Chapter 10

The Ocular Motor System:Gaze Disorders

optic nerve fibers

transmittingimpulses

from the rightvisual fieldstravel in left

optic tract

the visual fields areprojected onto the

retina both inverted and reversed

optic nervefiberstransmittingimpulsesfrom the leftvisual fieldstravel in rightoptic tract

the eyes must move so that the object is

focused on the visualreceptors in thebinocular zone

Types of eye movements:

1. Vergence movements eyes shift between distant and near objects

divergence vs.

convergence

(controlled by brainstem gaze centers and cortical gaze centers)

Types of eye movements:

2. Conjugate movements both eyes move in the same direction

up or downleft or right

saccadicsmooth pursuit

optokineticvestibulo-ocular

(controlled by brainstem gaze centers and cortical gaze centers)

Types of Conjugate movements:

Saccadic - voluntary rapidly moving from one target to another - reflexive nystagmus (ocular ataxia)

rhythmic oscillation of the eyeballs REM sleep

Smooth pursuit - reflex movements that keep the image of a moving target fixed on the retinae

Types of Conjugate movements:

Optokinetic - keep a visual field that is moving past the eyes fixed on the retinae as long as possible, then the eyes quickly fix on the next upcoming visual field

Vestibulo-ocular (ch. 13) - keep targets fixed on the retinae during brief movements of the head

left eye movements:

medial rectus lateral rectus

superior oblique

inferior oblique

inferior rectus

superior rectus

Brainstem gaze centers:

1. Horizontal gaze center in the paramedian pontine reticular formation (PPRF)

2. Vertical gaze center in the accessory oculomotor nuclei of the midbrain (in the periaqueductual gray matter) at the rostral end of the MLF

3. Vergence center in the rostral midbrain (near the oculomotor nuclei)

horizontalgaze center

Fig. 10-2

controlsconjugatemovementstoward theipsilateral side

rightipsilateralcontralateral

MLF

interneurons from the abducens nucleus ascend in the contralateral MLF

right

Horizontal Gaze Center

ipsilateral abducens nucleus

contralateral oculomotor nucleus

rightfrontal

loberight eye left eye

lefthorizontalgazecenter

result of a lesion of the right HGC

result of a lesion of the left MLF

*note - the affected eyewill still adduct

during convergence

right internuclear ophthalmoparesis (INO) upon attempted gaze to the left

T2-weighted axial MRI showing the responsible lesion involving the right pontine tegmentum (arrow).

location of the accessory oculomotor nuclei (vertical center) & vergence centers

In rostral midbrain:

Vertical gaze centers

neurons for upward gazeare more dorsal thanthose for downward gaze

Vergence gaze centers

control convergenceand divergence

(interconnected by the posterior commissure)

posterior commissure

midbrain gaze centers are affected by: pineal gland tumors dilation of cerebral aqueduct

Cortical gaze centers:

projects to the vertical and horizontalgaze centers and the superior colliculus

left

right

(to the contralateral side)

there is also (transient) conjugate deviation of the eyes to the side of the lesion

L Frontal eye field R Frontal eye field

L Horizontal gaze center R Horizontal gaze center

Bilateralism of cortical connections with the brainstem gaze centers:

dominant connectionnon-dominant connection

Fig. 16-6b

parietal association areas: 5, 7, 39, 40process tactile and

visual info.

area 7 has widespreadconnections with the visual

and motor areas of the cortex

affects saccadic eye movements

and visual attention

lesion difficulty moving eyes toward same side, neglect of objects on the opposite side

lesion loss of smooth pursuit & optokinetic movements (when targets are moving toward the side of the lesion)

smooth pursuit movements

& optokinetic nystagmus (slow drift and fast return)

vergencecenters

abducens nuclei

somatic oculomotor neurons medial rectus mm.

(visceromotor) parasympathetic neurons ciliary and pupillary constrictor mm.

temporal eye field

(convergence) (divergence)

Fig. 10-6

Superior Colliculus: involved in reflex turning of head and eyes in response to startling pain or auditory orvisual stimuli

lesion does not result in major eye movement abnormalities

(pain and auditory)

Fig. 10-5 fast

igia

l nuc

lei

the cerebellumhelps with coordination ofeye movements

FEF, prefrontal cortex, and posterior parietal cortex basal ganglia basal ganglia and thalamus FEF and adjacent prefrontal cortex

Parkinson’s disease: seldom or lacking spontaneous ocular movements infrequent blinking (staring appearance)

Flocculonodular lobe fastigial nucleus vestibular nuclei vestibulo-ocular connections to the ocular motor nerves

Unilateral cerebellum lesions: nystagmus (especially when the eyes are directed toward side of lesion)

Chapter 10know the difference between the two types of vergence eye movements know the difference between saccadic and smooth pursuit eye movementsknow the difference between optokinetic and vestibulo-ocular eye movementsknow the cranial nerves that control eye movements and the muscles they innervateknow the locations and functions of the brainstem gaze centersknow the result of a lesion of the horizontal gaze centerknow the result of a unilateral lesion of the medial longitudinal fasciculusknow the two conditions that can affect the vertical and vergence gaze centersknow the locations and functions of the cortical gaze centersknow the result of a lesion of the frontal eye field and whyknow which cortical eye field is associated with contralateral neglectknow the three components of the near response that occur during convergenceknow the function of the superior colliculusknow how basal ganglia and cerebellar disorders affect eye movements