Evaluation of the Ocular Motor System

Question 1

Strabismus is the term we use for misalignment of the visual axes. There are two basic types:

Answer 1

Paralytic (non-comitant) and non-paralytic (comitant)

Question 2

Describe paralytic (non-comitant) strabismus

Answer 2

Paralytic or non-comitant is characterized by the presence of variable angles of deviation in different fields of gaze. Weakness of one or more extraocular muscles is the usual cause. These usually affect adults and cause diplopia (double vision) in the direction of gaze where the affected muscle or muscles is (are) supposed to be working the hardest. Since they occur generally in adults, amblyopia does not result from these deviations.

Question 3

Describe non-paralytic strabismus

Answer 3

Non-paralytic or comitant strabismus is seen when the visual axes are misaligned early in childhood, usually before the age of 6, The angle of deviation is similar in all fields of gaze.

No diplopia occurs as the brain suppresses one of the images leading to amblyopia in that eye.

No specific muscle weakness is identified.

Question 4

There are two types of ocular deviation, namely:

Answer 4

tropia and phoria.

Question 5

Describe tropia. Phoria?

Answer 5

A patient with a tropia has the deviation of the visual axes present at all times;

A patient with a phoria has a deviation of the visual axes only when fusion is disrupted (such as covering one eye). With both eyes uncovered the fusion mechanism of the brain of the patient with a phoria sends signals to the extraocular muscles that corrects the misalignment.

Question 6

An ESO deviation means the eye and the visual axes are crossed (turned inward). An EXO deviation means that the eyes are turned outward.

Answer 6

A HYPER deviation means that one eye is higher than the other (hypertropia). HYPO means that one eye is lower than the other. Clinically, we usually refer to the HYPER (higher) eye.

The same prefixes are used for describing phorias.

Question 7

This slide shows examples of a large angle ESOtropia (upper photograph) and EXOtropia (lower photograph).

Question 8

What tests can be used to verify the alignment of the visual axes?

Answer 8

the alternate cover test and the light reflex test

Question 9

Describe how an alternate cover test is performed

Answer 9

The alternate cover test is performed by covering one eye and then quickly moving the cover to the other eye while the patient is fixated on a small target.

This motion is repeated several times, always pausing long enough to observe the action of the uncovered eye.

Question 10

How are the results of an alternate cover test interpreted?

Answer 10

If no motion of the uncovered eye is noted, then the visual axes are in normal alignment.

If there is motion of the uncovered eye, the direction of the motion is noted. If the uncovered eye moves INWARD, then it was turned OUT to begin with. The inward motion brings the visual axis to fixate on the target. This would be described as an EXO deviation.

If the uncovered eye moves OUTWARD, then it was turned IN to start. This would be described as an ESO deviation.

If the uncovered eye moves DOWNWARD, then the eye was UP to begin with. This would be described as a HYPER deviation.

Question 11

How is a light reflex test performed?

Answer 11

The light reflex test is performed by having the patient look at a distant target while the physician holds a light source in the patient’s midline at approximately arm’s length from the patient. The light is directed onto the patient’s corneas and the position of the light reflex there observed.

Question 12

How should a light reflex test be interpreted?

Answer 12

If normal alignment of the eye is present, the light reflexes should be symmetrically positioned on the cornea. If one light reflex is displaced TEMPORALLY when compared to the other side, that eye is deviated INWARDLY (ESO deviation). If one light reflex is displaced NASALLY when compared to the other side, that eye is deviated OUTWARDLY (EXO deviation). If one light reflex is displaced DOWNWARD when compared to the other side, that eye is deviated UPWARDLY (HYPER deviation).

This test is used in patients that are not very cooperative or those with good vision in only one eye.

Question 13

This diagram shows the position of the corneal light reflexes with normal alignment of the visual axes. Small deviations will NOT be visible when the patient is tested by this technique.

Answer 13

This diagram shows the position of the corneal light reflexes in a patient with ESOtropia. The left eye is fixating the target and the right eye is turned inward.

Question 14

This diagram shows the position of the corneal light reflexes in a patient with EXOtropia. The left eye is fixating the target and the right eye is turned outward.

Question 15

Movements of only ONE EYE are called ______

Answer 15

ductions.

ADduction means that the eye moves toward the nose (toward the midline).

ABduction mans that the eye moves towards the ear (away from the midline).

Elevation means the eye moves upward, while Depression means that the eye moves downward.

Question 16

Ocular _______ are movements of both eyes in the same direction. Clinically we usually refer to these as right gaze, left gaze, etc.

Answer 16

versions

Question 17

Ocular ________ are the movement of both eyes in OPPOSITE directions. The more common of these is Convergence.

