Eye Movements

Question 1

What are the classifications of eye movements?

Answer 1

• One Eye
• Abduction
• Adduction
• Elevation
• Depression
• Intorsion
• Extorsion

Two eye
• Both Eyes
• Conjugate
• Non-conjugate 
• Disconjugate

Question 2

Contrast the individual and movement of both eyes

Answer 2

Individual Eye Movements
When we look at an individual eye, we differentiate between abduction (lateral movement), adduction (medial movement), elevation (up), depression (down), intorsion (inward rotation around the pupil), extorsion (outward rotation).

Movements of Both Eyes
Coordinated movements of both eyes include conjugate eye movements (both eyes moving in the same direction), disconjugate eye movements (pathological aberrations of conjugate eye movements) and non-conjugate or vergence movements (eyes moving towards each other, or away from each other).

Question 3

What are the conjugate eye movements?

Answer 3

Saccadic, vestibulo-ocular and oculomotor movements are conjugate eye movements. When you follow a ship along the horizon with your eyes, this is a conjugate eye movement.
The conjugate eye movements discussed throughout this lecture series include:
• Saccadic Eye Movements
• Vestibulo-Ocular Reflex Movements (and
Vestibulo-Ocular Nystagmus)
• Optokinetic Reflex Movements (and
Optokinetic Nystagmus)
Conjugate eye movements are important in a clinical context.

Question 4

Eye movements can be…

Answer 4

Voluntary or reflex driven

Voluntary- Saccadic eye movements

 - fast= elements of the vestibuloocular movements
 - fast= elements of the optokinetic nystagmus

Reflex-
Vestibulo-ocular reflex = slow- elements of the vestibulo-occular nystagmus
Optokinetic reflex= slow- elements of the optokinetic nystagmus

Nystagmus: alternating eye movements with two components (fast: saccidic and slow:reflex)

Question 5

Briefly describe saccadic eye movements

Answer 5

Saccadic eye movements are voluntary movements. When you look at an oil painting in a museum (a portrait of a person for example), your eyes will “jump” from one point of interest (for example the nose) to another point of interest (the lips for example), and so on. These fast “jumps” are called saccades

Question 6

Briefly describe Vestibulo-ocular reflex movements

Answer 6

Vestibulo-ocular reflex movements occur when you rapidly turn your head. This stimulates the vestibular system, which keeps your eyes in position of your former point of fixation

Question 7

Briefly describe non-conjugate

Answer 7

Vergence movements are non-conjugate eye movements. When you stretch out your arm and look at the fingertip, and then follow your fingertip with your eyes while you move it towards your nose, this is a non-conjugate movement, in this case convergence. The opposite of convergence is divergence

Question 8

Briefly describe disconjugate

Answer 8

Disconjugate Eye Movements
Disconjugate eye movements are pathological deficiencies that occur instead of fully functional conjugate movements. For example, if one eye moves under certain conditions, but the other eye does not

Question 9

What is the near triad?

Answer 9

During convergence, not only do the eyes converge, but, in addition, near accommodation and pupillary constriction take place.

These three elements are called the “near triad” or “near response”:
• Convergence
• Accommodation
• Pupillary constriction

Question 10

What is the primary function and innervation of extraocular muscles?

Answer 10

In the view of clinically applicable neuroscience, we do not review all details of extraocular muscle movements. Instead, we focus on the very essence of what is relevant in a clinical scenario.

During neurological examination of extraocular muscle function, we try to isolate the primary function of each of the extraocular muscles. For example, to differentiate between the two muscles elevating the eye, we test their function separately when the eye is either abducted or adducted.

Two of the extraocular muscles are innervated exclusively by their own cranial nerve, the lateral rectus muscle by the abducens nerve (CN VI) and the superior oblique muscle by the trochlear nerve (CN IV). The remaining extraocular muscles are all innervated by the oculomotor nerve (CN III).

CN III also innervates the levator palpebrae superioris muscle, which raises the upper eye lid. It also contains parasympathetic fibers innervating the constrictor pupilae muscle, which constricts the pupil.

Question 11

What muscles are responsible for abduction and adduction?

Answer 11

To understand the primary function of each of the extraocular muscles, one needs to consider the anatomy of the orbit and the direction of the axis between origin (anulus tendinosus for all rectus muscles) and the point of insertion on the eye ball.

Adduction and Abduction

Contraction of the medial rectus muscle causes adduction, turning the eye towards the nose. Contraction of the lateral rectus muscle causes abduction, turning the eye away from the nose

Question 12

What eye muscles are responsibke fir elevation and depression?

Answer 12

Elevation and Depression

When the eye is abducted, contraction of the superior rectus muscle is most effective in causing elevation (eye turning upwards); contraction of the inferior rectus muscle in turn causes depression (eye down).

When the eye is adducted, the oblique muscles, which are pulling almost perpendicular to the rectus muscles, are most effective, with the superior oblique muscle causing depression (down) and the inferior oblique muscle elevation (up).

