eye movements

fovea centralis contains

sonly cone

macula lutea is temporal to

optic disc

optic disc contains NO

photoreceptors

what converge to form optic nerve?

retinal ganglion cell axons

Ophthalmoplegia

paralysis or weakness of eye muscles

ptosis

drooping eyelid

mydriasis

pupil dilated, loss of accommodation of lens

diplopia

double vision

eye movements muscles + CNs

Conjugate movements include

- Saccadic

- Smooth pursuit

Conjugate movements

eyes move in same direction

saccadic movements

rapid, ballistic jerky eye movements

Reflexive conjugate movements include

- Optokinetic movements

- Vestibuloocular movements

Optokinetic movements

combination of slow-phase and fast-phase eye movements

what eye movement is used when an individual tracks (pursuit movement) a moving object with their eyes, which then moves out of the field of vision, a point at which their eyes move back to the initial position (saccade movement) when they first saw the object?

optokinetic movements

Vestibuloocular movements

the sensory signals encoding head movements are transformed into motor commands that generate compensatory eye movements in the opposite direction of the head movement, thus ensuring stable vision

Vergence movements occur when

eyes shifts between distant and near objects

Vergence movements

- converge

- diverge

converge eye movements

when the eyes move toward each other

diverge eye movements

when the eyes move away from each other

where is the horizontal gaze center located?

pons (some rostral medulla)

where is Vertical gaze center located?

midbrain

where is the vergence gaze center located?

midbrain

what is needed when both eyes look in the same directions? !!!!

horizontal gaze centers

Horizontal gaze center is in the

paramedian pontine reticular formation (PPRF)

(horizontal gaze center) Tonic timing signals generated by

nucleus prepositus hypoglossi

(horizontal gaze center) what allows eyes to maintain their position) ?

tonic timing signals generated by nucleus prepositus hypoglossi

(horizontal gaze center) phasic/burst signals from PPRF to

- Ipsilateral abducens nucleus (Ipsilateral lateral rectus muscles)

- Contralateral oculomotor nucleus •MLF at superior colliculus and Contralateral medial rectus muscle)

pontine lesions (CN VI nucleus) affects

horizontal gaze

(horizontal gaze stroke) Median aspect of the pons is supplied by

paramedian branch of the basilar artery

(horizontal gaze) what happens if the frontal eye field is damaged? !!!!!!!

Transient paralysis occurs when all or some muscle control comes and goes periodically

(horizontal gaze) what happens if the right PPRF (contralateral to the FEF) is damaged? !!!!!!!!

really nothing works as well, you won't be able to move either eye to the right

(horizontal gaze) what happens if the ipsilateral (left) side MLF is damaged? !!!!!!

right side is normal, but the left side will not be able to adduct

(horizontal gaze) what happens if the the level of the abducens nerve is damaged? !!!!!

left eye (ipsilateral in this case) is functioning fine but that the right eye will be unable to abduct or gaze to the right

horizontal gaze damage !!!!!!!!!

Unilateral lesion of MLF at or superior (rostral) to the abducens nucleus causes !!!!!!!

paralysis of eye adduction ipsilateral to lesion -- affected eye can adduct during convergence

most common causes of unilateral lesion of MLF

- Multiple sclerosis

- Brainstem infarction

internuclear ophthalmoplegia (INO) !!!!!!!

lesions in MLF-->conjugate horizontal gaze palsy

CN VI nucleus activates ipsilateral lateral rectus; contralateral CN III nucleus does not stimulate medial rectus to fire

abducting eye gets nystagmus

normal convergence

Vertical gaze center is in the

rostral interstitial nucleus of the MLF (riNMLF) of midbrain

(vertical gaze center) riNMLF phasic/burst signal acts

bilaterally

(vertical gaze center) within riNMLF

- upward movements (dorsal)

- downward movements (ventral)

(vertical gaze center) what is the role of medial accessory oculomotor nucleus?

tonic signal to keep eyes fixed

Vertical gaze palsy (VGP)

limitation of upward gaze and/or downward gaze

Vertical gaze palsy (VGP) results from

- Pineal gland tumor

- Dilation of cerebral aqueduct

Paralysis of convergence with Vertical gaze palsy (VGP)

- L and R intact

- look up -- cant -- raise eyelids but eyes don't move

- look straight -- relax eyes

- downward -- look at you but relax eyelids

- can't cross their eyes

what is seen on radiograph with Vertical gaze palsy (VGP)?

