The eye pdf - Head and Neck

556

CHAPTER 11

The Head and Neck

pterygoid venous plexus. Both veins pass

ough

backward thr

the superior orbital fissure and drain into the

nous sinus.

caver

(Fig. 11.21). For the superior

rotate it medially

but also

they not only raise and depress the cornea, respectively,

on the medial side of the vertical axis of the eyeball,

Because the superior and the inferior recti are inserted

oblique muscles.

inferior

superior

lateral rectus,

rectus,

medial

inferior rectus,

superior rectus,

are the

wall of the orbital cavity to the eyeball (Fig. 11.18). These

There are six voluntary muscles that run from the posterior

Eye

Extrinsic Muscles Producing Movement of the

marker. The eye rotates either medially or laterally.

the eyeball use the upper rim of the cornea (or pupil) as the

is the rotation of the eye medially. Rotatory movements of

adduction

is the rotation of the eye laterally, and

abduction

is the rotation of the eye downward,

depression

upward,

is the rotation of the eye

Elevation

becomes as follows:

(horizontal, vertical, and sagittal). The terminology then

of the anterior pole as it rotates on any one of the three axes

of the eye are then related to the direction of the movement

as the anatomic “anterior pole” of the eye. All movements

The center of the cornea or the center of the pupil is used

Terms Used in Describing Eye Movements

or nodes are present in the orbital cavity.

No lymph vessels

Lymph Vessels

The Eye

Movements of the Eyeball

the

and the

and

rectus muscle to raise the cornea directly upward, the
inferior oblique muscle must assist; for the inferior

rect

carefully Figure 11.24.

muscles of the eyeball are summarized in Table 11.2. Study

The origins, insertions, nerve supply, and actions of the

rectus muscle.

erally and is inserted into the sclera beneath the superior

the frontal bone. The tendon now turns backward and lat

through a fibrocartilaginous pulley (trochlea) attached to

that the tendon of the superior oblique muscle passes

oblique muscle must assist (Figs. 11.21 and 11.22). Note

to depress the cornea directly downward, the superior

vertical axis

superior
rectus

transverse axis

medial
rectus

inferior
rectus

lateral
rectus

superior rectus

transverse axis

inferior rectus

sagittal axis

transverse axis

lateral rectus

superior
rectus

medial

recti

inferior rectus

lateral rectus

vertical axis

FIGURE 11.21

The actions of the four recti muscles in producing movements of the eyeball.

Basic Anatomy

you are testing the inferior oblique at its best position.

versely, by asking the patient to look medially and upward,

are testing the superior oblique at its best position. Con

medially and downward at the tip of his or her nose, you

the cornea. In other words, when you ask a patient to look

tion to lower (superior oblique) or raise (inferior oblique)

medially, thus placing these muscles in the optimum posi

the action of these muscles by asking the patient first to look

medial and anterior to their insertions. The physician tests

oblique and the origin of the inferior oblique muscles lie

oblique muscles can be tested. The pulley of the superior

Using the same rationale, the superior and inferior

rectus) or lower (inferior rectus) the cornea.

cles are placed in the optimum position to raise (superior

the patient is asked to turn the cornea laterally, these mus

about 23° medial to their insertions, and, therefore, when

The origins of the superior and inferior recti are situated

single action of each muscle predominates (Fig. 11.23).

downward, the physician tests the eye movements where the

a patient is asked to look vertically upward or vertically

superior and inferior oblique muscles are complicated when

Because the actions of the superior and inferior recti and the

and Inferior Recti and the Superior and Inferior

Clinical Testing for the Actions of the Superior

557

Oblique Muscles

rtical axis

superior oblique

oblique

inferior

transverse axis

superior oblique

sagittal
axis

rtical axis

transverse axis

oblique

inferior

oblique

superior

transverse axis

inferior oblique

sagittal axis

trochlea

FIGURE 11.22

The actions of the superior and inferior oblique muscles in producing movements of the eyeball.

and

medial

of the orbit by triangular ligaments called the

and lateral recti are attached to the medial and lateral walls

tubular sheath. The sheaths for the tendons of the medial

the orbital muscles and is reflected onto each of them as a

socket for free movement. It is perforated by the tendons of

rates the eyeball from the orbital fat and provides it with a

nerve to the corneoscleral junction (Fig. 11.25). It sepa

The fascial sheath surrounds the eyeball from the optic

Fascial Sheath of the Eyeball

cussed later.

take no part in the movement of the eyeball and are dis

dilator pupillae of the iris

constrictor,

ciliary muscle

The involuntary intrinsic muscles are the

Intrinsic Muscles

recti and oblique muscles are shown in Figure 11.24.