Question 13

What is the function and innervation of the lateral rectus?

Answer 13

Abduction

Abducens (CN IV)

Question 14

What is the function and innervation of medial rectus?

Answer 14

Adduction

Oculomoter nerve

Question 15

What are the functions and innervations of superior rectus?

Answer 15

Primary- elevation (tested during abduction)
Secondary- intorsion (during adduction)

Innervation: CN III

Subnucleus contralateral to the nerve

Question 16

What are the functions abd innervation of the inferior rectus?

Answer 16

Primary: depression (tested during abduction)
Secondary: extorsion (during adduction)

Innerv.: oculomotor

Question 17

What are the functions and innervations of the superior oblique ?

Answer 17

Primary: depression (tested during adduction )
Secondary function: intorsion (during adduction)

Trochlear nerve (nucleus contralateral to nerve)

Question 18

What are the functions and innervation of inferior oblique?

Answer 18

Primary: elevation (tested during adduction)
Secondary: (during abduction)

Oculomoter

Question 19

What is the primary gaze of the CN III lesion?

Answer 19

• Residual tone of lateral rectus muscle unopposed→abduction (out)
• Residual tone of superior oblique muscle unopposed→depression (down)
• Sympathetics unopposed→mydriasis
• Loss of levator palpebrae innervation / orbicularis oculi unopposed→ptosis (drooping of the eye lid)

Question 20

Describe the cranial nerve nuclei of the brainstem in control of eye movements

Answer 20

The nuclei of the cranial nerves innervating the extraocular muscles are located in the brainstem. CN III and IV nuclei are located in the tegmentum of the midbrain, close to the midline and to the cerebral aqueduct.

The level of the oculomotor nucleus is approximately in line with the superior colliculus, the trochlear nucleus with the inferior colliculus.
The nucleus of CN VI is located in the lower pons, close to the ponto-medullary junction.

In addition to the nuclei of the cranial nerves driving extraocular muscles, there are other control units in the brainstem.

Question 21

What are the additional control units of extraocular movements in the brainstem?

Answer 21

The midbrain contains the rostral interstitial nucleus of the medial longitudinal fasciculus (MLF), which participates in the 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.

Several nuclei in the pons participate in the control of eye movements. The pontine paramedian reticular formation (PPRF) participates in saccadic eye movements and lateral gaze. It is also called the horizontal gaze center.
Vestibular nuclei, which extend from pons to medulla, also contribute to the control of eye movements.

The cerebellum, in particular the vestibulo-cerebellum (flocculo-nodular lobe), participate in the control of optokinetic eye movements and smooth pursuit.

Question 22

What are the control units of the brainstem?

Answer 22

• Oculomotor nucleus
• riMLF
(= vertical gaze center)
• Trochlear nucle

Question 23

What are the control units of the Pons?

Answer 23

• PPRF
(= horizontal gaze center)
• Abducens nucleus
• Vestibular nuclei (extending into the medulla)

Question 24

What is the control unit of the cerebellum?

Answer 24

Cerebellum:
• Vestibulocerebellum
(= flocculo-nodular lobe)

Question 25

What are the cortical control units of extraocular movements?

Answer 25

A number of cortical units are involved in the control of extraocular movements. We will focus only on two of these units, the frontal eye field and the parieto-occipital eye field.

Please do not confuse “eye field” with “visual field”, which you have studied in an earlier lecture. Eye fields are certain areas of the cerebral cortex contributing to extraocular movements. The visual field of an eye describes the space visible at any given time without moving the eye.

The frontal eye field is located in area 8 of the frontal lobe. Its location alone suggests its role in the planning and initiation of eye movements. It plays a central role in the control of voluntary eye movements, in particular saccadic eye movements.

The parieto-occipital eye field is located in the area of the junction of the parietal lobe and the occipital lobe.

You will recall the parallel functional pathways discussed earlier in this lecture series. From the primary visual cortex onwards the dorsal (parietal) pathway for motion (and depth) leads up exactly into this area. So it is no surprise for us that the output from this area is involved in eye movements related to motion of the whole visual surround (optokinetic movements), or movements following a moving target (smooth pursuit

Question 26

Explain Saccidic eye movements

Answer 26

Saccadic eye movements are the fastest (up to 900° per second) eye movements that shift the fovea rapidly to another visual target in the visual field. Visual input is completely shut down during these fast movements. Saccades are followed by fixations, where the new target is kept in focus for a while and accurate vision is back again. Exploring the visual environment requires a series of alternating saccades and fixations.

The frontal eye field is the planning region and induces voluntary saccadic eye movements. Descending fibers originating in the frontal eye field cross the body’s midline in the pons and synapse on neurons in the pontine paramedian reticular formation (PPRF) on the contralateral side. Cells in the PPRF activate the adjacent abducens nucleus.