- Hummingbird sign

- mickey mouse appearance

convergence is controlled by

supraoculomotor area (SOA)

supraoculomotor area (SOA) projects to

- Medial rectus and lateral rectus motor neurons

- Edinger-Westphal (accessory oculomotor nucleus) preganglionic nucleus (lens and pupil)

where is the rostral midbrain reticular formation located?

behind oculomotor nuclei

(convergence) Lens and pupil contraction via what innervation?

autonomic parasympathetic

what is the chief center for voluntary eye movements?

Frontal eye field (BA8)

Frontal eye field (BA8) projects to

- Vertical and horizontal gaze centers

- Superior colliculus

where is the Frontal eye field (BA8) located?

posterior part of middle frontal gyrus

Superior parietal lobule affects what type of eye movements?

saccadic movements

Superior parietal lobule has reciprocal connects with?

frontal eye field and superior colliculus

Superior parietal lobule plays a role in?

visual attention

lesions to superior parietal lobule cause

neglect of contralateral objects and difficulty with eye movements toward that side

posterior part of lateral temporal lobes are in charge of what eye movements?

smooth pursuit

Posterior part of lateral temporal lobes lesions result in

ipsilateral loss of smooth pursuit when targets are moving toward the side of the lesion

what forms the occipital eye field?

Primary visual and visual association areas

Primary visual and visual association areas controls what eye movements?

vergence movements

Primary visual and visual association areas afferent limb

normal visual pathway

Primary visual and visual association areas efferent limn

- Occipital lobe > superior colliculus > oculomotor nucleus

From oculomotor nucleus, eye accommodate for near vision

- Medial recti

- Ciliary muscles

- pupillary sphincters

Superior colliculus consists of

alternating gray and white layers

Superior colliculus plays a role as _______ _________ center

visuomotor integration

Superior colliculus control what eye movements?

reflex ocular

lesions of Superior colliculus

do not result in major eye movement abnormalities

input side of basal nuclei

Eye movement-related cortical areas > caudate nucleus > substantia nigra > superior colliculus and thalamus > modulates cortical output

output side of basal nuclei

modulation of the frontal and supplementary eye fields and superior colliculus by varying levels of inhibition (from SNr)

Substantia nigra !!!!

source of the striatal input of the neurotransmitter dopamine, plays a role in basal ganglia function

Parkinson's disease

Loss of dopaminergic neurons from compact part of substantia nigra

parkinson disease affects what basal ganglia pathways?

Decreased activity of direct pathway and increased activity of indirect pathway

Huntington's disease

Loss of excitatory subthalamic projections disinhibits the thalamus

Huntington's disease lead to a failure

suppress some cortical outputs

Eye movement-related areas of cerebral cortex project via pontine nuclei to the

oculomotor vermis

where is the oculomotor vermis located?

upper part of posterior lobe

what is the role of the oculomotor vermis?

regulated timing of muscles contractions during saccades

oculomotor vermis project to _________ nucleus then to _______ ________ _______ for eye movements

fastigial; brainstem pattern generator (BPF)

Flocculonodular lobe

receives inputs from eye movement-related areas of the cerebral cortex

how does the flocculus produce smooth pursuit movements of the eye?

suppresses vestibulo-ocular reflex (VOR)

what happens if the flocculus is damaged?

- Impairment of smooth pursuit movements

- Loss of the ability to change the gain of the VOR

Which type of movement occurs when the eyes shift between distant and near objects? !!!!!

Converge or diverge movements

Which types of movements occur when the eyes move in the same direction? !!!

conjugate movements - smooth pursuit and saccadic

What is the horizontal gaze center called? !!!!

PPRF - paramedian pontine reticular formation

What is the vertical gaze center called? !!!!!

riNMLF - rostral interstitial nucleus of the medial longitudinal fasciculus

What is the brainstem center controlling convergence and divergence? !!!!!

Supraocular motor area

What is the chief cortical center for voluntary eye movements? !!!

frontal eye field

A patient complains of seeing two images of a single object (double vision or diplopia) whenever looking toward the right side. Examination shows that upon attempting to gaze to the right, the right eye abducts normally but the left eye fails to adduct. Both gaze to the left and convergence for near vision are normal. Which of the following structures has been affected?

Medial longitudinal fasciculus