Anatomy of Orbit and Lacrimal system

1. Anatomy of Orbit and
Lacrimal System
Tanat Tabtieang, MD
Fellowship of Royal College of Radiologists ofThailand
Diploma of theThai Board of Diagnostic Radiology
Lecturer, Department of Anatomy
Faculty of Medicine, Chulalongkorn University

2. Orbit

3. Orbit
• Bilateral conical-shape bony
cavities in facial skeleton
• Extending from eyelids
anterolaterally to orbital apex
posteromedially
• Above: anterior cranial fossa
• Medial: nasal cavity and
ethmoid air sinuses
• Below: maxillary sinus

4. Orbit
• Medial walls of two orbits separated by ethmoid sinuses and
upper part of nasal cavity, nearly parallel
• Lateral walls of two orbits are approximately perpendicular
• Orbital axes diverge at approx. 45°

5. Size
• Height of orbit measured anteriorly at rim is ~ 3.5 cm
• Width of orbit is ~ 4.0 cm
• Medial orbital wall measures ~ 4.5 cm from rim to apex
• Lateral wall is shorter than medial wall, measuring ~ 3.5 cm
• Volume of each orbit is variable but ranges from 16-30 cm³

6. Bones of orbit
• Frontal bone
– Forms superior rim and anterior roof (orbital process)
• Zygomatic bone
– Forms inferolateral rim, anterior portion of lateral wall (orbital
process), anterolateral floor (maxillary process)
• Maxillary bone
– Forms inferomedial rim (frontal process) and anterior portion of
inferomedial wall (orbital surface)
• Ethmoid bone
– Forms midportion of medial wall
– Very thin bone (lamina papyracea)

7. Bones of orbit
• Lacrimal bone
– Forms anterior portion of medial wall, just posterior to frontal process
of maxillary bone
– Fossa for lacrimal sac
• Sphenoid bone
– Forms posterior portion of lateral wall (GWS) and posterior portion of
medial roof (LWS)
– Complex contours between GWS and LWS create elaborate apical
fissures
• Palatine bone
– Forms small portion of inferomedial wall posteriorly
– Located between orbital portions of ethmoid and maxillary bones

10. Tubercles
• Whitnall’s and zygomatic tubercles in lateral wall
• Lacrimal tubercle in inferior orbital margin
• Infraoptic tubercle in medial margin of superior orbital
fissure.

11. Extent
Base of orbit
• Formed by orbital rim peripherally and soft tissues centrally
• Outlined by orbital margin, surround the orbital opening
• Afford protection to orbital contents, provide attachment for
orbital septum

12. Extent
Roof (superior wall)
• Formed mainly by orbital part
of frontal bone
• Near apex, formed by lesser
wing of sphenoid bone
• Lacrimal fossa: shallow
depression in orbital part of
frontal bone

13. Extent
Medial wall
• Formed primarily by orbital
plate of ethmoid bone
• With contribution from
frontal process of maxilla,
lacrimal, and sphenoid bones
• Anteriorly, indented by
lacrimal groove, fossa for
lacrimal sac
• Superiorly, trochlea for
tendon of superior oblique
muscle

14. Extent
Floor (inferior wall)
• Formed mainly by orbilal plate of maxilla, partly by
zygomatic and palatine bones
• Inferior orbital fissure: demarcate floor and lateral wall
– Gap between orbital surfaces of maxilla and sphenoid bones

15. Extent
Floor (inferior wall)
• Infraorbital groove >> infraorbital canal in the floor >> opens
into the infraorbital foramen
• Infraorbital groove and canal >>Weak spot in the floor of
orbit

16. Extent
Lateral wall
• Strongest for protection
• Formed by frontal process of
zygomatic bone and greater
wing of sphenoid bone
• Posterior part separating
orbit from temporal and
middle cranial fossa

17. Extent
Apex
• Optic canal
– In the lesser wing of sphenoid bone, medial to superior orbital fissure

24. Periorbita
• Orbital periosteum / orbital fascia
– Dense connective tissue lining bones forming the orbit
– Serves as attachment for muscles, tendons, and ligaments
• Posteriorly thickening to form annular fibrous ring encircling
optic nerve canal and portions of SOF, annulus of Zinn
• Continuous with
– Periosteal layer of dura mater at optic canal and superior orbital
fissure
– Periosteum of cranium (pericranium) through inferior orbital fissure
– Orbital septum at orbital margin
– Fascial sheaths of EOM
– Orbital fascia, forming fascial sheath of eyeball