The cardinal positions of the eyes and the actions of the

rectus.

turning the cornea directly medially tests the medial

her cornea directly laterally tests the lateral rectus and

relative to the eyeball, asking the patient to turn his or

Because the lateral and medial recti are simply placed

and the

The lower part of the fascial sheath,

lateral check ligaments.
which passes beneath the eyeball and

ts the check

connec

558

CHAPTER 11

central aperture, the pupil (Fig. 11.25). It is suspended in

The iris is a thin, contractile, pigmented diaphragm with a

The Iris and Pupil

refractive power of the lens.

elastic lens becomes more convex. This increases the

relieves the tension in the suspensory ligament, and the

meridianal fibers, pulls the ciliary body forward. This

Contraction of the ciliary muscle, especially the

Action:

ers pass forward to the eyeball in the short ciliary nerves.

synapsing in the ciliary ganglion, the postganglionic fib

asympathetic fibers from the oculomotor nerve. After

is supplied by the par

ciliary muscle

The

Nerve supply:

fewer in number and lie internal to the meridianal fibers.

junction to the ciliary processes. The circular fibers are

fibers run backward from the region of the corneoscleral

anal and circular fibers of smooth muscle. The meridianal

(Fig. 11.25) is composed of meridi

ciliary muscle

The

suspensory ligaments of the lens.

ridges, to the posterior surfaces of which are connected the

are radially arranged folds, or

ciliary processes

The

ciliary striae.

surface has shallow grooves, the

is the posterior part of the body, and its

ciliary ring

The

ciliary processes, and the ciliary muscle.

the iris (Fig. 11.25). It is composed of the ciliary ring, the

roid, and anteriorly it lies behind the peripheral margin of

is continuous posteriorly with the cho

ciliary body

The

an inner, highly vascular layer.

The choroid is composed of an outer pigmented layer and

ward, of the choroid, the ciliary body, and the iris.

The vascular pigmented coat consists, from behind for

Vascular Pigmented Coat

corneal epithelial cells should be stressed.

tear film in maintaining the normal environment for the

differs greatly from that of the air. The importance of the

the cornea, where the refractive index of the cornea (1.38)

eye. This refractive power occurs on the anterior surface of

The cornea is the most important refractive medium of the

Function of the Cornea

division of the trigeminal nerve

Long ciliary nerves from the ophthalmic

Nerve Supply

ous humor and from the capillaries at its edge.

phatic drainage. It is nourished by diffusion from the aque

The cornea is avascular and devoid of lym

Blood Supply

posteriorly with the aqueous humor.

tion of the light entering the eye (Fig. 11.25). It is in contact

is largely responsible for the refrac

cornea

The transparent

corneoscleral junction, or limbus.

sclera is directly continuous in front with the cornea at the

nerves and their associated veins, the venae vorticosae. The

The sclera is also pierced by the ciliary arteries and

the nerve fibers of the optic nerve.

is the area of the sclera that is pierced by

lamina cribrosa

The Head and Neck

The Cornea

-
-

The Choroid

The Ciliary Body

■

superior rectus

inferior oblique

inferior rectus

superior oblique

medial rectus

lateral rectus

FIGURE 11.23

Actions of the four recti and two oblique mus

suspensory ligament of the eye

it is called the

ligaments, is thickened and serves to suspend the eyeball;

page 557.

in the living intact eye are tested clinically, as described on

of the superior and inferior recti and the oblique muscles

horizontal planes should be noted in each case. The actions

alone. The position of the pupil in relation to the vertical and

cles of the right orbit, assuming that each muscle is acting

(Fig. 11.25).

fused with the dural sheath of that nerve (Fig. 11.25). The

is white. Posteriorly, it is pierced by the optic nerve and is

The opaque sclera is composed of dense fibrous tissue and

The Sclera

sclera, and an anterior transparent part, the cornea (Fig.

The fibrous coat is made up of a posterior opaque part, the

Fibrous Coat

nervous coat.

are the fibrous coat, the vascular pigmented coat, and the

eyeball consists of three coats, which, from without inward,

separated from it by the fascial sheath of the eyeball. The

The eyeball (Fig. 11.25) is embedded in orbital fat but is

lateral walls of the orbit, as if in a hammock.

