomitant SquintTreatment of Concomitant Squint

B) Treatment of Paralytic SquintB) Treatment of Paralytic Squint

A) Treatment of Concomitant A) Treatment of Concomitant SquintSquint

• A. Aim of treatment: A. Aim of treatment: 1. Treatment of amblyopia2. Development & consolidation of binocular binocular

vision vision (this can be only achieved before the age of 6 years)

3. Improvement of the cosmetic appearance(least important & much easier to achieve)

B. Lines of TreatmentB. Lines of Treatment

• 1. Cycloplegic refr1. Cycloplegic refraction action & correction of refractive error if present (e.g. Fully accomm eso. due to hypermetropia glasses)

• 2. Occlusion therapy 2. Occlusion therapy (of the normal eye) to treat amblyopia

• 3. Surgical treatment3. Surgical treatment

11 . .Cycloplegic refractionCycloplegic refraction

22 . .Occlusion therapyOcclusion therapy

3. Surgical treatment Surgical treatment

• Indications:Indications:a. Non accommodative esotropiaa. Non accommodative esotropiab. Treatment of residual angle in partially b. Treatment of residual angle in partially accommodative esotropiaaccommodative esotropiac. Cosmetic (in adult patients)c. Cosmetic (in adult patients)

• Technique:Technique:a.a.Unilateral squint (recession-resection)Unilateral squint (recession-resection)b.b.Alternating squint (operate on 2 eyes) Alternating squint (operate on 2 eyes)

Medial Rectus RecessionMedial Rectus Recession

Recession of medial (or Lateral) Recession of medial (or Lateral) rectusrectus

Left esotropiaLeft esotropia

Treated by Treated by recession-resection recession-resection procedureprocedure

Alternating Alternating Esotropia Esotropia

Treated by Treated by Bilateral medial Bilateral medial rectti recessionrectti recession

B. Treatment of Paralytic squint

• 1. Treatment of the causecause• 2. 2. Wait Wait for 6 months for spontaneous recoveryfor 6 months for spontaneous recovery• 3. CoverCover the affected eye to mask diplopia• 4. Surgery Surgery is indicated if no improvement occurs

after 6 monthsafter 6 months: • 1) Recession – Resection Recession – Resection : Weakening of the stronger

muscle, Strengthening of the weak (paralysed ) muscle.• 2) Muscle transposition Muscle transposition : : As in lateral rectus paralysis.

Muscle transpositionMuscle transposition