The Eye and Orbit
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temporomandibular joint | Main Anatomy
Index | The nasal cavity
Last updated 30 March 2006
The Eye and Orbit
- The orbit (eye socket) appears as a bony recess in the
skull when it is viewed from anteriorly.
- It almost surrounds the eye and their associated muscles,
nerves and vessels, together with the lacrimal apparatus.
- The orbit is shaped somewhat like a four-side
pyramid lying on its side, with its apex
pointing posteriorly and its base anteriorly.
- The supraorbital margin
is composed entirely of the frontal bone.
- At the junction of its medial and middle thirds is the supraorbital foramen
(sometimes a notch), which transmits the supraorbital
nerves and vessels.
- The lateral orbital margin
is formed almost entirely of the frontal process of the
- The infraorbital margin
is formed by the zygomatic bone laterally and the maxilla
- The medial orbital margin
is formed superiorly by the frontal bone and inferiorly
by the lacrimal crest of
the frontal process of the maxilla.
- This margin is distinct in its inferior half only.
Walls of the Orbit
- Each orbit has four walls:
superior (roof), medial, inferior (floor) and lateral.
- The medial walls of the orbit are almost
parallel with each other and with the superior
part of the nasal cavities separating them.
- The lateral walls are approximately
at right angles to each other.
Superior Roof of the Orbit (p. 703)
- The superior wall or roof of the
orbit is formed almost completely by the orbital plate of the frontal bone.
- Posteriorly, the superior wall is formed by the lesser
wing of the sphenoid
- The roof of the orbit is thin, translucent, and gently
arched. This plate of bone separates the orbital cavity
and the anterior cranial fossa.
- The optic canal is
located in the posterior part of the roof.
Medial Wall of the Orbit (p. 703)
- This wall is paper-thin and is formed by the orbital lamina or lamina papyracea of the
ethmoid bone, along with contributions from the frontal,
lacrimal, and sphenoid bones (L. papyraceus,
"made of papyrus" or parchment paper).
- There is a vertical lacrimal groove
in the medial wall, which is formed anteriorly by the
maxilla and posteriorly by the lacrimal bone.
- It forms a fossa for the lacrimal
sac and the adjacent part of the nasolacrimal duct.
- Along the suture between the ethmoid and frontal bones
are two small foramina; the anterior
and posterior ethmoidal foramina.
- These transmit nerves and vessels of the same name.
Inferior Wall of the Orbit (p. 703)
- The thin inferior wall of the orbit or the floor is formed mainly by the
orbital surface of the maxilla and partly by the
zygomatic bone, and orbital process of the palatine bone.
- The floor of the orbit forms the roof
of the maxillary sinus.
- The floor is partly separated from the lateral wall of
the orbit by the inferior orbital
Lateral Wall of the Orbit (pp. 703, 705)
- This wall is thick, particularly its posterior part,
which separates the orbit from the middle cranial fossa.
- The lateral wall is formed by the frontal process of the zygomatic bone and the greater
wing of the sphenoid bone.
- Anteriorly, the lateral wall lies between the orbit and
the temporal fossa.
- The lateral wall is partially separated from the roof by
the superior orbital fissure.
of the Orbit
Levator Palpebrae Superioris Muscles (p. 715)
- This is a thin, triangular muscle that elevates the upper
- It is continuously active except during sleeping and when
the eye is closing.
- Origin: roof of orbit, anterior to the optic canal.
- Insertion: this muscle fans out into a wide aponeurosis
that inserts into the skin of the upper eyelid. The
inferior part of the aponeurosis contains some smooth
muscle fibres that insert into the tarsal
- Innervation: the superior fibres are innervated by the oculomotor
nerve (CN III), and the smooth muscle component is
innervated by fibres of the cervical sympathetic
trunk and the internal carotid plexus.
Illnesses involving the Levator Palpebrae
Superioris (p. 715)
- In third nerve palsy,
the upper eyelid droops (ptosis) and cannot be raised
- This results from damage to the oculomotor nerve (CN
III), which supplies this muscle.
