Strabismus Flashcards
What is binocular single vision?
Two images from two eyes combine to form one central image
What is Stereopsis?
3D depth perception
Which is greater? Binocular acuity or monocular acuity?
Binocular acuity
What is the importance of Stereopsis and Binocular single vision?
1) Increase field of vision
2) Eliminate the blind spot
3) Depth perception
4) Estimation of distance
Binocular eye movements are called __.
Versions
Monocular eye movements with the other eye covered are called __.
Ductions
What are the 6 muscles of the eye?
1) Medial Rectus
2) Lateral Rectus
3) Superior Rectus
4) Inferior Rectus
5) Superior Oblique
6) Inferior Oblique
Which muscles of the eye does the third cranial nerve (Oculomotor) supply?
1) Medial Rectus
2) Superior Rectus
3) Inferior Rectus
4) Inferior Oblique
Which muscle of the eye does the fourth cranial nerve (Trochlear) supply?
Superior Oblique
Which muscle of the eye does the fifth cranial nerve (Trigeminal) supply?
Lateral Rectus
The total number of the positions of gaze is _.
9
What are Yoke muscles?
A pair of muscles (one muscle in each eye) moving the eye to the same direction of gaze
What is squint (strabismus)?
Misaligned eyes (both eyes are not looking in the same direction)
What is concomitant (non-paralytic) squint?
The angle of deviation is not affected by the direction of gaze. (Eye muscles all move normally)
What causes concomitant (non-paralytic) squint?
UNCLEAR IMAGES AS A RESULT OF:
1) Refractive error
2) Opacities in the media of eye
3) Abnormalities of the retina that prevent the translation of a correctly formed image into neural impulses
Is concomitant (non-paralytic) squint congenital or acquired?
Congenital
Is non-concomitant (paralytic) squint congenital or acquired?
Acquired
When is diplopia at its peak in non-concomitant (paralytic) squint?
When attempting to look in
the direction requiring the action of the weak muscle.
What is non-concomitant (paralytic) squint?
The degree of misalignment varies with direction of the gaze (An eye muscle is not functioning properly)
Non-concomitant (paralytic) squint may indicate:
1) A nerve palsy
2) An extra-ocular muscle disease
Which nerve palsies may cause non-concomitant (paralytic) squint?
1) 6th nerve (Abducens)
2) 4th nerve (Trochlear)
3) 3rd nerve (Oculomotor)
What does a 6th nerve palsy cause?
Failure of Abduction
What does a 4th nerve palsy cause?
Defective depression of the eye when in adduction
What does a 3rd nerve palsy cause?
1) Failure of adduction, elevation and depression of the eye
2) Ptosis
3) Dilated pupil
What causes dysthyroid eye disease?
Infiltration of the extraocular muscles with lymphocytes and the depositions of glycosaminoglycans
Which muscle is most commonly affect in dysthyroid eye disease?
Inferior rectus
What are the complications of dysthyroid eye disease?
1) Chemosis & corneal ulcers = corneal perforations
2) Compressive optic neuropathy = blindness
Management of dysthyroid eye disease?
1) Systemic steroids
2) Radiotherapy
3) Surgical orbital decompression
4) Prisms
How do you diagnose myasthenia gravis?
Edrophonium test
How do you treat myasthenia gravis?
1) Neostigmine (acetylcholine esterase inhibitor)
2) Thymectomy
What is ocular myositis?
Inflammation of the extraocular muscles
Signs and symptoms of ocular myositis?
1) Pain
2) Diplopia
3) Restriction of movement
Mode of inheritance of Ocular Myopathy?
Mitochondrial DNA mutation
Describe the eye movement in ocular myopathy?
Slowly and symmetrically
reduced
What is seen pathologically in ocular myopathy?
Ragged red fibers
What is Brown’s syndrome also called?
Superior oblique tendon sheath syndrome
What is Brown’s syndrome?
Movement of inferior oblique muscle is restricted by the superior oblique muscle tendon failing to pass smoothly through its trochlear pulley or a stiff inelastic tendon
Brown’s syndrome results in:
Restriction of elevation in adduction
Duane’s Syndrome is caused by:
Faulty innervation of the medial and lateral rectus muscles
Duane’s Syndrome results in:
Faulty abduction and adduction
Do children in Duane’s syndrome develop amblyopia?
No, because binocular alignment is normal is some gaze positions
What is the Parapontine Reticular Formation
(PPRF)?
A part of the pontine reticular formation involved in the coordination of horizontal eye movements
What happens if there is a lesion in the Parapontine Reticular Formation
(PPRF)?
Horizontal gaze palsy to the side of the lesion
When do we normally see lesions in the Parapontine Reticular Formation
(PPRF)?
1) Brainstem disease
2) Vascular diseases
3) Tumors
What is Internuclear ophthalmoplegia?
Conjugate lateral gaze in which the affected eye shows impairment of adduction
If the right eye is affected in Internuclear ophthalmoplegia, what will the patient see?
