Download The Orbit and the Eye, Moore 4th ed

The Orbit and the Eye, Moore 4th ed. pp. 899-916
A. Overview of the Orbit
1st. It is the cavity in the facial skeleton that holds the eye. The apex of the
triangle is to the back, the base in front. The periosteum of the orbit is called
the periorbita, and is the fascia of the eyeball. It is continuous with the dura at
the optic canal and the superior orbital fissure. Through the inferior orbital
fissure, it is continuous with the external skull periosteum.
2nd. Parts of the orbit:
1. Superior wall, or roof: formed by the frontal bone, and in the
back part, by part of the sphenoid bone. There is a fossa for the
lacrimal gland and a hole in the sphenoid bone, the lacrimal
foramen.
2. Medial wall: is mostly made of the ethmoid bone, but most
medially, also the lacrimal bone, and above, the frontal bone. The
medial wall is very thin and has a lacrimal fossa for the lacrimal
sac. The two sides are separated by the ethmoidal sinuses and the
upper nasal cavity.
3. Inferior wall: is mostly the maxilla, but also the zygomatic and
palatine bones. Between the inferior and lateral wall, there is a
fissure, the inferior orbital fissure from the bottom edge of the
sphenoid bone.
4. Lateral wall: in front, is the zygomatic bone, and toward the
back of the head is the greater wing of the sphenoid bone.
5. Apex of the orbit: the optic canal is the “tip” of the triangle. The
actual hole is in the sphenoid bone. The superior orbital fissure is
to the outside of it
B. Eyelids and the Lacrimal Apparatus
1st. Eyelids
1. Are thin skin on the outside and lined on the inside by palpebral
conjunctiva, which, at the edges, folds onto the eyeball to become
the bulbar conjunctiva. The bulbar conjunctiva is thin and
transparent and is loose over the sclera, is attached to the
periphery of the cornea. The folds between the two types are the
conjunctival fornices (sup. and inf.).
2. The eyelids have tarsal plates which are thickenings of CT that
help them hold their shape, and are deep to fibers of orbicularis
oculi. These plates contain tarsal glands that secrete a lubricating
lipid. It also shields against tears absorbing too much into the
tissue. (When you cry a lot, it can’t do the job, so the fluid goes in
to the tissue and your eyes swell.)
3. The eyelashes have sebaceous glands called ciliary glands.
4. Ligaments and dividers
One. Medial palpebral ligament connects the tarsal
plates and some fibers of orbicularis oculi to the medial
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edge of the orbit.
Two. Lateral palpebral ligament does the same on the
lateral side, but only to the tarsal plates, not the
muscle.
Three. The orbital septum is a membrane from the tarsal
plates to the orbit all the way around the top or bottom
part of the eyelid/orbit that is joined to the periosteum
that contains fat and blocks the spread of infection.
2nd. Lacrimal Apparatus
1. Lacrimal glands secrete the fluid and are found in the
aforementioned fossae for the lacrimal glands, which is upper and
outside in the orbit. It has superior and inferior parts, divided by
the lateral end of the tendon of levator palpebrae superioris.
2. Lacrimal ducts move the fluid to the eye. There can be up to
twelve, and they open into the superior conjunctival fornix which
is the line where the conjunctiva folds onto the eye. The
conjunctival sac is the space between the palpebral and bulbar
parts.
3. The inner corner of the eye collects liquid (where you see tears
“well up”) and is called the lacrimal lake. The punctum is the little
hole dot you see at the inner corner of the eye. It drains tears into
the lacrimal canaliculi , which drain into the lacrimal sac (the
bulge under the punctum) and then into the nasal cavity through
the nasolacrimal duct. (Weird, you think you cry from the inside
but actually it’s from the outside of the eye inward, where tears
collect.)
4. Innervation of the system is by CN VII which sends
parasympathetic and sympathetic signals
One. The parasympathetic path is through the greater
petrosal nerve and the nerve of the pterygoid canal, to
the pterygopalatine ganglion to synapse with the postganglionic fibers. This causes production and release of
fluid.
Two. The sympathetic system causes vasoconstriction,
and they come from the superior cervical ganglion
through the carotid plexus, joining the deep petrosal
nerve then follow with the above.
