DISSECTION 6
The Orbital Contents
References: M1 63, 893-907; 909-914, N 80-86, 98, 115; N 84-90, 104, 121; R 70-71, 130-140
AT THE END OF THIS LABORATORY PERIOD YOU WILL BE RESPONSIBLE FOR
THE IDENTIFICATION AND DEMONSTRATION OF THE STRUCTURES LISTED
BELOW:
l. Muscles: levator palpebrae superioris, the superior oblique, the superior rectus, medial rectus,
inferior rectus, lateral rectus, inferior oblique and ciliary muscles.
2. Fasciae: the trochlea, the anulus tendineus, and the bulbar fascia.
3. Nerves: primary branches of the ophthalmic division of the trigeminal nerve (lacrimal, frontal,
nasociliary) within the orbit as well as the oculomotor, trochlear, abducens, and optic nerves,
ciliary ganglion.
4. Vessels: ophthalmic artery and superior ophthalmic vein.
YOU SHOULD ALSO BE ABLE TO DO THE FOLLOWING THINGS:
1. State the actions of each of the muscles listed above when the eyeball is in the primary position
and tell how you would test for weakness or paralysis of each muscle.
2. Identify and demonstrate the following structures on the bovine eyeball: cornea, sclera,
limbus, choroid, ciliary body, ciliary muscle, iris, retina, ora serrata, anterior chamber,
posterior chamber, lens, vitreous body.
3. Diagram the ciliary ganglion, its nervous connections and the fibers they contain. List the
structures innervated by the neurons within the ganglion. State the location of the
preganglionic neurons whose axons terminate in the ciliary ganglion.
4. Identify structures on cross sectional drawings, C-T scans, or tissue sections through the orbit.
Before beginning today's dissection, use
your ophthalmoscope to examine the fundus
of your lab partner's eye. Be sure to note the
optic disk and look for branches of the central
retinal artery and the associated veins.
Identify again the FRONTAL NERVE and its
branches and the LEVATOR PALPEBRAE
SUPERIORIS, SUPERIOR RECTUS and SUPERIOR
OBLIQUE MUSCLES. Again identify and preserve
the LACRIMAL NERVE. Find the TROCHLEAR
where it enters the superior oblique and
trace it posteriorly. Bone forceps may be used to
remove additional bone from the roof of the orbit
to allow exposure of the superior oblique and the
TROCHLEA, the pulley through which the superior
oblique tendon passes as it turns back toward its
insertion into the eyeball. (See A806, A809-810;
G7.37A, G7.36A2; N82; N86).
NERVE
Look for the SUPERIOR OPHTHALMIC
which is usually a large thin-walled
structure associated with branches of the
VEIN,
Dissection 6, The Orbital Contents
(A777; Gp647; N81;
N85). The two vessels are found in relation to the
superior oblique muscle in the anterior part of the
orbit. In its course through the orbit the superior
ophthalmic vein passes between the superior
rectus and the OPTIC NERVE and exits from the
orbit through the superior orbital fissure outside
of the ANULUS TENDINEUS (of Zinn), which is the
common tendinous origin of the four rectus
muscles (G7.40A; A809, 815; N80; N84).
OPHTHALMIC ARTERY
Identify and clean the LATERAL RECTUS
and its nerve, the ABDUCENS NERVE
(A805; G7.36A; N82; N86). (Be careful not to
disturb the orbital fat adjacent to the optic nerve
which contains the short ciliary nerves and ciliary
ganglion.) You may find it helpful as the
dissection proceeds to cut the lateral rectus at its
midpoint and to reflect the two parts of the
muscle. As the anterior half of the lateral rectus
is reflected toward the eyeball, note how it
becomes ensheathed with fascia that is continuous
with the BULBAR FASCIA on the eyeball.
(G7.39A; A816; N83; N87)
MUSCLE
Look on the inferior surfaces of the levator
palpebrae superioris and the superior rectus for
their nerves, which are branches of the
OCULOMOTOR NERVE. (A804; G7.36A; N82;
N86) Ask your lab partner to look up. What
happens to the upper lid? In addition to the
eyelid what other structure is elevated as the
pupil is turned upward? (See H818 and H33-21;
968; G7.39B).
