Week 2 - H - Ophthamology 7 - CN III,IV,VI palsies, INO &visual field defects

Question 1

What muscles of the eye are supplied by the oculomotor nerve? (try name 7)

Answer 1

Superior rectus Inferior rectus Medial rectus Inferior oblique Levator palpebrae superioris

Question 2

What are the features of an oculomotor nerve palsy?

Answer 2

The eye points down and out There is a ptosis (due to the LPS not being supplied - drooping eyelid) There is also a dilated pupil

Question 3

What are the causes of oculomotor nerve palsy?

Answer 3

Microvascular eg diabetes Tumour If painful - anuerysm

Question 4

Which muscle of the eye has the main function to abduct, depress and internally rotate the eye? What is the end eye position?

Answer 4

This is the superior oblique muscle Moves the eye down and out

Question 5

What nerve supplies the superior oblique muscle? WHat does it look like if there is a palsy of this nerve?

Answer 5

Supplied by trochlear nerve. If CN IV palsy Then head is tilted, the eye points up and in and also a vertical diplopia

Question 6

Which way does the head tilt in a fourth nerve palsy?

Answer 6

To compensate for the double-vision resulting from the weakness of the superior oblique, patients characteristically tilt their head down and to the side opposite the affected muscle ie if Right SO palsy, patients head will tilt left

Question 7

What is the most common cause of fourth nerve palsies?

Answer 7

Congenital trauma

Question 8

Blunt nerve trauma can cause a bilateral trochlear nerve palsy What happens here as presentation?

Answer 8

Will cause depressed chin

Question 9

What muscle causes abduction of the eye? What nerve supplies it? What does palsy if this nerve present like?

Answer 9

Lateral rectus supplied by the abducent nerve Palsy presents like eye is unable to look laterally and eyes will be medially deviated, horizontal diplopia

Question 10

What type of squint is the one seen in abudcent nerve palsies?

Answer 10

This would be an esotropic squint (convergent squint)

Question 11

What is the main cause of sixth nerve palsies? and therefore what is ususally also seen on fundoscopy?

Answer 11

Raised intracranial pressure Therefore may seen papilloedema on fundsocopy

Question 12

Which cranial nerve palsy is common in diabetic retinopathy - a microvascular complication of diabetes? (all three can have palsies due to it remember)

Answer 12

This would be cranial nerve VI palsy

Question 13

Why is cranial nerve VI palsy more likely to be affected by an increase intracranial pressure?

Answer 13

This is because it has to curve around the petrous part of temporal bone therefore raised ICP may cause it to push down on this

Question 14

Why are the pupils involved in oculomotor nerve palsies?

Answer 14

The parasympathetics run on the outside of the nerve and therefore if there is something pressing on the nerve it will also affect this

Question 15

Eyes need to be able to work at the same time Eg look left involves the left eye using the abducent nerve and the right eye using the oculomotor nerve The nerves are therefore connected by pathways What are these pathways known as?

Answer 15

Known as inter-nuclear pathways

Question 16

Ophthalmoplegia is paralysis of the muscles within or surrounding the eye. Where is the lesion in the eye that would cause inter-nuclear opthalmopegia?

Answer 16

The lesion lies within the medial longtiudional fasciculus - this is a heavy myelinated tract connect nerve nuclei

Question 17

What is the main cause of inter-nuclear ophthalmplegia? (in bilateral and unilateral)

Answer 17

In young patients with bilateral INO, multiple sclerosis is often the cause. In older patients with one-sided lesions a stroke is a distinct possibility.

Question 18

In internuclear opthalmoplegia, a the medial longtiduinal fasciculus connects the abducent and the oculomtor nerves Which oculomotor nerve side does the medial longitudinal fasciculus connect the abducent nerve to?

Answer 18

Connects the abuducent nerve to the contralateral oculomotor nerve

Question 19

If a patient has a right medial longitudinal fasciculus injury, how would you be able to tell this on examination? Asking the patient to look right

Answer 19

The patient would be able to abduct the ipsilateral and adduct the contralateral eye The patient would not be able to adduct the eye on the ipsalteral side and would have a horizontal diplopia Also the contralateral eye would be able to abduct but would have a nystagmus

Question 20

Describe the type of gaze seen in the internuclear ophthalmoplegia? This is the gaze palsy when the eyes are meant to move the same way

Answer 20

Would have a conjugate gaze palsy - inability to move both eyes in a single horizontal gaze motion

Question 21

Which eye in INO shows affected adduction?

Answer 21

It is the affected eye which shows affection adduction with the contralteral eye showing nystagmus on abduction

Question 22

Describe the visual field defect at each number Dont include number 2 or 7

Answer 22

1. Right monocular blindness 2. - 3. Bitemporal hemianopia 4. Left homonymous hemianopia 5. Left homonymous superior quadrantanopia 6. Left homonymous inferior quadrantanopia 7. - 8. Left homonymous hemianopia with central (macular) sparing

Question 23

* 1. Left monocular blindness * 2. Bitemporal hemianopia * 3. Right homonymous hemianopia * 4. Right homonymous superior quadrantanopia * 5. Right homonymous inferior quadrantanopia * 6. Right homonymous hemianopia with central (macular) sparing Where are the lesions?

Answer 23

1. Right optic nerve
2. Optic chiasm
3. Left optic tract
4. Left temporal lower optic radiation
5. Left parietal upper optic radiation
6. Left occipital cortex

Question 24

What are some causes of optic nerve pathology causing a visual field defect?

Answer 24

Optic neuritis - due to MS usually Ischaemic optic neuropathy (occluded posterior ciliary arteries supply the optic nerve head)

Question 25

What are some optic chiasm causing pathologies?

Answer 25

Pituitary adenoma - most commonly is a prolactinoma so will have the associated effect, can also be a growth hormone adenoma Craniopharyngioma - usually in patients under 20 and can press on pituitary gland also

Question 26

What type of tissue are craniopharnygiomas derived from?

Answer 26

Dervied from the pituitary gland embryonic tissue known as rathke’s pouch

Question 27

Both craniopharyngiomas and pituitary adenomas can cause bitemporal hemianopias however tend to infect the visual fields differently at the start How is this?

Answer 27

Craniopharyngiomas, which tend to be suprasellar - the visual field defect will first appear as bitemporal inferior quadrantanopia if originating inferior to the optic chiasm, the visual field defect will first appear as bitemporal superior quadrantanopia. like in pituitary adenomas

Question 28

• Optic Tracts & Optic Radiations – Tumours (primary or secondary, Demyelination, Vascular anomalies) What is the loop which the temporal lobe optic radiation goes around the lateral ventricle known as?

Answer 28

Known as Meyer’s loop

Question 29

What is the most common cerbrovascular incident causing the occipital cortex disruption?

Answer 29

Stroke