Strabismus Flashcards

1
Q

What is meant by antagonist-agonist muscles?

A

These are muscles which are found on the same eye but move the eye in different directions e.g. MR and LR

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2
Q

What is meant by the term synergist muscles?

A

These are muscles in the same eye which work to move the eye in the same direction e.g. Inferior rectus and Superior orbital both depress the eye

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3
Q

What orbital muscles are innervation by CNIII

A

Superior Rectus
Inferior Rectus
Medial Rectus
Inferior Oblique

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4
Q

What orbital muscle is innervated by CNIV

A

Superior rectus

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5
Q

What orbital muscle is innervated by CNVI

A

Lateral Rectus

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6
Q

What muscle primarily elevates the eye?

A

Superior Rectus

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7
Q

What muscle is responsible primarily for depressing the eye?

A

Inferior rectus

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8
Q

What muscle primarily adducts the eye?

A

Medial rectus

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9
Q

What muscle primarily abducts the eye?

A

Lateral rectus

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10
Q

What muscle is primarily responsible for the intorsion of the eye?

A

Superior oblique

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11
Q

What muscle is primarily responsible for the extorsion of the eye?

A

Inferior oblique

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12
Q

What is meant by the term yolk muscles?

A

These are the muscles which are responsible for moving both eyes in the same direction? e.g. right LR and Left MR are responsible for moving the eyes to the right

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13
Q

What does Hering’s Law state?

A

That yolk muscles in a particular direction of gaze receive equal stimulus and simultaneous flow of innervations.

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14
Q

What does Sherrington’s Law state?

A

An increase in the innervation of one muscle results in a decrease to the innervation of the antagonist muscle.

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15
Q

What is meant by Amblyopia?

A

This is when the visual acuity is reduced in the early years of life (<8) due to developmental failure of the visual pathway between the eye and the occipital lobe’s visual cortex.
(Usually unilateral)

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16
Q

What can cause amblyopia?

A

Strabismus
Refractive errors
Stimulus deprivation e.g. cataracts

17
Q

How can amblyopia be managed/prevented?

A

Manage underlying cause.

Eye patches on the good eye to allow visual connections to develop. Pharmacological penalisation using atropine

18
Q

What is meant by the term binocular vision?

A

This is the ability to fuse images from both eyes into one single image

19
Q

Define stereopsis:

A

Perception of depth

20
Q

What are the different components of fusion in binocular vision?

A

Stereopsis
Sensory fusion
Motor fusion

21
Q

What is heterophoria?

A

This is deviation of the eye which is hidden by fusion

22
Q

When would heterophoria become apparent?

A

When the fusion is broken, often by covering one eye

23
Q

Define eso and exo - phoria:

A

Esophoria: inward deviation
Exophoria: outward deviation

24
Q

Define heterotropia:

A

this is an abnormal alignment of the eye, also referred to as a manifest squint.

25
Q

Define eso and exo tropia:

A

Esotropia: Convergent squint
Exotropia: Divergent squint

26
Q

Which squint is the most common in children in the UK and what is it usually associated with?

A

Esotropia

Hypermetropia

27
Q

What are the different subtypes of accommodative esotropia?

A

Fully accommodative - resolves following hypermetropia correction
Partially accommodative - partially resolves following hypermetropia correction
Convergence excess - requires bifocal or surgery. Occurs in near vision only due to high convergence

28
Q

What is Brown syndrome?

A

This Is a unilateral syndrome caused by mechanical restriction of the tendon of the SO at the trochlea leading to limited elevation in adduction or on up gaze.
Can have an associated click sensation.

29
Q

What is Duane Retraction Syndrome?

A

This is a rare condition which arises from innervation of the LR muscles by CNIII rather than CNVI.
It is often assoc. w/ CNVI nucleus hypoplasia and can cause retraction of the globe on adduction.

30
Q

What other symptoms may be seen in Duane retraction syndrome?

A

Deafness
Goldenhar syndrome
(split into three types)

31
Q

What surgical technique may be used for a highly active IO:

A

Disinsertion.

involves separating the tendon at its insertion to make it weaker

32
Q

What is the indication for the surgical ‘tucking’ procedure?

A

Congenital 4th nerve palsy

Involves strengthening the superior orbit

33
Q

What is the indication for the surgical advancement procedure?

A

This involves bring the muscle closer to the limbus, and is done to strengthen the muscle. Often done in a previously recessed EOM.

34
Q

What is surgical resection vs recession used for?

A

This involves shortening the muscle to strengthen it, while recession is loosening the muscle to weaken it.
In constant exotropia, bilateral LR recession and MR resection corrects the eye misalignment

35
Q

What can exotropia’s be classified as and what are they associated with?

A

Constant
Intermittent
Assoc. w/ myopia

36
Q

What is intermittent exotropia:

A

This is the more common form of exotropia, and can be further classified as near or distance.
In near exotropia the exotropia gets worse on near objects.
In distance exotropia, the exotropia is worsened by looking at a distance with a normal A/C ratio.

37
Q

What is constant exotropia and how is it managed?

A

This type of exotropia is commonly seen in neurological anomalies, and occurs within the first 6 months of life. It is a constant large angle exotropia and is managed surgically with bilateral LR recession and MR resection.

38
Q

What class of patients is a near exotropia often seen in?

A

Young adults and teenagers with myopia.

39
Q

Define microtropia:

A

This is a small angle squint. patients will have a subnormal binocular singular vision with sensory and motor fusion, and reduced stereopsis.