The Ciliary Ganglion
In company with the ophthalmic artery and
the superior ophthalmic vein is the NASOCILIARY
NERVE (A805; G7.36A; N82; N86). Carefully
dissect along this nerve looking for small hairlike
branches which pass anteriorly to the back of the
eyeball and to the ciliary ganglion. The CILIARY
GANGLION is about the size of a pin head and is
located just lateral to the optic nerve in the
posterior half of the orbit. It may be found in
three different ways by finding the nerves which
connect it to other structures. Look at A804, 805,
807 or Gp649 or N82, N86 and note that the
ciliary ganglion is connected to the nasociliary
Page 2
nerve by the communicating branch just referred
to. The ganglion is also connected with the
inferior division of the oculomotor nerve. The
latter connection may be found by following the
branches of the oculomotor nerve innervating the
superior rectus and levator palpebrae superioris
back to the main trunk of the oculomotor nerve.
Then identify the inferior branches of the nerve
which supply the medial rectus, the inferior rectus
and the inferior oblique. The oculomotor root of
the ciliary ganglion comes from the branch to the
inferior oblique muscle. Finally, there are a
number of delicate filaments, the short ciliary
nerves, which pass from the ganglion to the
posterior surface of the sclera along the lateral
aspect of the optic nerve. These nerves may be
identified in the fat surrounding the optic nerve
and traced back to the ganglion. Be sure that you
know that the short ciliary nerves contain
postganglionic parasympathetic fibers from nerve
cells in the ciliary ganglion. These fibers supply
the ciliary muscle (causing accommodation of the
lens) and the sphincter pupillae. The oculomotor
root of the ciliary ganglion contains preganglionic
parasympathetic fibers from the nucleus of
Edinger-Westphal. What other types of fibers are
found in the short ciliary nerves? (See N115;
N121)
When the ciliary ganglion and its
connections have been secured, remove the
remaining orbital fat from the INFERIOR
OBLIQUE, the INFERIOR RECTUS, and the
MEDIAL RECTUS and demonstrate their insertions
and their origins. Note that the inferior oblique
can be best approached anteriorly by making a
small incision in the lower eyelid near the floor of
the orbit.
Dissection of the Beef Eye
Remove most of the fat, fascia, and muscles
from the beef eye. Do not be concerned with the
identification of the extraocular muscles, as the
arrangement is quite different from the human
eye. Carefully cut through the coats of the eyeball
so as to separate them into anterior and posterior
halves. Cut into the VITREOUS BODY as little as
possible. Identify the SCLERA, the CHOROID, and
the RETINA. The shiny greenish layer is the
tapetum, a reflective layer not found in the human
Dissection 6, The Orbital Contents
Page 3
eye. Gently manipulate the vitreous body and the
LENS to demonstrate the zonular fibers
(suspensory ligament of the lens). Now, remove
the CORNEA by making an incision at the
LIMBUS, and push the IRIS and the CILIARY
BODY away from the sclera. Note that the cavity
of the eyeball in front of the lens is divided by the
iris into an ANTERIOR CHAMBER and a
POSTERIOR CHAMBER. The white line on the
external surface of the ciliary body is the CILIARY
MUSCLE (A817, 820) and the jagged peripheral
margin is the ORA SERRATA.
____________________________________________________________________________________
STUDY QUESTIONS
1.
Name the coats of the eyeball.
1.
The outer fibrous coat, the middle vascular
coat, and the retina.
2.
What are the subdivisions of the
fibrous coat?
2.
The fibrous coat is made up of the cornea and
sclera.
3.
What are the subdivisions of the
vascular coat (also called the uveal tract)?
3.
The vascular coat is divided into the iris, the
ciliary body, and the choroid.
4.
What are the subdivisions of the retina?
4
The retina is divided into three parts
corresponding to the parts of the vascular coat
which they line. They are the iridial retina, the
ciliary retina, and the pars optica of the retina.
5.
What term is given to the anterior limit
of the pars optica retinae?
5.
The ora serrata.
6.
Are the ciliary and iridial parts of the
retina sensitive to light?
6.
No.
7.
Where is there smooth muscle in the
eyeball?
7.
The ciliary muscle in the ciliary body and the
sphincter pupillae and the dilator pupillae muscles
in the iris are smooth muscle.
8.
What is the nerve supply to these
muscles?
8.
The ciliary muscle and the sphincter pupillae
muscle are innervated by postganglionic efferent
fibers from the ciliary ganglion. The dilator of the
pupil is innervated by postganglionic fibers from
the superior cervical ganglion.