Answer 17

vergences

Convergence is part of the near reflex. Other components are miosis (constriction of the pupil) and accommodation (activation of the ciliary muscle to focus the lens at a near object).

Question 18

T or F. Divergence is not well developed in humans and usually only serves to return the eyes to normal alignment following convergence.

Answer 18

T.

Question 19

Intorsion is the rotation of the 12 o’clock position of the cornea toward the nose. What ocular muscles mediate this?

Answer 19

The superior rectus and superior oblique muscles are intorters.

NOTE: Extorsion is the rotation of the 12 o’clock position of the cornea away from the nose. The inferior rectus and inferior oblique muscles are extorters.

Question 20

Answer 20

The most confusing part of this subject is that the primary, secondary, and tertiary actions of the extraocular muscles depend on whether the eye is ABducted or ADducted. This is further complicated by the fact that in different gazes one eye is ABducted while the other is ADducted.

Question 21

This diagram shows the relative positions of the extraocular muscles when the eye is in primary position (looking straight ahead). This diagram views the orbits from the top and shows the superior muscles, but there are inferior muscles that roughly correspond to the superior muscles shown. Their actions will of course be different (opposite) from the superior muscles.

Note that not all of the superior oblique muscles have been included in the diagram. Only the tendon portion that passes through the trochlea is shown because the mechanical pulling force of the superior oblique muscle comes from the trochlea.

Question 22

The action of bringing the eyes into RIGHT GAZE is primarily accomplished by the actions of the RIGHT LATERAL RECTUS and the LEFT MEDIAL RECTUS muscles.

The actions of the vertically acting muscles are a bit more complicated.

In RIGHT GAZE the right eye is ABducted while the left eye is ADducted. This puts the two recti muscles of the right eye more in line with the visual axis of the right eye and thus are the primary elevator (RIGHT SUPERIOR RECTUS) and depressor (RIGHT INFERIOR RECTUS) of the right eye while the eyes are in RIGHT GAZE. At the same time the left eye is ADducted, putting the superior and inferior oblique muscles more in line with the visual axis of the left eye. These two muscles now become the primary elevator (LEFT INFERIOR OBLIQUE) and depressor (LEFT SUPERIOR OBLIQUE) of the left eye while the eyes is are in RIGHT GAZE.

Also note that in RIGHT GAZE the right eye is ABducted and the RIGHT SUPERIOR OBLIQUE is ALMOST PERPENDICULAR to the visual axis of the right eye and thus is primarily an INTORTER of the right eye in this position. In RIGHT GAZE the left eye is ADducted and the LEFT SUPERIOR RECTUS is ALMOST PERPENDICULAR to the visual axis of the left eye and thus primarily an INTORTER of the left eye when the eyes are in this position.

Question 23

This table contrasts the actions of the vertically acting extraocular muscles when the eye to which they are attached is either ADducted or ABducted.

Question 24

This slide shows the six cardinal positions and the pairs of muscles primarily responsible for moving the eyes into these fields of gaze. While straight up and straight down are not considered to be cardinal positions in the classical sense, clinically it may be helpful to have the patient move into these directions in addition to the classic six.

Question 25

What is nystagmus?

Answer 25

Nystagmus denotes a rhythmic involuntary to and fro motion of the eyes. The motion may be horizontal, vertical, rotary, or combinations of directions.

Question 26

When is jerk nystagmus seen?

Answer 26

Jerk nystagmus is the type typically seen in neurological disorders, while pendular nystagmus is usually the result of poor vision in one or both eyes.

Question 27

How can jerk and pendular mystagmus be differentiated?

Answer 27

They can be differentiated by observing the motion of the eyes. Jerk nystagmus has a slow phase followed by a rapid recovery phase, while pendular nystagmus has movements that are equal in amplitude in each direction.

Question 28

Binocular diplopia is the result of what?

Answer 28

misalignment of the visual axes. The doubling of the images will be relieved by closing or covering either eye. This type of diplopia is often the result of paresis or paralysis of one of the cranial nerves that innervate the extraocular muscles. The resulting lack of normal muscular response causes the visual axes to loose their alignment resulting in images of an object stimulating different areas of the retina in the two eyes. The patient then sees one image in two places (diplopia). The angle of deviation and the distance between the two images the patient sees will increase as the eyes are brought into the gaze direction where the affected muscle is supposed to be most active. Monocular diplopia will go away when the patient closes the affected eye but remains when the unaffected eye is closed or covered. This type of diplopia is usually the result of opacities or irregularities in the optical system of the eye.

Question 29

If the patient has horizontal diplopia, the physician should suspect the action of the medial or lateral muscle to be weakened. If the patient has vertical diplopia one of the vertically acting muscles should be suspected.

