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Ophthalmology > 9 - Strabismus > Flashcards

9 - Strabismus Flashcards

1
Q

What is squint or strabismus?

A

Condition in which the eyes do not align with each other when looking at an object
The eye focused on the object can switch
can be present occasionally or constantly

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2
Q

What are the 6 muscles that control eye movement?

A

4 rectus muscles (superior, inf, lat, medial)

2 oblique muscles (sup & inf)

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3
Q

Innervation & function of the lateral rectus

A 
innervation - VI/Abducens
function - moves the eye outwards
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4
Q

Innervation & function of the superior oblique

A 
innervation - IV/ Trochlear 
function - rotates the top of eye to the temple, and to a lesser extent, moves the eye outwards
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5
Q

Function of the lateral, medial & superior rectus muscles.

A

lateral - moves the eye outwards
medial - “ inwards, towards the nose
superior - “ upwards, and to a lesser extent, rotates the top of the eye to the nose

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6
Q

Function of the superior & inferior oblique muscles.

A

superior oblique - ROTATES the top of the eye towards the temple, and to a lesser extent, moves the eye down
inferior oblique - ROTATES the top of the eye towards the nose, and to “ “ moves the eye up

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7
Q

What are some causes of a squint?

A

majority –> unknown cause

accident or illness that affects the eye muscles:

  • diabetes
  • thyroid dx (Graves’ dx)
  • myasthenia gravis
  • brain tumours
  • head trauma
  • strokes
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8
Q

What are the risk factors of developing a squint?

A
  • premature birth
  • cerebral palsy
  • family history
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9
Q

Symptoms of a squint in adults & children

A

Adult

  • eye fatigue
  • double vision
  • overlapped or blurred images
  • pulling sensation around eyes
  • loss of depth perception

Children
- amblyopia/ lazy eye –> bc of brain ignoring one eye

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10
Q

What is amblyopia and how is it caused?

A

AKA lazy eye due to the brain ignoring one eye
= failure of 1 or both eyes to achieve normal visual acuity despite normal structural health

to avoid double vision –> signal from deviated eye is suppressed by brain & this causes failure of visual dev in that eye

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11
Q

What are the 4 types of strabismus (according to morphological classification)?

A
  1. Esotropia - 1 eye deviated to the nose, other is centred. cross eyed
  2. Exotropia - 1 eye is deviated to the temple, “ “ “. the eyes diverge
  3. Hypertropia - 1 “ “ to the ceiling, “ “ “
  4. Hypotropia - 1 eye deviated to the floor, “ “ “ 2
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12
Q

How is strabismus diagnosed?

A

observe light reflecting from person’s eyes & finding that its not centred on the pupil

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13
Q

What are the 3 types of strabismus based on “kind of angle” classification?

A
  1. Apparent/ Pseudo-strabismus
  2. Latent strabismus/ Heterophoria
  3. Manifest strabismus/ Heterotropia, divided in:
    - concomitant or non-paralytic
    - incomitant or paralytic
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14
Q

What are the 2 subtypes of manifest strabismus/ heterotropia?

A
  • concomitant or non-paralytic

- incomitant or paralytic

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15
Q

What is apparent/ pseudo-strabismus?

A

a false appearance of strabismus caused by an optical illusion.

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16
Q

What is latent strabismus/ heterophoria?

A
  • the eye turns only when it is covered or shut.
  • eyes have a tendency to become misaligned when not being used e.g. when
    the eye is covered. However, when being used normally, the eyes are straight.
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17
Q

What are the 2 subtypes of latent strabismus/ heterophoria?

A
  • Esophoria, if the covered eye turns inward
  • Exophoria, if the covered eye turns
    outward (one eye drifts away from the
    other).
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18
Q

What is manifest strabismus/ heterotropia? What are the subtypes?

A

squint present when the eyes are open and being used.

  1. Concomitant/ non-paralytic = size of deviation does not vary w/ direction of gaze (Most begin early in childhood, 2-4y/o)
  2. Incomitant/ paralytic = direction of gaze does affect size or presence of squint
    - in childhood & adulthood due to neurological, mechanical or myogenic problems affecting eye muscles
    - always due to a cranial n palsy (3, 4, 6 CN)
19
Q

What are the 3 MAIN causes of CN III palsy?

A
  • aneurysm
  • vasculopathy
  • tumor
20
Q

What are the MAIN causes of CN IV palsy?

A
  • trauma
  • congenital
  • vasculopathy
  • tumor
21
Q

What are the MAIN causes of CN VI palsy?

A
  • increased cranial pressure or vasculopathy, esp diabetes
22
Q

What happens to the eye in CN VI palsy?

A

6th CN innervates the Lateral Rectus Muscle, if damaged –> no opposition to the medial rectus, that prevails

23
Q

What does CN III innervate?

A

innervates 4/6 eye muscles –> that move eye inward, up & down + rotate the eye

(CN III palsy –> eye is down & turned out)

CN III also controls:

  • pupil constriction
  • position of upper eyelid
  • ability of eye to focus
24
Q

What does the eye look like in a CN III palsy?