By this means, the eye is suspended from the medial and

Structure of the Eye

Coats of the Eyeball

11.25).

Basic Anatomy

559

FIGURE 11.24

The cardinal positions of the right and left eyes and the actions of the recti and the oblique muscles principally

of light of low intensity or in the presence of excessive

The dilator pupillae dilates the pupil in the presence

the presence of bright light and during accommodation.

The sphincter pupillae constricts the pupil in

Action:

pass forward to the eyeball in the long ciliary nerves.

is supplied by sympathetic fibers, which

dilator pupillae

pass forward to the eyeball in the short ciliary nerves. The

synapsing in the ciliary ganglion, the postganglionic fibers

parasympathetic fibers from the oculomotor nerve. After

is supplied by

sphincter pupillae

The

Nerve supply:

posterior surface.

consist of a thin sheet of radial fibers that lie close to the

dilator pupillae

the pupil. The radial fibers form the

and are arranged around the margin of

sphincter pupillae

of circular and radiating fibers. The circular fibers form the

The muscle fibers of the iris are involuntary and consist

posterior chamber.

anterior

the cornea into an

the ciliary body. It divides the space between the lens and

periphery of the iris is attached to the anterior surface of

the aqueous humor between the cornea and the lens. The

eye, inferior rectus muscle.

Right eye, superior oblique muscle; left

Both eyes, inferior recti and superior oblique muscles.

Right eye, inferior rectus muscle; left eye,

Right eye, medial rectus muscle; left eye, lateral rectus muscle.

Primary position, with the eyes fixed on a distant fixa

Right eye, lateral rectus muscle; left eye, medial rectus muscle.

Right eye, inferior oblique muscle; left eye, superior rectus muscle.

eyes, superior recti and inferior oblique muscles.

Both

Right eye, superior rectus muscle; left eye, inferior oblique muscle.

responsible for the movements of the eyes. A.

tion point. F.

superior oblique muscle. H.

and a

and

■

sympathetic activity such as occurs in fright.

and the back of the iris.

This anterior part of the retina covers the ciliary processes

pigment cells, with a deeper layer of columnar epithelium.

rior part of the retina is nonreceptive and consists merely of

and the nervous tissues end here. The ante

ora serrata,

is the receptor organ. Its anterior edge forms a wavy ring,

body (Fig. 11.25). The posterior three quarters of the retina

choroid, and its inner surface is in contact with the vitreous

Its outer surface is in contact with the

inner nervous layer.

outer pigmented layer

The retina consists of an

Nervous Coat: The Retina

and an

the

560

CHAPTER 11

The Head and Neck

venous sinus

conjunctiva

ora serrata

medial check ligament

medial rectus

retinal

arteries

sclera

choroid

retina

optic disc

dura mater

arachnoid mater

subarachnoid space

pia mater

optic nerve

central artery and vein of retina

lateral check ligament

suspensory ligament

medial check ligament

cerebrospinal fluid

short ciliary nerve

long ciliary nerve

fovea centralis

hyaloid canal

vitreous body

orbital fat

fascial

sheath

vitreous

membrane

lateral rectus

lateral check

ligament

suspensory ligament

ciliary muscle

posterior chamber

iris

pupil

anterior chamber

cornea

lens

FIGURE 11.25

away through the spaces at the iridocorneal angle into the

the anterior chamber through the pupil and is drained

which it enters the posterior chamber. It then flows into

believed to be a secretion from the ciliary processes, from

and posterior chambers of the eyeball (Fig. 11.25). It is

The aqueous humor is a clear fluid that fills the anterior

Aqueous Humor

the aqueous humor, the vitreous body, and the lens.

The contents of the eyeball consist of the refractive media,

color, much paler than the surrounding retina.

scopic examination, the optic disc is seen to be pale pink in

On ophthalmo

“blind spot.”

light and is referred to as the

so that it is insensitive to

cones

rods

plete absence of

At the optic disc is a com

central artery of the retina.

is slightly depressed at its center, where it is pierced by

optic

medial side of the macula lutea by the optic disc. The

The optic nerve leaves the retina about 3 mm to the

(Figs. 11.25 and 11.26).

fovea centralis

sion, the

retina for the most distinct vision. It has a central depres

which is the area of the

macula lutea,

yellowish area, the

At the center of the posterior part of the retina is an oval,

Check ligaments and suspensory ligament of the eyeball.

cross the subarachnoid space to reach the optic nerve.