Three. The zygomatic nerve brings both types of
innervation as well, by way of the ophthalmic nerve.
C. Orbital Contents
1st. Outer fibrous layer of the eyeball
1. Sclera - the opaque part covering the eyeball except for a little bit
at the front. It is the white of the eye.
2. Cornea - the transparent part of the coat covering the front 1/6th
of the eyeball.
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2nd. Middle Vascular Layer of the eyeball
1. Choroid - just interior to the sclera, a vascular layer that ends in
the front as the ciliary body. It is separable from the retina. The
ciliary body is muscular and vascular and has ciliary processes in
front that secrete the aqueous humor. The aqueous humor fills the
following spaces:
One. Anterior chamber - between the cornea and the
iris/pupil.
Two. Posterior chamber - between the back of the
iris/pupil and the lens.
2. Iris - lies on the lens and is the contractile diaphragm around the
pupil. The two muscles controlling the size of the pupil are the
dilator pupillae and the sphincter pupillae (parasympathetic).
The pupillary light reflex involves CN II and III.
3rd. Inner Layer of the Eyeball (retina)
1. Optic part
One. Neural layer and pigment layer
Two. Continued anteriorly as the ciliary and iridial parts
of the retina.
2. Fundus - The back of the eye, containing the optic disk, which is
the opening for the optic nerve to enter the eyeball. It, along with
the macula lutea form the blind spot. The is the specialized area
dense in cones and surrounds the fovea, the center of it, and the
most acute visual spot (no capillaries).
3. Misc. notes
One. The functional part of the retina stops at the ora
serrata which is just behind the ciliary body.
Two. The retina is supplied by the central artery and
central vein of the retina except for the rods and cones,
which are supplied by the choroid layer.
4th. Refractive Media of the Eye
1. Cornea - is the outer fibrous clear part of the eyeball. It refracts
light and is sensitive to touch. It has no blood vessels, getting
nutrients from the aqueous humor and somewhat absorbing
oxygen from the air.
2. Aqueous Humor - the fluid in the anterior and posterior
chambers, produced by the ciliary processes, drains into the Canal
of Schlemm.
3. Lens - sits in a fibrous capsule which is anchored by the
suspensory ligament of the lens to the ciliary body in front and by
fibers to the ciliary processes. It focuses by being pulled by the
fibers which are attached to the ciliary muscle in the ciliary body.
It naturally is pulled into far vision, but parasympathetic
stimulation contracts the ciliary body and lets the lens fold into
near vision. Therefore, in the absence of stimulus the eye is set to
far vision (“relax your eyes” like those stupid 3D pictures).
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4. Vitreous Humor - the watery fluid behind the lens in the vitreous
body, which is a mesh of jelly. Its pressure holds the retina down
and supports the lens.
D. Muscles of the Orbit
1st. Levator Palpebrae Superioris lifts the superior eyelid and is fan-shaped into
where it merges with an aponeurosis in the tarsal plate. Works opposite
orbicularis oculi. (Oculomotor nerve)
2nd. Recti Muscles arise from a fibrous ring, the common tendinous ring which
runs around the optic canal. (They fan out and around the eyeball.) They
attach to the sclera on the anterior part.
1. Medial Rectus Muscles obviously pull the eye inward.
Oculomotor nerve
2. Lateral Rectus Muscles obviously pull the eye sideways.
Abducent nerve
3. Superior Rectus Muscle pulls the eye upward and inward (look
up). Oculomotor nerve
4. Inferior Rectus Muscles pull the eye down and inward. (look
down). Oculomotor nerve
3rd. Oblique Muscles
1. Superior oblique comes from the body of the sphenoid bone,
passes through a tendon that bends it, and then goes into the
sclera. It puts the eye outward and downward (diagonal to the
outer corner). Trochlear nerve
2. Inferior Oblique - runs from the floor of the orbit to the sclera
and pulls the eye diagonally outward and upward. Oculomotor
nerve.
A note: eye motion
Abduction is to the side, while Adduction is to the center.
Depression is down, while elevation is up.
