Neuroanatomy Lecture #29: Eye Movements

Front 1

Define and describe the 2 classes and the corresponding 4 types of eye movements

Back 1

• Non-conjugate eye movements: are ones that produce a non-parallel shift or position of images on the eyes

- Vergence movements result in either convergence or divergence of the eyes

• Conjugate eye movements: movements that allow for bilateral fixation on an object
- Saccadic eye movements: quick, simultaneous movements of both eyes in the same direction

- Vestibulo-ocular reflex: stabilizes the image on the center of the visual field during head movement

- Optokinetic reflex: allows the eye to follow objects in motion while the head remains stationary

Front 2

Describe the iNN and fxn of the extraocular eye muscles:
• Superior rectus
• Inferior rectus
• Medial rectus
• Lateral rectus
• Superior oblique
• Inferior oblique

Back 2

Front 3

Cranial Nerve Nuclei:

• general location of the nuclei that control extraocular eye movements

• Specific location of CN III & IV, include relative locations w/ respect to parts of the tectum

• Specific location of CNVI (near which jxn?)

Back 3

Cranial Nerve Nuclei:

• in the brainstem

• CN III & IV are in the tegmentum of the midbrain close to the midline and cerebral aqueduct.
- specifically, CNIII is line w/ the superior colliulus
- while......... CN VI is line w/ the inferior colliculus

• CN VI is located in the lower pons, close to the pontomedullary jxn

Front 4

Other control units are responsible for extraocular eye movements are located in the following regions. Name them and describe their fxn:

• Midbrain
• Pons
• Pons to medulla
• Cerebellum

Back 4

Other control units:

• Midbrain
- Rostral interstitial nucleus of the medial longitudinal fasciculus
> fxns to control vertical eye movements

- Superior colliculus
> receives input from retinal ganglion cells and described with having a generic role in eye movements

• Pons
- Pontine Paramedial Reticular Formation
> also called the "horizontal gaze center" it participates in saccadic eye movements and lateral gaze

• Pons to medulla
- Vestibular nuclei
> described for generic eye movements

• Cerebellum
- floccular nodular lobe of cerebellum
> optokinetic eye movements and smooth pursuit

Front 5

Two Cortical control units for extraocular eye movements

Back 5

Frontal eye field and Parietal-occipital eye field

Front 6

Cortical Control Units:
• Frontal eye field
- Brodmann's area
- what location tells us about its fxn
- its primary fxn

Parieto-occipital eye field
• location
• role in eye movements (2)
• The V1 pathway that leads to this region

Back 6

Cortical Control Units:
• Frontal eye field
- 8
- located in the frontal lobe, it must have a role in planning and initiation of eye movements
- saccadic eye movements

Parieto-occipital eye field
• Jxn of the parietal and occipital lobe
• output is involved in movements related to motion of the whole visual surround (optokinetic movements) and
movements following a moving target (smooth pursuit)

• Dorsal/Parietal pathway

Front 7

Saccadic Eye Movements:
• Definition
• Two types of actions they use to explore the visual field
• The field that trigger saccadic eye movements

Back 7

Saccadic Eye Movements:
• Extremely fast eye movements that shift the fovea rapidly to another visual target in the visual field

• saccades followed by fixations

• The frontal eye field, the planning region

Front 8

Pathway for Saccadic Eye Movements: (Hints)
• Start with descending fibers from the Frontal eye field
• How many fibers are involved in the pathway?
• When and where do fibers cross the midline?
• How many nuclei are involved?

Back 8

Pathway for Saccadic Eye Movements:
• Descending fibers from the Fronal eye field trave thrugh the internal capsule, cross the pons and synapse at the PPRF on the contralateral side

• Fibers from the PPRF synapse on and activate the ABducens nucleus

• The Abducens nucleus has two outputs -
1) Fibers exit to iNN the lateral rectus, ABducting the eye
2) Another set of fibers immediately cross the midline and ascend the contralateral MLF to synapse on to the oculomotor nucleus

• Fibers from the Oculomotor nucleus iNN the medial rectus, ADducting the eye

Front 9

Relationship:
The role of the Abducens nucleus in the Common Final Pathway of conjugate eye movements

Back 9

It synchronizes the ABduction of one eye and the ADduction of the opposite eye.

Front 10

Exam used to test extraocular eye movements

Back 10

H-Test

Front 11

Deficit seen in Trochlear nerve palsy
• Which muscle is unopposed?

Back 11

The inferior rectus is unopposed.
Deficit: when the affected eye is ADducted, the eyeball rotates up and inwards. Depression of the eyeball at a downwards and medial gaze is limited.

Front 12

Oculomotor nerve palsy:
• the unopposed muscles
• presentation of deficit
• two associated d/o

Back 12

Oculomotor nerve palsy:
• Superior oblique and lateral rectus
• Eyeball rotates down and outwards
• Partial ptosis, mydriasis

Front 13

Abducens nerve palsy:
• the unopposed muscle
• presentation of deficit

Back 13

Abducens nerve palsy:
• medial rectus
• Eye is deviated medially

Front 14

Diplopia
• Another term
• Definition

Back 14

Diplopia
• Double vision
• The center of the visual field for one eye differs from the center of the visual field from the other eye

Front 15

Internuclear Opthalmoplegia:
• Site of lesion
• Deficit
• An action of the eyes that is not affected

Back 15

Internuclear Opthalmoplegia:
• MLF

• the affected eye is unable to look medially when the opposite eye performs a lateral gaze

• Convergence

Front 16

One and a half syndrome:
• is a combination of these paralysis
• A voluntary movement that is still in tact only in one eye
• Cause/Lesions

Back 16

One and a half syndrome:

• Combination of these paralysis
1) Conjugate horizontal gaze palsy - gaze paralysis in one direction
2) internuclear opthalmoplegia in the other direction - the inability to ADduct on the side of the lesion during lateral gaze

• ABduction is intact

• PPRF lesion and an MLF lesion on one side of the brainstem