- If the cervical sympathetic trunk is interrupted, the
smooth muscle component of the levator palpebrae
superioris is paralysed and also causes ptosis.
- This is part of Horner's syndrome.
Rectus Muscles (p. 715)
Click here for a
schematic of the attachment of the muscles to the eye.
- There are four rectus muscles (L. rectus,
straight), superior, inferior, medial and lateral.
- These arise from a tough tendinous cuff, called the common tendinous ring, which
surrounds the optic canal and the junction of the
superior and inferior orbital fissures.
- From their common origin, these muscles run anteriorly,
close to the walls of the orbit, and attach to the
eyeball just posterior to the sclerocorneal
- The medial and lateral rectus muscles attach to the
medial and lateral sides of the eyeball respectively, on
the horizontal axis.
- However, the superior rectus attaches to the anterosuperior aspect of the medial
side of the eyeball while the inferior rectus attaches to
the anteroinferior aspect of the
medial side of the eye.
Superior Oblique Muscle (p. 715)
- This muscle arises from the body of the sphenoid bone,
superomedial to the common tendinous ring.
- It passes anteriorly, superior and medial to the superior
and medial rectus muscles.
- It ends as a round tendon that runs through a pulley-like
loop called the trochlea
- After passing though the trochlea, the tendon of the
superior oblique turns posterolaterally and inserts into
the sclera at the posterosuperior
aspect of the lateral side of the eyeball.
Inferior Oblique Muscle (p. 715)
- This muscle arises from the maxilla in the floor of the
- It passes laterally and posteriorly, inferior to the
inferior rectus muscle.
- It inserts into the sclera at the posteroinferior
aspect of the lateral side of the eyeball.
Nerve Supply of the Muscles of the Orbit (pp.
- The trochlear nerve supplies the superior oblique muscle.
- The abducent nerve supplies the lateral rectus muscle.
- The oculomotor nerve supplies everything else.
- A mnemonic that is used is this formula for this strange
of the Muscles (pp. 716-7)
- The six muscles rotate the eyeball in the orbit around
three axes (sagittal, horizontal and vertical).
- The action of the muscles can be deduced by their site of
insertion on the eyeball.
on the Eyeball
||Elevates, adducts, and
||Depresses, adducts, and
||Depresses, abducts, and
||Elevates, abducts, and
- The orbital contents are supplied chiefly by the ophthalmic artery.
- The infraorbital artery,
the continuation of the maxillary, also contributes blood
to this region.
- Venous drainage is through the superior orbital fissure
to enter the cavernous sinus.
Ophthalmic Artery (p. 716)
- This artery arises from the internal
carotid artery as it emerges from the cavernous
- It passes through the optic foramen within the dural
sheath of the optic nerve and runs anteriorly, close to
the superomedial wall of the orbit.
Central Artery of the Retina (pp. 716-7)
- This is the one of the smallest but most important
branches of the ophthalmic artery.
- It arises inferior to the optic nerve until it approaches
- It then pierces the optic nerve and runs within it to
emerge through the optic disc.
- The central artery of the retina spreads over the
internal surface of the retina and supplies it.
Superior Ophthalmic Vein (p. 719)
- The superior ophthalmic vein
anastomoses with the facial vein.
- It has no valves and blood can flow in either direction.
- It crosses superior to the optic nerve, passes through
the superior orbital fissure and ends in the cavernous
Inferior Ophthalmic Vein (p. 719)
- This begins as a plexus on the floor of the orbit.
- It communicates with the inferior orbital fissure with
the pterygoid plexus,
crosses inferior to the optic nerve, and ends in either
the superior ophthalmic vein or the cavernous sinus.
The Optic Nerve
Click here to go
to the optic nerve entry in cranial nerves.
- This is the second cranial nerve (CN II) and is the nerve of sight.
Click here for a diagram
on entry of nerves of the orbit into the orbital cavity.
Click here for a
diagram on the branches of the ophthalmic nerve (CN V1)