Chapter 10 The Ocular Motor System: Gaze Disorders

the visual fields are projected onto the retina both inverted and reversed 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 right visual fields travel in left optic tract 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 inferior oblique medial rectus lateral rectus inferior rectus superior oblique

Brainstem gaze centers: 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 horizontal gaze center contralateral ipsilateral MLF controls conjugate movements toward the ipsilateral side interneurons from the abducens nucleus ascend in the contralateral MLF Fig. 10-2

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

*note - the affected eye 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

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

L Frontal eye field R Frontal eye field 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. area 7 has widespread connections with the visual and motor areas of the cortex Fig. 16-6b

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 vergence centers somatic oculomotor neurons  medial rectus mm. (visceromotor) parasympathetic neurons  ciliary and pupillary constrictor mm. abducens nuclei (convergence) (divergence)

Superior Colliculus: involved in reflex turning of head and eyes in response to startling pain or auditory or visual stimuli Fig. 10-6 (pain and auditory) lesion  does not result in major eye movement abnormalities

the cerebellum helps with coordination of eye movements Fig. 10-5 fastigial nuclei Fig. 10-5

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