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Anatomy of Orbit and Lacrimal system

The document provides an overview of the anatomy of the orbit and lacrimal system. It describes the bones that make up the orbit, including the frontal, zygomatic, maxillary, ethmoid, sphenoid, and palatine bones. It also discusses the walls, foramina, tubercles, extent, and periosteum of the orbit. Regarding the lacrimal system, it outlines the lacrimal gland, accessory glands, innervation, tear film layers, lacrimal punctum, canaliculi, sac, and nasolacrimal duct.

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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
Orbit
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
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°
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
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)
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
Tubercles • Whitnall’s and zygomatic tubercles in lateral wall • Lacrimal tubercle in inferior orbital margin • Infraoptic tubercle in medial margin of superior orbital fissure.
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
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
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
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
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
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
Extent Apex • Optic canal – In the lesser wing of sphenoid bone, medial to superior orbital fissure
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
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
Foramina Superior orbital fissure • Separates the lateral wall from the roof • Formed by lesser wing of sphenoid medially, greater wing of sphenoid laterally
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
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
Lacrimal apparatus
Lacrimal apparatus • Secretory part – Lacrimal gland – Accessory lacrimal glands of Krause andWolfring • Drainage part – Lacrimal punctum – Lacrimal canaliculi – Lacrimal sac – Nasolacrimal duct
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
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
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
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
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
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.
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
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
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