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Ophthalmology > Pupillary reflexes | > Flashcards

Pupillary reflexes | Flashcards

1
Q

What is the effect of the sympathetic response on the pupils?

A

Mydriasis - pupil dilation

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2
Q

What is the effect of the parasympathetic response on the pupils?

A

Miosis - pupil constriction

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3
Q

What are the 3 pupillary pathways?

A
  1. Light reflex pathway - mediated by afferent arm (1st and 2nd order) and efferent arm (parasympathetic pathway)
  2. Sympathetic pupillary pathway (fight or flight response)
  3. Near reflex (mediated by parasympathetic pathway)
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4
Q

What is the sensory component of the pupillary response mediated by?

A

Optic nerve (II)

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5
Q 
What is the sequence of the light reflex pathway?
1st order
2nd order
3rd order
4th order
A

1st order (sensory)

  • retinal fibres in the eye detect light
  • nasal retinal fibres cross at the optic chiasm and pass up contralateral optic tract to contralateral pretectal nucleus
  • temporal retinal fibres do not cross and pass up the ipsilateral optic tract to ipsilateral pretectal nucleus
2nd order (internuncial)
-connects each pretectal nucleus to both Edinger-Westphal nuclei (resulting in consensual pupillary reflex)
3rd order (pre-ganglionic)
-parasympathetic fibres pass from EWN through the  oculomotor nerve, enters the inferior division and reach ciliary ganglion
4th order (post-ganglionic)
-Leaves ciliary ganglion and passes in short ciliary nerves to innervate sphincter pupillae to bring about pupil constriction
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6
Q

In the light pathway reflex, is the autonomic part sympathetic or parasympathetic?

A

Parasympathetic

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7
Q

Where does the parasympathetic part of the light reflex pathway begin?

A

From the EWS of oculomotor (III) nerve

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8
Q

Where do the parasympathetic fibres run in relation to the oculomotor (III) nerve?

A

On the outside

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9
Q

What is the sequence of the sympathetic pupillary pathway?
1st order
2nd order
3rd order

A

1st order

  • originates in the hypothalamus
  • passes down the brainstem and cervical spinal cord to synapse at T1 (2nd order)

2nd order
-U turns back up to synapse at superior cervical ganglion (3rd order)

3rd order
-runs along the ICA, hitchhikes on the CN V1, branches into long ciliary nerves to supply the dilator pupillae of the iris

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10
Q

Where does the sympathetic pupillary pathway originate from?

A

Hypothalamus

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11
Q

When is a near reflex activated?

A

When gaze changed from distance to a near target

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12
Q

What are the 3 things that occur with a near reflex?

A
  1. Pupils converge
  2. Pupils constrict
  3. Accomodation
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13
Q

What is the afferent pathway for vision?

A

Optic nerve -> chiasm -> tract -> lateral geniculate body -> optic radiation -> visual cortex

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14
Q

What is the efferent pathway for:

a) pupillary reflexes
b) adduction of eye

A

Visual cortex -> internal capsule -> oculomotor nuclei (EWN) -> Oculomotor nerve

a) ciliary ganglion -> short ciliary nerves -> sphincter pupillae and ciliary muscle
b) medial rectus

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15
Q

What is the aim of the pupil examination?

A

We are trying to establish if the defect is:

Afferent or Efferent

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16
Q

What are the components of the pupil examination (3)?

A
  1. Inspection
    - pupils, its reaction and size (light and dark)
    - eyelid
    - eye position
  2. Pupil responses (in dark)
    - direct
    - consensual
    - swinging light test
  3. Near reflex (triad)
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17
Q

What would you look for in a pupil inspection (3)?

A
  1. Pupil sizes
  2. symmetry
  3. colour

-in light and dark

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18
Q

What is anisocoria?

A

Different sized pupils

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19
Q

What defect is the pathway usually in with anisocoria?

A

Usually efferent

May be severe afferent problem

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20
Q

What would you look for in inspection of the eyelids?

A

Droopy eyelids

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21
Q

What would you look for in inspection of the eye position?

A

Eyes pointing down and out

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22
Q

If anisocoria is present, what would you do next?

A

See if it is =< 1mm

  • if yes it can be physiological
  • if no, determine which pupil is abnormal
23
Q

What are the 3 afferent problems?

A
  1. Afferent pupillary defect (complete)
  2. Relative afferent pupillary defect (anything less than complete)
  3. Light - near dissociation
24
Q

What are the 3 clinical features of an afferent pupillary defect (APD)?

A
  1. Both pupils equal in size
  2. On direct, a light is shone on the affected eye and it doesn’t constrict, sometimes it even dilates
  3. When the light shines in unaffected eye, both pupils react
25
Q

What is the cause of an APD?

A

Optic nerve lesion

26
Q

What is the visual acuity in an eye with APD?

A

Zero

27
Q

What test is used to demonstrate RAPD?

A

Swinging light test

28
Q

How is a swinging light test performed?

A

Light source swung from one eye to the other and back stimulating each eye in rapid succession

29
Q

What does an eye with RAPD show with the swinging light test (4)?

A
  1. Both pupils are equal in size
  2. When normal eye is stimulated, both pupils constrict
  3. Light swung to diseased eye, both pupils dilate instead of constricting
  4. When normal eye stimulated again, both pupils constrict once more
30
Q

Why does an eye with RAPD dilate with light?

