Module D-08 Flashcards
What are the 3 classes of eye movements?
1) Conjugate
2) Non-conjugate
3) Dysconjugate
what are the 3 types of conjugate eye movements?
1) Saccadic eye movements (and gaze)
2) Vestibulo-ocular reflex
3) Optokinetic reflex (and smooth pursuit)
What are the 2 types of non conjugate eye movements ?
1) convergence
2) Divergence
What type of movements are saccadic eye movements?
- Voluntary, extremely fast eye movements that shift the fovea rapidly to another visual target in the visual field.
- used to explore the
visual environment
What type of movements are vestibulo-ocular eye movements?
keeping your eyes fixed on a point when your head turns away (vestibular system is activated)
What type of movements are Optokinetic eye movements?
- your head stays still, but your visual surround is in motion relative to your head
- keeps an object in the center of your visual field as long as possible, by keeping your eyes pointed towards this object
What type of movement does smooth pursuit follow?
similar function as optokinetic
keeps fovea focused on a moving target
What is the origin point for the 4 rectus muscles?
Annulus tendinosus
Name the 6 extraocular miscles
1) Superior rectus
2) Inferior rectus
3) Medial rectus
4) Lateral rectus
5) Superior Oblique
6) Inferior Oblique
Name the 3 nerves that innervate the extraocular muscles
CN III (Oculomotor) CN IV (Trochlear) CN VI (Abducens)
Which extraocular muscles does the Oculomotor nerve innervate?
1) Superior Rectus (elevates on lateral gaze)
2) Inferior Rectus (Depresses on lateral gaze)
3) Medial Rectus (adducts)
4) Inferior Oblique (Elevates on medial gaze)
Which extraocular muscles does the Trochlear nerve innervate?
Superior Oblique ( Depresses on medial gaze)
Which extraocular muscles does the Abducens nerve innervate?
Lateral Rectus (abduction )
In what part of the brainstem is the nucleus for CN III located?
- tegmentum of the midbrain, close to the midline and to the cerebral aqueduct.
- approximately in line with the SUPERIOR colliculus
In what part of the brainstem is the nucleus for CN IV located?
- tegmentum of the midbrain, close to the midline and to the cerebral aqueduct.
- approximately in line with the INFERIOR colliculus
In what part of the brainstem is the nucleus for CN VI located?
the lower pons, close to the ponto-medullary junction
Besides the nuclei of the 3 CN nerves what other nuclei participate in control of eye movements?
1) Rostral interstitial nucleus of the medial longitudinal
fasciculus (MLF), (In the midbrain)
2)the superior colliculus (receives input from the retinal
ganglion cells)(also in midbrain)
3) Pontine paramedian reticular formation (PPRF)
4)Vestibular nuclei, which extend from pons to medulla
5)The cerebellum, in particular the vestibulo-cerebellum (flocculo-nodular lobe),
What type of Eye movements does the MLF control?
control of vertical eye movements, and
the superior colliculus, which, as we know already, receives input from the retinal
ganglion cells can participate in the control of eye movements.
What type of Eye movements does the PPRF control?
participates in saccadic eye movements and lateral gaze. It is also called the horizontal gaze center.
What type of Eye movements does the Flocculo-nodular lobe control?
Control of optokinetic eye movements and smooth pursuit.
Which are the 2 cortical control units of eye movements?
1) Frontal eye field
2) Parieto-occipital eye field
What is the location of the frontal eye field?
frontal lobe
Which brodmann’s area is the frontal eye field in?
Area 8
What is the role of the frontal eye field?
1) the planning and initiation of eye movements.
2) The control of voluntary eye movements,in particular saccadic eye movements
What is the location of the parieto-occipital eye field?
The junction of the parietal lobe and the occipital lobe
What is the role of the Parieto-occipital eye field?
eye movements related to motion of the whole visual surround (optokinetic movements), or movements
following a moving target (smooth pursuit)
Speed of Saccadic eye movements
up to 900° per second
Exploring the visual environment requires a series of alternating _______ and _________.
saccades ; fixations
What are fixations?
where the new target is kept in focus for a while and vision becomes fully functional again
Describe pathway that causes both eye to move together in saccadic eye movements (conjugate horizontal eye movements).
1)the frontal eye field receives visual information.
2) Descending fibers originating in the frontal eye field cross the body’s midline in the pons and synapse on neurons in the PPRF on the contralateral side.
3)Cells in the PPRF activate the adjacent abducens nucleus.
4)The output from the abducens nucleus is twofold.
a)Some of the fibers form the abducens nerve and
innervate the lateral rectus muscle, inducing
abduction of the innervated eye.
b)Other fibers cross the body’s midline immediately
after exiting the abducens nucleus and ascend in the
contralateral medial longitudinal fasciculus (MLF)
until they reach the oculomotor nucleus.
5) Fibers forming the oculomotor nerve innervate the medial rectus muscle, inducing adduction of the innervated eye
What causes Trochlear nerve Palsy?
A lesion of the trochlear nerve (CN IV) causes deficit
of the superior oblique muscle
What occurs in Trochlear nerve Palsy?
the inferior oblique muscle unopposed at medial gaze.
Depression at medial and downward gaze is limited
and does not exceed the midline
What causes Oculomotor nerve Palsy?
a lesion of the oculomotor nerve (CN III)
What is seen in Oculomotor nerve Palsy?
- the eye is deviated down (and out) due to unopposed action of lateral rectus muscle and superior oblique muscle,
- usually associated with ptosis (drooping of the upper eye lid) and mydriasis (dilation of the pupil).
What causes Abducens nerve Palsy?
the abducens nerve (CN VI) is lesioned
What is seen in Abducens nerve Palsy?
the eye is deviated medially, due to unopposed action of the medial rectus muscle
What is diplopia?
Double vision
What causes diplopia?
the center of the visual field (point of fixation) of one eye differs from the center of the visual field of the other eye
What test is used for diplopia?
the Red Glass Test
What color is seen in normal vision for red glass test?
Pink
What color is seen in diplopia for red glass test?
a red and a white light, the eye taht is normal and can follow sees white light and teh other eye sees teh red light
What is Internuclear ophthalmoplegia?
a lesion of the medial longitudinal fasciculus (MLF), which prevents adduction of the eye on the side of the lesion during attempted lateral gaze
How can differentiate Internuclear ophthalmoplegia and damage to medial rectus?
In Internuclear ophthalmoplegia, the converge works and both eyes adduct
What is seen in lesions of the PPRF , pontine gaze center?
- a paralysis of ipsilateral horizontal eye movements
- Conjugate horizontal gaze towards the side of the
lesion is interrupted - vertical gaze is intact
What is One-and-a-half Syndrome?
A combination of gaze paralysis in one direction (counts for the “one”) and
internuclear ophthalmoplegia in the other direction (counts for the “half”, since
one eye is still able to move, but not the other one). Abduction is intact only in
one eye.
What causes One-and-a-half Syndrome?
an extensive paramedian pontine lesion involving the PPRF and the MLF on one side of the brainstem.
