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Chapter 10
The Ocular Motor System:
Gaze Disorders
the visual fields are
projected onto the
retina both inverted
and reversed
optic nerve
fibers
transmitting
impulses
from the right
visual fields
travel in left
optic tract
the eyes must move
so that the object is
focused on the visual
receptors in the
binocular zone
optic nerve
fibers
transmitting
impulses
from the left
visual fields
travel in right
optic tract
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 down
left or right
saccadic
smooth pursuit
optokinetic
vestibulo-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:
superior rectus
medial rectus
inferior rectus
inferior oblique
lateral rectus
superior oblique
Brainstem gaze centers:
1. Horizontal gaze center
in the paramedian pontine reticular formation (PPRF)
• 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)
right
right
contralateral
ipsilateral
MLF
horizontal
gaze center
interneurons from the
abducens nucleus ascend
in the contralateral MLF
Fig. 10-2
controls
conjugate
movements
toward the
ipsilateral side
contralateral oculomotor nucleus
ipsilateral abducens nucleus
Horizontal Gaze Center
right
frontal
lobe
right eye
left eye
left
horizontal
gaze
center
result of a lesion of the right HGC
result of a lesion of the left MLF
*note - the affected eye
will 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 gaze
are more dorsal than
those for downward gaze
Vergence gaze centers
control convergence
and divergence
posterior
commissure
(interconnected by the
posterior commissure)
midbrain gaze centers are affected by:
pineal gland tumors
dilation of cerebral aqueduct
Cortical gaze centers:
projects to the vertical and horizontal
gaze centers and the superior colliculus
left
(to the contralateral side)
right
there is also (transient)
conjugate deviation
of the eyes to the
side of the lesion
Bilateralism of cortical connections with the brainstem gaze centers:
L Frontal eye field
R Frontal eye field
L Horizontal gaze center R Horizontal gaze center
dominant connection
non-dominant connection
parietal association areas: 5, 7, 39, 40
process tactile and
visual info.
Fig. 16-6b
area 7 has widespread
connections 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
smooth pursuit movements
& optokinetic nystagmus
(slow drift and fast return)
lesion  loss of smooth pursuit & optokinetic
movements (when targets are moving
toward the side of the lesion)
temporal
eye field
(convergence)
somatic oculomotor neurons
 medial rectus mm.
(visceromotor) parasympathetic neurons
 ciliary and pupillary constrictor mm.
vergence
centers
abducens nuclei
(divergence)
Superior Colliculus:
(pain and auditory)
involved in reflex turning of head and eyes
in response to startling pain or auditory or
visual stimuli
Fig. 10-6
lesion  does not result in major eye movement abnormalities
fastigial nuclei
Fig. 10-5
the cerebellum
helps with
coordination of
eye 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 10
know the difference between the two types of vergence eye movements
know the difference between saccadic and smooth pursuit eye movements
know the difference between optokinetic and vestibulo-ocular eye movements
know the cranial nerves that control eye movements and the muscles they
innervate
know the locations and functions of the brainstem gaze centers
know the result of a lesion of the horizontal gaze center
know the result of a unilateral lesion of the medial longitudinal fasciculus
know the two conditions that can affect the vertical and vergence gaze centers
know the locations and functions of the cortical gaze centers
know the result of a lesion of the frontal eye field and why
know which cortical eye field is associated with contralateral neglect
know the three components of the near response that occur during
convergence
know the function of the superior colliculus
know how basal ganglia and cerebellar disorders affect eye movements