Cranial nerves/neuro-ophtho

Question 1

Which is the only nerve that exits dorsally from the brainstem?

Answer 1

CN 4

Question 2

Describe pathway of CN 4

Answer 2

CN 4 deccusates just before exiting dorsally at level of midbrain. It then curves around the cerebral peduncle and passes btwn the posterior cerebral and superior cerebellar arteries. It goes on to innervate superior oblique muscle

Question 3

CN3 palsy can be caused by aneurysms in what locations? (4)

Answer 3

most commonly PCOMM, but also basilar tip, PCA, and SCA

Question 4

What is INO?

Answer 4

impaired adduction of the affected side and nystagmus of the abducting contralateral eye (the normal side). Lesion at the ipsilateral MLF

Question 5

Describe the pathway mediating horizontal eye movement?

Answer 5

PPRF receives contralateral cortical input –> PPRF activates ipsilateral abducens nerve nucleus –> ipsilateral lateral rectus muscle. Abducens nerve also crosses midline via MLF and activates the contralateral medial rectus subnucleus –> activates contralateral medial rectus muscles

Question 6

What is WEBINO (wall-eyed bilateral INO)?

Answer 6

bilateral INO due to bilateral MLF lesions will cause exotropia of both eyes

Question 7

What is one and a half syndrome?

Answer 7

A lesion to both the ipsilateral abducens nucleus or PPRF and ipsilateral MLF results in loss of all horizontal eye movements on that side, and abduction of the contralateral eye is the only lateral eye movement retained. Typically associated with abduction nystagmus.

Question 8

Which CN is most likely affected by increased ICP and why?

Answer 8

CN 6 because it is long and prone to a stretching injury, especially as it passes over the petrous ridge.

Question 9

In a patient with Adie’s pupil (idiopathic tonic pupil), where is the lesion? What is the attributable etiology?

Answer 9

postganglionic parasympathetic pathway to either the ciliary ganglion or the short ciliary nerves; viral etiology although evidence is lacking

Question 10

What is the acute presentation of Adie’s pupil?

Answer 10

Acutely, there is unilateral mydriasis and the pupil does not constrict to light or accommodation because the iris sphincter and ciliary muscle are paralyzed

Question 11

What’s a test you can do to diagnose Adie’s pupil?

Answer 11

Within a few days to weeks, denervation supersensitivity develops so that low-concentration pilocarpine 0.125% will cause the tonic pupil to constrict. The normal pupil is unaffected by such a low concentration.

Question 12

What are chronic features of Adie’s pupil?

Answer 12

slow sustained constriction to accommodation and slow redilation after near constriction occur, and the baseline pupil decreases slightly in size (in ambient lighting). Accommodation reflex does improve, although it often remains slower (tonic). This is termed “light near dissociation”.

Question 13

What is Holme’s Adie syndrome?

Answer 13

When Adie’s tonic pupil is associated with absent DTRs.

Question 14

What is AION? How does it present?

Answer 14

Anterior Ischemic Optic Neuropathy. It is caused by ischemia of the optic nerve head. It presents with acute unilateral painless vision loss.

Question 15

What is the common optic nerve disorder over 50 years old?

Answer 15

AION. Especially in patients with cardiovascular/cerebrovascular risk factors.

Question 16

What does the fundoscopic exam of AION look like?

Answer 16

1: optic disc edema 2. hyperemia with splinter hemorrhages 3. crowded and cupless disc

Question 17

What is PION and how does it appear different on fundoscopy from AION?

Answer 17

Posterior Ischemic Optic Neuropathy; affects retrobulbar optic nerve rather than optic head as seen in AION. Unlike AION there is no optic disc edema

Question 18

The upper and lower banks of the calcarine cortex makes up the visual cortex. The upper and lower banks of the calcarine cortex receives input from which visual fields?

Answer 18

The upper bank of the calcarine cortex receives projections representing the inferior visual field. The lower bank of the calcarine cortex receives information from the superior visual fields.

Question 19

How does chronic optic neuritis appear on fundoscopic exam?

Answer 19

The discs appear shrunken and pale, especially in the temporal half and this pallor extends beyond the margins of the disc

Question 20

How does chronic optic neuritis present?

Answer 20

persistent visual loss, color desaturation (especially red), and possibly persistent APD

Question 21

How does mucormycosis of the cavernous sinus present?

Answer 21

1. proptosis 2. visual blurring 3. unilateral or bilateral cavernous sinus syndrome (combination of III, IV, V1, V2, and VI cranial nerve involvement) 4. decreased visual acuity

Question 22

Answer 22

AION

Question 24

Describe visual pathways

Answer 24

Question 25

What are the functions of:

superior oblique muscle

Answer 25

depression and intorsion

Question 26

What are the functions of:

inferior oblique

Answer 26

elevation and extorsion

Question 27

What are the functions of:

superior rectus

Answer 27

elevates and intorsion

Question 28

What are the functions of:

inferior rectus?

Answer 28

depression and extorsion

Question 29

What are the functions of:

medial rectus

Answer 29

adduction

Question 30

What are the functions of:

lateral rectus?

Answer 30

abduction

Question 31

Which nerve is most likely to be affected in a patient p/w papilledema, HA, and obstrucive hydrocephalus?

a. facial nerve
b. trochelear nerve
c. abducens nerve
d. trigeminal nerve
e. oculomotor nerve

Answer 31

c. abducens nerve

prone to stretching injury especially as it passes over the petrous ridge

called the “false localizing sign” because this long cranial nerve could be affected anywhere along its path