A

When normal eye is stimulated, both pupils constrict. Then when the diseased eye is stimulated, the constriction produced is less that the one produced by stimulating the normal eye. Therefore, there is a paradoxical dilation of the pupils.

31
Q

What is the pathophysiology behind RAPD?

A

There is reduced stimulation of the visual pathway by the pupil on the affected eye thereby not being able to relay the intensity of the light as accurately as the
healthy pupil and visual pathway.
The affected side causes the visual pathway to mistakenly respond to the decrease in stimulation as if the flashlight itself were less luminous.

32
Q

What are some causes of RAPD (6)?

A
  1. Optic neuritis
  2. Ischaemic optic disease or retinal disease
  3. Severe glaucoma causing trauma to optic nerve
  4. Direct optic nerve damage (trauma, radiation, tumour)
  5. Large retinal detachment
  6. Very severe macular degeneration
33
Q

What is light near dissociation?

A

Failure to constrict to light with a retention of the response to near vision

34
Q

What structures does light near dissociation involve?

A

Pretectal interneurones to EWN involved (dorsal midbrain)

centrally located accommodative reflex neurones are spared

35
Q

What are the 5 causes of light near dissociation?

A
  1. Bilateral APD
  2. Alcoholism
  3. Diabetes
  4. MS
  5. Neurosyphilis
36
Q

How do you know which pupil is abnormal in anisocoria?

A

Inspect pupils in light and dark

-Big pupil in bright light is bad (my rule of Bs)

37
Q

What are the 2 efferent problems that can occur?

A
  1. The dilated pupil - problem with the parasympathetic

2. The constricted pupil - problem with the sympathetic

38
Q

When there is a problem with the parasympathetic pupillary pathway, what are the possible points that it can go wrong (5)?

A
  1. EWN
  2. CN III
  3. Ciliary ganglion
  4. Cilary nerves
  5. Pupil
39
Q

What are the signs and symptoms of 3rd nerve palsy (3)?

Why?

A
  1. Complete ptosis
    - III nerve supplies levator palpebrae
  2. Eye looks down and out
    - lateral rectus is supplied by VI nerve and unantagonised, so eye is pulled out, and Superior oblique is supplied by IV nerve and unantagonised so eye is pulled down
  3. +/- Dilated pupils unreactive to direct light and to accommodation
    - III nerve supplies sphincter pupillae
40
Q

What type of lesions causing 3rd nerve palsy involve the pupil?

A

Surgical lesions

-Aneurysms, trauma, and uncal herniation involve the pupil by compression

41
Q

What type of lesions causing 3rd nerve palsy spare the pupil?

A

Medical lesions

  • neural infarction of the trunk of the nerve
  • affects from inside out, sparing the superficial pupillary fibres
42
Q

What is Adie’s pupil?

A

Damage to the ciliary ganglion and ciliary nerves - loss of innervation to the sphincter pupillae (3% fibres) and the ciliary muscle (>90%)

43
Q

What are the 2 causes of Adie’s pupil?

A
  1. Post viral

2. DM

44
Q

What 2 groups of people does Adie’s pupil usually affect?

A
  1. Young adults

2. Females > males

45
Q

What are the 4 clinical features of Adie’s pupil?

A
  1. Dilated pupil aka tonic pupil
  2. Vermiform movements of pupil border
  3. Poor reaction to light and near response (acute phase)
  4. Light near dissociation (late phase) due to aberrant regeneration (upregulation) of fibres to serve the near response (ciliary muscle and sphincter pupillae)
46
Q

How do you diagnose Adie’s pupil?

What is the science behind it?

A

Use of pilocarpine (5%) will constrict the Adie’s pupil

-denervated iris sphincter is hypersensitive to any parasympathomimetics

47
Q

What are 2 other causes of dilated pupil distal to the ciliary ganglion?

A
  1. Pharmacologically indiced mydriasis

2. Iris trauma

48
Q

What is Horner’s syndrome?

A

Damage to the sympathetic trunk

49
Q

What are the 3 clinical features of Horner’s syndrome?

A
  1. Miosis due to unapposed action of sphincter pupillae
  2. Mild ptosis 1-2mm as a result of weakening of Mullers muscle
  3. Reduced ipsilateral sweating but only if lesion is below the superior cervical gangion because the sudomotor fibres that supply the face run along the external carotid artery, which branches off only after the SCG (superior ciliary ganglion)
50
Q 
What are the causes of Horner's syndrome according to:
1st order (central) (3)
2nd order (preganglionic) (3)
3rd order (postganglionic) (2)
A

1st order

  1. Brainstem disease
  2. Spinal cord tumour
  3. Diabetic autonomic neuropathy

2nd order

  1. Pancoast tumour (tumour of pulmonary apex)
  2. Carotid and Aortic aneurysm and dissection
  3. Neck lesions

3rd order

  1. Internal carotid artery dissection
  2. Cavernous sinus mass
51
Q

How is Horner’s syndrome diagnosed?

A

Cocaine 4% test - Horner’s pupil will not dilate

-Cocaine blocks the reuptake of norepinephrine at the sympathetic nerve terminal in the iris dilator muscle

52
Q

How common is physiological anisocoria?

A

20% of population

53
Q

What determines if anisocoria is physiological (3)?

A
  1. <1mm
  2. Pupils of different sizes in both bright light and dim conditions
  3. Both pupils dilate and constrict by the same amount relative to each other e.g. in light and dark, the bigger eye is the same amount bigger than the other when dilated and constricted

Ophthalmology (12 decks)

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