1b Visual System Defects Flashcards

1
Q

What is seen in a patient with 3rd cranial nerve palsy?

A

Down and out eye deviation
Ptosis
Dilated Pupil

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2
Q

Explain why cranial nerve palsy (CNIII) results in the symptoms seen?

A

Down and Out Eye: Unopposed actions of the Lateral Rectus and Superior Oblique muscles which are innervated by cranial nerves 6 and 4

Complete ptosis - due to failure of the levator palepbral superioris, when stimulated = lifting of the eyelid, and since it is innervated by CNIII it is now non functioning

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3
Q

What causes dilation of the pupil?

A

Either overactivation of sympathetic
Underactivation of parasympathetic

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4
Q

What innervation does the oculomotor nerve carrt?

A

Parasympathetic to the eye

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5
Q

What are the two categories of lesions to the oculomotor nerve?

A

Medical
Surgical

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6
Q

What are medical lesions?

A

Typically affect the vasculature of the nerve and not pupil - pupil sparing as the parasympathetic fibres run to the outer portion of the eye

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7
Q

What are some causes of medical lesions?

A

Hypertension
Microvascular effects of diabetes

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8
Q

What usually causes surgical lesions?

A

Posterior communicating artery aneurysm - compresses the outer portion of the nerve fibres = where the parasympathetic fibres run

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9
Q

Where does the CNIII run in relation to the circle of willis?

A

Between the posterior cerebral and superior cerebellar artery

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10
Q

What is Pilocarpine and how does it work?

A

Muscarinic receptor agonist which acts on the M3 receptors in the iris sphincter muscle = results in contraction of the ciliary muscles and therefore leads to constriction of the pupil = independant from the parasympathetic response

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11
Q

What is Adie’s pupil?

A

Light-near dissociation

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12
Q

What causes Adie’s Pupil?

A

The re-innervation which occurs due to the damage to the ciliary ganglion - fibres directed to the ciliary ganglion end up targeting the iris instead

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