If we go around the eye, starting at the middle and going upward and outward (which is
clockwise on one side and counterclockwise on the other), the muscles controlling
movement to that direction are: MR, SR, IO, LR, SO, IR. This does not help the
attachments, however, either to the eye or to the tendon ring.
The nerves are: oculomotor moves everything except two: the abducens nerve moves the
lateral rectus, which is the abducer (duh), and the trochlear nerve moves the superior
oblique because it does not emerge from the central tendon like the others, so its nerve is
different.
4th. Fascial Sheath of the Eyeball
1. It wraps the eyeball from the optic nerve to the cornea.
2. The tendons of the muscles enter it and reflect. (?)
3. Ligaments - (badly explained, find another book)
One. The medial and lateral rectus muscles expand into
triangular sheaths that are called medial and lateral
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check ligaments that attach to the lacrimal (medial)
and zygomatic (lateral) bones. This limits how far you
can roll the eye inward and outward.
Two. The suspensory ligament comes from the check
ligaments blending with the fascia of inferior rectus
and inferior oblique.
E. Innervation of the Orbit
1st. The optic nerve supplies vision, of course.
2nd. CN III, Oculomotor, supplies levator palpebrae superioris, superior rectus,
medial rectus, inferior rectus, and inferior oblique.
3rd. CN IV (trochlear, remember rye looking up) supplies superior oblique.
4th. CN VI, Abducens, supplies lateral rectus. (Think, a child abductor is a
sneaky guy, he’s always sneaking looks to the side.)
5th. CN V1 (Ophthalmic) passes through the sup. orbital fissure to supply some
of the orbit.
6th. The Lacrimal Nerve comes from the wall of the cavernous sinus to the gland,
conjunctiva, and skin of the eyelid. With it run CN V2 which from the
zygomatic part brings the secretory fibers.
7th. The frontal nerve divides into supraorbital and supratrochlear.
8th. The nasociliary nerve is the sensory nerve to the eye.
1. It gives off the infratrochlear nerve, to the eyelids, conjunctiva,
skin of the nose, and lacrimal sac.
2. It gives off the ethmoidal nerves to the mucous membranes of
the ethmoid and sphenoid sinuses and nasal cavities.
9th. The ciliary ganglion is found in the gap between the optic nerve and lateral
rectus in the back of the orbit. It gives off:
1. The short ciliary nerves which carry parasympathetic and
sympathetic to the ciliary body and iris.
2. The long ciliary nerves which are branches of CN V1 and carry
postsynaptic sympathetic fibers to dilator pupillae and afferents
from the iris and cornea.
F. Vasculature of the Orbit
1st. Arteries
1. Ophthalmic - comes off the internal carotid to cross optic
foramen to get to orbital cavity. Gives off, in order: (these are
probably too small to see and not important but I’m not sure)
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One. Posterior Ciliary - pierces near the optic nerve to
serve choroid and photoreceptors
Two. Anterior Ciliary - from muscular rectus branches of
ophthalmic artery, entering the sclera at the rectus
attachments and to the ciliary body and iris.
Three. Central artery of the retina - in dura of optic nerve
and runs with it, piercing it near the eye and fans out
over the retina, but does not supply the photoreceptors.
Four. Lacrimal - along top of lateral rectus to lacrimal
gland, conjunctiva, and eyelids
Five. Supraorbital - from supraorbital foramen to
forehead and scalp
Six. Posterior Ethmoid - through posterior ethmoidal
foramen to the ethmoidal cells
Seven. Anterior Ethmoid - through anterior ethmoidal
foramen to anterior cranial fossa - ethmoidal cells,
frontal sinus, nasal cavity, skin of nose.
Eight. Dorsal Nasal - dorsal part of nose
Nine. Ends as Supratrochlear - supraorbital margin to
forehead and scalp.
2. Maxillary artery gives off infraorbital, which runs down
infraorbital groove to face.
2nd. Veins of the Orbit
1. Superior and inferior ophthalmic veins go through the superior
orbital fissure and drain to the cavernous sinus.
2. Central vein of the retina goes either directly into cavernous
sinus or through one of the ophthalmic veins.
3. Vorticose veins from the vascular layer pierce the sclera and
drain to the inferior ophthalmic vein.
