The extraocular muscles

Movement of the 6 extraocular muscles (isolated): MR

MR- Moves the eye inward, toward the nose (adduction)

An extraocular palsy may cause the eyes to be

misaligned, which is a strabismus.

Through the annulus, and alonf the middle of this cone of muscles, runs the:

optic nerve (cranial nerve II)

If the person's brain has learned to suppress the image of the strabismic eye, the brain will

perceive only the single image from the other eye.

In cases of muscle palsy, muscle surgery is another option. However, it should not be

performed for at least six months after the onset of diplopia, since the effects of the palsy may resolve spontaneously over a few weeks or months.

The apex of this cone is located in the? Base?

posterior aspect of the orbit, while the base of the cone is the attachment of the muscles around the midline of the eye.

Excycloduction (extorsion) is a

temporal or outward rotation (of the top of the eye), caused by the contraction of the IR and IO muscles, with an equal relaxation of the SR nad SO muscles.

Infraduction (depression) is a vertical movement downward, caused by?

the contraction of the IR and SO muscles, with an equal relaxation of the SR and IO muscles.

Divergence:

Both eyes moving temporally or outward

Diplopia:

Double vision

Movement of the 6 extraocular muscles (isolated): LR

LR- moves the eye outward, away from the nose (abduction)

Chemical formula (cranial nerves):

LR6(SO4)3

The angle of deviation of the strabismus is measured in

Prism diopters

Some cases of low angle esotropia do not require surgery but, instead, respond successfully to____. When is is this possible?

Visual therapy. - This is possible in a child or an adult for which the esotropia is of recent onset and for which there is no macular damage (that is, when the strabismic eye is capable of good visual acuity.

Antagonist

While the muscle in the same eye that moves in the opposite direction of the agonist

Adduction is a horizontal movement toward the nose, caused by?

a contraction of the MR muscle, with an equal relaxation of the LR muscle.

The cause of the palsy usually is

acquired due to lesion, a stroke, or other trauma, although occasionally it can be congenital.

A vergence or disconjugate movement, involves simultaneous movement of...

both eyes in opposite directions.

Convergence:

both eyes moving nasally or inward

More commonly, exotropia develops in.....

infancy or in early childhood, often beginning as an intermittant (ocasional) strabismus and sometimes leading to a constant strabismus.

(IO) This muscle attaches to the

inferior portion of the eye.

When considering how to the eyes work together, a version or conjugate movement involves ...

simultaneous movement of both eyes in a certain direction.

If one eye constantly is turned inward (crossed eye), outward (wall eye), upward or downward, this is referred as a

strabismus or heterotropia

Exotropia also can be congetinal, although this is very

unsual

Describing movement around a horizontal axis, supraduction is a... Caused?

vertical movement upward, caused by the contraction of SR and IO muscles, with an equal relaxation of the IR and SO muscles.

Levoversion?

(looking left) - Left lateral rectus - Right medial rectus

dextrodepression

(looking right and down) - Right inferior rectus - left superior oblique

Dextroelevation

(looking right and up) - right superior rectus - left inferior oblique

Strabismus will result in?

diplopia, since two different objects are viewed in the macula of the eyes.

Infraversion or deorsumversion

(looking straight down) - left and right Inferior recti - left and right Superior obliques

Supraversion or sursumversion

(looking straight up) - left and right superior recti - Left and right inferior obliques

Levoclycloversion

(rotation to the left) - Left inferior rectus and inferior oblique - Right superior rectus and superior oblique

The six cardinal positions:

up/right up/left right left down/right down/left

Supraduction

upward or elevation

There are two principle vergence movements:

Convergence and divergence

When considering each eye separately, any movement is called a

duction

According to "Henring's Law", yoked muscles receive .....

equal and simultaneous innervation.

A carefully planned regimen of visual therapy often can be used to treat.....

exotropia, especially in cases where complete suppression of the strabismic eye has not yet occurred and the eye is capable of good visual acuity.

When the oculomotor nerve (cranial nerve III) is damaged, a palsy in the..

medial rectus, superior rectus, inferior rectus, and or inferior oblique muscles may occur.

Eye muscles work together with other eye muscles, of the same eye and the opposite eye, to/

move the eyes in various directions.

In a certain position of gaze, a muscle of one eye is "yoked" with muscle of the other eye to

move the eyes, together, in a certain direction.