9.
Locate the cell bodies of the preganglionic
fibers to the ciliary ganglion.
9.
Nucleus of Edinger-Westphal.
10. How do these fibers reach the ciliary
ganglion?
10. Through the oculomotor nerve and the motor root
of the ciliary ganglion.
Dissection 6, The Orbital Contents
Page 4
11. Locate the cell bodies of the preganglionic
fibers to the superior cervical ganglion.
11. Intermediolateral cell column of the upper
thoracic spinal cord.
12. What other smooth muscle in the orbit is
supplied by postganglionic fibers from the
superior cervical ganglion?
12. The superior tarsal muscle in the upper lid.
This is the smooth muscle part of the levator
palpebrae superioris.
13. Draw and label a diagram showing the
route taken by the aqueous humor from
the point of its secretion until it leaves the
anterior chamber.
13.
14. Trace the route of the circulation of the
aqueous humor.
14. Secreted by the epithelium of the ciliary processes
posterior chamber
pupil
anterior
chamber
trabecular meshwork
canal of
Schlemm.
15. What is glaucoma?
15. Glaucoma is a condition of increased intraocular
pressure leading to optic nerve damage and
defects in the visual fields. It is usually the
result of some imbalance in the production and
absorption of the aqueous humor.
16. What are the functions of the
aqueous humor?
16. The aqueous humor helps to maintain intraocular
pressure and helps to nourish the lens and the
cornea.
17. What is accommodation?
17. Accommodation is the process by which the
refractive power of the lens is increased so that
near objects may be sharply focused on the retina.
It is caused by an increase in thickness and
curvature of the lens which in turn is the result of
contraction of the ciliary muscle.
18. How does contraction of the ciliary
muscle result in rounding up of the lens?
18. When the ciliary muscle is relaxed, the lens is
flattened by the tension of the ciliary zonule
(suspensory ligaments of the lens). Contraction of
the ciliary muscle causes the zonule to relax. With
relaxation of the zonule the lens is no longer
subject to the flattening force and its own natural
elasticity causes it to become more spherical.
Dissection 6, The Orbital Contents
Page 5
19. How is the retina supplied with blood?
19. The retinal blood supply is derived from the
ophthalmic artery in two ways. The central artery
of the retina supplies the inner layers of the retina,
while the outer layers of the retina are supplied by
diffusion from the choroid.
20. How does most of the blood which
enters the vascular coat leave the
eyeball?
20. Through the vorticose veins which drain into the
ophthalmic veins. These veins in turn drain into
the cavernous sinus.
21. What are the refractive media of the
eyeball?
21. The refractive media are the cornea, the aqueous
humor, the lens, and the vitreous body.
22. What separates the anterior and posterior
chambers of the eye?
22. The iris separates the anterior and posterior
chambers, which, therefore, communicate through
the pupil.
23. What is the fundus of the eye?
23. The fundus is the interior back wall of the eyeball.
24. What is the optic disc (papilla)?
24. The optic disc is a whitish circle in the retina
about l.5 mm in diameter which is located just
medial to the posterior pole of the eyeball. It is
produced by the optic nerve as it leaves the retina.
The central artery and central vein of the retina
enter and leave the retina at the optic disc.
25. What is the macula?
25.
What is the fovea centralis?
26. Label as indicated?
The macula is the area of central vision located
directly at the posterior pole of the eyeball and
just lateral to the optic disc.
The fovea centralis is depression in the center of
the macula where the retina is thinnest and vision
is most acute.
26.
a.
fovea centralis
b.
sclera
c.
choroid
d.
retina
e.
vitreous body
f.
posterior chamber
g.
anterior chamber
h.
lens
i.
iris
j.
cornea
k.
iridocorneal angle
l.
ciliary body (ciliary muscle)
Dissection 6, The Orbital Contents
Page 6
27. What is the usual anatomical explanation
for the development of papilledema or
"choked disc"?
27. The optic nerve is surrounded by the meningeal
sheaths of the central nervous system. Increased
intracranial pressure can be transmitted through
the cerebrospinal fluid to the subarachnoid space
surrounding the optic nerve. The central vein of
the retina passes out of the retina through the
optic nerve and passes through the meningeal
sheaths. Increased pressure in the subarachnoid
space thus results in interference with normal
venous drainage of the retina and edema of the
optic nerve. The optic disc becomes elevated and
the retinal veins become markedly dilated.