4. Scleral venous sinus encircles the anterior chamber and collects
aqueous humor.
Internal Aspect of the Cranial Base, Moore 4th ed. pp. 842-847
A. Anterior Cranial Fossa
1st. Formed by:
1. Frontal bone
2. Ethmoid bone
3. Body and lesser wings of Sphenoid bone
2nd. Details:
1. The orbital parts of the frontal bone suport the frontal lobes of the brain
and on the other side make the roof of the orbits. You can see the
orbital gyri left dents
2. Frontal crest is the midline - a bony point of the frontal bone.
One. The foramen cecum and crista galli (a ridge of bone) of the
ethmoid bone are in the groove.
Two. Along the sides, there are anterior and posterior ethmoidal
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foramina, which pass the vessels and nerves with the same
name.
Three. The cribriform plate of the ethmoid lies to the sides of the
crista galli. Holes in the plate let the olfactory nerves pass
to the olfactory bulbs.
B. Middle Cranial Fossa
1st. Borders:
1. Greater wings of sphenoid and squamous parts of temporal bones on
the sides.
2. Petrous parts of temporal bones in the back. The petrous crests are the
boundaries between the middle and posterior fossae.
3. Lesser wing of sphenoid in front.
2nd. The optic canals pass in the sphenoid bone.
3rd. Sella Turcica is a bony formation on the upper surface of the sphenoid bone. It
has the anterior and posterior clinoid processes as “corners.” (They are raised
parts of the sphenoid bone.)
1. Tuberculum sellae - is the olive shaped swelling in front of the
hypophyseal fossa
2. Hypophyseal fossa
3. Dorsum sellae - piece of bone of the sphenoid posterior and medial to
the posterior clinoid processes.
4th. Lesser wings of the sphenoid on the inside end in the anterior clinoid processes.
5th. There are four foramina that poke through the greater wing of the sphenoid
bone, making a C - shaped sweep:
1. Superior Orbital Fissure - between the two wings, most frontward. Lets
the ophthalmic veins and nerves to the orbit pass.
2. Foramen rotundum - is most medial, along the side of the hypophysial
fossa and lets the maxillary nerve (CN V2) pass.
3. Foramen ovale - is a little to the side of the rotundum. It opens into the
infratemporal fossa to let the mandibular nerve (CN V3) pass.
4. Foramen spinosum - more to the side. Lets the middle meningeal
vessels and meningeal branch of mandibular nerve through.
5. The foramen lacerum isn’t in the C-shape pattern, but a bit behind,
tucked at the corners of the posterior clinoid processes and is an
artifact in a dry skull but covered by cartilage in life. Some things
cross it, and a groove for the greater petrosal nerve extends outward
from it.
C. Posterior Cranial Fossa
1st. Contains in life:cerebellum, pons, medulla.
2nd. Boundaries:
1. Dorsum sellae in front
2. Petrous ridge and mastoid parts of temporal bone in the front laterally
3rd. The clivus is a groove running down the middle from the back of the dorsum
sellae and ending at the foramen magnum.
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4th. Behind the foramen magnum, there is a line, the internal occipital crest that
splits down the middle. In front of it are the cerebellar fossae. The crest ends in
the internal occipital protuberance
5th. There are grooves for the transverse sinus and the sigmoid sinus in the temporal
and occipital bones.
6th. The jugular foramen is at the base of the petrous ridge. It lets the sigmoid sinus
drain into and become the IJV, and also CN IX, X, and XI.
7th. The internal acoustic meatus is between the temporal and occipital bones, and
transmits the labyrinthine artery and facial and vestibulocochlear nerves.
8th. The hypoglossal canal is in the foramen magnum’s wall.
9th. The condylar canal is behind the condyles and lets a small vein pass to the
vertebral veins in the neck from the sigmoid sinus.
The Dural Sinuses, Moore 4th pp. 879-884
A. Dural Venous Sinuses
1st. They are endothelium lined spaces between the periosteal and meningeal layers
of the dura that collect blood from large veins from the surface of the brain and
they all eventually bring blood to the internal jugular.
