Anatomy of eye movements

Question 1

What muscles control torsion when eye is abducted?

Answer 1

Obliques

Question 2

What muscles control torsion when eye is adducted?

Answer 2

Rectus

Question 3

Third nerve palsy resting gaze

Answer 3

Down (IV) and out (VI), with ptosis and nonreactive to light.

Question 4

What can cause III nerve palsy

Answer 4

PCOM aneurysm, uncal herniation

Question 5

Right trochlear nucleus innervates?

Answer 5

Left superior oblique.

Question 6

IVth nerve palsy

Answer 6

Eye is up and in.

Question 7

Abducens nerve palsy

Answer 7

One eye can’t look laterally, one eye deviated inwards

Question 8

Draw the pathway of lateral gaze and conjugate gaze in the other eye.

Answer 8

PPRF tells ipsilateral abducens nucleus to fire, abducens nucleus tells ipsilateral VI nerve to fire, and sends a projection via the CONTRALATERAL MLF to contralateral III nucleus, which tells contralateral eye to look medially.

Question 9

Lesions of abducens nerve

Answer 9

CN VI palsy, no abduction of ipsilateral eye

Question 10

Lesion of abducens nucleus or PPRF

Answer 10

Neither eye can look to affected side because abducens nucleus knocked out, so ipsilateral eye cannot abduct, and contralateral eye cannot adduct.

Question 11

Lesion of MLF

Answer 11

Ipsilateral eye cannot adduct, but contralateral eye can abduct.

Question 12

INO

Answer 12

One eye cannot adduct, but the other can abduct. This is an MLF lesion.

Question 13

Parts of brain that initiate eye movements

Answer 13

Frontal and parietal cortical eye fields, send projections to subcortical regions (SC, pretectum, reticular formation).

Question 14

Saccades and pathway for horizontal and vertical

Answer 14

Fast conjugate eye movements. Cortical eye fields, superior colliculus, PPRF and riMLF (rostral interstitial nucleus of MLF in midbrain, vertical).

PPRF projects to ipsilateral 6 nuc

riMLF projects to ipsilateral 3 to control up down movements.

Question 15

Smooth pursuit

Answer 15

Dependent on a cortico-ponto-cerebellar network.

Question 16

Nystagmus

Answer 16

Named for fast phase (under midbrain control). There’s also a smooth pursuit phase (under pontine/cerebellar control).

Question 17

Vestibular Ocular Reflex, pathway of turning head to right

Answer 17

Mediated by a 3 neuron arc. Activates right horizontal canal and inhibits left horizontal canal, causes conjugate gaze to left. Activated vestibular nerve fibers project to medial vestibular nucleus. MVN excites contralateral 6 nuclei, which projects to ipsilateral rectus muscle and to contralateral medial rectus via MLF. Simultaneously, MVN inhibits ipsilateral abducens. This relaxes ipsilateral lateral rectus and relaxes the contralateral medial rectus.

Question 18

Caloric testing

Answer 18

Cold = opposite, warm = same.

So, cold in right ear = nystagmus fast phase to the left because the body thinks the head is turning to the left.

Hot in right ear = nystagmus to the right because body thinks head is turning to the right, so it sends eyes left, eyes will try to correct by turning right quickly.

Question 19

Fast phase commanded by?

Answer 19

Cortex

Question 20

Slow phase commanded by

Answer 20

Gaze centers.

Question 21

Vergence eye movements

Answer 21

Complicated, but disconjugated.

Vergence
accomodation
miosis.

Question 22

One and a half syndrome

Answer 22

Neither eye can look right (abducens nucleus lesion), right eye cant adduct either (lesion in MLF).