28. Locate two separate nerve lesions,
each of which can result in ptosis of
the upper lid.
28. Complete ptosis can be produced by injury to the
oculomotor nerve or to the part of it that supplies
the levator palpebrae superioris muscle. Partial
ptosis can be produced by damage to the cervical
sympathetic trunk or interruption anywhere else of
the preganglionic fibers to the superior cervical
ganglion or the postganglionic fibers which
supply the superior tarsal muscle.
29. What is Horner's syndrome?
29. Horner's syndrome is ptosis, pupillary
constriction, vasodilation, and lack of sweating
on one side of the head and neck.
What causes it?
It is the result of damage to the cervical
sympathetic trunk.
30. Locate the preganglionic and
postganglionic nerve cells involved
in the secretion of tears.
30. The preganglionic nerve cell is located in the
superior salivatory nucleus. It leaves the brain in
the seventh cranial nerve. The postganglionic
neuron is located in the pterygopalatine ganglion.
31. Name the extraocular muscles and
give their nerve supply.
31. Levator palpebrae superioris –oculomotor
Superior rectus--oculomotor
Medial rectus--oculomotor
Inferior rectus--oculomotor
Lateral rectus--abducens
Superior oblique--trochlear
32. What are the axes about which
the eyeball moves? What are the
movements about each axis?
32. Vertical axis--adduction and abduction, transverse
axis—elevation and depression, anterior—
posterior axis--medial rotation and lateral rotation
(intorsion and extorsion).
33. Which of the rectus muscles have
only one action?
33. Medial rectus--adduction
Lateral rectus--abduction
Dissection 6, The Orbital Contents
Page 7
34. What is the position of rest for
the eyeball?
34. The position of rest or the primary position of the
eyeball is the position with the pupil directed
straight ahead.
35. In the position of rest, what is the primary
action of the following muscles?
35.
Superior rectus
Inferior oblique
Inferior rectus
Superior oblique?
36. In the position of rest, what is the secondary
action of each of the following muscles?
Superior rectus - elevation
Inferior oblique - elevation
Inferior rectus - depression
Superior oblique - depression
36.
Superior rectus – adduction
Inferior rectus – adduction
Superior oblique – abduction
Inferior oblique – abduction
Superior rectus,
Inferior rectus
Superior oblique,
Inferior oblique?
37. Draw simple diagrams showing which
muscles act on the vertical axis when
the eyeball is in the position of rest.
(See G7-49)
37.
38. Draw simple diagrams showing which
muscles act on the horizontal axis when
the eyeball is in the position of rest.
(See G7.50)
38.
39. In what position could the eyeball be
placed to eliminate the secondary action
of the superior and inferior recti?
39. When the eye is abducted, the line of all of the
superior and inferior recti is directly along the
visual axis, and their secondary action, adduction,
is lost.
40. In what position could the eyeball be
placed to eliminate the secondary action
of the superior and inferior oblique muscles?
40
When the eye is adducted, the line of pull of both
oblique muscles coincides with the visual axis,
and their secondary action, abduction, is lost.
Dissection 6, The Orbital Contents
Page 8
41. How then could you test for weakness
or paralysis of one of the extraocular
muscles?
41. By having the patient position his eye so that the
muscle being tested is lined up with the visual axis
and then having him move his eye in the direction
that only that muscle can move it.
42. For example, how would you test for
weakness of the superior rectus?
42. Have the patient elevate his eye from the abducted
position.
43. How would you test for weakness of the inferior rectus, the superior oblique, or the inferior oblique?
44. When you test the right superior rectus, what muscle in the left eye is also tested?
45. What would be the effect of loss of the oculomotor nerve? Of loss of the abducens nerve?
46. What is a cataract?
47. How do you spell (ophthalmic, opthalmic)?
(acomodate, accomodate, accommodate)?
48. What is the basic structural defect in presbyopia?, myopia?, hypermetropia?, astigmatism?
49. Name two ways by which blindness could be caused by interference with the retinal blood supply.
Dissection 6, The Orbital Contents
Page 9
50. Label the diagram below and add the afferent, preganglionic efferent, and postganglionic efferent nerve cells
and fibers which supply structures in the eyeball.
LJ:bh
revised 06/18/09