2nd. Superior Sagittal Sinus is in the cerebral falx from the crista galli to the
internal occipital protuberance, where there is a confluence of sinuses (superior
sagittal, straight, occipital, and transverse). It receives superior cerebral veins
and communicates through lateral venous lacunae.
3rd. Arachnoid Granulations are folds of arachnoid that poke into the venous
sinuses and drain CSF. They may form pits in the bone.
4th. Inferior Sagittal Sinus runs in the bottom of the pit of the cerebral falx and
ends in the straight sinus.
5th. Straight Sinus is formed by the inferior sagittal sinus joining the great cerebral
vein. It joins the confluence of sinuses (continuation of inf. sag.)
6th. The Transverse Sinuses run from the confluence of sinuses around the back
of the head and upward and become the sigmoid sinuses as they get close to the
petrous ridges of the temporal bones.
7th. The Sigmoid Sinuses follow grooves in the temporal and occipital bones then
turn anteriorly and down to become the IJV after they cross through the jugular
foramen.
8th. Occipital Sinus runs in the cerebellar falx and ends at the top at the confluence
of sinuses. It gets some blood from the internal vertebral venous plexuses.
9th. Cavernous Sinus is along the sides of the sella turcica on the sphenoid bone.
The sellar compartments (one on each side) are really a plexus of small veins.
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1. They extend from the superior orbital fissure in the front to the apex of
the petrous part of the temporal bone in back.
2. They get blood from the ophthalmic veins, superficial middle cerebral
vein, and sphenoparietal sinus.
3. They communicate with each other through channels running in the
front and back of the pituitary, the intercavernous sinuses.
4. They drain backwards to the petrosal sinuses and emissary veins to the
pterygoid plexuses.
5. The internal carotid artery runs in the plexus, the carotid plexus of
sympathetic nerves, and CN VI.
6. The lateral wall of the cavernous sinus contains:
One. Oculomotor nerve
Two. Trochlear Nerve
Three. Trigeminal Nerve 1st part.
7. The Superior Petrosal Sinuses run from the back of the cavernous
sinus plexus to the transverse sinuses, meeting where they become
the sigmoid sinus. They lie in the cerebellar tentorium, which is
attached to the petrous ridge.
8. The Inferior Petrosal Sinuses begin at the same place, the back of
the cavernous sinuses, and run between the petrous part of the
temporal bone and the basilar part of the occipital bone and empty
into the origin of the IJV.
9. The Basilar Plexus connects the inferior petrosal sinuses and the
internal vertebral plexuses.
10th. Emissary veins connect the dural sinuses with external veins. Usually blood
flows from the brain outward.
1. The frontal emissary vein runs through the foramen cecum and
connects the superior sagittal sinus with the frontal sinus and nasal
cavity veins.
2. The parietal emissary vein passes through the parietal foramen (top of
head) to connect the sup. sagittal sinus to external veins of the scalp.
3. The mastoid emissary vein passes through the mastoid foramen and
connects the sigmoid sinus to either the occipital or posterior
auricular vein.
4. The posterior condylar emissary vein may exist, connecting the
sigmoid sinus through the condylar canal to the suboccipital plexus.
B. Vasculature of the Dura
1st. The middle meningeal artery branches from the maxillary artery and enters the
foramen spinosum where it runs sideways and forward, splitting into two
branches on the greater wing of the sphenoid.
1. Anterior branch runs above the pterion and curves toward the top of the
skull. It is susceptible to injury.
2. The posterior branch runs up and back over the back of the skull.
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2nd. Veins accompany the arteries and are susceptible to injury. The middle
meningeal veins drain into the pterygoid venous plexus
Sara’s note: the pterygoid venous plexus is not described in the text except that things drain
into it. Look where it is on the picture.
C. Nerve Supply of the Dura
1st. Anterior and middle cranial fossae areas of the dura are mostly parts of the
trigeminal nerve.
1. The anterior meningeal branches come off the ethmoid nerves, which
are a part of CN V1, and the meningeal branches of the maxillary and
mandibular nerves supply the anterior cranial fossa.
2. CN V2 and CN V3 give branches that supply the middle cranial fossa
2nd. The posterior cranial fossa is mostly supplied by the tentorial nerve which is a
branch of the ophthalmic nerve, by sen
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