Visual System tutorial

Question 1

What could complete ptosis be due to?

Answer 1

The complete ptosis is due to failure of Levator Palpebrae Superioris

Question 2

What happens when the Levator Palpebrae Superioris is innervated?

Answer 2

• elevation of the lid

- innervated by the oculomotor nerve

Question 3

Why is there a dilated pupil?

Answer 3

• due to either overaction of the sympathetic nervous system (causes mydriasis via dilator pupillae)
• or underaction of parasympathetic nervous system (causes miosis via sphincter pupillae
• In this case the oculomotor nerve, which carries parasympathetic innervation to the eye, is the most likely explanation given the other clinical findings

Question 4

Why is the lesion for this right eye?

Answer 4

Right Oculomotor Nerve (cranial nerve III)

Question 5

What are medical lesions affecting the oculomotor nerve?

Answer 5

1. typically affecting the vasculature to the nerve (and hence the central portion of the nerve)
2. tend to not affect the pupil (‘pupil sparing’) as the parasympathetic fibres running to the eye are in the outer portion of the nerve
3. Microvascular disease due to hypertension, diabetes mellitus

Question 6

What are surgical lesions affecting the oculomotor nerve?

Answer 6

1. usually in the form of a posterior communicating artery aneurysm, tend to affect the nerve
2. aneurysm typically compresses the outer portion of the nerve fibres, which is where the parasympathetic nerves run

Question 7

Where does CN III run in relation to Circle of Willis?

Answer 7

runs in between the posterior cerebral and the superior cerebellar artery

Question 8

What treatments are offered for this cranial nerve palsy?

Answer 8

-Treatment will depend on the cause of the cranial nerve palsy
-cause is likely to be a posterior communicating artery aneurysm
-Hence a neurosurgical opinion is advised, and assessment of the aneurysm is needed (this may involve clipping)
-For patients with microvascular disease, they will need better metabolic control of their condition.

Question 9

Presents, tonically dilated pupil in the right eye. Upon shining light into the right eye, the pupil is slow to react compared to the left. The left eye reacts when light is shone into the right eye.
Addition of pilocarpine drops, however, causes rapid constriction of the right pupil. On further examination, she has an absent knee-jerk reflex and impaired sweating.

Answer 9

• Damage to parasympathetic ciliary ganglion which is involved in the pupillary-light reflex
• Parasympathetic fibres travel with CNIII (oculomotor) to synapse at the ciliary ganglion before innervating the iris and ciliary body

Question 10

What is the site of damage causing the absent reflex and impaired sweating?

Answer 10

Dorsal root ganglia of the spinal cord

Question 11

How does pilocarpine work?

Answer 11

1. Pilocarpine is a muscarinic receptor agonist that acts on M3 receptors in the iris sphincter muscle
2. This results in contraction of the muscle (miosis) and constriction of the pupil
3. These are independent of the parasympathetic tract, hence the response

Question 12

What is Adie’s pupil?

Answer 12

light-near dissociation

Question 13

What is Aidie’s pupil due to?

Answer 13

• reinnervation that takes place as a result of damage to the ciliary ganglion
• this process involves up regulation of postsynaptic receptors but the reinnervation is aberrant, causing fibres directed for the ciliary body to end up targeting the iris
• As a result, the patient develops more meiosis with near accommodation than they do to light

Question 14

Why is there a response after pilocarpin drops?

Answer 14

1. Loss of parasympathetic supply so when put in pilocarpin which is a muscuronic agonist get rapid response for pupil because denervation hypersensitivity so more rapid constriction of pupil
2. Knee jerk reflex relevance in Holmesany syndrome which is association of this pupil with knee reflex