Oculomotor Mechanisms Flashcards
(45 cards)
What type of lesions do eye exams reveal?
Central lesions.
Pick 2 conditions that are not a symptom of occulomotor disturbance:
- Diploplia
- Oscillopsia
- Aphasia
- Vertigo
- Dysequilibrium
- Brainstem related syptoms
- Blindness
Aphasia, blindness
How many postural control adjustments are generated each day by the oculomotor complex?
100,000
What level of the brainstem is the occulomotor nucleus and nerve?
Rostral midbrain
Name the muscles not innervated by CNIII and name their nerve and function.
TROCHLEAR
Superior oblique
-down and out
ABDUCENS
Lateral rectus
-abduction
With a lesion to CNIII, what is the resting position of the eye?
- Exotropia (outward)
- Ptosis (eyelid drop)
- Diploplia
What functional deficits exist with a CNIII lesion?
NO
- upward gaze
- medial gaze on side of lesion
What does the pupillary light reflex test?
Integrity between retina and midbrain (CNII, CNIII):
-retina>CNII (optic nerve) >midbrain>CNIII (sphincter)>direct consensual response
-important test of increased intracranial pressure
When describing the pupillary light reflex, what is direct and consensual response?
DIRECT
-the pupil in which the light is entering constricts
CONSENSUAL
-the pupil which is not receiving light constricts somewhat
What is the direct response circuit?
Retina (sensory) to optic nerve to optic tract to pretetum to CN III (motor).
The consensual response to light includes a crossing effect where?
The pretectum.
-cross to opposite side CN III which effect a response.
What happens to the pupillary light reflex with a CNIII lesion?
No constriction on side of lesion, but still consensual response.
What happens to the pupillary light reflex with a CN II (Marcus Gunn) lesion and how would you determine what side the lesion is?
No direct or consensual with light in the side of the lesion. When light is in non-lesion side, there will be direct and consensual.
Where is the nucleus of CN IV (trochlear)? What movement do you lose with a lesion?
CAUDAL MIDBRAIN
No downward gaze when adducted
Where is the nucleus of CN VI and what movement do you lose with a lesion? Does the resting position change?
CADUAL PONS
Esotropia (medial strabismus) & diploplia
No lateral gaze side of lesion
What level of the brain stem hosts horizontal conjugate gaze? What nucleus drives the gaze?
Pons.
Abducens nucleus handles all traffic.
Describe the recruitment pathway for horizontal conjugate gaze.
Lateral rectus neuron > abducens nucleus > interneuron > MLF (on opposite side) > CN III nucleus > medial rectus
If you had a lesion to CNVI nucleus on the right side, how does that affect conjugate horizontal gaze?
You would lose lateral rectus (CNVI) on the right and medial rectus (CNIII) on the left.
What is the function of the medial longitudinal fasiculus, and where is it located?
interconnects CN VI with contralateral CN III as well as vestibular nuclei.
Located medial to abducens nucleus.
What happens with a lesion just to the MLF (internuclear opthalmoplegia)?
No ipsilateral adduction of the right eye with gaze to the left (contralateral).
Where and what are the center s for vertical conjugate gaze? What nerves produce it?
Reticular formation in the midbrain.
CNIII innervating superior rectus bilaterally.
Do eye movements involves lower motor neurons?
Yes, of III, IV and VI.
What types of eye movements exist to hold the image on the fovea?
- Gaze fixation
- Vestibulo-ocular reflex (VOR)
- Optokinetic nystagmus
What is gaze fixation?
Ability to hold eye in fixed position.