Horizontal section through the eyeball and the optic nerve. Note that the central artery and vein of the retina

disc
the

and

Contents of the Eyeball

Basic Anatomy

561

pigmentation of retina

branch of central artery of retina

optic disc

tributary of central vein of retina

site of fovea
centralis

FIGURE 11.26

The left ocular fundus as seen with an oph

rectus muscles.

eyes results from the coordinated contraction of the medial

that a single object, not two, is seen. Convergence of the

from a distance toward an individual, the eyes converge so

of objects (single binocular vision). When an object moves

In humans, the retinae of both eyes focus on only one set

of the Lens

Convergence of the Eyes during Accommodation

muscle contracts so the pupil becomes smaller.

accommodation for near objects, the sphincter pupillae

of the lens so spherical aberration is diminished during

To ensure that the light rays pass through the central part

Constriction of the Pupil during Accommodation

eye in focusing on nearby objects.

use of an additional lens in the form of glasses to assist the

ened (presbyopia). This disability can be overcome by the

elastic, and, as a result, the ability to accommodate is less

With advancing age, the lens becomes denser and less

lar shape.

relaxed. This allows the elastic lens to assume a more globu

so that the radiating fibers of the suspensory ligament are

cle contracts and pulls the ciliary body forward and inward

To accommodate the eye for close objects, the ciliary mus

Accommodation of the Eye

flattened so that the eye can be focused on distant objects.

ers of the suspensory ligament tends to keep the elastic lens

The pull of the radiating fib

suspensory ligament.

by the

lens is attached to the ciliary processes of the ciliary body

disc shape. The equatorial region, or circumference, of the

constantly to endeavor to assume a globular rather than a

The elastic lens capsule is under tension, causing the lens

lens. The lens fibers make up the bulk of the lens.

formed from the cuboidal epithelium at the equator of the

which are

lens fibers,

the anterior surface of the lens; and

which is confined to

cuboidal epithelium,

the structure; a

which envelops

capsule,

The lens consists of an elastic

ciliary processes.

iris and in front of the vitreous body and is encircled by the

enclosed in a transparent capsule. It is situated behind the

The lens (Fig. 11.25) is a transparent, biconvex structure

of the retina against the pigmented part of the retina.

rior surface of the lens and assists in holding the neural part

to the magnifying power of the eye. It supports the poste

The function of the vitreous body is to contribute slightly

is filled by the hyaloid artery, which disappears before birth.

optic disc to the posterior surface of the lens; in the fetus, it

row channel that runs through the vitreous body from the

hyaloid canal

11.25) and is a transparent gel. The

The vitreous body fills the eyeball behind the lens (Fig.

Vitreous Body

lens do not possess a blood supply.

these functions are important because the cornea and the

and the lens and removes the products of metabolism;

maintaining its optical shape. It also nourishes the cornea

wall of the eyeball by exerting internal pressure and thus

The function of the aqueous humor is to support the

the retina, with consequent blindness.

This can produce degenerative changes in

glaucoma.

called

aqueous humor results in a rise in intraocular pressure

Obstruction to the draining of the

canal of Schlemm.

thalmoscope.

is a nar-

The Lens

of the Eye

Eye Trauma

ing loss of sensation of the skin of the cheek and the gum on

such as golf balls, which can cause severe damage to the eye.

globe. The bony orbit provides no protection from small objects,

tennis balls, which tend to strike the orbital margin but not the

orbit, it is protected anteriorly only from large objects, such as

Although the eyeball is well protected by the surrounding bony

Careful examination of the eyeball relative to the orbital mar-

gins shows that it is least protected from the lateral side.

Blowout fractures of the orbital floor involving the maxil-

lary sinus commonly occur as a result of blunt force to the

face. If the force is applied to the eye, the orbital fat explodes

inferiorly into the maxillary sinus, fracturing the orbital floor.

Not only can blowout fractures cause displacement of the

eyeball, with resulting symptoms of double vision (diplopia),

but also the fracture can injure the infraorbital nerve, produc-

that side. Entrapment of the inferior rectus muscle in the frac-

ture may limit upward gaze.

Strabismus

Many cases of strabismus are nonparalytic and are caused

by an imbalance in the action of opposing muscles. This type

C L I N I C A L N O T E S

(continued)