Question 30

How would a CN III palsy present?

Answer 30

- ptosis (weakness of leavtor palpebrae superioris) - non-reactive pupil - eye is down and out

Question 31

What important thing can a blown pupil or CN III plasy suggest?

Answer 31

An aneurysm at the junction of the posterior communicating and posterior cerebral arteries is an important cause of paralysis of CRANIAL NERVE III (Oculomotor). If the patient presents to the physician with a headache and paresis/paralysis of CRANIAL NERVE III (Oculomotor), an aneurysm must be ruled out and appropriate imaging studies and consultations requested immediately.

Question 32

A paralysis of CRANIAL NERVE III (Oculomotor) with normal pupillary responses usually indicates what?

Answer 32

A microvascular cause (due to occlusion of internal vessels). These patients are usually older and most commonly have diabetes mellitus. They may or may not have pain at the beginning and usually recover spontaneously in three to four months. There must be no other associated neurological findings, and the patient must be watched carefully for a change in the status of the pupil.

Question 33

Total paralysis of CRANIAL NERVE VI (Abducens) causes loss of ABduction by the eye. How does it present?

Answer 33

The unopposed medial rectus muscle then pulls the eye inward causing an ESOtropia in primary position. The ESOtropia decreases in magnitude as the gaze moves toward the side OPPOSITE the weak lateral rectus muscles and increases in magnitude as the gaze moves toward the side of the weakened muscle. As the magnitude of the ESOtropia increases, the separation of the two images seen by the patient also increases. As the magnitude of the ESOtropia decreases, the separation of the images decreases and the patient may be able to fuse the two images into one, eliminating the diplopia.

Question 34

What are the major causes of CN VI palsy?

Answer 34

increased ICP, tumor, trauma, stroke, microvascular It is a non-localizing neurological sign and may be seen as one of the features of increased intracranial pressure, but microvascular causes are common in older patients, particularly those with diabetes.

Question 35

This series of photographs shows the patient with a RIGHT CRANIAL NERVE VI (Abducens) paralysis The top photograph shows the ESOtropia in primary position. The patient is fixing with her right eye. The lower left photograph shows her attempting to look into right gaze. The right eye does not ABduct. In the lower right photograph the patient is looking into left gaze and seems to have her visual axes well aligned.

Question 36

How might CN IV palsy present?

Answer 36

Paralysis of CRANIAL NERVE IV (Trochlear) causes weakness or paralysis of the SUPERIOR OBLIQUE muscle resulting in vertical or oblique diplopia. The patient may have a SPONTANEOUS HEAD TILT toward the side OPPOSITE the weakened muscle.

Question 37

What are some common causes of CN IV palsy?

Answer 37

The most common causes are head trauma, microvascular (usually diabetes mellitus), and congenital.

Question 38

CN IV Palsy

Answer 38

Paralysis of the SUPERIOR OBLIQUE causes that eye to be pulled higher by the unopposed action of the INFERIOR OBLIQUE of the same eye. When the patient’s eyes move into gaze to the OPPOSITE SIDE from the weakened muscle, the eye with the weakened muscle is in the ADducted position, thus the SUPERIOR OBLIQUE is more in line with the visual axis of that eye and should be primarily an DEPRESSOR muscle. However, since it is weak, the opposing INFERIOR OBLIQUE muscle pulls the eye UPWARD, increasing the vertical deviation in that gaze.

Question 39

CN IV Palsy

Answer 39

In gaze toward the SAME SIDE as the weakened muscle, that eye is now in the ABducted position, and the SUPERIOR OBLIQUE is primarily an INTORTER and creates less effect on the vertical alignment. Tilting the head toward the side of the eye with the paretic Superior Oblique causes an increase in the vertical deviation while tilting toward the opposite direction causes a decrease in the vertical separation of the two images. This is caused by the attempt of the OTHER INTORTER of the eye with the paretic Superior Oblique (the SUPERIOR RECTUS) to bring about INTORSION. But the SUPERIOR RECTUS is a better ELEVATOR than an INTORTER, thus ELEVATING the eye with the paretic Superior Oblique causing an increase in the vertical separation of the two images. The patient will SPONTANEOUSLY want to tilt his/her head to the side opposite the eye with the paretic Superior Oblique to reduce or eliminate the diplopia. **By observing the results of the previous three steps in the examination, the physician can verify that indeed the vertical diplopia is caused by a paralysis of CRANIAL NERVE IV (Trochlear).**

Question 40

This series of photographs illustrates the abnormal ocular positions of a patient with a LEFT SUPEIOR OBLIQUE MUSCLE weakness secondary to paralysis of the LEFT CRANIAL NERVE IV (Trochlear) due to head trauma.