A

CN III innervates 4/6 eye muscles –> that move eye inward, up & down + rotate the eye

palsy –> eye is down & turned out

(Nobody likes you when you’re down & out)

25
Q

What does the term “palsy” refer to?

A

a complete weakness of a muscle,

paresis = a partial weakness

26
Q

What are the consequences of a COMPLETE CN III palsy?

A
  1. completely closed eyelid
  2. deviation of eye outward & downward

affected eye = DOWN & OUT
- eye can’t move inward or up, pupil enlarged & doesn’t react normally to light

27
Q

Symptoms of CN III palsy

A
  1. Double vision - due to misalignment of eyes, pts >10y.o usually. Due to ptosis/ drooping eyelid –> diplopia may not be noticeable. In pts <6y.o –> may have lazy eye instead (amblyopia)
  2. Ptosis
  3. Enlarged pupil

Ptosis of the eyelid or enlarged pupil –> may be 1st sign of CN III palsy

28
Q

What are the causes of CN III palsy?

A
  1. Congenital
  2. Acquired
    - head injury
    - infection
    - migraine
    - brain tumour
    - ANEURYSM
    - DIABETES
    - high b.p
29
Q

What is another term for a CN IV (trochlear) palsy?

A

AKA superior oblique palsy

CN IV innervates superior oblique muscle

30
Q

What is the consequence of a CN IV (trochlear) palsy?

A

weakness of superior oblique –> combo of vertical, horizontal & torsional misalignment of eyes

31
Q

Which is most noticeable in a CN IV (trochlear) palsy: vertical, horizontal or torsional misalignment of eyes ?

A

vertical misalignment = most noticeable feature

32
Q

Is CN IV (trochlear) palsy unilateral or bilateral?

A

usually unilateral, can be bilateral too

33
Q

Symptoms of CN IV (trochlear) palsy?

A
  • may be asymptomatic until later childhood or adulthood
  1. compensatory head tilt/ TORTICOLLIS –> compensate for underacting superior oblique (towards contralateral side, allows better alignment of eyes)
  2. facial asymmetry (from chronic head tilt)
  3. diplopia (vertical, diagonal, & less often torsional)
34
Q

What are the causes of CN IV palsy?

A
  1. Congenital
  2. Acquired -> head trauma.

Rare causes:

  • stroke
  • tumor
  • aneurysm
35
Q

What is the consequence of a CN VI (abducens) palsy?

A

weakness of lateral rectus muscle which rotates the eye away from the nose –> eye crosses inward towards nose –> ESOTROPIA

36
Q

Symptoms of isolated CN VI (abducens) palsy ?

A
  1. Deviation - eyeball is converged due to unopposed action of medial rectus
  2. Ocular movements - abduction is limited
  3. Diplopia –> MOST COMMON. Younger children don’t dev this but are prone to amblyopia
  4. Head posture - face is turned towards paralysed muscle to minimise diplopia
  5. Depending on the neurologic struc.s involved: (CN VI goes from BS to lat rectus)
    - hearing loss
    - facial weakness
    - decreased facial sensation
    - droopy eyelid and/or
    - abnormal eye movement
37
Q

What are the causes of CN VI (abducens) palsy?

A
  • INCREASED INTRACRANIAL PRESSURE
  • stroke
  • trauma
  • viral illness
  • brain tumour
  • inflammation
  • infection
  • diabetes
38
Q

Treatment of strabismus?

A
  1. resolution w/ time – usually 6 months
  2. treatment
    - patching
    - prism spectacles
    - surgery
39
Q

What is the treatment of congenital strabismus?

A
  • none
40
Q

Does an acquired CN palsy resolve? If so, how?

A

Yes they can resolve, depending on cause

  1. Viral illness - generally resolves completely
  2. Trauma - incomplete resolution
  3. Tumor or aneurysm - relief of pressure on n from tumour or bld vessel w surgery may improve
41
Q

How long does the ophthalmologist wait for potential spontaneous improvement/resolution?

A

at least 12 months/ 1 yr

42
Q

What are the 2 results of squint treatments?

A
  1. improve appearance of eyes &/or

2. help diplopia or eyestrain

43
Q

What are the 3 treatment options for squints? Briefly explain each.

A
  1. Patching
    - patching 1 eye eliminates diplopia –> but req careful monitoring to avoid dev of amblyopia in kids
  2. Prism spectacles
    - can realign images & allow single binocular vision
    - does not eliminate diplopia in every gaze position (bc degree of misalignment varies in diff gaze pos)
    - power of prism reduced as palsy improves
  3. Surgery
    - after observation period for improvement (12months)
    - needed in most cases, not mandatory
    - must be dine after correction of refractive defect & in kids, the treatment of amblyopia
    - surgery changes the position of muscles that move the eyes
44
Q

What are the basic principles of squint surgery?

A
  1. to weaken the strong muscle by recession
  2. to strengthen the weak muscle by resection (shortening the muscle)

often 2 muscles need to be operated on & may do surgery on 1 or both eyes
done under general anaesthetic

Ophthalmology (12 decks)

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