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Block 3 > The Eyes > Flashcards

The Eyes Flashcards

1
Q

What is accommodation?

A

Eye convergence and pupillary constriction that enables us to look at and focus upon objects close to the eye (requires midbrain to be functional)

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2
Q

Describe the accommodation response.

A
  1. Light hits retina and info goes to the 1o visual cortex and then to the frontal eye field
  2. From CNIII n. CNIII goes to medial rectus causing vergence
  3. From EWN (PS), CNIII goes into ciliary ganglion where sphincter pupillae causes pupil constriction whilst ciliary body causes lens fattening
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3
Q

How and why does the ciliary body cause lens fattening?

A

Contraction of the ciliary body relaxes the suspensory ligaments enabling the lens to recoil thus making it fatter so the lens can better bend and refract light allowing you to focus on items close to face (elasticity of lens decreases with age decreasing this - why older people need reading glasses)

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4
Q

What is Argyll-Robertson pupil?

A

No pupillary light reflex BUT accommodation response is functioning as the PTN is knocked out bilaterally - commonly seen in tertiary neurological syphilis (hence the name ‘Prostitutes pupil’) and diabetic neuropathy

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5
Q

How could the Edinger-Westphal nucleus (EWN) become damaged? What symptoms would you see?

A

Vascular issues, tumours or brainstem problems could damage the EWN so there would be no direct or consensual reflex on damaged side and a dilated/unreactive pupil as there is no ciliary ganglion output

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6
Q

What symptoms would occur if there was a problem with CNIII?

A

No direct or consensual reflex on damaged side and pupil would be dilated/unreactive

Compression = loss of all CNIII functions causing full ptosis
Vascular lesion = sparing of pupillary functions with partial ptosis (vascular lesions affect motor fibres but not PS fibres)

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7
Q

What is a Marcus-Gunn pupil? How is it tested?

A

Medical sign observed during the swinging flashlight test where the patients pupils constrict less (so appear to dilate) when a bright light is swung from the unaffected to affected eye where affected eye senses light and produces pupillary sphincter constriction but to a lesser degree

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8
Q

What does Marcus-Gunn pupil indicate?

A

Optic nerve (CNII) lesion between retina and optic chiasm

Severe retinal disease

Contralateral optic tract (due to the different contributions of the intact nasal and temporal hemifields)

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9
Q

What are the 3 different muscles acting on the eyelid? What do they do and what is there innervation?

A
  1. Levator palpebrae superiosis (CNIII) - opens eye
  2. Orbicularis oculi (CNVII) - closes eye
  3. Superior tarsal (sympathetic) - opens eye
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10
Q

What would be the difference in symptoms if you lost the levator palpebrae superioris or the superior tarsal muscle?

A

CNIII lesion causing loss of levator palpebrae superioris = full ptosis

Loss of superior tarsal sympathetic supply = partial ptosis

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11
Q

How does the orbicularis oculi contribute to keeping the eye free of matter?

A

Forms a sphincter around the eye closing eyelids laterally to medially pushing tear fluid across the eye so grit and dust end up in the inner corners and can be wiped out

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12
Q

What is the golden rule regarding extraocular muscles?

A

ALL are innervated by CNIII (inc. sphincter pupillae, cillary body + levator palpebrae superioris) EXCEPT superior oblique (CNIV) and lateral rectus (CNVI) - their positions tell you what they do to the eye (think about what contraction/shortening would cause the muscle to do)

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13
Q

What are the extraocular muscles?

A 
Superior rectus (SR)
Inferior rectus (IR)
Medial rectus (MR)
Lateral rectus (LR) 
Superior oblique (SO)
Inferior oblique (IO)
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14
Q

Where does the rectus muscles originate from?

A

Common tendinous ring at posterior of orbit

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15
Q

Where does the inferior oblique arise from?

A

Antero-medial floor of orbit (like a hammock sitting under the eye and cupping it)

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16
Q

If the eye muscles were to act on their own, what movements would they cause?

A 
LR = abduction (lateral)
MR = adduction (medial)
SR = superior (elevation) + lateral
IR = inferior (depression) + lateral
IO = superior (elevation) + medial
SO = inferior (depression) + medial
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17
Q

What are the 3 axis the eyes can move around?

A
  1. Transverse: L/R
  2. Sagittal: up/down
  3. Coronal: torsion i.e. twisting in and out
18
Q

What type of diplopia occurs if the corrective torsional eye movements are affected? What will this cause?

A

If CNIV is lesioned images feel like they are rotating/tilting off of each other (torsional) rather than to the side (horizontal) or above/below (vertical) each other so patient may tilt head to compensate complaining of neck pain

19
Q

How can eye movements be tested using the H test?

A

Testing pattern that isolates the actions of specific muscles that involves moving the eye into a new starting position (different to neutral anatomical position) and then performing a specific movement

20
Q

What eye movement test do most clinicians use?

A

Cardinal positions of gaze: diagonal pattern of testing comparing cardinal movements of the L and R eye in 6 directions (2 x diagonal + 2 x horizontal) allowing comparison of conjugate movements in L and R eye at same time -used more as it can bring to light even subtle lesions unlike the H test

21
Q

In terms of the eyes, what do we mean by a medial or lateral direction?