Describing movement around an antero-posterior axis, "incycloduction" (intorsion) is a

nasal or inward rotation (of the top of the eye), caused by a contraction of the SR and SO muscles, with an equal relaxation of the IR and IO.

In a complete cranial nerve III paralysis, the upper eyelid also will be ____________. The pupil might be ______

nearly closed from a ptosis. - dilated and unreactive as well.

Strabismus also can occur due to a?

nerve paralysis or paresis, or even due a retinal disease. or even when there is very different refractive error in the strabismic eye compared to the other eye.

If the angle of deviation is not the same in all cardinal positions of gaze, the strabismus is classified as

nonconcomitant (paralytic)

Movement around the vertical axis, abduction is a horizontal movement away from the... Caused?

nose, caused by a contraction of the LR muscle, with an equal relaxation of the MR muscle,

Levodepression

(looking left and down) - Right superior oblique - Left inferior rectus

Levoelevation

(looking left and up) - Right inferior oblique - Left superior rectus

Damage to cranial nerve III, IV or VI often will cause a

"palsy" (paralysis or paresis) of the extraocular muscles innervated by that nerve.

Agonist muscles in both eyes, which work together to move the eyes in the same direction , are said to be

"yoked" together

Dextroversion?

(Looking right) - Right lateral rectus - Left medial rectus

Dextrocycloversion

(Rotation to the right) - Right inferior rectus and inferior oblique - Left superior rectus and superior oblique

Movement of the 6 extraocular muscles (isolated): IR

- Primarily moves the eye downward (depression) - Secondarily rotates the top of the eye away from the nose (extorsion) - Tertiarily moves the eye inward (adduction)

Movement of the 6 extraocular muscles (isolated): IO

- Primarily rotates the top of the eye away from the nose (extorsion) - Secondarily moves the eye upward (elevation) - Tertiarily moves the eye outward (abduction)

Movement of the 6 extraocular muscles (isolated): SO

- Primarily rotates the top of the eye toward the nose (intorsion) - Secondarily moves the eye downward (depression) -Tertiarily moves the eye outward (abduction)

What are the 6 extraocular muscles?

1. Medial rectus (MR) 2. Lateral Rectus (LR) 3. Superior rectus (SR) 4. Inferior Rectus (IR) 5. Superior Oblique (SO) 6. Inferior Oblique (IO)

The misalignment of a strabismic eye occurs in about (percentage of children)?

2%

The apex of the conic structure is a tendonous ring called?

Annulus of Zinn

Synergist

A muscle in the same eye that moves the eye in the same direction as the agonist

Esotropia can be _______ and usually the angle of deviation is_________. Management involves surgical correction, typically at?

Congenital (a muscle imbalance present from birth). - large - at age six months or earlier.

There are six (10) principle version movements, where both eyes look or move together, in tandem, in the same direction simultaneously:

Dextroversion, levoversion, supraversion or sursumversion, infraversion or deorsumversion, dextroelevation, dextrodepression, levoelevaation, levodepression, dextrocycloversion and levocycloversion

If all the muscles controlled by the cranial nerve III are going under palsy what is the result of the strabismus?

Eye will be turned outward and downward (due to unopposed action of the lateral rectus and superior oblique muscles. The affected eye cant turn inward past the midline and cant turn upward past the midline.

Eccentric fixation?

In this case, when the normal eye is covered, thus forcing the strabismic eye to take over, the strabismic eye usually does not point exactly straight at the object being fixated. Therefore, the image of the object being viewed does not fall directly upon the macula, as it should. Rather, the image falls upon some eccentric point, away from the macula, where the acuity is not as good. Thus, this is referred to as "eccentric fixation."

Sherringtons Law

Increased innervation to any agonist muscle is accompanied by a corresponding decrease in innervation to its antagonist muscle(s)

All of the extraocular muscles, with the exception of the ___________, form a __________ within in the bony orbit.

Inferior oblique, cone

When the abducens nerve (Cranial nerve VI) is damaged, a palsy of the _________ may result, resulting in ______.

Lateral rectus. esotropia. The eye will not only be able to look outward past midline, but it will also turn inward when the other eye is fixating straight ahead.

An image of the object is focused upon the ______ of each eye, and the brain _____________

Macula, merges the two retinal images into one.

