STRABISMUS
*Eye Movements Ductions: Monocular eye movement Adduction (inward movement) Abduction (outward movement) Tortional duction; intorsion (inward rotation) extortion (outward rotation) Versions: Binocular, conjugate eye movement in the same direction Dextroversion; both eyes move toward right Levoversion; both eyes move toward left Vergences: Binocular, disconjugate eye movement in opposite directions Convergence; eyes move inward Divergence; eyes move outward
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ANATOMY AND PHYSIOLOGY EYE MOVEMENTS ARE ACHIEVED BY SIX EXTRA-OCULAR MUSCLES: EYE BALL CAN BE MOVED IN ALL DIRECTION OF GAZE. MOVEMENTS OF BOTH EYES IS PRECISELY COORDINATED TOGETHER.
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Muscle
Nerve supplyAction
Medial rectus
Oculomotor n.( III )
Adduction (inward movement)
Lateral rectus
Abducent n. (VI)
Abduction (outward movement)
Superior rectus
Oculomotor n.( III )
Elevation, Intorsion (inward rotation), adduction
Inferior rectus
Oculomotor n.( III )
Depression, Extorsion (outward rotation), adduction
Superior oblique
Trochlear n. (IV)
Intorsion (inward rotation), depression, abduction
Inferior oblique
Oculomotor n.( III )
Extortion (outward rotation), elevation, abduction
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SIX CARDINAL POSITION OF GAZE: IN EACH ONE CARDINAL POSITION, ONE MUSCLE IS THE PRIME MOVER:
Outward; Lateral rectus Inward; Medial rectus Outward and above; Superior rectus Outward and below; Inferior rectus Inward and above; Inferior oblique Inward and below; Superior oblique
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Visual axis line between point of fixation and fovea Normally the two visual axes intersect at the same point of fixation. The two images formed in the retina of both eyes will be fused in the brain into one.
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BINOCULAR SINGLE VISION;
coordinated use of both eyes in order to produce a single unified perception. Advantages of Binocular single vision: Better V.A. Wider field of vision Stereopsis Compensation for each blind spot Requirements for Binocular single vision: Clear vision in both eyes Precise coordination of the two eyes for all direction of gaze The ability of the brain to fuse the two images*
Is a unilateral or bilateral decrease in the best corrected visual acuity caused by vision deprivation and / or abnormal binocular interaction, for which there is no pathology of the eye or visual pathway
AMBYLOPIA
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Types of amblyopia: A-Strabismus amblyopia B-Stimulus deprivation amblyopia e.g. congenital cataract. C-Anisometropic amblyopia D. Bilateral Ametropic
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TREATMENT OF AMBLYOPIA
1-Treatment of the cause2- Closure of the normal eye and stimulate vision in the amblyopic eye.
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Concomitant: Movements of both eyes are full (non-paralytic). The angle of deviation is constant unrelated to the direction of gaze. Primary deviation is equal to the Secondary deviation. Incomitant: Under action of one or more of the extraocular muscles due to a nerve palsy or muscular disease. The angle of deviation is different with the direction of gaze. Primary deviation is less than the Secondary deviation.
TYPES OF SQUINT
*Primary deviation; deviation of the squinting eye when fixation taken by the normal eye Secondary deviation; deviation of the normal eye when fixation taken by the squinting eye
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SQUINT MISALIGNMENT OF THE TWO VISUAL AXES
Consequences of squint 1- Diplopia; simultaneous perception of two images of one object 2- Confusion; simultaneous perception of two superimposed dissimilar images*
Compensatory mechanism to eliminate confusion and diplopia 1-Suppression In young children. Central cortical phenomena will neglect vision in the squinting eye. Continuous suppression in young children will cause amblyopia. 2-Abnormal head posture in adult who cannot eliminate diplopia by suppression. Turning the head in a position that the normal eye will be aligned with the squinting eye.
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Accommodation: increase in the refractive power of the eye on looking to a near object so that its image is clearly focused on the retina. Accommodation is part of the near reflex, includes; Accommodation Convergence (inward movement of the eyes) Miosis (constriction of the pupil) Normally one dioptre of accommodation is associated with 4 prism dioptres convergence AC/A = 4/1
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Esotropia Accomodative Refractive Non Refractive Mixed 2. Non Accomodative Essential infantile Sensory Basic Convergence excess
Exotropia Constant exotropia Intermittent exotropia Sensory exotropia Consecutive exotropia
Strabismus
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ESOTROPIA
1- Accommodative Convergence is related to accommodation, age of 6 months to 7 years*
a- Refractive , due to excessive hypermetropia b-Non-Refractive, High AC/A c- Mixed excessive hypermetropia and high AC/A
High AC/A
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TREATMENT
-Refractive type: correction of hypermetropia by convex lenses -Non-Refractive type: Miotic eye drops (e.g. pilocarpine), which cause decrease in the AC/A ratio. - Mixed: Bifocal lenses Amblyopia by closure of the normal eye and stimulate vision in the amblyopic eye. Surgery In long standing cases with large angle.*
2- Non-Accommodative a- Infantile Present during first 6 months of life, no refractive error. Large angle, cross fixation Treatment, surgery within first year b- Sensory deprivation: Monocular loss of vision in young children
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Constant Exotropia often present at birth and treatment is surgical Intermittent present at around age of 2 years exophria which break down to exotropia inattention, bright light, fatigue and illness
EXOTROPIA
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3.Sensory Exotropia
Treatment: Spectacle (myoia). Ambylopia therapy. Surgery*
Incomitant Strabismus: 1- Paralytic; Oculomotor nerves palsies
2- Myopathy: Myasthenia gravis, Thyroid myopathy, Myositis*
Oculomotor, Trochlear, Abducent nerves 1- Congenital 2- Vascular; diabetes, hypertension 3- Trauma; head injury 4- Tumors; e.g. meningioma, acoustic neuroma 5- Aneurysm of the posterior communicating artery 6- Infections; e.g. meningitis
CAUSES OF OCULAR NERVES PARALYSIS
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OCULOMOTOR NERVE PALSIES
Ptosis Eye deviated outward (exotropia ) Inability to elevate the eye Inability to move the eye downward Inability to move the eye inward (Adduction) Fixed dilated pupil*
TROCHLEAR NERVE PALSIES
Hyperdivation of the eye inward position Impairment of depression inward position
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ABDUCENT NERVE PALSIES
Inward deviation of the eye (esotropia) Inability to move the eye outward (Abduction)*