A 
Medial = towards nose
Lateral = above from nose towards ears
22
Q

What is Hering’s law?

A

Extraocular muscles normally have equal and simultaneous innervation

23
Q

If a certain muscle of the eye is not working, what is the general principle for its resting position?

A

It will be in the opposite direction to which the affected muscle should be pulling the eye e.g. if lateral rectus is damaged, the eyes resting position will be medial as action of these muscles is unopposed (the eye needs all muscles to keep eyes in the middle at rest normally)

24
Q

Whats the difference between a convergent and divergent squint?

A

Convergent: medial
Divergent: lateral

25
Q

What are the different ways in which the eyes can move?

A
  1. Track target: smooth pursuit when target is moving
  2. Stabilise target: you are moving but target is not
  3. Scan target-target: saccade (fast movement)
26
Q

What control centres control eye movement?

A
  1. Vestibular nuclei + PPRF
  2. Frontal eye field (frontal cortex)
  3. Saccade centres (several locations)
  4. Visual association areas
27
Q

What is the medial longitudinal fasciculus (MLF)?

A

Neuronal tract controlled by multiple pathways/control centres (voluntary/autonomic)that enables lateral/conjugate gaze and tracking neck movement along with other things making you look L or R as it connects CNIII, IV and VI (APs travel from CNVI to CNIII) with vestibular nuclei, cerebellum and neck muscle LMNs

28
Q

What is internuclear opthalmoplegia?

A

MLF lesion (NOT same as CN lesion) cutting the interneuron connections between CNVI and CNIII where 1 eye (unilateral) or both (bilateral) cannot look to one side (lateral gaze) but able to converge during accommodation as this pathway does not involve the MLF its direct to oculomotor (CNIII) nuclei from cortex (does not have to go through MLF pathway) but involves the frontal eye field (FEF) part of brain

29
Q

How are voluntary saccades brought about?

A

By control centres in cerebral cortex and elsewhere - info synapses on PPRF and then goes down the MLF pathway involving CNVI then CNIII (also directly due to direct connection to higher centres for accommodation)

30
Q

What is the vestibulo-ocular reflex?

A

When head is rotating axially in a given direction, the lateral semi-circular canals (LSCCs) of the vestibular system make both eyes look to the opposite side in a corrective manner so eyes remain fixed on object/area e.g. R lateral semicircular canals activated by R head movement (signals decrease if head moved away from it) so eyes move to L

31
Q

What system is responsible for corrective head movements so vision does not bounce around with movement?

A

Vestibular system

32
Q

What is Doll’s eye sign?

A

In comatose patients the vestibulo-ocular reflex can be tested to determine if brainstem is functioning:

  • Dolls sign +ve = eyes stayed fixed on you as head is moved axially - good thing as brainstem is functioning
  • Dolls sign -ve = eyes move with head movement - bad thing as indicates brainstem death
33
Q

How do eyes stay still when the head is in a resting position?

A

Signal from both semi-circular canals (L and R) is equal so eyes stayed centred

34
Q

If a patient’s lateral semi-circular canals stop working or a brainstem infarction prevents vestibular nuclei feeding information to CNVI and CNIII (MLF pathway)?

A

Eyes will drift towards the damaged eyes but then the cortex will realise and quickly put them back to centred position = horizontal jerk nystagmus

35
Q

What direction do vestibular nucleus (VN), lateral semi-circular canals (LSCC) or frontal eye fields (FEF) generally make eyes move?

A

R VN, LSCC or FEF = L - damage causes eye to drift/look R

L VN, LSCC or FEF = R - damage causes eyes to drift/look L

36
Q

What is jerk nystagmus?

A

Repetitive eye movement with a fast and slow phase but described according to fast phase:

  • Slow = eyes slowly drift to damaged side
  • Fast = eyes move quickly back to midline via action of saccade centres in brainstem + cortex
37
Q

What does putting cool/cold water into the external auditory meatus (EAM) of an ear mimic?

A

Vestibular system/nucleus lesion on that side cooling the LSCC fluid causing it to move

38
Q

What is the cold caloric test?

A

Putting cool/cold water into the EAM of ear will mimic a vestibular system/nucleus lesion on that side by cooling the LSCC fluid inducing movement so it can be used to test brainstem function by inducing nystagmus:

  • Normal = horizontal jerk nystagmus to cold water side with fast flick back to midline
  • Depressed CNS = horizontal jerk nystagmus to cold water side with slowed flick back to midline
  • Cortical damage/no communication with brainstem = horizontal jerk nystagmus toward cold water side and no flick back to midline
  • Coma (CNS/brainstem depressed) = nothing
39
Q

In what conditions should you test nystagmus?

A

Dimmed lights as light shining in the eye will mask a patients nystagmus

40
Q

What is difference about the system involvements in the accommodation, voluntary and automatic (vestibulo-ocular reflex) eye movements?

A
  1. Accommodation: FEF allows you to fix gaze on an object
  2. Voluntary looking L + R: CNVI -> MF -> CNIII between 2 nuclei in pons
  3. Automatic: vestibular system/LSCC feeds into CNVI -> MF -> CNIII

Block 3 (40 decks)

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