The orbit is a pyramid-shaped cavity located in the skull that houses the eyeball and surrounding structures. It is comprised of four bony walls - the frontal, zygomatic, maxillary, and ethmoid bones. Within the orbit are six extraocular muscles that control eye movement: the superior and inferior rectus, medial and lateral rectus, and superior and inferior oblique muscles. These muscles originate from the back of the orbit and insert on the eyeball to produce actions like elevation, depression, adduction, and rotation. The orbit also contains nerves, vessels, fat and connective tissues that support eye function.

1. ORBIT
Dr.Prathap Kumar J

2. The Orbit

3. Sinuses exist in 4 Orbital Bones
• Air filled
• Mucosa lined
• Lighten bone
• Acustic
• Possible infection
site

4. a pyramid of four walls
that converge
posteriorly. The medial
walls of the right and
left orbit parallel and
are separated by the
nose.

5. The basic shape of the orbit is a
pyramid:
The medial walls are parallel
The depth is 1.5 x base

6. • In each orbit, the
lateral and medial walls
form an angle of 45
degrees, which results
in a right angle between
the two lateral walls.
The orbit is compared
to the shape of a pear,
with the optic nerve
representing its stem.

7. • volume of the adult
orbit :30 mL
• eyeball occupies only
about one-fifth of the
space. Fat and muscle
account for the bulk of
the remainder.

8. • The anterior limit of the
orbital cavity is the
orbital septum, which
acts as a barrier
between the eyelids
and orbit

9. • frontal sinus above, the
maxillary sinus below,
and the ethmoid and
sphenoid sinuses
medially.

10. • The thin orbital floor is
easily damaged by
direct trauma to the
globe, resulting in a
"blowout" fracture with
herniation of orbital
contents into the
maxillary antrum.

11. • Infection within the
sphenoid and ethmoid
sinuses can erode the
paper-thin medial wall
(lamina papyracea) and
involve the contents of
the orbit.

12. • Defects in the roof (eg,
neurofibromatosis) may
result in visible
pulsations of the globe
transmitted from the
brain.

13. Orbital Walls

14. • The roof : frontal bone.
Posteriorly, the lesser
wing of the sphenoid
bone containing the optic
canal completes the roof.
• The lacrimal gland is
located in the lacrimal
fossa in the anterior
lateral aspect of the roof.

15. • The lateral wall is
separated from the roof
by the superior orbital
fissure, which divides the
lesser from the greater
wing of the sphenoid
bone. The anterior
portion of the lateral wall
is formed by the orbital
surface of the zygomatic
(malar) bone. This is the
strongest part of the bony
orbit.

16. • Suspensory ligaments,
the lateral palpebral
tendon, and check
ligaments have
connective tissue
attachments to the
lateral orbital tubercle.

17. • The orbital floor is
separated from the
lateral wall by the
inferior orbital fissure.
The orbital plate of the
maxilla forms the large
central area of the floor
and is the region where
blowout fractures most
frequently occur.

18. • The frontal process of
the maxilla medially and
the zygomatic bone
laterally complete the
inferior orbital rim. The
orbital process of the
palatine bone forms a
small triangular area in
the posterior floor.

19. • medial wall :
• ethmoid bone ;
lacrimal bone; The
body of the sphenoid (
most posterior aspect
of the medial wall).
the angula r process of
the frontal bone forms
the upper part of the
posterior lacrimal crest.

20. • The lower portion of the
posterior lacrimal crest is
made up of the lacrimal
bone. The anterior
lacrimal crest is easily
palpated through the lid
and is composed of the
frontal process of the
maxilla. The lacrimal
groove lies between the
two crests and contains
the lacrimal sac

22. Orbital Apex

23. • entry portal for all
nerves and vessels to
the eye and the site of
origin of all extraocular
muscles except the
inferior oblique.

24. • The superior
ophthalmic vein and the
lacrimal, frontal, and
trochlear nerves pass
through the lateral
portion of the fissure
that lies outside the
annulus of Zinn.
•

25. •
• The superior and
inferior divisions of the
oculomotor nerve and
the abducens and
nasociliary nerves pass
through the medial
portion of the fissure
within the annulus of
Zinn.
•

26. • The optic nerve and
ophthalmic artery pass
through the optic
canal, which also lies
within the annulus of
Zinn

29. LR
SO
IRIO
MR
SRLP
Identify the extra-ocular muscles.
Side view
Frontal views
Levator palpebrae
Superior oblique
Inferior rectus
Superior rectus
Lateral rectus (cut)
Inferior oblique
Medial rectus
Optic nerve
LP
SR
SO
IO
IR
MR
LRLR
SO
IRIO
MR
SRLP

30. Clinical Anatomy
• Muscular Anatomy:
– Inferior Rectus
– Superior Rectus
– Medial Rectus
– Lateral Rectus
– Inferior Oblique
– Superior Oblique

31. Clinical Anatomy
• Eye Movement Terminology:
– Duction – movement of one eye by itself
– Version – movement of the 2 eyes in the same direction
– Adduction – eye looks toward the nose
– Abduction – eye looks toward the ear
– Dextroversion – both eyes look to the right
– Levoversion – both eyes look to the left
– Supraversion – both eyes upgaze
– Infraversion - downgaze

32. Clinical Anatomy
• Medial Rectus:
– Strongest of the extra-
ocular muscles
– Most mass of EOMs
– Most anterior insertion
(extra leverage)
– Action – Adduction
(eyes move towards the
nose)
• Lateral Rectus:
– Action - Abduction

33. Clinical Anatomy
• Superior Rectus:
– Action – elevation,
upward rotation
• Rotation – angles
nasally toward site of
origin
– Tendon of the Superior
Oblique muscle passes
underneath the SR

34. Clinical Anatomy
• Inferior Rectus:
– Action – depression,
downward rotation,
adduction

35. Clinical Anatomy
• Superior Oblique:
– Keeps the eyeballs level
as the head tilts
– Longest of the EOMs
– Passes through a “pully”
called the trochlea
• Redirects the action
– Action:
• Abduction of globe
• Depression of globe
• Rotation of globe

36. Clinical Anatomy
• Inferior Oblique:
– Passes underneath the
inferior rectus
– Action:
• Elevation of globe
• Adduction of globe
• Rotation of globe
• Keeps the eyeballs
level as the head tilts

37. Muscle Action Origin Insertion Innervation
Inferior
Rectus
Depression,
adduction
extrosion
From a tendinous
ring on posterior
aspect of orbit
Middle of the
inferior aspect of
anterior globe
Oculomotor
Superior
Rectus
Elevation,
adduction
Intorsion
From a tendinous
ring on posterior
aspect of orbit
Middle of the
superior aspect of
anterior globe
Oculomotor
Medial
Rectus
Medial Rotation
(Adduction)
From a tendinous
ring on posterior
aspect of orbit
Middle of the
superior aspect of
anterior globe
Oculomotor
Lateral
Rectus
Lateral Rotation
(Abduction)
From a tendinous
ring on posterior
aspect of orbit
Middle of the
superior aspect of
anterior globe
Abducens
Inferior
Oblique
Abduction,
Elevation of globe,
Rotation of globe
when abducted
extrosion
From the periosteum
of the maxilla
Posterio- superior
quadrant of the
globe
Oculomotor
Superior
Oblique
Abduction,
Depression of
globe, Intorsion
Greater wing of the
sphenoid
Posterio- superior
quadrant of the
globe
Trochlear