The output from the abducens nucleus is twofold. Some of the fibers form the abducens nerve and innervate the lateral rectus muscle, inducing abduction of the innervated eye. 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.

Fibers forming the oculomotor nerve innervate the medial rectus muscle, inducing adduction of the innervated eye.
It should be noted that the abducens nucleus has a prominent position in all conjugate eye movements, since it not only directly controls the abduction of one eye, but also indirectly the
adduction of the other eye

Question 27

Explain the velocity, function, control, vision of saccidc eye movements

Answer 27

• Velocity: very fast, up to 900 degrees per second
• Function: rapidly shifts the direction of gaze from one point of fixation to another point of fixation
• Control: voluntary, through the frontal eye fields
• Vision: switched off during saccades; continues between the saccades during periods of fixation

Question 28

What is the function of H-test?

Answer 28

Extraocular movements are examined using the “H-test”. The examiner moves his/her finger in in the six directions of the patient’s gaze, similar to writing the letter “H”, and instructs the patient to follow these movements.
In the horizontal plane, eye movements are tested in two directions of gaze (gaze to the left and to gaze to the right). Vertical movements are tested for each eye in the abducted and in the adducted states.

To familiarize yourself with this examination, watch the hyperlinked youtube video: neurological examination of extraocular movements using the H-test. Please note: elevation and depression of the eyes in mid-position, as shown in this video (0:19 to 0:29), does not isolate extraocular muscle function and is usually excluded from the test.

You will be performing the test in the small group practical session

Question 29

Explain isolation of primary function of extraocular muscles

Answer 29

The patient is asked to follow the examiner’s finger to each of the six cardinal positions of gaze (A, B, C, D, E and F).

• The examiner observes the patient’s eye movements.
• The table below indicates which extraocular muscle is tested in which of the six cardinal positions of gaze

Question 30

Dedcribe trochlear nerve palsy

Answer 30

A lesion of the trochlear nerve (CN IV) causes deficit of the superior oblique muscle. This leaves the inferior oblique muscle unopposed during primary gaze. Depression at medial and downward gaze is limited and does not exceed the midline.

Question 31

Describe oculomotor nerve palsy

Answer 31

DLA: Oculomotor Nerve Palsy
In a lesion of the oculomotor nerve (CN III), the eye is deviated down and out during primary gaze, due to unopposed action of lateral rectus muscle, innervated by the abducens nerve and superior oblique muscle, innervated by the trochlear nerve; usually associated with ptosis (drooping of the upper eye lid) and mydriasis (dilation of the pupil)

Question 32

Describe abducens nerve palsy

Answer 32

Abducens Nerve Palsy
When the abducens nerve (CN VI) is lesioned, the eye is deviated medially, due to unopposed action of the medial rectus muscle, innervated by the oculomotor nerve.

Question 33

Explain diplopia

Answer 33

Double vision is a common complaint of patients with visual problems. The cause for diplopia lies often in a mismatch of pictures produced by the two eyes, when the center of the visual field (point of fixation) of one eye differs from the center of the visual field of the other eye. In the example on the right, the palm tree is in the center of the visual field of the left eye. In the visual field of the right eye, the same palm tree is located in the periphery, left of the center.

As a consequence, when both pictures are merged in the cerebral cortex, the palm tree appears twice on the calculated picture, once in the center, based on the picture produced by the left eye, and a second time to the left of the center, based on the picture produced by the right eye

Question 34

With normal extraocular function…

Answer 34

With normal extraocular function, the same point of fixation should be projected on the fovea (center of the visual field) of both eyes, and the person should see a single image.

Question 35

What is the clinical correlation of Diplopia?

Answer 35

• Eyes not pointed at the same target
• Mismatch of the visual field centers of left and right eye
• The patient has double vision (diplopia)
• Complaints may include “blurry” vision

Question 36

What is MLF Lesion/ Internuclear Ophthalmoplegia?

Answer 36

Internuclear ophthalmoplegia is based on a lesion of the medial longitudinal fasciculus (MLF), which prevents adduction of the eye on the side of the lesion during attempted lateral gaze.
The example in the figure below shows a patient with a lesion of the right MLF (adduction of the right eye is impacted).
Convergence does not involve the MLF and is not affected by the lesion

Question 37

What is a PRRF Lesion?

Answer 37

Lesions of the pontine gaze center (PPRF) result in a paralysis of ipsilateral horizontal eye movements. Conjugate horizontal gaze towards the side of the lesion is interrupted. When the left PPRF is damaged, for example, horizontal eye movements of both eyes towards the left are impaired (left gaze palsy). Vertical gaze can still be intact.

Question 38

What is One-and-a-half Syndrome?

Answer 38

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. It is caused by an extensive paramedian pontine lesion involving the PPRF and the MLF on one side of the brainstem.

Question 39

MLF+ PPRF lesion=

Answer 39

One-and-a-half syndrome