If the vision in a strabismic eye is suppressed (turned off) for too long, that eye very well may...

develop "amblyopia" (lazy eye) condition. This means that the visual acuity in that eye no longer is as good as the visual acuity in the other eye, which is used all the time.

The trochlea acts as a

Pulley for the superior oblique muscle

Nerve innervations (cranial nerve): SO, IO, SR, IR, MR and LR

SO: Cranial Nerve IV(Trochlear) IO: Cranial Nerve III(Oculomotor) SR: Cranial Nerve III(Oculomotor) IR: Cranial Nerve III(Oculomotor) MR: Cranial Nerve III(Oculomotor) LR: Cranial Nerve VI(Abducens)

Movement of the 6 extraocular muscles (isolated): SR

SR: - Primarily moves the eye upward (elevation) - Secondarily rotates the top of the eye towards the nose (intorsion) - Tertiarily moves the eye inward (adduction)

Alternating strabismus?

different eyes will deviate at different times

The most common symptom of a muscle palsy is

diplopia (double vision)

Agonist:

The primary muscle that moves an eye in a given direction

The cardinal positions are six position of gaze which allow:

comparisons of the horizontal, vertical, and the diagonal ocular movements produced by the six extraocular muscles when both eyes and multiple muscles are working together.

If the angle of deviation remains the same in all cardinal positions of gaze, the strabismus is classified as

concomitant (or nonparalytic)

If the strabismus occurs all of the time, it is said to be

constant

The esotropia also can be accommodative, usually due to a high amount of uncorrected hyperopia (farsightedness). This causes a great deal of accomodation to be required to _____. Treatment?

focus retinal images, resulting in a subsequent overconvergence (by the medial rectus muscles) and a subsequent esotropia. The usual treatment for accommodative esotropia is eyeglasses or contact lenses, which compensate for the hyperopia, allowing the deviating eye to straighten.

An extraocular muscle palsy may resolve on its own with time; however, this may not occur. If the palsy and resultant diplopia are permanent, a prismatic correction may be

incorporated into spectacle lenses to merge the double images into a single image. Some people prefer simply to keep one eye patched to take away their double vision.

If the strabismus occurs sometimes, but not all of the time, it is said to be

intermittent

Tropias: Inward, outward, upward, downward,

inward- esotropia outward- exotropia upward- Hypertropia Downward- Hypotropia

An eye is referred to as lazy eye because

it does not see as clearly as the other eye. The most common reason for amblyopia is the presence of eccentric fixation in a strabismic eye.

The inferior oblique, which is not a member of the cone of muscles originating from annulus of Zinn, arises from the

lacrimal fossa in the nasal portion of the bony orbit.

With in the optic nerve are contained the:

ophthalmic artery and vein

When the abducens nerve (Cranial nerve VI) is damaged, diplopia will be observed by the person when he/she gazes to the

side with the palsied muscle, and the person will compensate for this by turning his/her face toward the side of the palsied eye.

The nerve innervations that cause all of the gaze movements are very complex, but suffice it to say that, normally, all of it happens very...

smoothly and efficiently.

Sometimes, due to some type of extraocular muscle imbalance, one eye is not aligned with the other eye, resulting in a

strabismus, AKA heterotropia, or simply a tropia.

When the trochlear nerve (cranial IV) is damaged, a palsy of the _______. Typically, this will result in_____. People with this condition will experience both ______

superior oblique muscle may occur. - excyclotorsion (outward rotation), along with a lesser hypertropia and esotropia. - Vertical and a torsional diplopia, and they will compensate for this by tilting the head toward the shoulder of the unaffected eye.

If a ptosis (drooping upper eyelid) is involved, such as in a in a cranial nerve III paralysis, probably the best option is

surgical elevation of the eyelid.

Normally, when viewing an object, the lines of sight of both eyes intersect at?

the object

The superior oblique, although part of the cone of muscles, differs from

the other muscles in a significant way

(SO) before it attaches to the eye, it passes through a ring-like tendon,..

the trochlea, in the nasal portion of the orbit

When utilizing the Bielschowsky head-tilt test, the person is told to

tilt his/her head toward the shoulder of the affected eye. An overeaction of the inferior oblique, and an elevation of the affected eye (and marked diplopia) will result.

when visual therapy is not successful to treat exotropia, surgical correction should be

used to provide a cosmetically improved appearance of the deviating eye. This does not necessarily ensure that binocular vision will result.