They will see double when looking to the left
What does divergence of the eyes lead to in Internuclear ophthalmoplegia?
Horizontal diplopia
What does convergence of the eyes lead to in Internuclear ophthalmoplegia?
Nothing. It is preserved
What causes Internuclear ophthalmoplegia?
Injury to MLF (medial longitudinal fasciculus)
What is the cover test?
A test to detect strabismus
Cover test: If the unaffected eye is covered and the affected eye moves outward, it is:
Esotropic
Cover test: If the unaffected eye is covered and the eye moves inward, it is:
Exotropic
Cover test: If the unaffected eye is covered and the eye moves upward, it is:
Hypotropic
Cover test: If the unaffected eye is covered and the eye moves downward, it is:
Hypertropic
What is the Hirschberg corneal light reflex?
Objective assessment of ocular alignment
What are the signs of pseudoesotropia?
1) Small Interpupillary distance
2) Epicanthal folds
3) Flat nasal bridge
What are the signs of Infantile Esotropia?
1) Not associated with hypermetropia
2) Large angle of deviation
3) Both eyes are convergent (crossed fixation)
4) Left fovea fixes right field & vice versa
How do you assess infantile esotropia?
1) Fixation reflex
2) Cover uncover test
3) Refraction by cycloplegic drugs
4) Fundoscopy to evaluate any organic disease (retinoblastoma)
How do you treat infantile esotropia?
Surgery (recession of both medial recti)
What is Mobius Syndrome?
6th and 7th nerve underdevelopment
Signs & symptoms of Mobius Syndrome?
1) Crossed eyes (bilateral 6th)
2) Lack of facial expression
(facial palsy)
3) Clubbed feet
4) Missing fingers or toes
5) Chest wall anomalies
The combination of these three movements (__, __ and __) is under the control of the Edinger-Westphal nucleus and is referred to as the near triad.
1) Accommodation
2) Convergence
3) Miosis
The combination of these three movements (accommodation, convergence and miosis) is under the control of the ____ and is referred to as the near triad.
Edinger-Westphal nucleus
The combination of these three movements (accommodation, convergence and miosis) is under the control of the Edinger-Westphal nucleus and is referred to as the ___.
Near triad
Accommodative esotropia occurs as a consequence of:
A reduction in zonular tension induced by ciliary muscle contraction
Accommodative esotropia is often seen in patients with
a moderate amount of:
Hypermetropia
What are the 2 types of Accommodative Esotropia?
1) Fully accommodative esotropia
2) Convergence excess esotropia
Non-accommodative esotropia is induced by:
1) Emotional or physical stress (illness)
2) Sensory deprivation (untreated congenital cataract,
optic atrophy)
3) Retinoblastoma
What are the causes of intermittent exodeviations?
1) Divergence excess
2) Convergence weakness
3) Basic
What are the causes of constant exodeviations?
1) Congenital
2) Sensory
3) Consecutive
Intermittent exodeviations manifest during times of:
1) Visual inattention
2) Fatigue
3) Stress
4) During illness
If intermittent exodeviation is exposed to bright light, it
causes:
Reflex closure of one eye
What are the types of concomitant exotropia?
1) Accommodative exotropia
2) Non-accommodative exotropia
3) Consecutive exotropia
Accommodative exotropia is associated with:
Uncorrected myopia
Treatment for accommodative exotropia?
Correct myopia
Accommodative exotropia can be seen when the child looks:
Far away
What is Crouzon’s syndrome (branchial arch syndrome)/Non-accommodative exotropia caused by?
Defect in Fibroblast growth factor receptor 2 (Autosomal Dominant, Chromosome 10)
Signs & symptoms of Crouzon’s syndrome (branchial arch syndrome)/Non accommodative exotropia?
1) Shallow eye sockets after early fusion of surrounding bones
2) Cranial synostosis
3) Hypertelorism (greater than normal distance between the
eyes)
4) Patent ductus arteriosus
5) Aortic coarctation
Secondary exotropia is seen in cases of:
Unilateral loss of vision
Consecutive exotropia is due to:
Surgical overcorrection of an esodeviation
What causes amblyopia?
1) Suppression (monocular or cortical process producing absolute scotoma)
2) Non-use of the retino-cortical pathway
What are the types of amblyopia?
1) Strabismic
2) Anisometropic
3) Form Deprivation
Adult-onset strabismus usually causes __ rather than amblyopia, since the two eyes are not fixated on the same object.
Double vision
Refractive amblyopia may result from:
Anisometropia (unequal refractive error between the two eyes)
Amblyopia is associated with a
combination of __ and __.
Anisometropia; Strabismus
Form-deprivation amblyopia results when:
The ocular media become opaque
What are some examples of Form-deprivation amblyopia?
1) Cataracts
2) Corneal scarring
From forceps injuries during birth
If not treated quickly, form-deprivation amblyopia may:
Persist even after the cause of the opacity is removed
