control of eye movements

Question 1

types of eye movements

Answer 1

conjugate- two eyes move same amount in same direction (fast and slow movements)

vergence- two eyes move in opposite directions (convergence and divergence)

Question 2

saccades

Answer 2

horizontal or vertical conjugate eye movements that rapidly shift gaze to a new visual target

uses- scanning the environment, reading

Characteristics: fast, can be voluntary, reflexive (auditory or visual or tactile

Question 3

horizontal saccades

Answer 3

paramedian pontine reticular formation (PPRF) is a horizontal gaze center

project to the abducens and controls the lateral rectus muscle

controlled by the left frontal eye field which project to the iipsilateral superior colliculus and the contralteral PPRF

Question 4

vertical saccades

Answer 4

rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF)

verticle gaze center

and interstitial nucleus of cajal

stimulate the oculomotor and trochlear nucleus ipsilateral and contralateral

goes through the posterior commissure

Question 5

parinauds syndrome

Answer 5

impaired vertical gaze
large irregular pupils (EW nucleus)
eyelid abnormalities (retraction or ptosis)
impaired convergence

Question 6

vestibular ocular reflex

Answer 6

neuron 1: sensory neurons with cell bodies in vestibular ganglion detect head movement and send signal to vestibular nuclei

neuron 2: neurons in vestibular nuclei project to brainstem nuclei that control extraocular muscles

neuron 3: neurons whose cell bodies are in extraocular muscle nuclei project to extraocular muscles to cause contraction, moving the eyes to the correct side to maintain foveation

Question 7

smooth pursuit

Answer 7

conjugate eye movements that keep the image of a moving target stabilized in the fovea

characteristics: slow, initiated by Parito-occipito temporal cortex

stimulate ipsilateral PPRF

Flocculonodular lobe must suppress the VOR for smoth pursuit

Question 8

optokinetic nystagmus

Answer 8

parieto-occipito temporal cortex–> smooth pursuit phase (ipsilateral)

FEF–> saccadic phase (contralateral)

Question 9

vergence

Answer 9

reflexive movements of the eyes on opposite directions to stabilize an image on the fovea of BOTH eyes

convergence or divergence

Question 10

cortical centers for eye movements

Answer 10

Frontal eye fields (FEF):
Normal–> contralateral conjugate eye deviation (voluntary saccades)
irritative lesion (overstimulation)–> contralateral conjugate eye deviation
destructive lesion–> ipsilateral conjugate eye deviation

Parietal eye fields:
Normal–> visual attention (involuntary saccades)
Destructuve lesion–> attentional deficit

Parieto-occipito-temporal eye fields:
Normal–> smooth pursuit
Destructive lesion–> difficulty tracking a slow moving object

Question 11

brainstem centers for eye movements

Answer 11

abducens nucleus/ PPRF: horizontal gaze center

rostral interstitial nucleus of the MLF and interstitial nucleus of Cajal: vertical Gaze center