26. Foramina
Optic canal
• Communicates the cranial cavity to the orbital cavity
• Formed completely by lesser wing of sphenoid bone
• Separated from superior orbital fissure by optic strut

27. Foramina
Superior orbital fissure
• Separates the lateral wall from the roof
• Formed by lesser wing of sphenoid medially, greater wing of
sphenoid laterally

28. Foramina
Inferior orbital fissure
• Formed by greater wing of sphenoid and zygomatic bone
laterally, maxillary and ethmoid bones medially
• Mostly contiguous with superior orbital fissure, separated
only at posterior aspect by short bony roof of foramen
rotundum
• Anterior continuation of foramen rotundum
• Separates the lateral wall from the floor

29. Orbital margin
Superior & inferior orbital margin
• Orbital septum
– Fascial sheet extending from the superior/inferior orbital margin to
the upper/lower border of the tarsus
– Almost separate the orbital contents from the lids

30. Lacrimal apparatus

31. Lacrimal apparatus
• Secretory part
– Lacrimal gland
– Accessory lacrimal glands of Krause andWolfring
• Drainage part
– Lacrimal punctum
– Lacrimal canaliculi
– Lacrimal sac
– Nasolacrimal duct

32. Lacrimal gland
• Almond shaped, ~2 cm long
• Located in the lacrimal fossa, in the superior temporal
quadrant of the orbit
• Orbital and palpebral parts: divided by the lateral horn of the
levator aponeurosis

33. Accessory lacrimal glands
Accessory lacrimal glands of Krause andWolfring
• Located in the conjunctiva of the superior fornix and the
superior tarsal border
• “Basal secretors”
– Their secretions are normally sufficient to maintain the health of the
cornea
• Lack ductules

35. Innervation
Afferent pathway
• Ophthalmic branch of the trigeminal nerve
Efferent pathway
• Parasympathetic innervation
– Pontine superior salivary nucleus >> greater petrosal nerve >> nerve
of the pterygoid canal (vidian nerve) >> pterygopalatine ganglion >>
lacrimal gland
– Production of lacrimal fluid
• Sympathetic innervation
– Superior cervical ganglion >> internal carotid plexus >> deep petrosal
nerve >> join parasymp nerve forming nerve of pterygoid canal >>
pterygopalatine ganglion
– Vasoconstriction

37. Tear film
• Lipid layer
– Produced by the meibomian glands of
the tarsus
– Regulating evaporation
– Forming a watertight seal
• Aqueous layer
– From main and accessory lacrimal
glands
– Containing water-soluble salts and
proteins
• Mucous layer
– Produced by unicellular goblet cells of
the conjunctiva
– Glycoprotein in the form of mucin
– Hydrophilic surface for the aqueous tears
to spread over

38. Lacrimal punctum
• Hole present in a papilla at the junction of the ciliary and
nonciliary parts of the lid margin
• Point inward and medially toward the globe
• Capillarity and partly by sucking caused by negative pressure
into the sac by contraction of the orbicularis

39. Lacrimal canaliculi
• Drain lacrimal fluid from lacrimal lake (lacus lacrimalis) to
lacrimal sac
• Upper canaliculus is 6.0 mm, Lower canaliculus is 6.5 mm
• Both open separately through the lacrimal fascia into the
medial wall of the lacrimal sac
• Two limbs of Y of medial canthal ligament enclose the
lacrimal parts of the lid margin and have the canaliculi inside
them.

41. Lacrimal sac
• Lodged in the lacrimal fossa
in the medial wall of the
orbit between the anterior
and posterior lacrimal
crests
• Makes an angle with the
upper end of the
nasolacrimal duct
– Common site of blockage of
the lacrimal passages

43. Nasolacrimal duct
• Convey lacrimal fluid to inferior nasal meatus
• Elasticity of the lacrimal sac and gravity help tear to reach the
nasolacrimal duct
• Normally, the tears do not reach the nose because of
constant evaporation

45. Thank you for your attention