1b Visual System Defects Flashcards
What is seen in a patient with 3rd cranial nerve palsy?
Down and out eye deviation
Ptosis
Dilated Pupil
Explain why cranial nerve palsy (CNIII) results in the symptoms seen?
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
What causes dilation of the pupil?
Either overactivation of sympathetic
Underactivation of parasympathetic
What innervation does the oculomotor nerve carrt?
Parasympathetic to the eye
What are the two categories of lesions to the oculomotor nerve?
Medical
Surgical
What are medical lesions?
Typically affect the vasculature of the nerve and not pupil - pupil sparing as the parasympathetic fibres run to the outer portion of the eye
What are some causes of medical lesions?
Hypertension
Microvascular effects of diabetes
What usually causes surgical lesions?
Posterior communicating artery aneurysm - compresses the outer portion of the nerve fibres = where the parasympathetic fibres run
Where does the CNIII run in relation to the circle of willis?
Between the posterior cerebral and superior cerebellar artery
What is Pilocarpine and how does it work?
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
What is Adie’s pupil?
Light-near dissociation
What causes Adie’s Pupil?
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
